1 a H Presented by §Alfons I. Wray, B. 0., F. 0. C. 0. A^L COl LEGE OF OSTEOPATHIC PHYSICIANS VND SURGEONS • LOS ANGELES, CALIFORNIA AN AMERICAN TEXT-BOOK OF DISEASES OF THE EYE, EAR, NOSE, AND THROAT 7 EDITED BY G. E. deSCHWEINITZ, A.M., M. D. Professor of Ophthalmology In the Jefferson Medical College, Philadelphia ; Consulting Ophthalmologist to the Philadelphia Polyclinic; Ophthalmic Surgeon to the Philadelphia Hospital and to the Orthopedic Hospital and Infirmary for Nervous Diseases AND B. ALEX. RANDALL, M.A., M. D., Ph.D. Clinical Professor of Diseases of the Ear in the University of Pennsylvania; Professor of Diseases of the Ear in the Philadelphia Polyclinic ; Ophthalmic and Aural Surgeon to the Methodist and Children's Hospitals, Philadelphia ILLUSTRATED WITH 766 ENGRAVINGS, 59 OF THEM IN COLORS PHILADELPHIA W. B. SAUNDERS 925 Wai mi Stri 1899 Copyright, 1899, By W. B. SAUNDKRS. ELECTBOTYPEO BY PRESS OF WESTCOTT & THOMSON, PHILAOA. W. B. 8AUNDERS. PHILAOA. CONTRIBUTORS. HENRY A. ALPERTOX, M. D., Brooklyn, N. Y. Chief of Aural Clinic, Polhemus Memorial Clinic, Long Island Medical College : \ural Surgeon to the Brooklyn Eye and Ear Hospital. HARRISON ALLEN, M. D„ Philadelphia. Pa. Late Professor of Comparative Anatomy, University of Pennsylvania: late Professor of Diseases of the Nose and Throat, Philadelphia Polyclinic. ERANK ALLPORT. M. D., Chicago, III. Professor of Ophthalmology, Chicago Polyclinic ; Professor of Ophthalmology and Otology, Northwestern University, Woman's Medical College. MORRIS J. ASCH, M. D., New York City. Surgeon to the Throat Department of the New York Eye and Ear Infirmary ; Surgeon to the Throat Department, Manhattan Eye and Ear Hospital. S. C. AYRES, M. D., Cincinnati, Ohio. Professor of Ophthalmology and Otology, Medical College of Ohio, Medical Department of the University of Cincinnati. R. O. BEARD, M. D., MINNEAPOLIS, MlNN. Professor of Physiology in the Department of Medicine of the University of Minnesota. CLARENCE J. BLAKE. M. D., Bosto.v. Mass. Professor of Otology, Harvard Medical School; Aural Surgeon to the Massachusetts Charitable Eye and Ear Infirmary. ARTHUR AMES BLISS. A. M., M. D., PHILADELPHIA, Pa. Larynjjolojfist and Aurist to the German Hospital ; late Attending Laryngologisl to the Pennsylvania Institution for the Deaf and Dumb. A. P. BRIT5AKER. M. I)., PHILADELPHIA, l'\. Adjunct Professor of Physiology and Hygiene, Jefferson Medical College; Professor of Physiology and General Pathology, Pennsylvania College of Dental Surgery. J. H. BRYAN. M. I).. WASHINGTON, \>. i\ Late Passed issistanl Surgeon, U. S. Navy; Surgeon to the Throat and Ear Depart- ment, Garfield Memorial Hospital. ALBERT IL BUCK, M. !>.. New York city. Clinical Professor of Diseases of the Ear, College of Physicians and Surgeons, Medical Department of Columbia University; Consulting Aural Surgeon, New York Eye and Ear Intirmary. F. BULLER. M. I).. MONTREAL, CANADA. Professor of Ophthalmology and Otology, McGill University; Ophthalmic and Aural Surgeon t" the Royal Victoria Hospital. SWAN M. BTTBNETT. M. D.. Washington, D. C. Professor of < (phthalmology and < ttology, Medical Department, < teorgetown I'niv. Director of the Eye and Ear Clinic, Central Dispensary and Emergency Hospital. FLEMMING CAEEOW, M. D.. Ann \ri:..r, MlCH. Professor of Ophthalmology and Otology, University of Michigan. 3 Li xJ .A G %J 4 CONTRIBUTORS. \Y. E. i ISSELBEEEY, M. D.. Chicago, III. Professor of Laryngology and Ehinology, Northwestern University Medical School. COLMAN W. CUTLEB, M D., New York City. Attending Ophthalmologist to St. Luke's and II. I. Hospitals: Assistanl Surgeon, New York Eye and Ear Infirmary. EDWAED B. I»K\i- of i Ophthalmology, College of Physicians and Surgeons, Columbia University ; Surgeon to the New York Ophthalmic and Aural Institute. I BARLES W. EOLLOCK, M. 1).. Charleston, S. C. Lecturer on Diseases of the Eye and Ear in the Charleston Medical School ; Ophthalmic Surgeon to the Charleston City Hospital. (i. \. LELAND, A. M . M. D., Boston, Mass. Aural Surgeon bo < >ut-Patient Department, and Assistant in Throat Department, Boston City Hospital; Professor of Laryngology and Otology, Dartmouth Medical School. J. A. LIPPINCOTT, A. B., M. D., PlTTSBUBG, Pa. Ophthalmic and Aural Surgeon, Allegheny General Hospital. G. HUDSON MAKUEN, M. D.. Philadelphia, Pa. Professor of Defects of Speech, Philadelphia Polyclinic and College for Graduates in Medicine; Laryngologist to St. Mary's Hospital and to the Frederick Douglass Memorial Hospital. JOHN H. McCOLLOM, M. D., Boston, Mas& Instructor in Contagious Diseases, Harvard University; Resident Physician. Smith Department, Boston City Hospital. HOEA( E G. MILLER. A. M.. M. D., Providence, R. I. Ophthalmic and Aural Surgeon to the Rhode Island Hospital : Consulting Ophthalmic and Aural Surgeon to St. Joseph's Hospital. B. L. MILLION, M. D., Cleveland, Ohio. Professor of Ophthalmology, Medical Department. Western Reserve University ; oph- thalmic Surgeon to Lakeside Hospital. EOBEET C. MYLES, M. D., New Yoek City. Professor of ( >tology and Adjunct Professor of Rhinology and Laryngology, New York Polyclinic: Assistant Surgeon to the .Nose. Throat, and Ear Department of the New Amsterdam Eye and Ear Hospital. JAMES E. NEWCOMB, M. D., New Yoke City. Attending Laryngologist to the Out-Patieut Department, Roosevelt Hospital, and to the Demilt Dispensary; Instructor in Laryngology, Cornell University Medical College. R. J. PHILLIPS. M. D., Philadelphia, Pa. Ophthalmic Surgeon to the Presbyterian Hospital, the Presbyterian Orphanage, ami the Friend-' Home for Children. GEORGE A. PIEESOL, M. D.. Philadelphia, Pa. Professor of Anatomy. University of Pennsylvania. w. PEYEE POB< BEE, M. D., Chaeleston, S. C. Lecturer on Diseases of the Throat and Nose, Charleston Medical School; \i-it iiiLT Laryngologisl to city Hospital. B. ALEX. BANDALL, M. A., M. D., Philadelphia, Pa. Clinical Professor, Diseases of the Ear. University of Pennsylvania; Professor of Diseases of the Ear, Philadelphia Polyclinic. ROBERT I.. RANDOLPH, M. D., Baltimore, Md. Associate in Ophthalmology and Otology, Johns Hopkins University; Associate Oph- thalmic and Aural Surgeon to the Johns Hopkins Hospital. JOHN <». ROE M. I).. Rochest] b, N. Y. Laryngologisl to the Rochester City Hospital. CHAS. F. de M. SAJOUS, M. l>.. Philadelphia, Pa. Fellow of the American, British, and French Laryngological Associations. J. E. SHEPPARD, M. D., Bbooki \ v N Y. clinical Professor of Diseases of the Ear, Long Island College Hospital ; Prof Otology, New York Polyclinic Medical School and Hospital. 6 CONTBIBUTORS. i: I.. SHTJRLY, M. D.. Detkoit, Mich. Professor of Laryngology and Clinical Medicine, Detroit Collegefof Medicine; Consult- ing Physician to St. Luke's Hospital. W. M. SWEET, M. D., PHILADELPHIA, PA. Associate in Ophthalmology, Philadelphia Polyclinic; Instructor in Ophthalmology Jefferson Medical College. SAMUEL THEOBALD, M. I>., Baltimore, Md. Clinical Professor of Ophthalmology and Otdlogy, Johns Hopkins University; Oph- thalmic and Aural Surgeon to the Johns Hopkins Hospital. ARCHIBALD G. THOMSON, M. D, Philadelphia, Pa. Ophthalmic Surgeon to the Children's Hospital; Assistant Ophthalmic Surgeon, Wills Eye Hospital. CLARENCE A VEASEY, A. M., M. D., Philadelphia, Pa. Adjunct Professor of Diseases of the Eye, Philadelphia Polyclinic; Demonstrator of Ophthalmology, Jefferson Medical College. JOHN E. WEEKS, M. D., New York City. Surgeon to the New York Eye and Ear Infirmary, Ophthalmic Department ; Clinical Professor of Ophthalmology and Otology, Woman's Medical College of the New York Infirmary. CASEY A Wood. c. M.. M. D, Chicago, III. Professor of Ophthalmology, Chicago Post-Graduate Medical School ; Ophthalmic Sur- geon to the l'assavant Memorial Hospital. JONATHAN WRIGHT, M. D., Bb £LYN, N. Y. Clinical Professor of Diseases of the Nose ami Throat, Woman's Medical College of the New York Infirmary. H. V. WtJRDEMANN, M. D., Milwaukee, Wis. Ophthalmic and Aural Surgeon to the Milwaukee Children's Hospital and to the Milwaukee County Hospital for the Chronic Insane. PREFACE. This book is offered to students and practitioners of medicine and surgery in general, and to those especially interested in the subjects of which it treats in particular, in the hope that it may take rank with the other volume- of the "American Text-book" series, which have demonstrated their worth and have had their reward in the appreciative reception which has been accorded to them. In the portion of the work devoted to the Eye, its Embryology, Anatomy, Histology, Physiology, Diseases, and Injuries are discussed in twenty-four sections by twenty-four authors; its Operative Surgery in ' Eyes, The Most Important .Micro-organ- isms having Etiological Relationship to Ocular Disorders, etc. It is unnecessary to discuss the "collaboration-method" thus employed, which ha- too often demonstrated its value to need either defence or explana- tion in thi- place, except to point out its greatest use, and the one to which no doubt it is indebted for it- suec< namely, that by it- mean-, in the words of Dr. W. H. Howell, "the student gains the point of view of ;i number of teachers, reaping, in ;i measure, the -nine benefit as would be obtained by following courses of instruction under different teachers." Thi- work i- essentially a text-book on the one hand, and. on the other, a volume of reference to which the practitioner may turn and find a series of article- written bv men who are authorities on the subjects portrayed by them. Therefore the practical side of the question has been brought into pr inen< — i. e. Functional Testing, Etiology, Symptomatology, Diagnosis, and Ti ment, but never to the neglect of Pathology or the important facts coi in the special chapters on Embryology, Anatomy, Physiology, Physi 8 PREFACE. Optics, etc., to which, indeed, special attention is directed. Thus it is hoped thai the student will receive nol only the point of view of a number of teachers, but a number of points of view of each subject. A word should be said with reference to the effort t<> comprise within one volume studies of the Eye, Ear, Nose, and Throat — an effort which may chal- lenge criticism in this day of highly differentiated specialties. Yet it has seemed to the Editors that each of these branches could receive text-hook treatment within the space here assigned, while their important correlations could he better brought out by such juxtaposition. Specialism has often been carried much too far in the exclusion of attention to the adjacent tields. The oculist cannot dispense with a fair working knowledge of affections of the nose and it- accessory cavities ; nor should the aurist have to learn at second hand the important teachings of the ophthalmoscope as to his cases. Indeed, no practitioner, general or special, should be unfamiliar with all the types of disease and the most precise methods of their study, for it must often happen that he cannot avail himself of help from others. He should, like Brougham's educated man. "know a little of everything and all about some one thing." The latter part, as to the specialties here treated, the reader must seek in more voluminous encyclopedic works; hut it is hoped that the labors of the eminent teachers here brought shoulder to shoulder will afford a good intro- duction for the beginner, as before stated, a valuable handy reference-hook for the practitioner, and at least quicken some weakening memories in the advanced specialist. Each author i- responsible for the statements and opinions in his article : occasional editorial comment is always suitably marked. For the most part, wherever the same subject receives consideration in different articles, cross references have been supplied, again with the idea of facilitating a study of the point of view. It seems proper to note that there has been complete division of the editorial labor and responsibility, that of the Ophthalmic portion being assumed by Dr. de Schweinitz, and that of the Otological and Laryngological sections by Dr. Randall. We have to note and diploic the loss to ourselves and to the profession in the death, during the preparation of this work, of Dr. Harrison Allen, robbing us of his finishing touches to hi- own contribution and the continu- ance of hi- friendly counsel ;i- to other portions of the hook. Of the greater loss in hi- many field- of activity we cannot here speak. In conclusion, the Editors desire to express their hearty thanks to all the contributors for their uniform courtesy and for the presentation of the sub- jects entrusted to them in a manner which, they fed sure, cannot fail to be satisfactory to -indent-. Also, their thank- are due to Mr. T. V. Dagney .•ind Mr. \l. \V. Greene for their efficient aid and constanl kindness. l i"i Locusi Street. , .,., - .. I'iiii. \ DELPHIA. 1604 \\ A I. Ml M l;l l i. | Februarj L899 CONTENTS. PART I.— THE EYE. PAGE EMBRYOLOGY, ANATOMY, AND HISTOLOGY OF THE EYE. . 17 By George A. Piersol, M. D., Philadelphia, Pa. GENERAL PHYSIOLOGY OF VISION 88 By Albert P. Brubaker, M. I)., Philadelphia, I'a. GENERAL OPTICAL PRINCIPLES: KATOPTRICS, DIOPTRICS, PHYSIOLOGICAL OPTICS 102 By William S. Dennett, M. I>., and Colman Ward Cutler, M. D., New York ( ity. EXAMINATION OF THE PATIENT AND EXTERNAL EXAMI- NATION OF THE EYE; FUNCTIONAL TESTING ... 142 By G. E. de Schweinitz, A. M., M. D., Philadelphia, Pa. THE OPHTHALMOSCOPE AND ITS USE; THE NORMAL EYE- GROUND 171 By B. Alex. Randall. A. M., M. D., Philadelphia, I'a. mfthods OF DETERMINING THE refraction of the EYE: OPHTHALMOMETRY; OPHTHALMOSCOPY, SKI- ASCOPY, OPTOMETRY; THK USE OF MYDRIATICS. . 196 By Edward Jackson, A. M., M. I)., Denver, Oil. NORMAL AND ABNORMAL REFRACTION: EMMETROPIA; AMETROPIA, HYPEROPIA, MYOPIA, ASTIGMATISM, PRESBYOPIA 212 By Edward Jackson, A.M., M. I>.. Denver, Col. SPECTACLES AND THEIR ADJUSTMENT By R. J. Phillips, M. I», Philadelphia, Pa. DISEASES OF THE EYELIDS - 11 By B. L. Mii.likin. M. I>. Cleveland, Ohio. DISEASES OF Till: LACHRYMAL APPARATUS 201 By Samuel Theobald, M. I>., Baltimore, Md. DISEASES OF THE CONJUNCTIVA By John E. Weeks, M. I'.. New York City. DISEASES OF THE CORNEA AND SCLERA FJy Swan M Burnett, .M. I>., Ph. I»., Washington, I> < '. l,i COX TENTS. PAGE DISEASES OF THE [BIS, CILIARY BODY, AND CHOROID; SYMPATHETIC INFLAMMATION AND IRRITATION . 331 By Robert L. Randolph, M. I»., Baltimore, Md. INJURIES OF THE EYE AND ITS APPENDAGES 358 By Ai.vin A. Hi bbell, M. D., I'll. D., Buffalo, X. Y. GLAUCOMA •■• 373 By .1. A. Lippincott, A. B., M. D., Pittsburg, Pa. DISEASES OF THE CRYSTALLINE FENS 386 By William E. Hopkins, M. 1»., San Francisco, Cal. DISEASES OF THE VITREOUS 398 By Flemming Carkow, M. I>., Ami Arbor, Mich. DISEASES OF THE RETINA 405 By Lttcien Howe, M. D., Buffalo, N. Y. DISEASES OF THE OPTIC NERVE 432 By Haiku. i) Gipford, M. D., Omaha, Neb. AMBLYOPIA, AMAUROSIS, AND DISTURBANCES OF VISION WITHOUT OPHTHALMOSCOPIC CHANGE 157 By Casey A. Wood, M. D., Chicago, 111. AMBLYOPIA OF THE VISUAL FIELD, SCOTOMAS, AND HEMI- ANOPIA 470 By II. V. WtJRDEMANN, M. I >.. Milwaukee, Wis. INTRAOCULAR GROWTHS 189 By Ward A. Holden, A. M„ M. I >.. New York City. MOVEMENTS OF THE EYEBALLS, AND THEIR ANOMALIES 197 By Alexander Dcane, M. I>., New York City. [NJURIES AND DISEASES OF THE ORBIT 523 By F. Bi i.i.i.i:. M. !»., Montreal, < lanada. OPERATIONS 539 Fn 'par; it ion of the Region <>f* < >peration, the [nstruments, and the Dressings; Anesthesia 539 By G. E. de Si hweinitz, A. M., M. I»., Philadelphia, Pa. Operations upon the Eyelids "»ll By 1 ■'. C. Ilmv. M. D., Chicago, 111. Operations upon the Conjunctiva, Cornea, and Sclera; Enucleation and Evisceration -~»< 1 1 By Charles W. Kollock, M. D., Charleston, S. C. Operations upon the Iris and the Crystalline Body -~>~ I By Herman Knapp, M. I»., New York City. Operations upon the Eye-muscles "» S T By S. < '. Ayres, M. I '., « incinnati, I ►hio, Operations upon the Lachrymal Apparatus 596 r. Samuel Th bob ild, M. I >.. Baltimore, Md. CONTENTS. 1 1 PAGE Operations upon the Orbit 599 By F. I'.i 1. 1.1:1:, M. I)., Montreal, Canada. APPENDIX gog The ."Methods for Detecting Color-blindness, with Special Reference to the Examination of Railroad Employed 603 By .). Ellis Jennings, M. D., St. Louis, Mo. Standards of Form and Color-vision Required in Railway Service . 605 By A. G. Thomson, M. D., Philadelphia, Pa. The Rontgen Rays in Ophthalmic Surgery 607 By William M. Sweet, M. D., Philadelpliia, Pa. The Practice of Ophthalmic Operations on Animals' Eyes (ill By Clarence A. Veasey, A. M., M. D., Philadelphia, Pa. The Most Important Micro-organisms having- Etiological Relation- ship to Ocular Diseases 614a By G. E. de Schweinitz. A.M., M. I)., Philadelphia, Pa. PART II.— THE EAR. THE ANATOMY OF THE P]AR, INCLUDING EMBRYOLOGY AND HISTOLOGY^ 617 By B. Alex. Randall, M. A., M. I)., Philadelphia, Pa. THE PHYSIOLOGY 7 OF THE EAR <;:;i By Frank Allport, M. D., Chicago, 111., and R. O. Beard, M. I>.. Minneap- olis, Minn. ETIOLOGY AND PATHOLOGY OF EAR AFFECTIONS 647 By C. R. HOLMES, M. D., Cincinnati, Ohio. EXAMINATION OF PATIENTS; SYMPTOMATOLOGY AND DIAGNOSIS; [NSTRUMENTS NEEDED, AND METHODS OE THEIR EMPLOYMENT 665 By John E. Sheppard, M. I>.. Brooklyn, X. Y. THE GENERAL THERAPEUTICS OF EAR AFFECTIONS .... 684 By Clarence .1. Blake, M. P.. Boston, Mass. AFFECTIONS OF THE EXTERNAL EAR 691 By Samuel Theobald, M. D., Baltimore, Md. INJURIES AND DISEASES < >V THE DRUMHEAD 711 By II. Y. Wi 1:1.1 mann. M. I)., Milwaukee, Wis. ACUTE AFFECTIONS OF Till'. TYMPANIC CAVITY AND EU- STACHIAN TUBE Tl") By Horace Cx. Mii.u r, A. M.. M. P.. Providence. R 1. 12 CONTENTS. PAGE ( BRONIC (ATA Kill I OF THE MIDDLE EAE 726 By Edward B. Dench, Ph. B., M. D., New York City. CHRONIC SUPPURATION OF THE MIDDLE EAR 739 By Albert II. Buck, M. D., New York City. COMPLICATIONS OF TYMPANIC INFLAMMATION 749 By Herman Knapp, M. I'.. New York City. DISEASES OF THE SOUND-PERCEIVING APPARATUS 765 By Henry A. Alderton, M. I>.. Brooklyn, N. Y. OPERATIONS 782 By •). Orne Green, A. M.. M. !>.. Boston, .Mass. PART III.— THE NOSE AND THROAT. ANATOMY OF THE UPPER AIR-PASSAGES, INCLUDING IIIS- TOLOGY AND EMBRYOLOGY 807 By Harrison Allen, M. I>. LL. I>.. an.! Arthub A. Bliss, A.M.. M. IX, Philadelphia, Pa. PHYSIOLOGY <>F THE UPPER AIR-PASSAGES 835 By Walteb J. Freeman, M. I». Philadelphia, Pa. GENERAL ETIOLOGY AND PATHOLOGY OF DISEASES OF TIM: UPPEB RESPIRATORY TRACT 844 By J. II. Bryan, M. D., Washington, D. ( '. METHODS OF EXAMINATION AND DIAGNOSIS IN AFFEC- TIONS OF THE NOSE AND THROAT 855 By John \V. Farlow, M. D., Boston, Mass. THERAPEUSIS AND PROGNOSIS 874 By Geo. A. Leland, A. M., M. I».. Boston, Mas-. ACUTE AFFECTIONS OF THE NOSE 89J By William !■'.. < vsselberry, M. 1 >.. I hicago, III. CHRONIC AFFECTIONS OF THE NOSE 905 B\ M irris J. \- ii. M. I»., New York < ity. DISEASES OF THE TONSILS, PALATE, AND PHARYNX . . . 921 By James Edward Newcomb, M. D., New York City. ATROPHIC RHINITIS 957 By W. I'l J l:l PORCHER, M. I ».. < liar]. stOD, 8. ( '. DISEASES OF THE ACCESSORY SINUSES OF THE NOSE . . . 966 By Roberi Cunningham Myles, M. D., New York City. ACUTE AFFECTIONS OF THE LARYNX AND TRACHEA. . . 985 By William E. Hopkins, M. D., S:m Francisco, Cal. CONTENTS. 13 PACE CHRONIC IXKl.AM.MATiHiV DISEASES OF THE LARYNX . . !)!ix By C. E. de M. Sajoi s, M. D., Philadelphia, Pa. DIPHTHERIA OF THE AIR-PASSAGES 1010 By J. II. McColxom, M. I>.. Boston, Ma--. TUBERCULOSIS OF THE AIR-PASSAGES 1034 By E. L. Shurly, .M. D., Detroit, Mich. SYPHILIS OF THE AIR-PASSAGES 1067 By William ('. Glasgow, M. I».. St. Louis, Mo. NEOPLASMS OF THE UPPER AIR-PASSAGES 1075 By Jonathan Wright, M. D., Brooklyn, X. Y. INJURIES AND DEFORMITIES OF THE NOSE AXD THROAT . 1116 By John O. Roe, M. D., Rochester, X. Y. NEUROSES OF THE UPPER AIR-PASSAGES 1140 By Jonathan Wright, M. D., Brooklyn, N. Y. THE VOICE— ITS PRODUCTION AND HYGIENE 1171 By G. Hudson Makuen, M. D., Philadelphia. Pa. OPERATIONS 1180 By John O. Roe, M. I)., Rochester, X. Y. THE EYE. THE EYE. THE EMBRYOLOGY, ANATOMY, AND HISTOLOGY OF THE EYE. By GEORGE A. PIERSOL, M. D., OF PHILADELPHIA. THE DEVELOPMENT OF THE EYE. The initial stages in the formation of the visual organ are so intimately related to those of the brain, that a brief sketch of the early development of the nervous system may with advantage precede the more detailed account of the development of the eye. The first definite trace of the embryo within the embryonal area appears as a pair of slightly converging folds, the medullary plate*, which partially Mesoderm Visceral mesoderm Pleuropericar- Perit ardial dial cavity. plates. Fig. 1.— Transverse section of a sixteen-and-a half-day slice), embryo (Bonnet). Extension of celom. enclose the anterior end of the transienl primitive streak. Originally widely separated and low, the folds rapidly increase in height, while the included neural groove becomes correspondingly deepened (Fig. 1). Very soon the growing medullary plates manifesi a tendency to approximate their freeed along the dorsal aspecl of the embryo, a disposition which eventually results in their fusion and the conversion of the open neural groove into the cl< 17 18 EMBRYOLOGY, ANATOMY, AND HISTOLOGY OF EYE. neural canal (Figs. 2 and 3). The poinl nt which this fusion earliest occurs does ii"t coincide with the anterior extremity of the canal, but with a point somewhat farther hack ; from this latter situation closure progresses toward the caudal pole. The anterior extremities of the medullary folds remain ununited for some Medullary furrow. I 'ucleft Ectoderm. mesoderm. Amnion. Fig. Visceral mesoderm. Notochord. Somite. Cut entoderm. Trans\ erse section of a sixteen-and-a half-day sheep embryo possessing six somites (Bonnet). time after the more caudally situated parts of the folds 'have undergone con- crescence and closure; the anterior portion of the folds, on the other hand, has meanwhile become locally expanded in such manner that even before the fusion of the folds indications of three distinct dilatations — the primary brain- Ectoderm Closing neural canal. Amnion. Cell -mass for Wolffian body. Notochord. ' m of a fifteen-and-a-half-day sheep embryo po en somites (Bonnel vesicles — have become apparent. The foremosl of these, the anterior brain- sac, occupies the extreme end of the neural canal, and i- of large size, the succeeding middle ami posterior vesicles being less expanded, although of greater length. PRIMARY OPTIC VESICLES. L9 The primary cerebral since the anterior and tl Anterior brain-vesicle. Middle brain-vesicle. - Posterior brain-vesicle. . Fore-brain. Primary optic vesicle. Stalk of optic vesicle. Inter-brain. Mid-brain. Hind-brain. After-brain. Fore-brain. Primary optic vesicle. Inter-brain. Mid-brain, Hind-brain. After-brain. vesicles, however, soon undergo further chan c posterior each become subdivided, the cephalic segmentof the neural tube being then repre- sented by the five secondary brain-vesi- cles. These latter are designated, from before backward, as the fore-brain, or prosencephalon ; the inter-brain, orthalam- encephalon ; the mid-brain, or mesenceph- alon ; the hind-brain, or epencephalon ; and the after-brain, or metencephalon (Figs. 4 Fig. 4.— Diagrams illustrating the pri- mary and secondary segmentation of the brain-tube (Bonnet). Fig. 5. — .4, brain of two-day chick embryo; />', brain of human embryo of three weeks (His); shows the develop ment of the optic vesicles and brain-vesicles; fb, lore brain; ib, inter-brain: ov, optic vesicle. and 5). The remains of the greatly modified and relatively reduced cavities of these early brain-segments are represented respectively by the lateral ven- tricles, the third ventricle, the aqueduct of Sylvius, and the fourth ventricle : while from the walls of the secondary brain-vesicles are developed the struc- tures situated around the corresponding part of the ventricular -pace. Coincidently with the development of the primary cerebral vesicles, even before the complete closure of the neural canal, the anterior brain-sac becomes distinguished by the evagination of a conspicuous diverticulum on either side, which extends almost at right angles to the general cerebral axis. These outgrowths fron the hinder part of the early anterior cerebral segmenl are the primary <>/>fi<- vesicles, from which the nervous tunic of the eye is largely developed. The optic vescicle at first open- so widely into the brain-sac thai there i- little differentiation of the ocular rudiment from the general cavity of the brain-segment; soon, however, the communication between the two becomes uarrowed and the optic vesicle better defined as an independenl organ. The (>/>//<■ stalk, which results from this constriction, lies almost transversely placed when first formed, but gradually assumes a more oblique axis as its development progresses. The relation- of the optic -talk- to the brain-segments also somewhat change, si when definitely formed the stalks open into tie- inter-brain, or thalaraencephalon, having seemingly become pos- teriorly removed during their growth. In attaining ii- full expansion the primary optic vesicle has encroached to such an extent on the mesoderm lying between the eye-sac and the surt of the embryo, that in mammal- an extremely thin stratum of mesodi tissue alone separates the optic vesicle from the surface ectoderm: in : even this is wanting, the mesoderm being entirely displaced and the ectod 20 EMBRYOLOGY, ANATOMY, AND HISTOLOGY OF EYE. of the exterior ami anterior wall of the <>|>tic vesicle coming into apposition (Fig. 6). Bach optic vesicle may lie regarded as possessing four walls — a lateral oi outer wall, including the area in apposition to the surface : a nu isial or inner wall, [narked by the position of the early optic stalk ; a lower wall, on a level with the floor of the inter-brain ; and an upper wall. After meeting the surface layers in its outward expansion, the primary optie vesicle becomes profoundly modified by the invagination of its lateral - i tion through head of ten-day rabbit embryo, exhibiting primary optic ves- icle [0) protruding from fore brain /.''. ami coming m contact with surface ectoderm (e); in. surrounding mesi derm Piersi il i. Fki. 7.— Section through developing eye of eleven-day rabbil embryo (Piersol) : /.'. fore t Tail i connected by stalls with optic vesic] whose anterior wall is partly invaginated ; I, thickened ami depressed lens area. or outer wall, in consequence of which pushing in, the cavity of the primary vesicle is gradually reduced, and, finally, obliterated by the application of the invaginated portion of the wall of the vesicle to the mesial segment of the same, which has not suffered displacement. The space which results from the invagination of the outer portion of the primary eye-sac gradually ac- quires a cupped form, and is known as the secondary <>/itir vesicle, or, more appropriately, as the optic cup (Figs. 7 and 8). Coincidently with the changes in the optic vesicle which result in the production of the optic cup, the ectoderm lying over the optic vesicle exhibits proliferation of its elements and becomes thickened, and. at the same time, sink- into the subjacent invaginating optic vesicle, thus forming a depression known ,-i~ the lens-pit. The thickened ectoderm lining the bottom and sides of the pit i- accurately applied to the receding lateral wall of the optic vesicle, separated in mammals, however, by a thin -heei ofmesodermic tissue. The invagina- ti f the early lens-pil increases, and, at the same time, the margins of the depression become approximated and eventually united, so that the lens-pit is converted into the lens-vesicle, a structure from which the fu- ture crystalline lens is developed in a manner presently to he described. The lens-sac thus formed for a time remains connected with the ectoderm : later, the union between the tw<> i- severed, and the primarj lens- rudimenl lie- :i- an isolated ectodermic vesicle completely Burrounded by mesoderm. The mesodermic stratum which separates the lens-sac from the 3i ction through developing eye ind-a-half-day rnhhit embryo brain connected with ■ .1 bj appo- ited anterior Begmenl i r) with ill (jp) ; /, lens sac com- pletely closed and separated from ecto- derm ; i. tissue within secondary optic cup m surrounding mesoderm. rum rn ve viTRKors chamber. 21 overlying ectoderm later contributes the conneetive-tisv the approximation and final union of its lips, the imprisoned mesoderm and the included blood-vessels being later represented by the arteria centralis retina,' and the associated connective tissue occupying the central area of the optic nerve. The Development of the I,ens.— The earliest phases of the forma- tion of the crystalline lens, including the conversion of the lens-pit into the closed lens-sac, have been already described ; the subsequent development of the lens is largely the history of the growth and differentiation of the walls of the lenticular vesicle. By the time the lens-sac has become completely isolated from its attachment with the surface ectoderm its walls consist of two or three layers of epithelial cells, externally limited by a delicate mem- brane, the earliest suggestion of the lens-capsule. Very soon the inner portion of the wall of the lens-sac becomes conspicuous by reason of its greater thickness — a disparity which becomes progressively more marked as development proceeds. The early mammalian lens-vesicle contains a mass of -mall cells derived from the proliferation of the surface elements of the primitive epidermis. These cells are unimportant, being transient, and later underuoinu- defeneration and absorption. The obliteration of the cavity of the lens-sac and the conversion of the organ intoa -olid ma— are effected by the phenomenal growth and elongation of the epithelial elements composing the posterior or internal wall of the sac. These cells rapidly increase in length, becoming converted into the primitive lens-fibers. At first the thickened inner wall projects into the lens-vesicle, the greatly reduced cavity of the sac intervening between it and tin- anterior wall. With the growth of the liber-ma— this -pace i- gradually reduced. until finally the now great!} thickened and specialized posterior wall comes into contact with the anterior layer and the lens becomes solid. The thickening and growth which have characterized the changes affecting the posterior or inner wall of the lens-sac are in marked contrast to the pro- gressive attenuation of the anterior or outer wall. The col ar type ot the early cell- of tlii- region i- replaced by the low cuboidal form which charac- terizes these elements in later stages. After the primitive lens bei - -olid in consequence of the obliteration of iln- cavity of the lens-vesicle by the growth and i lification of the posterior wall, the subsequent increase in the size of the lens take- place by the con- version of the cell- of the anterior wall, which are later known a- the DEVELOPMENT OF THE LENS. 23 epithelium of the anterior capsule, into Lens-fibers, and the addition of tl as peripheral increments. The transformation of the epithelial cells into fibers take- place at the equatorial zone, where the low columnar elements may be seen elongating and assuming the peculiarities of young fibers. The appositional growth <>t' the lens which thus takes place results in the forma- tion of layers of lens-fibers which cover the surface of the organ and enclose the lens-core. In consequence of their mode of equatorial formation the young fibers extend from the anterior to the posterior surface of the lens, their ends meeting along definite radiating lines which in the embryo and the new-born animal constitute three-rayed figures known as the lens-stars. The -tar of the anterior surface always has it- superior limb directed vertically. the remaining rays diverging laterally at an angle of 120°. The ray- of the posterior star are disposed in such manner that they fall between those of the anterior figure, the vertical limit being below and the others extending upward and outward. In the adult lens the figures lose, their former simplicity by the appearance of other and secondary ray-, the adult lens-stars being indis- tinct aud uncertain in their outlines. The modifications of the -tars in the fully-grown lens are largely due to the fact that in the enlarged organ the fibers are no longer capable of spanning the entire distance between the anterior and posterior surface-, as do the young embryonal fibers. The lens-eapsult i- early suggested by the appearance of a delicate mem- brane, which limits the outer surface of the lens-vesicle, and afterward undergoes thickening, becoming apparently homogeneous and of elastic character, which distinguishes this part of the eye. Two opposed view- exist regarding the source of the capsule : according to one, the capsule is developed a- a secretion from the cells of the lenticular vesicle, while the other regards it — and, the author believes, correctly — as derived from the mesodermic tissue surrounding the primitive lens. It will be noted from the foregoing description that the entire lens, excluding its capsule, is of ectodermic origin. The unusual demands made by the young, rapidly-growing and. at the same time, non-vascular lens on surrounding tissues for its nutrition result in the provision of a special, although temporary, structure designed to meet that need. The structure so developed consists of an envelope of vascular mesodermic tissue, the tunica vasculosa h ntis, which com- pletely surrounds the young lens from the second month to toward the end of gestation, at which latter period it has usually atrophied and dis- appeared. The tunica vasculosa is closely associated with the vitreous, since its blood-vessels are derived from those of that body. The large vessels over the posterior surface of the lens break up into smaller branches, which. bending around the equator of the lens, ramify within the mesodermic sheet covering the anterior surface, proceeding almost as far as the center of the pupil, where they end in terminal loop-. The different part- of the vascular membrane of the lens bear particular name-, in consequence of having been first observed at differenl times. The portion of the membrane opposite the pupil was called the membrana pupillaris; the more peripherally situated zone constituted the membrana capsulo-pupiUaris ; while thai cover- ing the posterior surface was designated the membrana capsularis. I evident that these are but parts of one and the same vascular sheet whi< now appropriately called the tunica vasculosa lentis. Usually this strucl is best developed at about the seventh month, after which time it und atrophy and absorption, so that at, or even before, birth it has entii 24 EMBRYOLOGY, ANATOMY, A XD HISTOLOGY OF EYE. appeared. Exceptionally, parts of the embryonal structure remain after birth, the anterior portions, when present, constituting the persistent pupil- lary membrane. (See page 331.) The early infolding of the lower wall of the optic vesicle is closelv related t<> an outgrowth of the surrounding mesoderm, which occupies the invagina- tion, and thus gains entrance into the secondary optic vesicle or optic cup, in which space it rapidly expands until the actively proliferating mesodermic tissue completely till- the space between the primitive lens and the retinal layer of the optic cup. In structure the primary vitreous corresponds to an embryonal form of connective tissue, in which a delicate network of branched connective-tissue elements is conspicuous. At a later stage these cell- atro- phy, while numerous leukocytes, derived from the ingrowing blood-vessels, invade the vitreous tissue. Coincidently with the growth of the primitive vitreous an extension of the artery occupying the young optic nerve, which later becomes the arteria centralis retina, take- place, the vessel invading the vitreous passing to the posterior pole of the young lens as the hyaloid artery. With the appearance of the latter vessel the vitreous becomes abundantly supplied with capillaries, from which not only the leukocytes already men- tioned pass into the proliferating mesoderm, hut also the watery constituents which later give to the vitreous tissue it- characteristic semi-fluid condition I Fig. 10). Fig. 10.— Projection from nasal side of the stalk of the optic vesicle and the centra] artery of the retina L, lens; A, anterior continuation of the central artery to the vascular tunic of the lens; /.'. /'. nervous and pigment lamella of the optic vesicle ; St, optic stalk, with i ntranci -i cen iral artery. In addition to providing the vitreous tissue with capillaries for it> direct nutrition during the early stages of its active growth, the hyaloid artery rami- fies within the mesodermic layer covering the posterior surface of the lens, thus first supplying that portion of the tunica vasculosa lentis known as the membrana capsularis. From tin- portion of the lens envelope, a- already mentioned, the blood-vessels extend forward, and finally spread out within the anterior segmenl over the corresponding surface of the lens, to constitute the vessels of the membrana pupillaris. During the last weeks of fetal life the 1.1 l-vessels of the vitreous, together with the tunica lentis, disappear, the onlv indication of this elaborate intraocular vascular network which persists being the remain- of the hyaloid artery within a passage, the hyaloid canal, which extend- from the optic, en- trance to the posterior pole of the lens. Sometimes, however, the hyaloid arter) undergoes less atrophy, and is then represented by ;i cord which extend- toward the lens, and may be provided with ;i lumen for a portion of it- length; in such cases the persistenl hyaloid artery may form a con- spicuous objeel when viewed with the ophthalmoscope. (Sec page U)3.) DEVELOPMENT OF THE RETINA. 25 Development of the Retina. — In the foregoing consideration of the initial changes in the formation of the optic cup the early conspicuous differ- entiation of the inner and the outer layer.- composing its walls has Keen pointed out. By the time the infolded portion of the vesicle has been closely applied to the uninvoluted segment, the former, or inner layer, has attained a thick- oess of many times thai of the outer layer: the latter, however, has become conspicuous, notwithstanding its attenuation, by reason of the pigment-granules which early accumulate within its cells. The pigment appears earliesl near the anterior margin or lip of the optic cup, gradually extending toward the posterior pole, until the entire outer layer appears uniformly dark. This layer becomes the future 'pigmented retinal epithelium (Fig. 11). The fate of the greatly thickened inner layer is largely identical with the history of the development of the retina, since it contributes the most import- ant parts of the nervous tunic. The early stages in the development of the retina resemble closely those seen else- where in the walls of the young brain- vesicles, active proliferation of the cells lining the neural tube being a conspicuous feature. As in other parts of the young cerebro-spinal tube, the differentiation of the cells constituting the inner layer of the optic cup results in the formation of two varieties of tissues — the nervous elements and the sustentacular tissue. The differentiation of the nervous constituents results in the formation of two groups of elements — the nerve- cells and their outgrowths, the nerve- fibers, and the retinal neuro-epitlielittni ; the latter eventually becomes special- ized as the layer of rods and cones and the outer nuclear layer, these two strata together constituting the layer of visual cells, as the sensory epithe- lium is here appropriately called. The further development of the sustentac- ular tissue produces the characteristic radial fibers of Miiller, which extend throughout the thickness of the retina and afford support and connection to the nervous elements. In addition to the derivatives from the involuted ectoderm, ingrowths of true connective tissue take place from the surround- ing mesodermic tissue which accompanies the ramifications of the early arteria centralis retinae. While the developmental changes jusl described affeel the far greater part of the optic cup, the anterior zone, corresponding to the double-layered lips of the cup, differ- materially in it- growth and fate. Coincidently with the increase of surface which the general expansion of the developing eye effects, the anterior zone of il ptic cup becomes greatly thinned, the inner layer becoming reduced to a single layer of low columnar elements, in marked contrasl to the conspici - thickening which this layer undergoes throughout the posterior -egnient of the cup. Fir.. 11.— Section through developing eye of thirteen-day raM>it embryo i Piersol \:e, ectoderm ; I, lens, consisting of anterior nucleated division represent in<_ r thin fronl wall of lens-sac, ami greatly thickened posterior division completely filling cavity of sac by elongated tii>ers whose uuclei present crescentic zone («); p, posterior pigmented layer; /■. specialized anterior retinal layer; i", point where layers of optic vesii come continuous; n, extreme peripheral section of tissue of primitive optic nerve connected \\ iih vascular tunic v), occupying posterior surface <>t" lens: //j. surrounding mesoderm, which (at h grow - betw een lens and retina. 26 EMBRYOLOGY, ANATOMY, AND HISTOLOGY OF EYE. Che extension of the anterior marginal zone of the optic cup is intimately associated with the changes within the surrounding mesoderm, which lead to the development of the structures composing the ciliary region and the iris: the forward growth of the attenuated Lips of the cup contributes the double- layered, and later deeply pigmented, epithelial investment covering the inner surface of the ciliary body and the iris as tar as the pupil. Thenars ciliaris /■( tina and the pars n Una iridica, which include the deeply pigmented stratum covering these respective regions, are, therefore, representatives of the ante- rior zone of the ectodermic optic cup. The line of demarcation between the posterior visual and the anterior rudimentary segments of the optic cup i> at first not sharply marked, but later, when the conspicuous differences in the growth of the layers in the two regions become established, the anterior limit of the retinal area gradually becomes well defined at the position later indi- cated by the <>rn S( rrata. Development of the Optic Nerve. — The early optic stalk, which establishes connection between the primary optic vesicle and the inter-brain, i- involved in its ocular end in the invagination which affects the lower wall of the optic vesicle and results in the formation of the choroidal fissure. This folding-in — in addition to affording a means of entrance into the interior of the future optic nerve for the vascular mesoderm, from which later are produced the central retinal blood-vessels — is rendered necessary by the new relations of the layers composing the walls of the optic cup: without the corresponding readjustment of the walls of the optic stalk, as effected by the invagination along its lower margin, the walls of the stalk-tube would be continuous with the outer layer of the optic vesicle alone. In consequence of the folding-in of the lower wall of the stalk and the subsequent obliteration of its lumen by the apposition of its walls the layers composing the latter remain continuous with the invaginated portion of the optic cup, as well as with that possessing the original relation ; hence the connection is maintained not only with the thickened retinal sheet, but also with the attenuated outer stratum. The early lumen of the primary optic stalk soon disappears, and is replaced by a solid condition of the young optic nerve. This solidification is effected by two processes, one of which affects the greater central part of the stalk a- far as its cerebral attachments, while the other, which includes the end applied to the optic vesicle, is limited to the peripheral and smaller seg- ment of the nerve. The greater part of the hollow .-talk is converted into a solid cord by the gradual thickening of its walls, due to active proliferation of the elements, which results in the subsequent apposition and final oblitera- tion of the lumen. The solidification of the ocular portion of the stalk i> the result of both invagination and proliferation : the early invagination of the Iow.t wall of the -t.-dk when completed effects the closure of the lumen of the tube by the appo-ition and final fusion of the wall- of the tube; while the proliferation of the margin- of the furrow results in the approximation and complete closure of thegroove, the growth of the so imprisoned mesoderm, together with t he accompanying blood-vessels, producing the connective tissue surrounding the central retinal blood-vessels as they occupy the interior of till' opt IC l|el'\ e. The development of the nerve-fibers is a secondary but coincident process, the newly-formed liber- occupying the wall- of the rapidly closing stalk. The older views which regarded the optic liber- as being produced in loco along the course of the optic stalk are no longer accepted since the investiga- tions of Muller, Kolliker, His, and others showing that the young liber- grow DEVELOPMENT OF THE FIBROUS AND VASCULAR GOATS. 27 into the optic stalk from the nerve-cells Located al it- extremities. The great majority of fibers of the optic nerve may be regarded as the centrally directed outgrowths of the young neuroblasts situated within the developing retina: the axis-cylinder processes of these element- are guided in their journey to form central relations with the brain-centers by the supporting tissue contributed by the <>|>tie stalk. In addition, however, to the centrally growing fibers, there are other- which pass in the opposite direction, and represent the peripherally directed axis-cylinder processes of the neuroblasts situated within the brain. Further complexity of structure later arises from the ingrowth of the vascular connective tissue constituting the pial sheath of the optic nerve, the extensions of which tissue form the septa subdivid- ing the nerve into the variously sized bundles which are so conspicuous in transverse sections. The posterior parts of the optic stalks become the optic tracts, while their middle portions unite to form the optic chiasm. The sheaths of the optic nerve are produced by the direct continuation of the mesodermic investment from which the cerebral dura, arachnoid, and pia are derived. Development of the Fibrous and Vascular Coats. — With the exception of the corneal epithelium, the lens, and the nervous tunic with its cerebral attachments, which are derived from the ectoderm, all parts of the eyeball are developed from the mesoderm surrounding the primary optic vesicle. Coincidently with the changes affecting the optic vesicle, as already noted, the surrounding mesoderm exhibits a differentiation, marked by active cell-proliferation and condensation, which results in the production of a dis- tinct envelope of actively growing embryonal connective tissue. The posterior segment of this mesodermic capsule undergoes further differentiation into an outer, relatively dense tunic, which becomes the sclerotic, and an inner coat, which later is distinguished by a looser texture and greater vascularity. Very early in the history of the eye the lens-sac is separated from the overlying ectoderm by a thin stratum of mesodermic tissue; later this layer becomes cleft, one part remaining as a thin mesodermic sheet over the outer surface of the young lens, the other adhering to the inner surface of the ecto- derm. The strata of mesoderm so formed constitute the pupillary membrane and the substantia propria of the cornea, the intervening cleft being the earliest indication of the future anterior chamber. The forward growth of the thin double-layered lip of the optic cup beyond the equator of the young lens and over its anterior surface is accompanied by a proliferation of the adjacent mesoderm and the extension of the primitive choroidal stratum which accompanies the retinal tissue in its growth forward. This anterior extension of the lip of the optic cup and the associated mesoderm give- rise to the rudiments of the iris and ciliary body, this expansion progressing until almost the entire anterior surface of the lens i< covered : the central unoccu- pied area thus corresponds to a circular aperture within the retino-iridial sheel which remains as the pupil. In the early stages this opening is closed by tin- vascular pupillary membrane, ;i temporary structure which disappear-; before birth. The active growth of the thin lip- of the optic cup results in -till greater attenuation of the component strata of epithelial cells until these are repre- sented by the low columnar and cuboidal element- of the par- ciliaris and pars iridica retinas; the pigmentation of these epithelial cell- also incn until the anterior portion of both layers is loaded with color-particles the conspicuous pigment layer covering the posterior surface "f th produced. The accompanying mesodermic layer thickens and gives '" 28 EMBRYOLOGY, ANATOMY, A .YD HISTOLOGY OF EYE. the stroma and muscular tissue of the iris and ciliary body, and for a time is also continuous with the vascular tunic of the lens. About the beginning of the third month, in consequence of an unusual active lateral expansion, the epithelial layers are thrown into a series of radial folds which surround the equator of the lens : these plications arc the earliest suggestion of the future ciliary processes, and into them shortly afterward delicate processes of mesodermic tissue extend; later these become more robust, and in them the characteristic richly vascular structures of the ciliary processes develop. In contrast to the deep pigmentation involving both epithelial layers of the pars iridica retinae, only the outer stratum of the pars ciliaris contain- pigment, the elements of the inner layer remaining uncolored and retaining to a greater extent their original columnar form. The corneal stroma becomes Mended with that of the sclerotic tunic, so that eventually the two become continuous. With the formation of the ante- rior chamber the mesodermic elements immediately in contact with the lymph-space differentiate into flattened cells which become the posterior endothelium of the cornea and the anterior endothelium of the iris. The formation of the spaces of Fontana and of the trabecular of the ligamentum pectinatum iridis is closely associated with the differentiation of the ante- rior extremity of the primitive choroidal tract and the production of the membrane of Descemet; to this tract the name pars uvealis cornea has been applied. Development of the Vitreous Body. — This is intimately related with the primary changes of the optic vesicle. As already described, the invagina- tion of the latter sac involves not only the external portion directed toward the surface, bu1 affects likewise its inferior wall, resulting in the production of the choroidal fissure, which leads from the exterior into the cavity of the secondary optic vesicle. The surrounding mesoderm takes advantage of the deft -o established to gain entrance into the interior of the optic cup, which soon becomes filled with an extremely delicate mesodermic tissue occupying the space between the young lens and the retina. The primitive vitreous early becomes vascular by the multiplication and extension of the branches of the hyaloid artery, which is continued from the central retinal vessel- as far forward a- the inner and posterior surface of the lens, where they spread out to aid in forming the vascular tunica lentis. The vitreous body, therefore, musl be regarded as composed of modified mesoderm, and presents the characteristics of embryonal connective tissue throughout the earlier periods of it- growth. Later, the blood-vessels of the vitreous disappear and the structural elements become reduced to atrophic cells of irregular form and distribution : the remains of the hyaloid vessels are sometimes observed even after birth asa delicate c<>\'(\ stretching from the optic-nerve entrance toward the lens. (See page !'»•"».) The peripheral zone of the young vitreous becomes condensed, and pro- duces the hyaloid membrane which limit- the vitreous on all sides except behind the lens, mid is continued forward to fade away over the ciliary regii >n. Development of the Eyelids.— This begins quite early a- an upper and lower fold of i he integumentary layer, which gro'H over the corneal surface until they meet and fuse. The fusion of the palpebral fold- in man takes place early in the third month of fetal life, the union continuing until shortly before birth, when the permanent separation is effected by cleavage through the common epithelial layer formed by the union of the ectoderm along the line of juncture. ANATOMY OF THE EYE. 29 During- the period of fusion the mesoderm contained within the palpebral folds, bounded externally and internally by coverings of ectoderm, dilleren- tiates into thin layers, which give rise t<» the subcutaneous tissues, the mus- cular structures, and the subconjunctival or tarsal stratum. The Meibomian and other glands contained within the lid are derived as ingrowth- and pro- liferations of the ectoderm covering the adjacent surface of the immature lid. The tear-gland appears during the third month as a solid ingrowth of the conjunctival ectoderm close to the upper lid ; later the epithelial ramifications acquire a lumen. The ocular muscles, together with the various structures contained within the orbit, with the exception of the nerve-fibers, primarily are derivatives of the mesoderm. The foregoing sketch of the development of the eyeball shows that the derivatives of the outer and middle blastodermic layers may be grouped as follows : A. From the ectoderm are derived — Anterior epithelium of the cornea and its conjunctival continuation. Crystalline lens, including the epithelium of its anterior capsule. Retina, including the anterior extensions forming the pars ciliaris and pars iridica. Sustentacular tissue of the optic nerve. B. From the mesoderm are derived — Corneal stroma and endothelium. Sclerotic coat. Vascular tunic, including the choroid and the connective-tissue stroma of the ciliary region and iris. Vitreous body. Suspensory apparatus of the lens. Connective-tissue investments of the optic nerve. Vascular tissues of the retina. The epithelial tissues of the eyelids and conjunctival sac, including the lid-glands, the lachrymal gland, and the lining of the tear-channels, are derivatives of the ectoderm ; the surrounding connective tissues are products of the mesoderm. ANATOMY OF THE EYE. The Orbits. — The orbits are horizontally-placed pyramidal fossse, the anteriorly and somewhat outwardly directed bases of which correspond with the facial plane, their apices being occupied by the inner extremity of the sphe- noidal fissure. The angles between the four conventional walls of the space are not sharply marked, but rounded off, so thai the surfaces pass gradually one into the other, each orbital cavity approaching often more closely the conical than the pyramidal form. The inner walls, composed of the nasal process of the superior maxilla, the lachrymal, the ethmoid, and Lhe body of the sphenoid, lie generally parallel with each other; the external walls, formed by the orbital surface of the malar bone and great wing of the sphenoid, on the contrary, form almost a right angle between their plane-. The roof and floor, composed respectively of i lie frontal and small wing of the sphenoid and of the malar, the superior maxillary, and the palate bone-, gradually converge toward the apex of the generally conical cavity. The orbital axes do not correspond accurately with the horizontal plane, since ;it their posterior pole- they lie from L5' to li < > above; when prolonged backward, the axes meet in the vicinity of the sella Turcica and include an angle of about 43°. The distance between the anterior ends of thi orbital 30 EMBRYOLOGY. AXATn.MY, AND HISTOLOGY OF EYE. axes is approximately 60 mm. The depth of the orbit varies from 40-45 Him., being usually from 3-5 mm. greater in the male than in the female skull. The capacity of the adull orbit approximates :}() c.cm. The irregularly quadrilateral base * > t * the orbit, corresponding to the facial apertures, is bounded by the thickened, rounded, and partially over- hanging margins contributed by the frontal, malar, and superior maxillary bones. The apex is occupied by the inner and wider extremity of the sphenoidal fissure, the narrower continuation of which extends upward and outward as a conspicuous cleft separating the roof and outer wall of the orbit throughout the posterior half of their line of meeting. The optic foramen lie- slightly to the inner and upper side of the apex of the orbit, within tin' -mailer ala of the sphenoid. The angle between the external wall and the floor i- occupied throughout it- posterior three-fourths by the narrow and elongated sphenomaxillary fissure, which communicates with the spheno- maxillary fossa at its posterior inner end, and with the zygomatic fossa at its anterior outer extremity. The posterior part of the orbital floor i- grooved by the beginning of the infraorbital canal ; the contour of the anterior mar-in of the root' is interrupted by the supraorbital noteh or foramen ; the inner wall below lodges the lachrymal groove, formed by the lachrymal and superior maxillary bones, while higher, in close relation with the internal boundary of the arched roof, is the depression occupied by the pulley of the superior oblique muscle. Behind the external angular process lies the lachrymal fossa for the accommodation of the tear-gland. The Eyelids and the Conjunctiva. — The eyelids are two broad mov- able folds of integument supplemented and strengthened by muscular bundles and dense fibrous tissue, and lined by a mucous membrane: they are attached to the upper and lower orbital margins, and aid in covering in the structures at the base of the orbit and the projecting anterior segment of the eyeball. A- already noted, the eyelids develop as duplications of integument which gradually approach, and, finally, about the end of the third month, fuse along the ap- proximated edges to form a closed sac sur- rounding the anterior segment of the eye- ball. Before birth the permanent scpara- irallj opened, from a graph i Merkel i. Horizontal pla nrough inner cantb the eye- lids separated by hooks (Quair Merkel i Rs, plica semilunaris : PI ior ami in i] Lachrymal puncta; Oar, lachrymal car- uncle: Lpm, internal tarsal ligament. Hon of the lid- take- place, by which lime the -kin in relation to the eyeball has lost its original integ entary characteristics, and has assumed those of a mucous membran* — the conjunctiva. The palpebral fissure, bounded by the arched free margins of the eyelids, resembles an almond in it- general form (Fig. L2). It- Length, measured EYELIDS AND CONJUNCTIVA. 31 from its extreme angles, is usually between 2. tarsal plate in which are lm bedded thi Meil lian gland g, sebaceous glands near haira of Integument ; j, sweat glands ; k, indi /: ) ' EL WS A ND CONJUNCTl I ' . I . 33 are arranged in double or triple rows near the anterior border of the lid. The average life of an eyelash is probably about four months, the older and thicker cilia being constantly replaced by the young and slender hairs. The muscular layer <>t* the eyelid consists essentially of the palpebral por- tion of the orbicularis palpebrarum, which is arranged as concentric fibers, which occupy the interval between the subcutaneous tissue and the tarsal plate and its associated tendons. The elliptical muscular bundles, when cut in Longitudinal section of the eyelid, appear as irregular groups of trans- versely cut fibers. The innermosl of the concentric bundles of the orbicularis lies close to the inner margin of the lid, and constitutes a robust and partly isolated group of fibers known as the ciliary muscle or mnscle of Riolan. The fibers composing these bundles surround the structures occupying this part of the border of the lid, including the hair-follicles, sebaceous glands, glands of Moll, and the ducts of the Meibomian glands (Fig. 15). Fir,, ic. —Dissection of the tarsal plates and their ligaments (Testut): 1, 2, upper and lower tarsus; 3, 4, external and internal tarsal ligaments; 5, expanded tendon of levator palpebra ; 6, 6', septum orbi- tale ; 7, lachrymal >a<- ; 8, supraorbital vessels and nerve ; 9, lachrymal artery and nerve ; 10, 11, openings for supra- ami infratrochlear nerves; 12, opening for the angular vein; 13, tendon of superior oblique muscle. The fibrous stratum of the eyelid has as its principal constituent the crescentic plate of firm fibrous tissue known as the tarsus or tarsal cartilage. This structure, composed entirely of dense connective tissue and without cartilage-cells, exists in both eyelids as a sustaining band, which is important in maintaining the proper form of the lid-margins. The tarsal plates vary in .-izc in the two eyelids, the upper tarsus being broader and more arched than that within the lower lid. The extremities of the tarsi are united to each other and to the orbital walls by firm band- of fibrous tissue, the mesial and lateral palpebral ligaments: The upper tarsus, corresponding with the greater width of the superior lid, is wider than the lower plate, measuring about 10 mm. al the point of its greatest breadth, or about twice the width of the lower. In length the tarsi are almosl equal, ami extend along nearly the entire lid-margin, aboul the middle of which tiny p..--.-- their greatesi thickness, diminishing toward either end as well as toward their convex b< >rders. The tendon of the levator palpebral, as it- lower broadened end expands 3 34 EMBRYOLOGY, ANATOMY, AND HISTOLOGY OF EYE. into the upper eyelid, becomes closely related to the inward extension of the orbital fascia, which, as the septum orbitale, passes from its peripheral attach- ment at the orbital margin into the eyelids, forming a partition which closes in the periocular structures and prevents the extrusion of the orbital fat be- tween the eyeball and orbit (Fig. 16). In the upper lid the septum orbitale or palpebral fascia blends with the tendon of the levator palpebral, the two forming a layer of connective tissue which intervenes between the orbicularis and the conjunctiva above, and is largely inserted into the tarsus below, some bundles passing in front of the tarsal plate. In the lower lid the septum joins the tarsus in common with fascial expansion connected with the inferior straight and oblique muscles. 'Idie relations of the upper tarsal plate to the expanded tendon of the levator palpebral muscle are most intimate. The fibrous tissue of the tendon of this muscle is arranged in three layers — the upper, which expands into bundles which are inserted into the summit of the conjunctival fornix and adjacent part of the orbital portion of the lid, while in the tarsal portion the fibrous bundles interlace with the nuisele-fihers of the orbicularis palpebrarum, on the inner surface of which they form an imperfect fibrous sheet. The middle part of the levator aponeurosis contains bundles of involun- tary muscle, the so-called superior palpebral muscle of Miiller, which are inserted principally into the upper margin of the tarsal plate. The lower stratum of the tendon consists of bundles of fibrous tissue, and is attached at various points to the conjunctiva, and is closely blended with the fascial pro- cess connected with the superior rectus muscle. In the lower lid the expan- sions of the fascial process connected with the inferior rectus replace the levator aponeurosis of the upper lid. Bundles of involuntary muscle occur also in the lower lid, and constitute the inferior palpebral muscle, while the fibrous bundles are interwoven with the fasciculi of the orbicularis palpe- brarum. I'he ocular surface of the tarsal plates, when inspected during life after eversion of the eyelids, presents numerous parallel vertical rows of small yellowish granules: these latter are the acini of the Meibomian or tarsal (//anils seen through the conjunctiva. When examined more carefully the tarsal glands are seen to be enlarged and modified sebaceous glands imbedded within, and occupying almost the entire thickness of, the dense connective tissue forming the tarsi : they number between thirty and forty in the upper lid ami from twenty to thirty in the lower. Each eland consists of a straight or slightly sinuous vertical duet, from the sides of which open numerous diverticula or alveoli. The Meibomian glands occupying the middle of the tarsi are longer and more vertically disposed than those placed nearer the extremities of the plate-, where the glands, in addition to being shorter, not infrequently terminate by sharply bending on themselves. The ducts ter- minate as minute puncta arranged in a row along the margin of the eyelid near n- -harp inner border, ami are lined by a direct continuation of the stratified squamous epithelium of the adjacent integument; the acini of the glands are clothed with cuboidal cell- which resemble the elements found in other sebaceous glands, containing numerous fat-droplet- within their proto- plasm. The free margins of the eyelids present an outer and inner border, which differ in their forms and relations ; t he outer border is somewhat rounded and besel with tie' long curved cilia, while the inner I- sharply defined by the line of juncture of integument and conjunctiva, along which open the orifices of the Meibomian elands. In addition to the hair-follicle- and associated EYELIDS AND CONJUNCTIVA. 35 sebaceous glands lodged within the palpebral margin, a Dumber of enlarged and modified sweat-glands, or glands of Moll, lie about midway between the two borders of the lid, and open in close proximity to or into the mouths of the hair-follicles ; the glands of Moll in the upper lid extend into the sur- rounding tissue to a depth equal to the extremities of the hair-follicles in the lower lid — indeed, exceeding the hair-follicles in length. The ends of the hair-follicles, sebaceous glands, and glands of Moll are surrounded l>v the deepest filters of the ciliary muscle of Riolan, the greater part of the group of muscular bundles lying between the glands of Moll and the tarsus. The conjunctiva invests the ocular surface of the eyelids and the anterior segment of the eyeball, and is, therefore, appropriately divided into the -pal- pebral and bulbar portions. The annular fold which marks the peripheral limit of the conjunctival sac is known as the fornix conjunetivce. The palpebral conjunctiva presents a further subdivision into the tarsal and orbital areas, based on the differences which characterize these two seg- ments. The conjunctiva covering the tarsus, directly continuous with the integument at the lid-margin, so closely adheres to the firm fibrous tarsal plate that the conjunctival membrane is immovably attached to the fibrous lamella ; the Meibomian glands indistinctly show through the conjunctiva as vertically arranged, parallel, yellowish-white lines. The orbital conjunctiva, covering the fascial and tendinous expansions which are blended with the arched border of the tarsi, is attached by the loose subconjunctival connective tissue to the subjacent structures, upon which it freely moves. In contrast to the velvety appearance of the tarsal portion, the orbital conjunctiva is smooth and glistening, although less firmly fixed to the underlying tissues. The peculiar velvety appearance of the tarsal conjunctiva depends upon the presence of minute interlacing furrows and intervening ridges and papillae; the latter are especially well developed near the orbital border of the tarsus. The lymphoid characteristics of the subepithelial layer of the tarsal conjunctiva are conspicuous in the situations in which the tarsal papillae are best developed; hence in the vicinity of the tarsal border the general lymphoidal infiltration is often replaced by local aggregations of cells in the form of lymph-follicles or trachoma-gland-. These structures, how- ever, are very variable in their position, number, and size, and may be entirely wanting or found in other parts of the conjunctival sac. At the mesial canthus the conjunctiva lines the lachrymal lake, and on the caruncle maintains its primary integumentary character. Just external or lateral to the punota the conjunctiva presents a well-marked vertical cres- centie fold, the plica semilunaris, which represents a rudimentary nictitating membrane. The conjunctiva covering the tarsi and the cornea is more fixed than else- where, being in these situations so inseparably attached to the subjacent structure- that it follows the frequent movements of these parts. The remaining portions of the conjunctiva are separated from the under- lying structures by the subconjunctival tissue, which, on account of it< loose ami elastic nature, allows the conjunctiva to be moved to and fro with readi- ness. The same loose character of this areolar ti<v an annular thickening- which corresponds to the limbus cornese in position. Glands have been described within the more concealed portions of the conjunctival sac, those of the fornix very closely resembling the tear-gland in structure. Adipose tissue not infrequently occurs as groups of fat-cells; in advanced age the accumulation becomes conspicuous as a yellowish patch (dose to the corneal margin. The blood-vessels of the eyelids are derived from several sources (Fig. 17), Pio.17.— Bl of the eyelids (Testut) : t, supraorbital artery and vein ; 2, nasal artery, anas- tomosing wiiii terminal branch of angular (3) of facial artery (4); 5, Infraorbital artery: 6, superficial temporal artery; 6', malar branches oi transverse facial: 7. lachrymal; 8, superior palpebral artery, with secondary arch (8')> and anastomoses (9) with temporal and lachrymal ; 10, Inferior palpebral artery ; ii. facial vein; 12, angul r vein; 13, superficial temporal vein. since all the surrounding neighboring arteries contribute branches which more or less directly take pari in the supply of the palpebral folds. The principal blood-supply of the eyelids is from the internal and external pal- pebral arteries; the former are direct branches from the ophthalmic, usually by a con n trunk given off jusi before the ophthalmic artery divides into ii- frontal and nasal branches, and the latter are derived from the lachrymal. The interna] palpebral arteries, commonly somewhat larger than the external, include a superior and inferior, which after piercing the palpebral fascia as the marginal arteries, inn along the free margin of the corresponding eyelid, from 2.5 •"> mm. removed, ami anastomose with the external palpebral vessels to form the upper and lower tarsal arches. The transverse facial and super- ficial temporal contribute branches which join in the anastomotic circuit at tin- outer margin of the orbit. CONTENTS OF THE Oh' HIT. 37 In the upper eyelid, and sometimes less perfectly developed in the lower as well, a secondary tarsal arch is formed by a branch of the superior pal- pebral, the superior marginal artery, which runs along the convex border of the tarsal plate between the lamellae of the tendon of the levator pal- pebral Numerous small twigs join the tarsal arches, and establish an elaborate anastomosis in which the infraorbital and facial arteries also take part. Branches of distribution pass forward from the tarsal arches for the supply of the integument and orbicularis, and backward, by means of per- forating and encircling twigs, to supply the tarsus and Meibomian glands and the palpebral conjunctiva. The supply of the tarsus is maintained especially bv the superior tarsal arch, while the inferior arch is devoted to the nutrition of the margin of the eyelid. Just before the internal palpebral artery reaches the lid numerous twigs are distributed to the lachrymal caruncle, tear-sac, and the tissues surrounding the latter and the canaliculi. The naso- lachrymal canal receives its supply from a branch formed by the anastomosis of the infraorbital with the inferior internal palpebral artery. The veins of the eyelids do not accurately follow the course of the arteries, but are arranged in two series, the post-tarsal and pre-tarsal. The former collects the blood from the conjunctival surface and a part of the Meibomian glands, and is tributary to the ophthalmic vein ; the latter receives radicles from the integument, muscular structure, and the Meibomian glands, and forms a subcutaneous network which passes into the superficial temporal and facial veins. The lymphatics of the eyelids are disposed as a pre-tarsal and a post-tarsal network, the former of which receives the tissue-juices from the integument and muscle, the latter from the conjunctiva and Meibomian glands. Per- forating branches establish communication between the two networks. The submaxillary and parotid lymph-glands receive the larger lymph-vessels from the palpebral networks. The sensory nerves of the eyelids are derived from the ophthalmic and superior maxillary divisions of the trifacial. The upper eyelid is supplied principally by branches from the frontal and supraorbital nerves, which freely join and form a superior marginal plexus along the edge of the eyelid. The chief supply of the lower lid is derived from the branches of the infraorbital nerve, which ascend to the border of the lower lid, where they form the inferior marginal plescus. These nerves are supplemented by twigs from the supra- and infratrochlear branches, which are distributed to the area around the mesial canthus. An especial lower branch from the infratrochlear nerve supplies the mucous membrane of the lachrymal sac The terminal branches of the lachrymal nerve become subcutaneous a short distance beyond and above the external canthus, contributing a few twigs to the eyelids, but end- ing chiefly in the integument to the outer side of the orbit. The motor nerves distributed to the muscular structures of the eyelids include branches from the oculo-motor to the levator palpebral, and from the facial to the orbicularis palpebrarum ; additional sympathetic libers are dis- tributed t<> the involuntary muscle of the lid-. The ramifications of the motor and sensory nerves freely intermingle, and constitute a network ol considerable complexity within the superficial structures of the eyelids. The Contents of the Orbit. — The orbital contents, including the visual apparatus, consisting of the eyeball and it- associated nerves, muscles, and glands and the incidental structures, a- branches of the ophthalmic U I- vessels and the trifacial nerve, which pas- through the orbit • u r<<"l' to more remote parts, are supported by the general fibro-adipose intraorbital tissue. 38 EMBRYOLOGY, ANATOMY, AND HISTOLOGY OF EYE. This periocular cushion of fat occupies the interspaces between the various connective-tissue partitions and bands constituting the fibrous framework, which separates, as well as holds together, the various constituents of the orbital contents. Variations in the amount of the intraorbital fat affect the relations of the eyeball to the orbital opening, a conspicuous example of such change being familiar in the sunken or '•hollow-eyed" appearance following illness or conditions favorable to the absorption of adipose tissue. Since the majority of the structures within the orbit are grouped around the eyeball as parts subservient and accessory to the visual organ, the position of the ocular bulb with relation to the orbit is of importance, inasmuch as this Fro. iv oniiar muscles of rfghl Bide, viewed from above, after removal of roof of it (Testut) /:. section of greal \vinj, r of sphenoid ; C, section of malar bone ; /', anterior clinoid pro /.'■i'ii'- nerve; 1, superior rectus ; 2, superior oblique muscle with its pulley (2') and its insertion into tin ej • !, internal rectus ; I, external rectus : ■">. common well as possessing the longest tendon and mosl anteriorly situated place of insertion. The superior rectus is the smallest and weakest of the straight muscles, and has its insertion farthest from the cornea, but possesses the broadest line of attachment ; the inferior and external recti exceed tin- utile]- ill their length. Shortly before reaching the eyeball the muscular liber- of the recti ter- minate in thin membranous and somewhat expanded tendons of insertion, the fibers of which not only blend, but become intimately interwoven, with the tissue of the sclerotic coat. The line- of attachment, the slight convexities of which are directed toward the cornea, vary in their relation to the corneal 10 EMBRYOLOGY, ANATOMY, AND HISTOLOGY OF EYE. margin, that of the internal rectus being Dearest, and that of the superior rectus farthest removed. The length of the tendons of insertion of the Mm , wr Fig. 19.— Ocular muscles viewed after removal of lateral wall of orbil (Testut): a, eyeball; b, optic nerve; ''.'•'. eyelids: d, maxillary sinus; '. pterygoid plate;/, foramen rotundum; g, roof of orbit ; h, frontal sinus ; i, supraorbital nerve ; fc, septum orbitale ; l. levator palpebra superioris; 2, 3, superior and inferior recti ; i, I, portions of the cut external rectus; 5, internal rectus; 6, inferior oblique ; 7, inser tion of superior oblique; 8, annular ligament or tendon of Zinn. ncti and the distance from the cornea, determined by the accurate measure- ments of Merkel and of Fuchs, are as follows: Length of Distance of insertion ti ndon. from cornea. Internal rectus 8.8 nun. 5.5 nun. Inferior rectus 5.5 " 6.5 " External rectus 3.7 " 6.9 " Superior rectus 5.8 " 7.7 " The insertion-lines, therefore, progressively recede from the corneal margin from the insertion of the internal rectus to that of the superior, with a cor- st B C D ■ •i the positions ol the Insertions of the oculai muscles Fuchs-Testut) Right eye : vecl_ from above; ft, from no* from below; 0, from temporal side ; x, x, antcro-posterior E>, c, tf, superior, inferior, internal, and externa] rectus; e, oblique. responding diminution in the effectiveness of the pull of the several mus- cles. As suggested by Tillaux, the distance of the insertions from the THE OCULAR MUSCLES. II Fn;. 21.— The eyeball in situ with its muscles after removal of surrounding parts of orbital con- tents (Testut) : l. eyeball; l', superior rectus; 3, levator palpebral 1, inferior rectus; •"■, internal rectus: fi, external rectus: 7. inferior oblique; x . superior oblique ; 8', pulley and reflected tendi Q of same. cornea may be taken, for practical purposes, respectively a- ~>, (J, 7, and 8 mm. ( Fig. 20). The superior oblique, or trochlearis, arises aboul 2 mm. in front of the inner margin of the optic foramen : it proceeds forward and upward in close relation to the orbital wall, as far as the trochlear fossa, where its rounded irndoii traverses the short fibrous tube of the trochlea, and, at the anterior extremity of the canal, changes its direction at an angle of about 50°, the muscle passing back- ward and outward between the eye- ball and the anterior end of the superior rectus, to find its inser- tion into the sclerotic beneath the latter muscle, about midway between the corneal margin and the optic nerve. The inferior oblique, situated within the anterior part of the orbit, arises from the mesial wall of the orbit, close to it< anterior margin, from a slight depression in the orbital plate of the maxilla over the outer wall of the naso-lachrymal duct. Starting in short tendinous fibers, the muscle leaves the orbital wall and sweeps in a gentle curve outward, backward, and upward, passing between the inferior rectus and the floor of the orbit, and terminates in a tendon which is inserted into the sclerotic at the posterior and outer part beneath the rectus externus f Fig. 21 |. The levator palpebral superioris, as indicated by its name, is related to the upper eyelid, and claims attention in this place only on account of its inci- dental association with the ocular muscles. In it- origin it is closely related to the superior rectus, arising by a pointed tendon above and in front of the optic foramen. The muscle broadens in its course along the roof of the orbit, close to the periosteum for the greater part of its length, and covers the posterior half of the superior rectus; on reaching the anterior part of the orbital cavity, a little behind its superior margin, it descends through the adipo-e tissue as a membranous expansion which is attached to the root of the upper eyelid. Its insertion i- peculiar, and consists of two distincl layers: tin- upper anterior of these i- fibrous and passes in front of the tarsal plate, blending with the fibers of the orbicularis, while the lower posterior layer contain- non-striped muscular tissue, and is inserted into the upper border of the tarsus, constituting what is often described as the supe)"ior palpebral muscle of MuUa r | Fig. 23 . Closely associated with the action- of' the superior and inferior recti are the oblique muscles, by mean- of which the obliquity of the pull of these straighl muscles i- neutralized. The action of the superior oblique, from the location of the insertion and direction of its liber-, when the eyeball is in the primary position, is to move the cornea downward and outward ; that of the inferior oblique is to cause the cornea to move upward and outward. The slight outward rotation thus effected takes place, however, in opposite direc- tions, since when caused by the superior oblique the movement of the cornea 12 EMBRYOLOGY, ANATOMY, AND HISTOLOGY OF EYE. is from within outward, while when produced by the inferior oblique the upper halt' <>t' the vertical diameter i> displaced outward, the lower half at the same time being deflected inward. The obliquity of the pull of the oblique muscles is, therefore, well adapted to neutralize the obliquity attending the contraction of the superior and inferior recti, and, in point of fact, simple elevation and depression of the cornea arc effected by the combined action of the superior straight and the inferior oblique and the interior straight and the superior oblique, respectively. Oblique movements arc also the results of* the associated efforts of the recti and oblique muscles, as instanced in the common action of the superior and internal recti and the inferior oblique in movements by which the cornea is carried upward and inward ; the inferior and external recti and the superior oblique arc similarly associated in moving the cornea downward and outward. Fig 22. Semi-diagrammatic view of the relations of the orbital fascia with the superior muscles tut i : a, frontal bone, with ii> periosteum [a')\ b, sclerotic; c, cornea; the margin of the cornea. II' the conjunctiva is divided by a circu- lar incision just posterior to the corneal margin, the capsule of Tenon will he found so closely united with the conjunctiva that reflection of the latter structure will open Tenon's space and expose the capsule at its anterior limit (Fig. 23). The tendon- of the various ocular muscles pierce the capsule of Tenon in order to gain their insertions into the sclera, which may thus he regarded as lying within the -pace of Tenon, although the tendons are separated from actual contact with the lymph-stream by means of an endothelial covering. The slit-like openings in the capsule made by the passage of the tendons are strengthened by local thickenings of the fibrous tunic, from which tubular extensions of the capsule are prolonged backward upon the muscles lor ;i variable distance, approximately for half their length. The fascial sheaths thus obtained become gradually more and more attenuated in their course toward the origin of the muscles, until finally they fade away by blending with the perimysium, [n the case of the superior oblique the tubular pro- longation of tin ■ capsule extends only over the reflected tendon of the muscle, and terminates at the trochlea, where it ends by becoming attached to the margin of the pulley. The -heath investing the inferior oblique extends as fat- a- the Ihioi- <<\' the orbit, and there fuses with that accompanying the inferior rectus. The inner or ocular border of the vertical slit-like openings through which the tendons of the straight muscles, particularly of the external ami THE LAI ll I: ) 'M AL APPABA 7V s. I :, internal, pass, is especially strengthened by thickenings "I" the fascia, which are further reflected outwardly along the adjacent sides of the tendon-sheaths, forming additional connections between the muscles and the capsule of Tenon. In view of the fad that the latter structure at certain points is firmly con- nected with the bony walls of the orbit, these supplementary hand- in a measure act as pulleys and effect the important object of preventing undue pressure on the eyeball during muscular contraction. In addition to the foregoing conjunctival and muscular relations, the capsule of Tenon is connected with the orbital walls by means of fascial hands, the most important of which are the suspensory and check ligaments ( Fig. 24). The suspensory ligament consists of a hand of orbital fascia in the anterior part of the orbit, where it forms a hammock-like hand of considerable breadth and density ; the suspensory ligament is attached mesially to the lachrymal and externally to the malar hone, while its broader central part blends with the capsule of Tenon below the eyeball, to the support and position of which it materially contributes. A somewhat similar hut less well-developed hand lies above the eyeball and blends witli the sheath of the superior rectus and the levator palpebral, its extension forward coming into close relations with the upper lid. Other fibrous bands stretch across the orbit above the levator palpebral from the trochlea to the fronto-zygomatic juncture, and thereby form a fascial arch of importance to the support of the upper division of the lachrymal gland. The cheek ligaments are robust bands which extend from the fascial sheaths surrounding the external and internal recti muscles laterally as far as the malar and lachrymal bones respectively, where they blend with the ex- tremities of the suspensory ligament already described. Their action in limiting the contraction of the outer and inner straight muscles and in pre- venting excessive rotation of the eyeball is appropriately suggested by their name of " check ligaments." A somewhat similar, but less complete, arrange- ment exists in connection with the superior rectus, the contraction of which muscle is still further limited by close association with the levator palpebral The fascial extension from the sheaths of the inferior rectus is joined by a process from that of the inferior oblique, the two constituting a fibrous hand of considerable strength which is attached to the floor of the orbit on the one hand, and blends with the suspensory ligament of the eyeball on the other. The I/achrymal Apparatus. — The lachrymal apparatus consists of the tear-gland, lodged in the anterior part of the upper and outer orbital wall, and the system of canals by which the tears are conveyed from the inner side of the conjunctival sac to the inferior nasal meatus. The lachrymal t>r/i<>ii of the gland, sometimes described as a distinct HISTOLOGY OF IV 11. Fig. 25. — Section exposing the lachrymal chan nels and pari of the lachrymal sac (Testut): I plica semilunaris; 2, lachrymal caruncle; 3, 3' lachrymal puncta; 4, 4', vertical portions of lach- rymal canaliculi; 5, ■■'. horizontal portions; »'> fused portion ; 7, opening into lachrymal sac 18). Iii structure the lachrymal gland corresponds to a tubulo-raceraose gland df the serous type, it- acini being drained by a number of small ducts which in the orbital portion of the gland unite to form from three to six larger canals : these receive as tributaries the ducts (Venn the lower portion <>f the gland, the canals so formed opening by distinct orifices arranged with consid- erable regularity in a line in the fornix. In addition to the chief duets, which open with definite regularity, a vari- able number of smaller, independent canals terminate in irregular groups about the apertures of the larger ducts. The lachrymal passages (Fig. 25), including segments of very varying lumen and course, begin at the small crater-like lachrymal puncta which surmount the conical lachrymal papillce. The latter elevations occupy the sharply defined margins of the lids just where the mesial end of the arched palpebral borders passes over into the approximately horizontal and more nearly parallel boundaries of the lachrymal lake. The upper punctum lies l> mm. from the mesial canthus, the lower one being slightly farther removed. The apex of each papilla is directed toward the conjunctival surface, over which it glides during the changes of position of the bulbar conjunctiva occa- sioned by the excursions of the eyeball. The lachrymal puncta are immersed in the collection of tears occupying the inner angle of t he conjunctival sac, and continually carry off the secretion of the tear-gland l>\ capillary attraction. When closely examined the upper and lower papilla? and puncta are seen to vary slightly, the upper papilla? being more slender, higher, and pierced by a punctum about 0.05 mm. less in diameter than that of the lower lid. In structure the papilla? resemble the adjacent tarsal hands, being largely composed of closely-felted bundles of fibrous tissue, meagerly sup- plied with blood-vessels, well calculated to resist the action of the orbic- ular muscle. The lachrymal canaliculi, into which the puncta open, have at first a vertical course; very soon, however, they bend sharply, and continue their converging course generally parallel to the margins of the lachrymal lake as far as the inner canthus, where the canaliculi usually unite in a common canal which almost at once terminates by opening into the lateral and slightly posterior wall of the lachrymal sac. In exceptional cases the canaliculi maintain an independent course, and terminate by separate orifices which open into n diverticulum of the lachrymal sac, the sinus <>/ Maier. The entire length of each canaliculus measures from 8 10 mm., the upper canaliculus being longer, more curved, and steeper in its descending course than the lower. The lumen of the canal varies at different poini>: beginning af the narrow orifice of the punctum. which marks the mosl constricted point and measuring only ".I mm. in ilia meter, the canal soon widens into a spindle-form dilatation, which is followed by a diverticulum occupying the bend of the canaliculus. The horizontal portion of the canal measures a lit tic over 0.6 mm. in diameter. The walls of the canaliculi consisf of ;i lining of stratified squamous epithelium supported l»\ a delicate tunica propria rich in elastic fibers ; out- Bide, the muscular bundles of the lachrymal portion <»f the orbicularis palpe- THE LA CI 111 ) r Mu I L A PPA BA Tl r S. 47 brarum contribute an additional stratum, and by their sling-like fibers constitute a sphincter around the vertical portion of the canaliculi. The lachrymal sac, into which the canaliculi open, may be regarded as the upper dilated orbital segment of the naso-lachrymal duet, the lower part of which, or the duet propel 1 , traverses the bony canal and opens into the inferior nasal meatus. The length of the sac approximates 12 mm., when distended measuring between G and 7 mm. in diameter. The sac is situated at the side of the nose, near the inner eanthus, and lies within the deep lachrymal groove between the superior maxillary and the lachrymal bone; its upper part is embraced externally by the mesial tarsal ligament and some of the inner fibers of the orbicularis palpebrarum, while the orbital surface of the sac is covered by the fibers which spring from the lachrymal bone and constitute the tensor tarsi, or Horner's muscle. The upper blind end of the sac, or fundus, usually reaches to the level of the upper margin of the tarsal ligament, sometimes a little higher. The lower portion of the sac, between the inferior margin of the tarsal ligament and the commencement of the bony canal, differs materially from the upper in being covered in by comparatively thin and weak structures, the anterior wall of this portion of the sac having the attenuated orbicular fascia alone interposed between the integuments. In consequence of this weakness this point is frequently the seat of dilatations, both normal and pathological ; the con- spicuous bulging often seen in connection with impeded escape of the tears corresponds to the lower part of the sac, which is unprotected by the dense fibromuscular covering which lies in front of its upper half. The wall of the sac, as well as that of the duct, is composed of fibro-elastic tissue, strength- ened by fibrous processes derived from the tarsal ligament. Externally the wall of the sac is loosely connected with the periosteum by fibrous tissue, and therefore capable of distention ; internally it is lined by mucous membrane directly continuous with that of the nasal duct. The epithelium covering the mucous membrane of the sac, as well as of the duct, is columnar in type and possesses areas in which cilia are present. The nasolachrymal duct, which constitutes the last segment of the tear- passage, lies within the bony canal formed by the apposition of the superior maxillary, lachrymal, and inferior turbinated bones. The length of the nasal duct is very variable, at times being little over 11 or 12 mm., at others measuring twice as much, the difference being largely due to the manner in which the duct terminates in relation to the nasal mucous membrane, since as much as from 6—8 mm. of its length may be included in the oblique passage through the mucous membrane. The diameter of the nasal duct is from 3- 4 mm. ; it is not uniform, however, since slight constrictions at its beginning from the sac ami about the middle of its course are very frequent. The position of the lower end of the nasal duct also varies, but it is usually about •'!') mm. behind the posterior margin of the anterior nasal opening, and about I" mm. Prom the front of the inferior turbinal. The direction of this canal, a- indicated by the position of probes, varies considerably with regard to the degree of inclination of the course of the canal in relation to both the frontal and sagittal planes. In determining on the living subjeel the inclination of the canal with the sagittal plane, both Arlt and Merkel regard :i- trustworthy a comparison of the distance between the middle of the tarsal ligaments of the two sides with the distance between the points where the nasal alaj join the cheek. When these measurements coincide the nasolachrymal canal descends vertically; when, as usually, a difference is noted, the deviation from the perpendicular will be equal t<> half the difference. The direction of 48 EMBRYOLOGY, ANATOMY, AND HISTOLOGY OF EYE. the duel with regard to the frontal plane is best determined, according to Merkel, by a line drawn from the inner canthus to the interval between the second premolar and first molar tooth of the upper jaw. The course of the nasolachrymal duct in general may, therefore, be described as deviating slightly backward from the vertical (Fig. 26). The mucous membrane of the duct is connected by areolar tissue with the periosteum lining the bony canal, the mucosa, however, being separated from the periosteum by a venous plexus. The exact manner in which the duct opens into the interior nasal meatus varies: it may terminate as a simple round or elliptical orifice or by an inconspicuous slit-like opening leading obliquely into the mucous membrane. The latter arrangement is sometimes described as forming the so-called ra/rc of Homer, but the presence of a distinct occluding fold must be questioned. The valves described in other parts of the nasal duct consist merely of imperfect, irregular, and inconstant folds of the mucosa, the most constant and best-marked of which lies at the Maxillary Internal palpebral ligament. Opening of canaliculus into sac. Constriction marking begin- ning of bony canal. Middle concha. Int:-r;:r it'ln: : itel : M 5/ 11OS0- lachrymal duct. Inferior concha. Fig 26— Section showing the course and relations of the lachrymal sac ami nasolachrymal duct (Merkel) junction of the lachrymal sac and the duct, which corresponds to the nar- rowest point of the entire lachrymal canal. The blood-vessels supplying the lachrymal duct consist of the arterial branches from the nasal and inferior palpebral ; the relatively large and numerous veins mostly join the nasal plexus and become indirect tributaries to the ophthalmic and facial. The nerves distributed to the tear-passages are derived from the infra- trochlear branch of the nasal division of the ophthalmic. MACROSCOPICAL AND MICROSCOPICAL ANATOMY OF THE EYEBALL. The general form of the eyeball, as represented by the outline- ot its outer fibrous coat, is spherical: when critically examined, however, the anterior segment of the globe presents deviation from the typical form, due to flattening within a /one lying in front of the equator, corresponding to the attachment of the recti muscles, and consequent apparent undue prominence of the corneal segment. In sagittal section the eyeball ie aeemingl) made ANATOMY OF THE EYEBALL. 19 up of the segments of two spheres — a larger posterior sclerotic segment, embracing approximately four-fifths of the globe, and a smaller anterior corneal segment, which contributes the remaining portion of the bulb. The junction of these segments is marked by an external broad annular groove, the sulcus sclerce, which surrounds the corneal periphery. The eyeball presents further deviations from the globular form in tho inequality of its three principal diameters, the anteroposterior diameter being the longest, the vertical the shortest, and the transverse intermediate. The exact determination of these measurements is by no means a matter of 9 Y" i i *. 10 2 i Fig. 2".— Diagram of horizontal section of human eye (Merkel Rauber) : I, optic nerve ; J. dura) shoatli; 3, sclera; 4, conjunctiva ; 5, cornea; 6, choroid; 7, ciliary body and processes; 8 iris; •.'. n i", fossa centralis; n, ora serrata; 12, lens; [3, vitreous body; W, anterior chamber; 15, posterior chamber; 16, /■•; transverse, 23.5. The eyeball may therefore be regarded as a sphere slightly flattened from above downward and from side to side. When directed toward distant objects or in a condi- tion of accommodative vest the axes of the eyes are very nearly parallel ; the axes of the optic nerves, on the contrary, are divergent, their entrance lying between 2 and •"> nun. to the inner or nasal side of the point at which the axis of the eyeball meets the posterior wall (Fig. 27). The eyeball consists of three coats or tunics : 1. The external fibrous tunic, of which the sclerotic forms the posterior four-fifths and the cornea the anterior fifth, upon which depend the protec- tion of the more delicate parts within and, to a limited degree, the main- tenance of the general form of the organ. 2. The middle vascular tunic, embracing the parts to which the chief blood-supply of the eyeball is distributed, including the choroid, the ciliary body, and the iris. •"'.. The inner nervous tunic, which contains the specialized neuro-epithelium for the reception of visual stimulus, the nerve-cells, and the nerve-processes, which, as the nerve-fibers, converge to form the optic nerve. The refractive media, the crystalline lens, the aqueous humor, and the vitreous body, are enclosed within these coats, which the media, in turn, materially aid in supporting. The Fibrous Tunic. — The Cornea. — The anterior fifth of the eyeball i- occupied by the cornea, which structure, although principally composed of closely-felted bundles of dense fihrous tissue, presents a remarkable glass-like transparency, so important in admitting the rays of light to the interior of the ocular bull). The refractive index of the cornea is about 1.37, or a little above that of water and the aqueous fluid. The transparency of the cornea is pre- served only when the close normal apposition of its elements is maintained, any disturbance of the normal arrangement, as by compression, resulting in impaired transparency. The form of the cornea, when examined from in front, is not quite circular, but elliptical, the greater transverse diameter measuring 11.6 mm., the smaller vertical only 11 mm. The apparent projection of the cornea beyond the sclera depends on a slight flattening of the latter near the equator, rather than on an actual projection of the corneal pole beyond the general sphere of the eyeball. The curvature of the anterior corneal surface does not accurately corre- spond to a sphere, since the radius of curvature in the transverse direction (7.8 nun.) is slightly greater than the vertical radius (7.7 mm.); while slight asymmetry of the corneal curvature is probably always present, marked variation- are also of frequency and then constitute astigmatism. The form of the inner surface of the cornea, on the contrary, corresponds to :i Bphere, the radii of curvature being equal in all meridians, and measur- ing about <; mm. The discrepancy in the curvatures of the outer and inner corneal surfaces shows that the thickness of the cornea necessarily varies : the cornea i- slightly thicker al the periphery, where it measures from 0.9 to 1.1 iiim.. being from 0.8 to 0.9 mm. thick at the centre. The cornea? of persons advanced in age usually present the arcus senilis, which appears a- a narrow gray or yellowish-white crescentic border extend- ing beyond the periphery to ward the pupil. Not infrequently a complete ring encircle- the corneal limbus, formed by the fusion of the upper and lower crescents. The appearance is due to the infiltration of the corneal THE CORXKA. 5] stroma by particle- which arc usually assumed to he of a Tatty nature, although this is questioned by Fuchs, who regards the change as due to a limited hyaline degeneration of the corneal fibers. (See also p. .*52b\) The cornea differs from ordinary fibrous tissue in not yielding gelatin on boiling, hut a modified form of chondrin. The structure of the cornea, a- seen in vertical section, includes five well- marked layers : these are, from without in — 1. The anterior epithelium ; 2. The anterior limiting membrane; 3. Thi' substantia propria ; 4. The posterior limiting membrane; 5. The posterior endothelium. The (interior epithelium of the cornea is a direct continuation of the ecto- dermic covering of the adjacent conjunctiva, and represents one of the few- parts of the eve derived from the outer embryonic layer. The epithelium is stratified squamous in type, and thinnest over the central part of the cornea, the six to eight layers in this position together measuring about <>.04o mm.; at the periphery the epithelium is almost twice as thick. The deepest cells approach the columnar form, their bases, often somewhat extended, resting upon the anterior limiting membrane, while the outwardly-directed rounded ends are received between the cells of the more superficial strata. The ele- ments composing the middle layers are polyhedral in form, and often present the appearance of prickle-cells. The cells of the superficial strata and free surface are greatly flattened and lie par- allel to the free surface (Fig. 28). The anterior limiting membrane, mt mbrane of Bowman, or lamina elastica anterior, is conspicuous in the human cornea and represents a highly devel- oped basement-membrane. This layer appears as a homogeneous glassy band, about 0.002 mm. in thickness, imme- diately beneath the epithelium ; it is thickest at the center and thinnest at the corneal periphery. The membrane is resolvable into the fibrous fibrillae upon the application of suitable reagents, thus demonstrating its true nature as a localized condensation of the fibrous corneal stroma, of which it is a special- ization. The substance proper constitute- the chief bulk of the cornea, and is com- posed of the fibrous stroma, which is built up of innumerable interlacing bun- file- of fibrous tissue. The interlacing fibrous bundles are disposed with some regularity as lamella;, although the exacl number and arrangement of these are variable. The fibrillae of fibrous tis- sue, a- well ;i- the bundle-, are held together by the interfibrillar cement substance, which likewise aid- in joining the lamellae. The fibrous bundles Pig. 28. — Section of cornea Piersol a, an- terior epithelium; <■. anterior limiting mem- brane : '■. '<. fibrous stroma of substantia propria, containing corneal corpuscles (/) lying within Hi.- corneal spaces ; st.-rior limiting mem- braue; < . endothelium lining anterior chamber. 52 EMBMYQLOGY, ANATOMY, AND HISTOLOGY OF EYE. cross one another at various angles, and are often united by bands which pass between the adjacent bundles; these fibres arcuatce are especially conspicuous in the anterior lamella 1 . The peculiarity of the substantia propria in yielding after boiling a modified form of chondrin, instead of the usual gelatin, has already been mentioned. The cellular elements, the corneal eorpuscles, are flattened, plate-like connective-tissue cells which lie between the lainelhe of the fibrous stroma within the intercommunicating lymph-spaces hollowed out within the cement substance. The corneal cells are irregularly branched, and form, by means of their united processes, a protoplasmic network throughout the corneal stroma. The corneal spaces in which the cells lie are larger than the cells, and are therefore only partially filled by the protoplasmic elements, the unoc- cupied space affording channels for the circulation of the nutrient tissue-juices upon which the investment of the non-vascular cornea depends. Communi- cation between the corneal spaces i- established by the canaliculi which pass from one space to the other. The corneal cells usually are applied to one wall of the space-, and, in principle, resemble the endothelial plates which line other and larger lymphatic cavities. Occasional migratory leukocytes, or wandering cells, are also found within the system of corneal juice-channels. The posterior limiting membrane, membrane of Descemet, membrane <>j I), mows, or posterior clastic nu mbrane, appears as a sharply-defined homogene- ous hand from 0.010 to 0.012 mm. in its thickest peripheral portion, at the inner boundary of the substantia propria. It differs from the anterior limiting membrane in its marked resistance to acids, alkalies, boiling water, and other reagents ; it resembles, but is by no means identical with, elastic tissue. It is capable of complete separation from the substantia propria after prolonged maceration in a 1<> per cent, solution of sodium chlorid. The layer in ques- tion contains no cells, and ordinarily presents no indication of being composed of secondary lamellae, although sometimes after reagents it show- traces of such structure. The relations of the posterior limiting membrane at the corneal periphery are of interest, since in this position it breaks up into numerous bands which are continued into the trabecules forming the pectinate ligament of the iris. The posterior endothelium covers the inner surface of the membrane of Descemet and forms part of the lining of the anterior chamber of the eye. This innermo-t stratum of the cornea is composed of a single layer of poly- hedral plate-, the outline- of which constitute a mosaic of considerable regu- larity. The cells closely resemble ordinary endothelial plates, possessing oval, sometimes reniform, nuclei which are usually of greater thickness than the surrounding cell-body. The endothelium and the membrane of Descemel are of importance as constituting almost impassable barriers to the escape of the aqueous humor into the lymph-channels of the cornea. The blood-vessels of the normal fully-developed cornea are limited to an extremely narrow peripheral /one, about 1 mm. in width, the remaining portions of the cornea being entirely devoid of blood-channels. The vascu- lar /one contain- tin' terminal loops of the episcleral branches derived from the anterior ciliary arteries. The venous radicles become tributaries of the anterior ciliary veins. The /" roes of the cornea constitute a rich supply arranged in the form of numerous plexuses. The corneal nerves are derived from the ciliary plexus, contributed by the long and short ciliary nerves, and form an annular plexus in the vicinity of the corneal margin. The twigs from the annular plexus pass either directly or indirectly to the corneal tissue, those destined for the THE SCLERA. .•interior layers first having joined the conjunctival nerves before proceeding to the cornea. The more numerous branches winch pass directly to the corneal stroma from the annular plexus enter the substantia propria near the posterior Limiting membrane, the far greater number, however, passing to the anterior lamella, only about one-third of the nerves which enter the cornea being distributed to the posterior layers. The nerve-bundles, on penetrating into the corneal stroma, are invested for a short distance, from 0.75— 1 nun.. by perineural lymph-sheaths, the individual nerve-fibers losing their medul- lary sheaths at about the same time. After entering the substantia propria the nerves form the fundamental plexus within the corneal stroma, from which numerous lateral branches are given off at various levels; these are composed of non-medullated fibers which soon break up into the component varicose fibrilke. In addition to the lateral twig-, perforating branches ascend through the anterior lamellae as far as the epithelium, beneath which they form the subepithelial plexus. The terminal tibers of this plexus in many instances enter the epithelium to end either in special end-bulbs or between the cells as the intraepithelial plexus. The plexuses within the substantia propria formed by the twigs given off at various levels spread out between the lamellae of fibrous tissue ; the nodal points or place- of meeting of the fibers are often marked by angular areas outlined by the interlacing fibers ; nuclei, belonging to the delicate nerve- sheaths, are sometimes present. The terminal fibers of the corneal nerves are related to various forms of end-organs, among which are intricate convo- lutions, less-contorted loops and hooks, and irregular quadrate plates. The Sclera. — The sclerotic coat forms the posterior four-fifths of the fibrous tunic of the eyeball, contributing largely to the protection and sup- port of the more delicate structures within, as well as affording the point- of attachment of the ocular muscles. Although composed of practically the same histological elements as the cornea, the disposition of these is such that the dead-white opacity is produced which so conspicuously contrasts with the beautifully transparent cornea. The sclera is thickest over the posterior third of the ball, where the maintenance of a uniform curvature for the support of the retina is of great importance : in the vicinity of the optic nerve the sclerotic coat measures nearly 1 mm. in thickness, graduallv becoming thinner toward the anterior boundary, until beneath, or just posterior to, the zone of attachment of the recti muscles the sclera is reduced to about 0.4 mm. Anterior to the tendon- zone the thickness of the fibrous tunic is augmented by the expansion of the muscle insertions until it reaches about \ the outer and inner scleral processes : of these the inner i- -holler and doe- not reach a- far toward the anterior pole as the outer. The connection- of the inner scleral process are of especial importance on account of the relation- to the structures marking the meeting <»l the Cornea, the iii-, and the ciliary muscle. Jusl anterior and external to the THE VASCULAR TUNIC. 55 inner scleral process a distinct, usually somewhat irregularly elliptical, open- ing indicates the position of the annular venous sinus, the tut mil of Srltlniun (Fig. 29). This channel, also called the circulus venosus ciliaris, as seen in meridional sections, elliptical or pyrii'orm in its transverse figure, measures about 0.3 and 0.045 mm. in the longest and shortest diameters respectively. The walls of the canal of Schlemm differ greatly in character, the outer boundary being dense, while the inner is composed of a spongy reticulated layer, apparently the continuation of the inner scleral process. The inner wall is closely united with the posterior limiting membrane of the cornea anteriorly, and internally with the pectinate ligament of the iris and merid- ional fibers of the ciliary muscle. The character of Schlemm's canal, whether a venous or lymphatic chan- nel, was long a subject of active controversy : the recent investigations of Leber, however, have brought the formerly opposed views into harmony by showing that the conflicting evidence, based upon carefully conducted ob- servations, was due to conditions of intraocular tension under which the experiments were carried out. It may be regarded as definitely established that the canal of Schlemm is an annular venous sinus which by means of the spaces of Fontana stands in close relation to the anterior chamber on the one hand, and directly communicates with the anterior ciliary veins on the other. Under usual conditions Schlemm's canal contains but little blood — a fact which is explained by Schwalbe upon the supposition that the sinus is an annular reserve diverticulum for the reception and storage of blood when for any reason there is a temporary retardation to the escape of the blood passing through the anterior ciliary veins ; the narrowness of the communicating branches between Schlemm's canal and the scleral veins under ordinary con- ditions favoring the more direct passage of the contents of the scleral veins into the anterior ciliary vessels, rather than its entrance into the canal. The tissue forming the wall of the anterior chamber at its angle, occupy- ing the space between it and the canal of Schlemm, is peculiar in character. being composed of an aggregation of interlacing trabecuhe composing a spongy mass containing interfascicular clefts, the spaces of Fontana. These spaces constitute a system of intercommunicating lymph-channels which are imperfectly lined with endothelial plates and freely communicate with the anterior chamber, the aqueous humor filling the spaces. The spongy tissue containing the spaces of Fontana collectively constitutes an annular prismoidal mass, the apex of which begins at the corneal margin, where the membrane of Descemet splits up into delicate bands : these bands mark the origin of the trabecuhe which pass toward the iris and constitute the ligamentum pectinabum iridis, a rudimentary structure in man representing the much more conspicuous scries of conical processes extending from the iris toward the cornea in ruminants. The imperfect character of the endothelial lining of the spaces of Fontana allows the ready entrance of the lymph con- tained within the anterior chamber, so that the clefts between the t rabecuhc are filled with the escaped aqueous humor; the loose nature of the septum forming the inner wall of Schlemm's canal is also favorable to the passage of fluid-, in consequence of which arrangement the aqueous humor i- continu- ally passing, under normal conditions of intraocular tension, through the spaces of Fontana into the canal of Schlemm, ami thence into the communi- cating venous radicles. This exit for the intraocular lymph IS of the utmost importance in maintaining an equilibrium of tension within the eyeball. The Vascular Tunic. — The middle <»r choroidal coat of the eyeball, dis- tinguished by its dark color, and therefore often called the uveal tract, is essen- 56 EMBRYOLOGY, ANATOMY, AND HISTOLOGY OF EYE. X Fig. 29. Section through cilia part of cornea and sclera, the Iris, ciliarj p and muscli clera; )/, ciliarj muscle ; r, radiating fibers; Mm, circular fibers of Midler ; //< , /.. . pi ci, anterior ciliary artery ; 8, canal of Schlemn ti of ciliary muscle; cc,ff, folds of anterior surface oi in iris : gp, sphincter pupilue; />. pupillary border of iris ; A, pigmenl partly detached from Iris; P, ciliary i lliarj i in" . " ora sei rata. tially a Bheel "I" vascular connective tissue. 1 1 includes I liree distincl | >< n-i i< >n- the choroid, thecilian region, and the iris —and extends from the optic nerve 77//; ciio n<> m. 57 U) the pupil. The character of its component structures renders the nutritive e*»at soft, friable, and extensible, and, owing to the presence of muscular tissue within its ciliary and iridial segments, it is subjected to constant variations in its tension. The blood-vessels of this tunic constitute the chief nutritive appa- ratus of the eye, since the functionally most active portions of the organ, as the percipient layers of the retina and the ciliary muscle, receive their nutri- tion from this source. The choroid constitutes the posterior two-thirds of the vascular tunic, extending from the optic-nerve entrance to the anterior limit of the visual portion of the retina, or ora serrata, lying closely united to the functionating segment of the nervous tunic, to the nutrition of which it ministers. The thickness of the choroid gradually diminishes toward the ora serrata, being about 0.1 mm. near the nerve and 0.00 mm. at the ora serrata. While ap- plied to the inner surface of the sclera the union between the two coats is not firm, since the opposed surfaces, covered with endothelium, are separated by the intervening suprachoroida! lymph-space ; irregular trabecular extend across this space, and, in addition to attaching the sclera and choroid imper- fectly, subdivide the cleft into numerous secondary compartments. When separated from the fibrous coat the outer surface of the choroid appears rough Fin. no.— Section <>f human choroid (Picrsoli : very intimately united with the adjacent pigmented layer of the retina, so that the latter often adheres to the choroid when the middle coat is removed. The choroid consists of a more or less compact connective-tissue stroma, which supports numerous blood-channels of very varying size; the arrange- ment of these vessels largely determines the peculiarities of the layers into which the choroid is divided (Fig. 30), These are three: 1. The layer of choroidal stroma containing blood-vessels of large size ; '1. The layer of dense capillary networks — the chorio-capillaris : 3. The homogeneous glassy lamina or membrana vitrea. The loose layer of trabecular bands connecting the outer surface of the choroid and the inner surface of the sclera constitutes the lamina supra- choroidea, sometimes described as an additional layer oi the choroid. The membrane-like trabecular consist of interlacing fibro-elastic bundles, upon 58 EMBRYOLOGY, ANATOMY, AND HISTOLOGY OF EYE. the surface of which lie the flattened, irregularly-branched pigmented con- nective-tissue cells, the deeply-pigmented protoplasm rendering them con- spicuous elements. The choroidal stroma consists of a ground-substance of closely interwoven connective-tissue lamella?, which supporl the blood-vessels. The structural elements include the usual bundles <»!' white fibrous tissue, numerous elastic fibers, and stellate pigmented cells; the stroma is especially dense in the im- mediate vicinity of the Mood-channels. The layer containing the large blood-vessels constitutes the larger part of the choroid, the vascular canals appearing as apertures and lighter channels within the darker choroidal stroma. The largest vessels occupy the most superficial or outer stratum of the choroidal stroma, those of medium size the C F I -Diagrammatic view of principal blood-vessels and nervesofthe eyeball (Testut): A, optic /: sclera /.". viewed in section; C, section of cornea; /', ciliary muscle ; I. ins: f, anterior chamber i I, Bhort postei ior ciliarj arteries ; 2, long posterior ciliary arteries; :'.. anterior ciliary arteries i ,., - , ... one "t tin- large venae vorticosse; 6, vena vorticosa after piercing the sclera ; 7, vasa \ orl Icosa i ■! i he choroidal i unic. middle layer, while the innermost layer i- devoted to the capillary network, t he chorio-capfflarix. The mosl conspicuous of the large superficial blood-channels are the four venous trunks, the /•- na vorticosa : these pierce the choroid within the equa- torial zone :it points aboul equidistant and establish foci toward which the -mailer veins within each quad rani converge; these tributaries form peculiar venous whorl- within the superficial layers of the choroidal stroma ( Fig. •"> I l. The vense vorticosse traverse the Buprachoroidal -pace, invested by a partial envelope contributed by the lamina Biiprachoridea, and pierce the sclera. running obliquely backward. Perivascular lymph-sheaths usually invesl the Venous trunk- within the choroid. The arteries within the choroidal stroma THE CILIARY /:<)/> )'. 59 possess longitudinally disposed muscle-bundles in addition to the customary circular fibers. A narrow boundary-zone separates the layer containing the large veins from the capillary stratum: it consists of closely felted fibro-elastic fibers intermingled with sparingly distributed connective-tissue cells devoid of pig- ment. In many animals, as the horse, cow, or sheep, the boundary-zone contains many bundles of dense connective tissue, which arrangement pro- duces the peculiar metallic reflex sometimes seen in such eyes; this shining layer constitutes the tapetum fibrosum, as distinguished from the tapetum cellulosum of the carnivora, which structure depends upon the presence of several layers of cells containing minute crystals. The inner capillary zone of the choroid, the chorio-capUlarifi or membrane of Rwysehj occupies the inner portion of the vascular tunic lying next the vitreous membrane, which alone separates the rich vascular layer from the nervous coat, to the nutrition of which it so largely ministers. The capil- laries are unusually uniform in size, measuring about 0.009 mm. in diameter; the meshes of the network are very small, even surpassing in closeness those of the lungs, being only 0.01 to 0.02 mm. in the macular region, and about 0.02 to 0.03 mm. toward the ora serrata. The red reflex seen in the eye when viewed with the ophthalmoscope is due to the reddish color of this vascular layer showing through the retina. The vitreous membrane, lamina basilaris, 'membrane of Brueh, or lamina vitrea, constitutes the inner boundary of the choroid, lying next the nervous tunic, which it separates from the chorio-capillaris. The membrane repre- sents a specialized condensation of the choroidal stroma, and appears as a homogeneous zone which measures only 0.002 mm. in thickness. The nerves of the choroid are derived from branches given oft' from the long and short ciliary nerves during their course between the vascular and fibrous tunics. The choroidal nerves, which are both medullated and non- medullated, form a wide-meshed plexus within the lamina suprachoroidea containing groups of ganglion-cells. From this plexus numerous slender, non-medullated fibers proceed to the arteries, the muscular tissue of which they especially supply ; isolated or very limited groups of ganglion-cells are found along the blood-vessels. / The lymphatics of the choroid are probably represented by distinct cap- illary vessels which communicate! with the lymph-spaces between the channels of the chorio-capillaris on the one hand, and the perivascular sheaths tribu- tary to the larger lymph-canals on the other. The ciliary body includes the middle segment of the vascular tunic, extending from the ora serrata behind to the sclero-corneal juncture in front. A- seen in meridional sections, this region appears as a triangle, the longer and outer side of which lies next the sclera and sclero-corneal juncture, the short anterior side against the pectinate ligament, and the inner margin in apposition with the irregular, deeply pigmented extension of the retinal tunic. The ciliary body presents three subdivisions— the ciliary ring, the ciliary processes, and the ciliary muscle. The ciliary ring, or orbiculus ciliai'w, includes the smooth annular tract lying between the sinuous border of the ura -errata behind and the ciliary proceases in front, constituting a band about I mm. in width. This zone differs in its structure from the choroid proper, chiefly in the absence ol the rich vascular supply, since the capillary layer ceases ai the ora serrata, oral the point where the percipienl element- of the nervous tunic end for whose 60 EMBRYOLOGY, ANATOMY, AXD HISTOLOGY OF EYE. nutrition the chorio-capillaris is especially designed. The larger blood- vessels of the choroid are here represented by the venous trunks which return the blood from the iris and ciliary processes and proceed as tributaries to the vena' vorticosae. When viewed from the posterior surface the ciliary rinir presents numerous delicate radial striations : these are due partly to the blood-vessels and partly to minute plications of the surface, best marked toward the anterior boundary of the ring. The ciliary processes appear on the posterior surface of the ciliary region as an annular series of pyramidal folds, about seventy in number, the con- spicuous projecting bases of which encircle the attached border of the iris, while their apices gradually lade away in the orbiculus ciliaris. The delicate radial striations seen on the surface of the latter are so related to the ciliary processes that each projection seemingly begins by the fusion of several striations, and rapidly increases in breadth and height to a point opposite the margin of the crystalline lens, and then abruptly diminishes to the level of the iris. The elevations measure between 2 and •"> mm. in length, 0.12 to 0.15 mm. in breadth, and in their boldest part from 0.8 to 1 mm. in height. The processes consist chiefly of convoluted blood-vessels supported by delicate connective-tissue stroma, and covered by the pigmented extension of the retinal tunic, thenars eUiaris retince. It is probable that the particular func- tion of the ciliary processes, in addition to aflbrding attachment lor the libers of the suspensory ligament of the lens, is the secretion of the aqueous humor, to which end their peculiar formation and unusual vascularity are especially adapted. When seen in meridional sections each process is observed to be composed of a number of irregular projections, varying greatly in size and arrange- ment ( Fig. 29) ; in general, the maximum elevation marks the inner angle next the iris, from which point they gradually diminish toward the orbicular ring, where they fade away. In addition to the connective-tissue stroma contain- in- the rich convolution of blood-vessels, the inner surlaee of the ciliary processes, a- well as that of the orbiculus ciliaris, is covered b\ a continuation of the vitreous membrane of the choroid, which in this region is somewhat thickened, measuring from 0.003 to (U*<)4 mm.; this limiting membrane sepa- rates the stroma of the ciliary process from the retinal layer represented by the double stratum of epithelial cells which covers the inner surface of the projections. Tin' ciliary muscle \< very conspicuous in meridional sections of the eye- ball, then appearing a- a triangular fold of involuntary muscle and connec- tive tissue which lie- between the sclera and the proper tissue of the ciliary processes. In its entirety the ciliary muscle forms a prismoidal annular band which surrounds the angle of the anterior chamber and attached mar- gin of the iris. The muscular area consists of three sets of bundle- of involuntary muscle, intermingled with connective tissue, arranged as meridional, radial, and circular fibers. The meridional bundles are closely grouped and con- stitute a compact muscular layer next the sclera, to which the) are loosely connected by liber- of the lamina suprachoroidea. These muscular bundles take origin from the inner scleral process and tissue, forming the inner wall of Schlemm's canal ; posteriorly, the meridional bundle- arc attached to the choroidal tract, into which they are inserted by delicate tapering processes; from their relation to the vascular tunic the meridional muscular bundles are often called the tensor choroidea. The typical meridional fibers lie next the Bclera; those more internally situated gradually assume a more radial THE IRIS. 61 disposition, and insensibly blend with those whose course is such thai they constitute the radial group (see Fig. 29). The radial fibers of the ciliary muscle arc less closely placed than the meridional, and form a reticulum in which the muscular bundles are -evi- rated by a considerable amount of intervening connective tissue. The fan- shaped mass of radial fibers diverges from their point of origin from the membrane of Descemet and inner wall of Schlemm's canal, the innermost tihers passing toward the ciliary processes and the outer to the anterior border of the orbiculus ciliaris. In addition to the meridional and radial bundles an isolated group of circularly disposed muscular libers occupies the inner angle of the triangular field formed by the ciliary muscle at the base of the iris; these fibers consti- tute the circular or ring museh of Waller. The general form of the ciliary muscle in the emmetropic eye approxi- mates a right-angled triangle, the hypothenuse corresponding to the long scleral margin : in the markedly abnormal refractive conditions of myopia and hypermetropia the circular fibers are respectively atrophic or over-devel- oped, which results in the obtusely-angled myopic muscle and the unusually acute-angled muscle of the hypermetropic eye. The blood-vessels of the ciliary body are derived from the anterior and long ciliary arteries, which form around the root of the iris the anastomotic ring, the eireulus ii-i1 mm. in the quiescenl condition, in a widely dilated state being nearly doubled. The diameter of the iris i- about 1 I mm., of which the pupil appropriates from .'>-<) nun. when at rest also p. 1 17). I'he attached or ciliary border of the iris joins the ciliary body behind, ami j- continuous with the membrane of Descemet through the pectinate ligament in front ; it- zone of attachmenl lies aboul •"> mm. behind the ap- parent corneal margin :i- viewed from before. The exact outline of the thin pupillary border i- difficult to see, owing to it> intense black color due to 62 EMBRYOLOGY, ANATOMY, AND HISTOLOGY OF EYE. the deeply pigmented tissue which forms the immediate boundary of the open- ing : critically examined, it presents a slightly irregular or dentated contour. The color of the iris, as viewed from the anterior surface, varies greatly, and depends for its production upon two factors — the deeply pigmented cells covering the posterior surface of the iris as well as lining the pupillary open- ing, and the amount of pigment contained within the iridial stroma. When the pigmented stroma-cells are very few or absent the dark color of the pos- terior layer shines through the thin stroma, and the iris appears blue; when the stroma is thicker the tint becomes modified to gray. With the presence of additional pigment within the stroma varying deeper shades, as green, hazel, brown, are produced; finally, when the stroma is laden with pig- mented cells, the darkest tints of brown appear — the so-called "black eyes" (see also page 147). The color is not uniform, but is distributed in irregular spots and patches, sometimes of fanciful form, of lighter and darker tints, so that a definite tint is produced only on viewing the iris at a distance sufficient to blend the variously tinged areas, ('lose examination shows a further disposition of the color in two /ones concentric with the pupil — the pupillary, from 1-2 nun. wide, which is lighter in dark eyes and darker in light eyes, and an outer or ciliary, from 3—4 mm. in width, which is darker in dark eyes and lighter in light eyes. The boundary-zone between the two is often marked by a series of festoon-like ridges, the circulus minor iridic. The (interior surface of the iris, when viewed from before, exhibits a dis- tinct sculpturing consisting in numerous radial striate ridges ; these are par- ticularly line and closely approximated within the pupillary zone, where they unite toward the inner margin, leaving deep intervening clefts. The broader ciliary portion is subdivided into three secondary zones concentric with the pupil — an inner smooth ring, not plicated during dilatation of the pupil ; a middle fwrowed band ; and an outer irregularly pitted marginal or cribriform zone. The first two are visible in the living eye, the third is covered by the scleral border. The posterior surface of the iris presents numerous radially arranged ridges separated by intervening furrows, which are intersected by concentric lines; within the pupillary zone the concentric markings almost disappear, while the radial are more numerous than elsewhere, resulting in the apparent plication of the inner zone of the iris. flic form of the human pupil is normally circular under all conditions of contraction ; in marked contrast are the elliptical or slit-like pupils of many mammals, in some of which, as the horse and ox, the long axis of the con- tracted pupil is horizontal; in others, as the cut and tiger, vertical. The structure of the iris, ;i- -ecu in radial sections, presents two chief layers — the iridial stroma proper and the pigment layer; these include five sub-layers ( Fig. .">'-^) : I . A nterior endot helium ; ■_'. A nterior boundary layer ; .'!. Vascular stroma layer ; I. I '"-tenor limiting layer ; 5. Pigment layer. Reference to the development <>l the iris shows thai the pigment layer is the contribution of the nervous tunic, and morphologically represents the anterior edge of the secondary optic vesicle, derived from the ectoderm, while the remaining parts of the iris are mesodermic in origin. The anterior endothelium forms part of the lining of the anterior cham- THE IRIS. 63 her, and consists of a single layer of irregular polygonal plates, directly con- tinuous with those covering the posterior surface of the cornea. The (inferior limiting membrane does not exist as a distinct layer, being simply the modified and condensed subendothelial stratum of the general stroma into which it blends. The connective-tissue cells are here unusually closely placed, with a corresponding meagerness of the intercellular fibrous tissue; minute interfascicular clefts represent a system of intercommunicating lymph-spaces. Blood-vessels are wanting within this part of the iris. The vascular stroma layer, forming the hulk (if the iris, consists of a loose connective tissue supporting the numerous blood-vessels and nerves which occupy this stratum, and enclosing interfascicular lymph-spaces, as well as Fig. 32. Sections of the human iris : A, radial section; B, section across the radii (Retzius) : 6, ante- rior condensed zone and endothelium; str, stroma-layer ; s, bundles of muscular libers composing the sphincter pupil he ; '/, muscle-cells constituting the dilat at' >r papillae; r, pigment layer of iris belonging to retinal tract. the groups of involuntary muscle-bundles which constitute the sphincter and dilatator pupillae muscles. The radially disposed blood-vessels and nerve- trunks are invested by local condensations of the iridial stroma, the peri- vascular sheaths so formed representing the most robust portions of the stroma layer, the intervening areas being occupied by a comparatively loos< connective-tissue reticulum. flic variable and often large amount of pigment contained within the stroma layer in dark irides occur- a- irregular accumulations of pigment-cells, the anterior layer and the pupillary zone usually containing the greatesl number of the colored elements. In very dark irides the distribution of the pigment i- very general, all portions of the stroma layer being tilled with tin colored particles. 64 EMBRYOLOGY, ANATOMY, AND HISTOLOGY OF EYE. The muscular tissue within the iris occurs within the vascular stroma layer, and includes the well-marked circular filters surrounding the inner margin of the iris and constituting the sphincter pupillce, and the much less evident and often disputed radially disposed fibers which form the dilatator pupilla . The sphincter pupillce consists of an annular hand of involuntary muscle, varying in width between 0.7 and 1.0 mm., according to the condition of con- traction, and from 0.07 to 0.10 mm. in thickness. The immediate edge of the pupil is not formed by the muscular tissue, since the pigmented retinal sheet intervenes. The muscle occupies the posterior plane of the stroma layer, behind the blood-vessels; the bundles composing its outer border are loosely disposed, certain fibers often assuming an arched course and fading- away in radial offshoots. While the presence of a sphincter muscle is universally admitted, the existence of a radially disposed dilatator pupillce is by no means undisputed. The demonstration of a distinct layer of radiating libers is very unsatis- factory, so much so that many competent observers have concluded that such fillers do not exist, and that a true dilatator is absent, although the presence of radially disposed delicate spindle-cells is indisputable. Without entering upon a rimme" of the various views relating to the nature of these spindle- cells lying in close relation with the posterior limiting lamella, it may be stated that the most recent and trustworthy investigations, both from the morphological and the physiological standpoint, as those by Retzius and by Langley and Anderson, tend to uphold the existence of dilatator libers — if not as a continuous sheet, at least as groups of radiating libers which collectively constitute the dilatator pupillse, the presence of which as a distinct dilatator muscle may be regarded as definitely established. The posterior limiting lamella has likewise been the subject of much dis- CUSsion, due largely to the uncertain relations of the layer of delicate spindle- cells occupying the iridial stroma in the immediate vicinity of the posterior pigment. The limiting lamella, or basal membrane, appear- as a clear layer of greal delicacy, its maximum thickness not exceeding 0.002 nun., which closely adheres to the deeply pigmented retinal zone, with which it is often inseparably united. The lamella in question may be regarded as the atten- uated anterior continuation of the membrane of Bruch, which extend- for- ward from the choroid over the orbiculns ciliaris and ciliary processes. The pigment layer covering the posterior surface of the iris as far as the anterior margin of the pupil, although a conspicuous anatomical portion of tiie iris, morphologically represents the anterior segment of the atrophic por- tion of the nervous tunic — thenars retinae iridica. The deeply colored layer, although ordinarily appearing as a uniform stratum of pigment- particles, in reality consists, as seen in suitable preparations, of two distinct layers — an outer, made up of low irregular fusiform elements, and an inner, composed of short polygonal cells ; these layers arc continuous as the anterior margin of the pupil and represent the double-layered anterior lip of the optic cup. On approaching the ciliary processes the amounl of pigrnenl gradually lessens, firsl in the inner layer, mid subsequently likewise in the cells of the outer layer ; finally, at the base of the ciliary elevations the outer layer alone contains pigment-particles. The inner cells are covered on their \'vct' surfaces l>v .in extremely delicate cuticular membrane, the limitans iridis, which is probably the continuation of the cuticle investing the ciliary portion of the retinal sheet. fhe l,li,nil-n ss< Is of the iris include the ;i it v profound modifications in the arrangemenl of the histological elements of i he ret ina. 'fhi' size of the fovea as usually given, between 0.2 and <*. ! nun., is to., Bmall, the recenl investigations of Dimmer, Golding-Bird, and Schafer indicating a diameter exceeding 1 nun., and, exceptionally, approximating nearly - nun. Owing 'o the absence of the rod- within the fovea, and there- THE RETINA. 67 fore, likewise, of the visual purple, this region possesses an inherently lighter tint than the surrounding retina, sometimes appearing as a faintly tinted spot when examined with the ophthalmoscope. The foveal reflex seen with the mirror is due t<> the direction and slope of the sides of the depression, the variations in these resulting in the differences observed in the ophthalmoscopic image (compare with page 188). The retina morphologically consists of two distinct layer — an outer and inner lamella, which correspond to the external and the internal layers of the optic vesicle; the outer lamella is represented by the pigment layer, while the inner lamella includes the remaining retinal strata. The inner lamella may be further subdivided into the neuro-epithelial and the cerebral layers. Sections of the nervous tunic, when perpendicular to the surface of the membrane, show numerous strata, the outermost of which i- distinguished by its dark color, and constitutes the retinal pigment; the succeeding layer- differ widely in the amount of protoplasmic elements which they contain, and hence vary in the intensity with which they stain, so that the retina pre- sents lighter and darker strata when seen in usual carmine or hematoxylin preparations. The designation of the retinal layers (Fig. 33), as well as their morphological relations from without inward, is as follows : I. Outer layer of ( optic vesicle, \ II. Inner layer of optic vesicle, J Pi grnent laver. Neuro-epithelial layer. Cerebral layer. Retinal Layers. Pigment layer, Layer of rods and cones, Layer of bodies of visual cells i or outer nuclear layer. External plexiform layer or outer reticular layer, Layer of bipolar cells or inner nuclear layer. Internal plexiform layer or inner reticular layer, Layer of ganglion-cells, Layer of nerve-fibers, J The retina may be regarded as an isolated portion of the central nerv- ous system immediately connected with a highly specialized perceptive sense- apparatus: a- other parts of the nervous axis, so the retina i< composed of two varieties of elements, the nervous and the sustentacular, the latter being represented by the modified neuroglial- reticulum and columns, the fibers of Miiller. The nervous elements constitute collectively the ganglion retinas, and represent the cortical cells of the brain. In principle, therefore, the retina consists of the percipient elements, closely applied to the pigment layer, the ganglion retinae and the ganglion-cells with their liber.-, which establish communication with the brain-centers. Tin Pignu nf Layer. — The conspicuous deeply-colored stratum of pigment- cell- which forms the most external layer of the retina is the direct repre- sentative of the attenuated outer lamella of the optic vesicle. It is composed of hexagonal element-, about 0.015 mm. in diameter, although subject t<> marked individual variation, smaller cells often surrounding larger ones. Close examination of the pigment-cells in section shows that the colored par- ticle- d< t invade the entire protoplasm, but that an outer zone, containing the nucleus, is clear, the pigment being confined to the middle and inner rnent- of the cell-. The inner margin of the pigment-cells is irregular, in contrast to the smooth external border and in close relation to the outer ends of the rod and cone segments of the visual cell- | Fig. :;i). 6S EMBRYOLOGY, ANATOMY, AND HISTOLOGY OF EYE. The pigment-cells are profoundly affected by light stimulus, since under the influence of light the colored particles migrate toward the rods and cones, between which the protoplasm of the pigment-cells extends (Fig. 35). After Layer of pigment-cells. Layer of rods and cone*. External limiting membrane. 6. Outer nuclear layer (layer of /indies of visual eells I. Outer plexiform layer (outer reticular layer i. Inner nuclear layer (layer of bipolar s). Inner plexiform layer [inner reticular layer). Layer of ganglion-cells. 1. Layer of nervt -fibers. Internal limiting membrane. Fig. 33. Diagrammatic section of the human retina (Max Schultze). being subjected to darkness, on the contrary, the pigment particles arc retracted and collected within the middle or so-called basal zone (Fig. 36). The relation between the pigment-cells and the rods and cones explains the variation- in the ; Pigmented epithelium from human r< tina (Max Schultze) : a, surface \ i« -\\ of cells, showing clear nuclei and intercellular lines; b, cells seen in profile, with protoplasm extended between per cipienl elements; c, cell Mill connected with rods. degree of attachment between the colored and remaining portions of the retina : after exposure to lighl the intimate relation between the pigmenl and percipient elements renders the attachment between the two originally distinct lamellae THE RETINA. 69 much stronger than that existing after seclusion in darkness, under which conditions the tendency to the natural separation of the embryologically dis- tinct lamella 1 becomes pronounced, the pignienl then remaining attached to the choroid when the retina is removed. The Layer of Neuro-epithelium. — Under this heading are included two strata, which are usually described as the layer of rods and cones and the external nuclear layer, the former being the specialized outer parts, and the latter the extended and attenuated nucleated bodies of the visual cells. The layer of rods and cones represents the highly differentiated outer extremities of two forms of light-perceptive elements, the rod- and the cone- visual eell. Under high amplification, as seen in section, rods of the human retina appear as elongated cylindrical forms, about 0.060 mm. in length and 0.002 mm. in thickness, each consisting of an outer and inner segment of about Fig. 35. — Section of frog's retina, showing the action of light upon the pigment-cells and upon the rods and cones (v. Genderen-Stort). The retina had been exposed to li<_dit for some time before killing; the pigment-cells have extended their protoplasm between the rods and cones nearly to their bases : the cones have retracted. Fig. 36. — Section of frog's retina, showing action of darkness upon the pigment-cells and upon the rodsand cones (v. Genderen-Stort). The retina had been kepi in the dark tor some hours before death, in consequence of which the pigmenl is retracted toward the nucleated part of the cells and from between the rods. The cones are elongated. equal length. The outer segment possesses a uniform diameter and presents a homogeneous structure, being probably of the nature of a cuticular appen- dage. The external segments of the rods are of interest as being the chief, if not the sole, possessor of the visual purple or rhodopsin, the color being uniformly distributed throughout this part of the rod. The inner rod seg- ment, with slightly increased diameter, is of feebly marked, ellipsoidal form, and exhibits more or less clearly a differentiation into an external faintly striated subdivision, the rod-ellipsoid, and an internal granular area, the li ntic- uhir body ( Fig. '■)!). The body of the rod-visual cell lies within the external nuclear zone and consists of the attenuated column of protoplasm, the rodrfiber, and the more conspicuous nucleus, the rod-grcmule. The rod-liber is directly continuous with the inner part of the rod at the outer end, and extends into the externa] plexiform layer, within which it ends iii a minute knob-like expansion in close relation with the terminal arborization- of the bipolar nerve-cells ( Fig. 38). 70 EMBRYOLOGY, ANATOMY, AND HISTOLOGY OF EYE. The nuclei of the rod-cells, which usually present transverse dark and li*dit stripes, are of much greater thickness than the rod-fiber, in consequence of which the position of the nucleus in each visual cell is indicated by a marked enlargement consisting of the nucleus surrounded by a thin envelope of pro- toplasm. The nuclei, or rod-granules, are situated at all layers, and con- tribute far the larger share of the deeply staining bodies which constitute the chief elements <>t' the outer granule-layer. The cone-visual rills are made up of the same general divisions as the associated rod-elements, including- the specialized outer part, the cone, and p„ ; p,7._.\ rod and a cone from the human retina (Max Schultze). The line, I, I, indicates the position of the external limiting membrane; the portion of the figure unshaded represents parts of the \ isual cells Contained Within the outer nuclear layer. Fig. 38 -Diagram of the neuro-epithelial ele- ments of the retina (Quain-Sehwalbe) : i, bipolar nerve cells, related t" the rod- and cone \ isual cells in the outer plexlform layer (5); 6, the nucleated bodies "!' the rod- and cone-visual cells, containing the rod- and cone-granules (nuclei) and the rod- and cone-fibers these parts of the visual cells constitute the outer nuclear layer) ; ~. the layer of rods and cones which represents the cuter highly specialized ends of the visual cells : each rod and cone is composed of ti iter and inner segment. the cone-cell body within the external nuclear layer. Each cone comprises .in outer ami an inner Begment, which differ both in length and in thickness. In contrast to the almost uniform diameter and length of the two parte of the rods, the outer Begmenl of the cone- i- shorter and ihiuiier than the inner segment, which i- conical, or, more accurately regarded, ellipsoidal, and rnea- auree about 0.006 mm. where it i- broadest. The com- do not extend a- far into the pigmenl layer ;i- the rods, terminating as blunted cone- at a point al t opposite the middle of the outer segments of the adjacent rod-. The cones do not contain the visual purple, bul possess a somewhat higher refrac- 77//: RETINA. 71 tive index than the r. While the outer cone segment displays a tendency to break up into transverse disks, the inner segment exhibits a faint 1 < n i ^ i - tudinal striation. The body of the eone-visual cell contributes to form the external nuclear layer, and consists of the attenuated cell-body, the cone-fiber, and broader conspicuous nucleus, the cone-granule. The latter, instead of occupying all levels of the nuclear layer, as do the nuclei of the rod-cell.-, are limited to the zone immediately below the external limiting membrane, being continu- ous with the bases of the inner cone-segments : additional characteristics of the cone-granules are their large size, lack of cross-stripes, and possession of nucleoli. The cone-fibers terminate within the outer plexiform layer in expanded bases or feet, which stand in close relation with the arborizations formed by the terminal expansions of the cone-bipolars. The entire number of rods within the human retina has been estimated by Krause at 130,000,000; that of the cones, by Salzer at 3,360,000; the number of rods, therefore in the man is greatly in excess of the cones throughout most parts of the retina — in the fovea, however, the cones are alone present. The numerical proportion between the two varieties of percipient elements varies in different parts of the nervous tunic, as shown by the variation in the pattern seen on inspecting the surface of the retina where the cones appear as larger circles surrounded by areas of smaller FlG sg.-surface view of the rinova ■ the eones are usnallv spnaratod l>v an rods and cones, showing the rela- imgb, uit com* aie usiuuiN .-epauiixu u\ ui tive distribution of these elements interval occupied l>v three or tour rods. In the (Koitiker): a, from macula lutea, ... n ,' ' l ,i ■ ,i where only cones are present; b, Vicinity OI the macula the COnes increase SO that from near macula, where only a only a single row of rods intervene, while in the contVTfrom r ^dwa P y a hefweeo fovea the cones alone are present (Fig. 39). p^pondlrate raserrata ' where r "' ls The External Plexiform, or Outer Reticular Layer. — This stratum lies next the layer of visual cells or neuro-epithelium, and is the first of the lamella? which constitute the cerebral division of the retina. The layer appears as a light, faintly staining zone, about 0.01 mm. in breadth, the apparent granular structure of which, as seen under moderate amplification, giving place to an intricate reticulum when examined with higher magnification. The true nature of this reticulum was demonstrated only after the introduction of the more recent improved methods of staining by the Golgi silver and methylene-blue processes: recent investigations have shown that the major part of the plexiform layer consists of the delicate ramifications and intricate interfacings of the processes of the nerve-cells constituting the ganglion retime and occupying the inner nuclear zone, held together by the delicate framework of sustentacular tissue. The exact relations between the central extremities of the cone- and rod- visua] cells ami the endings of the nerve-cell processes have long keen the subject of discussion. The direct connection formerly supposed t" exisl between the nerve-cells and the visual cell- i- no longer tenable in the light of our i lern conceptions regarding the ultimate endings of nerve-processes, since the best authorities are agreed that each nerve-cell exists a- an inde- pendent element, whose relation to other cells is one of contiguity and not of anatomical continuity. The nervous elements in close relation with the visual cell- are the ••rod" and "cone" hipolars, the nucleated bodies of which form the conspicuous "granules" of the inner nuclear layer. I lie peripherally directed processes of these nerve-cells extend within the external 72 EMBRYOLOGY, ANATOMY, AND HISTOLOGY OF EYE. plexiform layer and terminate in end-arborizations surrounding the inner extremities of the visual cells, which also penetrate into the reticular zone. Additional nervous elements, the horizontal, basal, or stellate cells, are found within the external plexiform layer ; they exist in two forms, the smaller outer and the larger inner cells. The former are flattened stellate elements which lie within the outer pact of the plexiform layer, through which their Long axis-cylinder processes extend for considerable distances to terminate in arborizations surrounding the ends of the visual cells, thus establishing indirect conduction between the elements lodged within the plexiform stratum. The larger inner horizontal cells occupy the deeper portions of the layer, some possessing descending processes which penetrate centrally as far as the inner plexiform layer, in which they terminate in arborizations. The Layer of Bipolar Nerve-cells, or the Inner Nuclear Layer. — This stratum, as usually seen, closely resembles the outer nuclear layer, being apparently composed of large numbers of deeply staining granules. The layer measures from 0.035 nun. in the vicinity of the optic disk to 0.018 mm. at the ora serrata. The ganglion-cells of the layer consist of two chief varieties — those especially related to the rod-visual cells, and hence appropriately called rod- bipolars ; and those associated with the cone-cells, known as the cone-bipolars. The particular purpose of the bipolars is to supply the connecting link be- tween the visual cells, around which they terminate on the one hand, and the large ganglion elements giving off the nerve-fibers to the brain, in rela- tion to which their centrally directed processes expand, on the other. Refer- ence to Fig. 40 shows thai the arrangement of the processes of the cone- bipolars diners from that of the processes of the rod-bipolars : the latter extend through the entire thickness of the inner plexiform layer to the bodies of the ganglion-cells, which they enclose with their arborizations. The descending' processes of the cone-bipolars, on the contrary, are limited to the inner plexiform layer, meeting with the expansions of the ascending dendrites of the large ganglion-cells at various levels, where the interlacing Fig. in. Elements of the mammalian retina after treatment with the Golgi silver method (Cajal): i. Section of the dog's retina: a, cone-fiber ; b, rod-fiber and nucleus; c, d, Dipolar cells (inner gran- ales) \\ i t 1 1 vertical ramification of outer processes destined to receive the enlarged ends of rod-fibers . i , bipolars with flattened ramification for ends of cone-fibers :./', giant bipolar with Battened ramification ; >r nerve-fiber process to the outer molecular layer; ft, amacrine cell with diffuse arborization in inner molecular layer: i, nerve-fibrils passing to outer molecular layer ; j, centrifugal fibers passing from nerve-fiber layer to inner molecular layer ; m, nerve-fibril passing into inner molecu lar layer : /», ganglionic cells. II. Horizontal or basal ceils of the outer molecular layer of the dog's retina. A. small cell with dense arborization; B, large cell, lying in inner nuclear layer, hut with its processes branching in the outer molecular : a, its horizontal Qeuroo : C, medium sized cell of the same character. III. Cells from the- retina of the ox: n. roil hi[.olars with vertical arborization: b, r, t' considerable extent. The peripheral arborizations of the cone-bipolars expand beneath the broad bases of the cone-visua] cells, forming horizontally-extended, terminal plate-like groups of ultimate fibril he. In addition to the bipolar cells the inner zone of the inner nuclear layer contains nervous elements which were long ago described by Miiller under the name of "spongioblasts," under the impression that the cells in question were concerned in the production of the sustentacular framework of the layer: these elements arc now regarded as nervous in character, and, from their peculiarity of seemingly being without axis-cylinder processes, have been named by Cajal amaerine cells. The richly branching dendrites of these elements extend into the inner plexiform layer, in which they end either in the expanded brush-like arborizations of the diffuse amacrines,or in the hori- zontally extending arborizations of the stratiform type. A few oval nuclei within this stratum belong to the long columnar supporting fibers of Miiller, which usually possess irregular nucleated expansions within the zone. The Internal Plexifoivn, <f the individual percipient elements. A.s already noted, the inner end.- of the fibers of Mullei are greatly enlarged, the bases of the conspicuous pyramidal or conical expansions coming into close contacl and producing the appearance, when treated with silver nitrate, of a continuous layer of endothelial plates: the bundles of retinal nerve- fibers pass between the diverging fibers to continue their radial course. Within the fiber layer additional sustentacular elements exist as the spider- cells, neurogliar element- whose characteristic appearance is due to the long, delicate processes which extend from the cell-body between the aerve-fibers in various direction-. The Macula In approaching the macula the ganglion-cells become so numerous that a single layer do longer suffices for their accommodation, and consequently they lie two deep ; within the macular area the number further increases, so that they constitute a stratum which includes from six to eight rows of the nervous ele- ments. On reaching the fovea centralis, however, the greatly thickened gan- glion-layer rapidly decreases in thickness toward the center of the depression, becoming scattered and do longer sufficient to constitute a complete stratum, until at the bottom of the pit the ganglion-cells are altogether absent. The fiber-layer consequently suffers a corresponding diminution, and disappears as a distinct stratum at the point where the ganglion-cells end. The bipolar cells continue to the center of the fovea as an irregular row of small elements sup- ported within the finely reticular tissue which represents the U\mh\ outer and inner plexiform layers, and fills the space between the visual cells and the inner surface of the retina. The most prominent stratum within the fovea is that formed by the visual cells, here composed entirely of the cone-cells, which present a depth about three times that of all the more internally placed strata combined. The cones gradually lengthen on approaching the foveal center until, over the middle of the depression, they measure more than double the length of the corresponding element- at the margins of the pit : associated with the increased length, the cones become greatly attenuated, appearing as long, delicate, -lender liber- of which the outer segment contributes by far the greater part ( Fig. 42). fhe external limiting membrane exhibits a slight inward deflection over the area included within the outward curve of the inner membrane: this outer depression, the so-called fovea externa, produces, however, but slight dipping inward of the outer surface of the retina, as the increased length of the cones in a measure compensates for the sinking of the limiting membrane. It i- probable that the position oi the external fovea corresponds to an asso- ciated thickening of the choroidal tissue. In recapitulation, therefore, the layer- occupying the center of the fovea are the cone visual cells, constituting the layer of cone- ami the external nuclear layer ami the fused outer and inner plexiform strata, with the included bipolar cell-. The ganglion-cells and their derivative oerve-fibers are absent in the center of the fovea. The Ora Serrata. — -The extreme anterior limit of the visual portion of the retina i- distinguished by :i sudden diminution in the thickness oi the aervous tunic, dependent upon the abrupt termination of the percipient element-, .i- well :i- t ho-e layers <•( n icer i ie< I in t he t ra u -i n i --ion 01 the light stimuli centrally, the layer oi retinal pigment alone retaining its identity in the further extension of the oervous coat. The characteristic series of aboul forty well-marked dentations observed THE OPTIC ENTRANCE. 77 in the adult retina are closely associated with the accommodative function, since in early life, before accommodation is fully exercised, the typical ser- rated border i> wanting, the termination of the visual part of the retinal sheet being marked by a comparatively smooth line, the "transition border" of Schon, beset with numerous minute projection- which afford attachment to certain of the delicate zonular fibers. The sudden reduction of the retina depends especially upon the disap- pearance of the plexiform strata, the layer of rods and cone-, however, hav- ing previously lost its integrity as a distinct zone. The inner nuclear layer is continued farthest, at the anterior limit of the ora passing into the single layer of columnar elements, which, in conjunction with the pigmented cells, are continued over the ciliary zone and processes as the pars ciliaris retinae. m.l.e Fig.4'2.— Iiiagrammatif section through the fovea centralis of the human retina (Golding-Bird and Schafer) : 2, ganglion-cell layer; i. inner nuclear layer; 6, miter nuclear layer, the cone-fibers forming the so-called external fibrous layer of Henle; 7, cones; m.l.e., external limiting membrane; m.l.i., in- ternal limiting membrane: o.g., i.g., outer and inner granules (cone-nuclei and bipolars). The radial fibers of Miiller are especially well developed in the vicinity of the ora serrata, being of large size and numerous. So close is tin- relation between the sustentacula!' tissue and the ora that it has been suggested that the supporting fibers are continued beyond the limits of the serrated border and become connected with the zonular fibers. The Optic Entrance. — The point toward which the centrally directed axis-cylinders of the fiber-layer converge to escape from the interior of the eyeball and to form the optic nerve is marked by a light-colored circulai area, varying from 1.5 to 1.7 nun. in diameter, the optic entrance, <>/>fic disk, or optic papilla. The surface of the yellowish- or bluish-white di-!< i- broken by the central retinal vessels which pierce the area eccentrically, lying usually somewhat nearer the nasal side, and pass over the margins of the disk to train the surrounding fiber-layer. On examining a vertical section through the optic entrance Fig. 13) it 78 EMBRYOLOGY, ANATOMY, AND HISTOLOGY or EYE. will be seen that the thick bundles of the optic fibers which arch over the margins of the interrupted retinal and choroidal layers to gain the disk pro- duce a slight elevation, the />i//in reaching the fibrous tunic of the eyeball all these sheaths, together with the included spaces, terminate by blending with the fibro-elastic stroma of the sclera, tin lymph-spaces extending sometimes for a short distance between the filmm- bundles of the outer tunic. The external limit of the intraocular segment of the optic nerve is dis- tinguished by the position at which the nerve-fibers acquire a medullary sheath on emerging from the sclerotic tissue which they traverse. I hi' scleral bundles separate to allow the passage of the groups of optic fibers, and interlace with one another to form a sieve-like structure, the lsu/c .- the latter is resistant to reagents, such as alco- hol and acids, a- well as to putrefactive changes. While possessed of considerable strength, it is brittle and readily torn by sharp instruments; when incised it> cut edges roll in a characteristic manner, with the outer surface inward. When viewed in section that portion of the enveloping membrane covering the front surface of the lens is seen to be distinctly thicker than the corresponding part behind : these differences have given rise to the designation of these portions of the membrane as the (interior and jms- terior capsule, although both are but parts of the same general envelope. Invested by its capsule, the lens measures from 9—10 mm. in its trans- verse diameter, being larger in old and large subjects ; its average thickness i- about 4 nun., but this dimension necessarily varies with the condition of accommodation, being somewhat greater when the eye i- fixed on near objects and less when accommodated for distance. The radius of curvature of the -in face- also varies under such changing conditions, that of the anterior sur- face, however, manifesting greater change under the extremes of accommoda- tion than that of the posterior ; thus, while the radii of the anterior surface for distant and near vision are respectively 1<> and and 5 mm. These figures establish the fact that the curvature of the anterior surface of the lens is much more affected in accommodation than that of the posterior, which remains almost unchanged. (See also page 135.) The length of a meridian of the lens measures about 12 mm. The average weight of the lens is about 0.22 gin., and the specific gravity 1121. The anterior pole of the lens lie- about *_!..'! nun. behind the cornea under passive con- dition- of accommodation ; it- posterior pole, about 15.5 mm., in front of the macula lutea. Critical examination ha- demonstrated a slight outward devi- 77/ /•; < 'it ) -s r. \uj . v /•; l ENS. 81 ation, of from three to seven degrees, of the antero-posterior Lens-axis from that of the eye ; an additional, but smaller, vertical deviation has also been noted. The structure of the crystalline lens can best be appreciated alter recall- ing what has already been stated in connection with its mode of formation. The lens develops by the elongation and modification of the original ecto- dermic epithelial cells, which become converted into the lens-fibers, those constituting the posterior wall of the primary lens-sac at first composing the entire lens substance. Subsequently additional layers of lens-fibers arc produced by the elongation and specializa- tion of the cells constituting the anterior wall of the lens-sac, which later are known as the epithelium of the (inferior capsule. The region in which the transformation of the epithelial cells into lens-fibers takes place corresponds to the equatorial area, and is known as the transitional zone; throughout the entire period of growth this region exhibits the conversion of the columnar epithelial elements of the anterior capsule into the elongated meridionally arranged lens-fibers. The lens substance, therefore, is composed of modified epi- thelial tissue. The capsule of the lens is of entirely different origin, since its development is due to mesodermic tissues, and is distinct from that of the lens substance. The capsule of the lens envelops the lens substance on all sides with a delicate, highly elastic membrane, which, in addi- tion to supporting the soft material con- stituting the bulk of the lens, affords attachment for the fibers of the suspensory ligament. The capsule varies in thick- ness, being most robust in the central area of its anterior surface, where it measures from 0.010 to 0.015 mm. in thickness, and thinner at the periphery ; its most attenuated part is the central area of its posterior portion, where it measures from 0.005 to 0.007 mm. The capsule does not exhibit any details of structure, and in chemical composition and reactions differs from both fibrous and elastic tissue. The the canal <>f Petit. to the periphery of the lens. These fibers collectively constitute the suspen- sory ligament, or zone of Zinn, a structure of greal importance not only for the support <>t" thr leu-, hut also in effecting the changes in the curvature of the lens surface associated with accommoda- tion | Figs. 16 and 47). Viewed from the posterior surface, the suspensory ligament appears as a delicate annular structure, about evidently not a contin- uous membrane, but a .-erics of interlacing hands between which numerous apertures and clefts occur. The insertion of the zonular fibers into the lens is so regular and the fibers hound together so intimately that it is possible to inject air between the constituents of the zone, so that the lens is surrounded Fir,. -47.— Meridional section through ciliary region, including part of the lens (Fuchs): C, cornea; pe,pc, pigmented and non-pigmented cells of the pars ciliaris retina-: L, lens ; M, ciliary muscle; r, h< radiating, .'/», its circular fibers: d, anterior ciliary artery; s, canal of Schlemm; z, origin of ciliary muscle; c,/,anterior surface of iris; break at er; gp, sphincter pupillae; /». edge of pupil; /', ciliary process; A, pigment lining in-, partly separated at v; ".blood-vessel; z, zone of Zinn: z Xt z x , fibers of suspensory ligament, enclosing spaces i, i; k, lens-capsule. by an annular scries of headed dilatations. This appearance was long ac- cepted as demonstrating the existence of a delicate channel, the en mil < chemical composition the aqueous humor consists chiefly of water : in addition to the 98.6 parts of this constituent, small quantities of solids, extractives, and proteids are present. The aqueous humor possesses the property of absorbing certain organic substances with which it comes in contact, such as Mood and the lens substance; it also possesses solvent properties to an extra- ordinary degree for many drugs. With the exception of a few migratory leukocytes, the aqueous humor is without morphological elements. Trie Blood-vessels of the Eyeball. — The terminal arrangement and distribution of the blood-vessels of the various parts of the eye have already been described in connection with the consideration of the various structures: a brief description of the general arrangement of the vessels supplying the visual organ is here added. All the arteries supplying the eyeball are derived from the ophthalmic artery as two sets of branches, the retinal and the ciliary. These form two separate systems, which communicate only in the vicinity of the optic en- trance by means of minute anastomotic twigs. The retinal system is based upon the distribution of the central artery <>/ flu retina, a small branch which arises from the ophthalmic close to the optic foramen, usually in common with the internal ciliary, seldom as an inde- pendent trunk. On gaining the interior of the eyeball th< central stem divides into the retinal arteries, and during the fetal stages continues, forward to the posterior lens surface a- the hyaloid artery, a vessel which later dis- appears. The ciliary system supplies the remaining parts of the eyeball, and con- sists of two sets of vessels, the posterior and anterior ciliary arteries. The posterior arise by two chief trunks, an inner and an outer, which are given off from the ophthalmic artery while it lies below the optic nerve. These stems each divide into from four to ten branches, which surround the optic nerve, and on reaching the eyeball pierce the sclerotic coat in the vicinity of the point of entrance of the nerve. The posterior ciliary arteries then form two group — the short, which pass at once to the choroidal tract to take pari in forming the rich vascular network of the middle tunic; and the long, which pass forward, one mi each side of the eye, between the sclera and choroid, to the ciliary region, where, after giving direct branches to the ciliary muscle, they join the anterior ciliary arteries to form the vascular plexuses from which the adjacent parts are supplied. THE LYMPHATICS OF THE EYEBALL. 87 The anterior eiliary arteries, usually from -i.\ to eight in number, arc derived from the muscular and lachrymal branches of the ophthalmic : in the vicinity of the corneal margin they penetrate the scleral coat, and finally join the long posterior ciliary vessels to form the circulus arteriosus iridis major. Before passing- through the sclerotic these arteries give off anterior and pos- terior branches which supply the conjunctiva and anterior |>art~ of the fibrous tunic. After piercing the sclera twigs are given off which pa— to the ciliary muscle, as well as other- which as recurrent branches, together with similar branches from the long posterior ciliary arteries, anastomose with the choroidal vessels derived from the short ciliary trunk-. An important anastomotic communication is thus established between the blood-vessels supplying the choroid proper and those distributed to the ciliary region. The branches of the long posterior and the anterior ciliary arteries inos- culate within the ciliary region to form in the vicinity of the root of the iris an arterial circuit, the circuit's arteriosus iridis major, from which vessel- are given off to the ciliary processes and the iris, as well as recurrent anastomotic twigs to the choroid. The venous fruit/:* draining the eyeball in general correspond in their arrangement to that of the arteries, the chief groups being the retinal, posterior, and anterior ciliary veins. The retinal veins receive the blood from the closed retinal system and follow closely the corresponding arteries. The posterior ciliary veins, or, more familiarly, the vena vorticosa?, collect the blood from the iris, the ciliary processes, part of the ciliary muscle, the orbiculus ciliaris, and the choroid, and pierce the sclerotic coat within the equatorial region as four large trunks, which converge at points about equi- distant from one another : after penetrating the fibrous tunic they additionally receive the episcleral veins. The anterior ciliary veins drain a much more limited area than that supplied by the corresponding arteries, since within the eyeball they receive only the blood returned from the ciliary muscle, taking up the small radicles communicating with Schlemm's canal : after emerging from the sclerotic coat the anterior ciliary veins receive a- tributa- ries the episcleral and the anterior conjunctival vessels. The Lymphatics of the Eyeball. — The lymph-channels of the eye- ball comprise two systems, the anterior and the post* rim-. The anterior lymph-tract embraces i 1 ) the chambers occupied by the mosl important intraocular collection of lymph, the aqueous humor, together with the system of -pace- by which this fluid is normally carried off, a- represented by the -pace- of Fontana and canal of Schlemm : and ( '1) the elaborate system of juice-channels within the cornea and adjacent part of the sclera. The posterior lymph-tract includes two separate systems, that of the choroid and of the retina. The lymphatic fluid of the choroid is collected within the perichoroidal lymph-space, between the choroid and the sclera, from which cleft the lymph escapes chiefly into the -pace of Tenon, or episcleral lymph- space, by means of the perivascular lymphatic canals accompanying the venae vorticose : additional perivascular channels may also exist in connection with the posterior ciliary arteries. The accumulated lymph within the space of Tenon find- its way into the large intracranial lymph-spaces, probably by mean- of tin- supravaginal space which surrounds the exterior of' the optic nerve. The retinal system of lymphatics is represented bythe perivascular lymph-sheaths surrounding the retinal vessels, a- well a- by the hyaloid canal within the vitreous. These channel- communicate with the lymph- cleft- within the optic nerve, which are connected with the greal intracranial lymph-spaces by mean- of the subarachnoidal spaces of the optic nerve. GENERAL PHYSIOLOGY OF VISION. By ALBERT P. BRUBAKER, M. D., OF PHILADELPHIA. Introduction. — The visual apparatus in its entirety constitutes a mechanism the excitation of which gives rise (1) to the sensation of light and its different qualities — colors; (2) to the perception of light and color under the form of pictures of external objects; (3) to the production of muscular sensations by which we judge of the size, distance, and direction of objects. The specific physiological stimulus to the terminal apparatus of the optic nerve is the impact of the undulations of a perfectly elastic medium, the ether. The transfer of the energy of the ether-vibrations into that form of energy known as a nerve-impulse takes place in the pigment of the neuro- epithelial layer of the retina. The nerve-impulses so generated are trans- mitted by the fibers of the optic nerve to the cells of the cerebral cortex, in which some molecular process takes place out of which the mind forms the sensations of light and color. In general, it may be said that, at least for the same color, the intensity of the objective vibrations determines the inten- sity of the sensations. The optic nerve, obeying the same general laws of nerve-stimulation, reacts also to the electric current and to mechanical agencies, as shown by Hashes of light with varying shades of color. The formation of images on the percipient elements of the retina, which by their forms and associated colors give rise to the perception of objects, is made possible by the introduction of a complex refracting apparatus consist- ing of the cornea, aqueous humor, crystalline lens, and vitreous humor. Without these agencies ether-vibrations would only give rise to a sensation of diffused luminosity. The movements of the eyeball occasioned by the contractions of the ocular muscles are attended by muscular sensations, out of which the mind draws its conclusions as to the size, distance, and direction of objects. The Bye a laving Camera. — En its construction, in the arrangement of its various parts, ami in their mode of action the eve may be com- pared to a camera obscura. Though the comparison may not be absolutely exact, yet in a general way it is true that there are many striking points of similarity between them — e.g. the sclera and choroid maybe compared to the walls of the camera ; the combined refractive media to the single lens, the action of which results in the focussing of the light-rays ; the retina to the sen- sitive plate receiving the image formed ;it the focal point; the iris to the diaphragm lor the regulation of the amount of lighl to he admitted, and for the partial exclusion of those marginal rays which give rise to spherical aber- ration; the ciliary muscle to the adjusting screw, by means of which the image is broughl t" m focus on the sensitive plate, notwithstanding the varying distances of the objeel from the lens. The presence of the visual j>nr/)/< in THE DIOPTRIC APPARATUS. 89 the rods of the retina capable of being altered by light makes the comparison still more striking. The Retinal Image. -The existence of an image on the retina can be readily seen in the excised eye of an albino rabbit, the coats of which are quite transparent from the absence <>t' pigment. Its presence in the human eye can be demonstrated with the ophthalmoscope. It is this image, com- posed of focal points of luminous rays, which is the basis of our sight- perceptions, and which stimulates the rods and cones, and out of • which the mind constructs space-relations of external objects. In only two essential respects does the image on the retina differ from the object, aside from the fact that the object has usually three, the image only two, dimensions — viz. in size and relative arrangement of its parts. Whatever the distance, the image is generally smaller than the object: it is also reversed, the upper part of the object becoming the lower part of the image, and the right side of the object the left of the image, and the reverse. The Dioptric Apparatus. — The media by which rays of light entering the eye are refracted and brought to a focus with the production of an image consist of the cornea, aqueous humor, lens, and vitreous body. As the two surfaees of the cornea are practically parallel, and as the index of refraction of the aqueous humor is the same as that of the cornea, they may be regarded as but one medium. The refracting surfaees may therefore be reduced to the anterior surface of the cornea, the anterior surface of the lens, and the posterior surface of the lens. Rays of light emanating from one point — that is, Jwmocentric ray* — entering the eye must traverse successively the different refractive media. In their passage from one to the other they undergo at their surfaees changes in direction before they are converged to a focal point. In order to mathe- matically follow the rays in all their deviations through the media, to determine their focal point, and to construct the image, a knowledge of the form of the refracting surfaces, the refractive index of the different media, and the distance of the surfaces from each other, must be obtained. The following constants are now accepted: The radii of curvature of that portion of each refracting surface used for distinct vision are for the cornea 7.829 mm., for the anterior and posterior surfaces of the lens 10 and 6 mm., respectively. The indices of refraction of the different media are as follows: cornea and aqueous humor, 1.3365; lens, 1.4871; vitreous body, 1.3365. The distance from the vertex of the cornea to the lens is 3.6 mm. ; the thickness of the lens, 3.6 mm. ; the distance from the posterior surface "I the lens to the retina, 15 mm. Homocentric rays of light entering the eye pass from air with a refractive index of 1.00025 into the cornea with an index of 1.3365. In passing from the rarer into the denser medium they undergo refraction and are rendered somewhat convergent. The extent of this firsl refraction and con- vergence is sufficiently great to bring parallel rays, if continued, to a focus about 10 mm. behind the situation of the retina. On entering the leu- they are for the same reason again refracted and converged, and if continued would come to a focus about 6.5 mm. behind the retina. ( )u passing into the vitreous body they are again converged to an extent sufficient t" focalize them on the retina f fig. 4iitf, \ ,, is the image of the first, .V, : a ray which in the firsl medium is directed to the first nodal point passes after refraction 'In gh the second lal point, and the direction- of the rays before and after refraction an' parallel to each other. In Fig. I!» let .1 />' represent the axis. fhe distance of the first focal point, /•',, from the first principal plane, //,. i- the anterior focal distance. The distance of the posterior focal point, A , from the second principal plane, //,. is the posterior focal distance. The distance of the first nodal point. A',, from the first focal point is equal to the 9econd focal distance. The distance of the second nodal point, .Y_„ from the posterior focal point is equal to the anterior focal distance. It is evi- 1 For additional consideration of iliis subject sec pajjes lo'.i ami !•_!.">. properties or the cardinal points. 91 dent, therefore, that the distance of the corresponding principal and nodal points from cadi other is equal to the differences between the two focal dis- tances. Also the distance of the two principal points from each other is equal to the distance of the two nodal points from each other. Finally, the A ?, #, ' hA V 2 /■:■ Fjq, 49.— Diagram showing the position and relation of the cardinal points. focal distances are proportional to the refractive indices of the first and last media. Planes passing through the focal points vertically to the axis are known as focal planes. From these properties of the cardinal points the position of an image in Fig. 50— Diagram to find the image in last medium of a luminous point in the first. the last medium of a luminous point in the first may be determined, and the course of a refracted ray in the last medium be constructed if its direction in the first be given according to the following rules : 1. To find the image in the last medium of a luminous point in the first : Let A (Fig. 50) be this given point. Draw A B parallel to the axis until it meets the second principal plane in B ; then B F 2 will be this ray after refraction. Draw a second ray from A to the first nodal point; then draw another ray, D E. from the second nodal point parallel to A C. This will be the refracted ray in the last medium. Where the two refracted ravs, BF 2 and D E, intersect, the image of A will be = A v * If, If. Fig. 51.— Diagram to find the refracted ray in the last medium of a given ray in the first medium. ■1. To find the refracted ray in the last medium of a given ray in the firsl medium: Le1 .I B Fig. 51 be the given ray. Continue this ray until it met- the first prin- * If the point A \- infinitely far from the eye, all the rays Btriking the eye will be parallel to each other. The nodal rav musl therefore be drawn, and the point where this nodal ray meets the Becond focal plane will be the image of A .1 ,. where all rays parallel to the nodal ray will meet. 92 /•>', becomes the course of tlie refracted ray. The Schematic Bye. — A.ccepting the system of cardinal points. List- ing, Donders, and v. Helmholtz have constructed "schematic" eves to be substituted lor the refracting system of the natural eye. For this purpose it is necessary to deduce from the various estimates of the indices of refraction of the different media, of the radii of curvatures of the differenl refractive surfaces, and of the distances separating them an average eye as a basis for calculation. The most recent attempt is that of v. Helmholtz. The data he assumed are as follows : The refractive index of air- 1 ; of the cornea and aqueous humor, 1.3365 ; of the lens, 1.4371 ; of the vitreous hmnor, 1.3365; the radius of curvature of the cornea, 7.829 rum. ; of the anterior surface of the lens, 10 mm. ; of the posterior surface, li mm. ; the distance from the apex of the cornea to the anterior surface of the Fig. 52. Diagram showing the position of tin' cardinal points in the "schematic eye." The con- tinuous lines in tlir upper halt of tin- flgure show their position in the passive emmetropic eye. The dotted lines indicate the change in their position in an eye accommodated for the objeel .1 at the distance a from tin- cornea, or 152 nun. The lower half of the figure shows the formation of a distinct image on the retina of an eye accommodated tor the object A at the distance a from the cornea. lens, -'I.'; mm. ; thickness of lens, 3. (J nun. From these data v. Helmholtz calculated tli«' position of the cardinal points for the eye as follows (see Fig. 52): The first focal point is situated 13.745 nun. before the anterior surface of the cornea; the posterior focal point i- situated 15.619 turn. behind the posterior surface of the lens; the first principal point, 1.753 mm. behind the cornea ; the second principal point, "2. KM! mm. behind the cornea ; tin- firsl ami -croud n<,dal point-. 6.968 and 7.321 mm. behind tin' apes of the cornea, respectively. The anterior focal distance of this schematic eye there- fore amounts to 15.498 mm., and the posterior focal distance to 20.713 mm. \\ hen the eye, however, i- accommodated for near vision, the relations of the cardinal point- are changed a- follow-, if the point accommodated for lie- [52 mm. from the cornea ; Anterior focal distance, L3.990 nun. ; posterior focal distance, L8.689 mm.; distance from cornea of the firsl and second THE REDUCED EVE. 93 principal point-, 1.858 and 2.257 mm. respectively ; distance of the posterior focus, 20.955 nun. from cornea. Given this schematic eye in the accommo- dated state, the course of the rays and the determination of the position of an image in the last medium of a luminous point in the first can easily be determined by the rules above given. The Reduced Bye. — As suggested by Listing, this schematic eye may be yet further simplified or reduced to a single refracting surface hounded anteriorly by air and posteriorly by aqueous or vitreous humor. Without introducing any noticeable error in the determination of the size of the retinal image, the anterior principal and the anterior nodal points may he disregarded, owing to the minuteness of the distances (0.39 mm.) separating the two sys- tem- of points. There is thus obtained one principal point and one nodal point, which latter becomes the center of curvature of the single refracting surface. The dimensions of this "reduced" eye are as follows (see Fig. 53) : Fig. 53.— DiagTam showing the position of the cardinal points in the " reduced eye." The continuous lines in the upper half of the figure show their position in the passive eye. Tin- dotted lines refer to their change of position when the eye is accommodated for the near object, .1. Tin- lower half of the figure shows the formation of an image in the reduced eye and the relation between the size < >f the object and the size of the image. From the anterior surface of the cornea to the principal point. 2.106 mm.; to the nodal point, 7.321 mm. The anterior focal distance is 15.498 mm.; the posterior focal distance, 20.713. There is thus substituted for the nat- ural eye a single refracting surface having a radius of curvature of 5.215 mm. The index of refraction of this eye i- 1.3365, which is that of the vitreous humor. In such an eye luminous rays emanating from the anterior focal point are parallel to the axis niter refraction in the interior of the eye. Also rays parallel to the axis before refraction unite at the posterior focal point. By means of this reduced eve the construction of the refracted ray, the various calculations a- to the size of the image, the size of diffusion cir- cles, etc. are much facilitated. In Fit:. 54 lot .1 B represenl an object. From .1 homocentric rays fall on tin- sin- gle refracting surface //. One of the rays, the nodal ray. falling en the surface per- pendicularly, passes unrefracted through the single nodal point, .V. to the posterior focal plane. The remaining ray-, falling en this surface under varying degrees of incidence, undergo corresponding degrees of refraction, by which they form a converging con.- of 94 GENERAL PHYSIOLOGY OF VISION. rays which unite at a point situated on the nodal ray. These two points arc known as conjugate foci. The same holds true for homocentric rays emanating from B or any other point of the object. The size of the retinal image, /, may now be easily calculated, when the size of the object, 0, and its distance, J), from the refracting surface with radius of curvature, R, are* known, by the following formula: ( > : 1 = D + R : F, - R. For, a> the triangles .1 N B and a N b are equal, we have A B: ab = f N: A g, or a b = — — u . Fig. 54. — Diagram to illustrate formation of images in reduced eye. Accommodation. 1 — In a normal or emmetropic eye homocentric parallel rays of lighl after passing through the optic media are converged and brought to a focus on the retina. Hays, however, which conic from a luminous point situated near the eye, and which are therefore divergent and passing through the optic media at the same time, arc intercepted by the retina before they arc focussed, and give rise to the formation of diffusion-circles and indistinctness of vision, 'flic reverse is also true. When the eve is adjusted for the refrac- tion and focussing of divergent rays, parallel rays will he brought to a focus before reaching the retina, and, again diverging, will form diffusion-circles. It is evident, therefore, that it is impossible to simultaneously focus both parallel and divergent rays, and to see two objects distinctly at the same time which are situated at different distances. The eye must be alternately adjusted first to one object and then to another. The capability which the eye possesses of adjusting itself to vision at different distances is termed accommodation. The following table of Listino- shows the size of the diffusion-circles for d of objects situated at different distances when the accommodative power i- suspended : i listance of the focal Distance of Luminous point. [mint behind the posterior Diameter of the diffusion-circle. 65 25 12 >; 3 L.500 0.750 0.375 0.188 0.094 0.08.8 surface of the retina. o. mm. o.i lor. " 0.012 '• 0.025 " 0.050 " 0.100 " 0.20 0.40 o.so •■ 1.60 3.20 3.42 0. 0.0011 0.0027 0.0056 0.0112 0.0222 0.0443 0.0825 0.1616 0.3122 0.5768 or, hi Iditional consideration of this subject consult page 134 and page 155. OPTICA I. DEFECTS. 95 The normal eve when adjusted f'<»r distant vision is in a passive condition and unattended with fatigue. I n the act of adjustment, however, lor near vision the eye passes into an active state, the result of a muscular effort, the energy of which is proportional to the nearness of the object toward which the eye is directed. From the above table it is evident that ray- of light coming from infinity or from any object even but <> m. distant are so nearly parallel and the diffusion circles so very small that the indistinctness of the image is scarcely perceived, and hence no perceptible accommodative effort is required. Rays coming from objects situated progressively nearer the eye require for their localization a constantly increasing effort of accommodation. During accommodation the lens undergoes a change of shape, becoming more convex, especially on its anterior surface. The greater the degrees of divergence of tiie rays the greater must be the increase in lens convexity, in order that they may be sufficiently converged and focalized on the retinal surface. Changes in the curvatures of the lens, either of increase or decrease, are attended with corresponding changes in the distinctness of the image. Mechanism of Accommodation. — Though it is generally admitted that the increase in the convexity of the lens is caused by the contraction of the ciliary muscle and the subsequent relaxation of the suspensory ligament, the exact manner in which this is brought about is not well understood. When the eye is in repose and adjusted for distant vision the lens is somewhat flat- tened from the traction of the suspensory ligament. When the eye requires adjustment for near vision the ciliary muscle contracts, the suspensory liga- ment relaxes, and the lens, in consequence of its inherent elasticity, bulges forward and becomes more convex. Its antero-posterior diameter is thus increased and its refractive power is proportionally greater. It is generally admitted that during accommodation the meridional fibers of the ciliary muscle draw forward the ciliary processes and relax the liga- ment. At the same time the outer border of the iris is drawn somewhat backward. In extreme efforts of accommodation it is also believed by some observers that the circular fibers, the so-called "annular muscle," contract and exert a pressure on the periphery of the lens, and thus aid other mechan- isms in increasing the convexity. This view appears to be supported by the fact that in hyperopia, where there is a constant effort required for distinct vision even of distant objects, the annular muscle becomes very much hyper- trophied, thus serving to reinforce the action of the meridional fibers. In myopia, on the contrary, where the accommodative effort is at a minimum, the entire muscle possesses less than its average size and development (com- pare with page 135). Optical Defects. 1 — From a purely physical point of view the eye i- not a perfect instrument. It is not quite achromatic, is not free from spherical aberration, and is not exactly centered. Moreover, its area of distinct vision i- quite limited, and does not correspond with the field of projection, the retina. In first-class optical instruments the lenses are centered — that is, their exact centers are situated on the same axis. In viewing an object through such a system the visual line corresp Is with the axis of the lens- system. This is not the case with the lens-system of the eye. A line passing through the Center of the cornea and the center of the eye, the optic cuxi& ' > .1 in hig. oo, does not pass exactly through the center of the lens, and does not fall into the point of most distinct vision, the fovea. 'I his 1 For a lull consideration of the optical defects of the eye, see sections devoted t" < >|>ii the fact that the circular fibers of the iris alternately contract and relax with increasing and decreasing intensities of light, it serves to regulate the amount of light entering the eye accessary for distinct vision. In the absence of light the sphincter pupiUa relaxes and the pupil enlarges. As the light increases in intensity the muscle contracts and the pupil becomes smaller. The contrac- tion of tin' sphincter nni-ele i- with a given intensity of light greater when the lighl fill- directly into the fovea. Contraction of this muscle also occurs a- :m associated movement in the act of convergence of the optic axes in accommodative efforts and in consensus with the other eye. The movements of the iris by which the size of the pupil is determined from moment to moment are caused by the contractions of the sphincter pupilla and dilatator /itij>i//6.— To demonstrate the blind spot. left eye closed, and the paper be held at a distance of 10 inches, the circle will entirely disappear. This occurs when the image fill- on the optic oerve at it- entrance. (See also page 470.) The experiment of Purkinje demon- strates the same fact. It is well known that the blood-vessels of the retina are situated in its innermost layers a short distance behind the optic-nerve fibers. Owing to this anatomical arrangement, a portion of the light coming through the pupil will be intercepted by the vessels and a shadow projected <>n the layer of rods and cones. Ordinarily, these shadows are not perceived, for the reason 7 GENERAL PHYSIOLOGY OF VISION. that the shaded part- arc more sensitive and their excitability less readily exhausted, and perhaps because the mind has Leaned to disregard them. Bui if light be made to enter the eye obliquely, the position of the shadows will l«c changed, when at once they become apparent. This can be shown in the following way : It' in a darkened room a lighted candle be held several inches to the side and to the f'mnt of the eve, and then moved ii|> and down, there will be perceived, apparently in the field of vision, an arborescent figure correspond- ing to the retinal blood-vessels. This i- due to the falling of the shadows on unusual portions of the layer of rods and cones (see also page 141). Excitability of the Retina. — The retina is not equally excitable in all parts of it- extent. The maximum degree of sensibility is found in the macula lutea, ami especially in it- central portion, the fovea. In this region the layers of the retina almost entirely disappear, the layer of rods and cones only remaining, and in the fovea only the latter are present. That this area is the point of mosl distinct vision is shown by the observation that when the eye i- directed to any given point of light, its image always falls in the fovea. Anv pathological change in the fovea i- attended by marked indis- tinctness <>f vision. The sensibility of the retina gradually but irregularly diminishes from the macula toward the periphery. This diminution in sensibility hold- true for monochromatic as well as white light. A- stated above, the nature of the molecular processes which take place in the retinal tissue, and which arc caused on one hand by the light-vibra- tions, and on the other hand develop ncrve-inipnlses, is entirely unknown. The discovery of the visual purple in the outer segment of the rods gave promise of some explanation of the process, especially when it was shown to mdergo changes when exposed to the action of light. Ki'ihne even succeeded in obtaining an optogram, or a fixed image, of an external object in a manner similar to that by which an image i- fixed on the sensitive plate of a camera. But a- tin- pigmenl i- wanting in the cones, and especially in the fovea, it cannot be considered essential to distinct vision, although that it plays some important role in the visual process is highly probable. The visual purple disappears when the eye is exposed to light, but is restored when light is excluded. It ha- also been observed that under the influence of light- -timnlation the «• - become shorter, and in the darkness again become longer (see page 'i'.'i. Color-perception. — A beam of sunlight passed through a glass prism is decomposed into a series of colors — red, orange, yellow, green, blue, indigo, and violet — the so-called spectral colors, so well exemplified in the rainbow. The spectral color- are termed simple colors, because they cannot be any further decomposed by a prism. Objectively, the spectral color- consist of very rapid transverse vibrations of the ether, from about l<><> millions of million- per second for red to about 760 million- of million- for violet, but subjectively they are sensations caused l>\ the impact of the ether-waves on tin- percipient layer of t he retina. It i- possible to mix "i- Mend these spectral color-sensations in the eye by stimulating the same area of the retina by differenl spectral color-, either at the -ami' time or in rapid succession. The following table -how- the results of -ml, experiments as performed by v. rlelmholtz (Dk. dark; Wh. = whitish I. THEORIES OF COLOR-PERI EPTION. 99 Violet. Indigo. Cyan-blue. Bluish- green. '•rr> II. yellow. Yellow. Purple Dk.-rose Wh.-rose White Wh.-yellow Gold-yellow |Orange Dk.-rose Wh.-rose White Wh.-yellow Yellow Yellow Wh.-rose White Wh.-green Wh.-yellow Gr.-yellow . . White Wh.-green Wh.-green Gn White-blue Water-blue Bl.-green Bluish-green Water-blue Water-blue ('van-blue Indigo . . Red < > ramie Yellow ( rr.-yellow Green These are the mixed colors. But it is to 1"- observed that only two new color-sensations can be produced, white and purple, the remaining mixed colors already finding their equivalent in the spectrum. White ami purple, therefore, are color-sensations, which have do objective equivalent in a simple number of ether-vibrations like the spectral colors. Two spectral colors which by their mixture produce the sensation of white are called complementary colors. Such are red and green-blue, golden yellow and blue, green and purple. The mixture of all the spectral colors produces white again. This is the result of adding two or more color-sensa- tions. Different results are obtained, however, by adding colored pigments. Yellow and blue, for example, produce in the eye white, but on the painter's palette green. For the explanation of such facts reference must be made to larger treatises. The colors of nature are usually mixture- of simple colors, as can be shown by spectroscopic analysis or by a synthesis of spectral colors. In all color-sensations we must distinguish three primary qualities : (1) hue ; (2) purity or tint ; (3) brightness or luminosity. The first quality f r. Helmholtz, originated by Thomas Young (1807), assumes in it- latest form the existence in the human retina of three different kind- of end organs, each of which i< loaded with its own photo-chemical substance capable of being decomposed by a certain color, and thus exciting the fiber of the optic nerve. In the first group these end organs are loaded with a red-sensitive sub- stance, which is affected mainly by the red part of the spectrum ; the second group has it- end organ- provided with a green-sensitive substance, which i- mainly excited by the green color; while the third group i- provided with a blue-sensitive substance, thi- latter being mainly affected and decomposed by the blue-violet portion of the spectrum. AH these three differenl end organs are present in every part of the most sensitive area of the retina, and are connected by separate nerve-fibers with special parts of the brain, in the cells of which each call- up it- separate sensation of red or green or blue. 1 For further discussion of thi- subjeel see page 167. tOO GENERAL PHYSIOLOGY OF VISION. Out of these three primary color-sensations all other color-sensations arise, [fa Light mainly excites the red- or green- or blue-sensitive substance of a retinal area, we term it red, green, or blue, respectively. But if two of these photo-chemical substances arc stimulated simultaneously, quite different sensations arise, 'rim- simultaneous stimulation of the red ami green sub- stances gives rise to the sensation of yellow, that of red ami blue to the sensation of purple, and that of Wine ami green to the sensation of blue-green. Simultaneous stimulation of all three ssbstances of a certain area produces thesensati f white. According to this theory, complementary colors are all those which together excite all the three substances. Color-blindness is explained by this theory, on the assumption that two of the photo-chemical substances have become similar or equal in composition to each other. fhe theory of Hering, brought forward in 1874, has the underlying as- sumption that the process of restitution in a nerve-element is capable of exciting a sensation. This theory asserts that there are three visual sub- stance- in the retina— a white-black, a red-green, and a yellow-blue visual substance. A destructive process in the white-Mack substance, such as is induced not only by white fight, but also by any other simple or mixed color, produces the sensation of white, while the process of restitution or assimila- tion m this substance produce- the sensation of black. Similarly, red Light produce- di-a— imitation or decomposition in the red-green substance, and this, again, the sensation of red. Green Light, however, favors the process of restitution or assimilation in the red-green substances, and thus gives rise to the sensation of green, [n the same way the sensation of yellow has its cause in the decomposition of the yellow-blue substance induced by yellow Light, while the sensation of blue i- produced by an assimilative process in the same substance. Simultaneous processes of disassimilation and assimilation in the same visual substance antagonize each other, and consequently produce no color-sensation by mean- of this substance, but only the sensation of white, by reason of decomposition, by both color-, in the white-black substance. Thus, yellow and fine, impinging on the same retinal area, have no effect on the yellow-blue substance, because they are antagonistic in their action on this substance, but only produce the sensation of white, as both yellow and blue decompose the white-black material. Color-blindness is explained by tin assumption of the absence of either the red-green or the yellow-blue visual substance in the retina. Movements of the Eyeball. — The almost spherical eyeball lies in a correspondingly shaped cavity of the orbit, like a ball placed in a socket, and i- capable of being moved to a considerable extent by the six ocular muscles which are attached to it. 'fhe movements of each eye are referred to three fixed line- or axes which have their origin at the point of rotation of the eye- ball, this point lying about 1.7 mm. behind the center of the globe. If the eve looks straight forward in the horizontal plane (the head being erect), the Line joining the center of rotation with the object looked at i- the visual line or visual axis. Around this antero-posterior axis the eye may be regarded as performing it- circular rotation or torsion. At right angles to this line, and joining the center of rotation of both eye-, i- the horizontal or transverse axis around which the movements of elevation (up to 34 land depression (down to 57 i lake pi; ice. \| right angles to both of tlie-e line- there is the m Ileal axis, around which the movements of adduction (toward the nose up to 45°) and abduction (toward the temple up to L2 i occur. The six muscles may be divided into three pairs, each of which has a common axis around which it tend- to move the eyeball. Km only the common axis of the internal and MOVEMENTS OF THE EYEBALL: 101 external recti coincides with one of three axes before mentioned — namely, with the vertical axis — thus moving the hall only inwardly or outwardly, respectively. The other two pairs, however, have their own axes of action, and their movements of the hall must he therefore analyzed with regard to all the three axes, each of these four muscles producing rotation, elevation, and depression, and abduction or adduction. The superior and inferior recti muscles, forming one pair, move the eye around, a horizontal axis which intersects the median plane of the body in front of the eyes at an angle of 63°, and the superior and inferior oblique muscles forming the third pair rotate the globe around a horizontal axis which cuts the median plane of the body behind the eyes at an angle of 39°. Thus it is that each muscle moves the eye as follows, the movement for practical purposes being referred to the cornea : The rectus externus draws the cornea simply to the temporal side, the rectus interims simply to the nose ; the superior rectus displaces the cornea upward, slightly inward, and turns the upper part toward the nose (medial torsion); the inferior rectus moves the cornea downward, slightly inward, and twists the upper part away from the nose (lateral torsion) ; the superior oblique displaces the cornea downward, slightly outward, and produces medial torsion ; while the inferior oblique moves the cornea upward, slightly out- ward, and produces lateral torsion. These facts show that for certain move- ments of the eye at least three muscles are necessary (see following table) : Intra nl. Outward, Upward, Doivnward, Inward and upward, Rectus interims. Rectus externus. ( Rectus superior. { Obliquus inferior, f Rectus inferior. { Obliquus superior. ( Rectus interims. < Rectus superior. I Obliquus inferior. Inward and downward, Outward and upward, Outward and downward. Rectus internus. Rectus inferior. Obliquus superior. Rectus externus. Rectus superior. Obliquus inferior. ( Rectus externus. ■< Rectus inferior. ( ( >bliquus superior. If both eyes have their line of vision in the horizontal plane parallel with each other and with the median plane of the body, they are said to be in the primary 'position. All other positions are called secondary. Both eyes always move simultaneously, which is called the associated movement of the ci/cs. There are three forms of associated movements : (1) movement of both eye- in the same direction ; (2) movements of convergence by which the visual lines are converged on a point in the middle line of the body; (3) movements of divergence, by which the eyes are brought back from convergence to paral- lelism, or even to divergence, as in certain stereoscopic exercises. A combi- nation of (1 ) and (_!) or of ( 1 ) and (3) takes place for certain positions of the object looked at. 1 1 For further and similar consideration of the physiological action of the ocular muscles see pages 41, 42, 497, and 498. GENERAL OPTICAL PRINCIPLES: KATOPTRICS, DIOPTRICS, PHYSIOLOGICAL OPTICS. liv WILLIAM S. DENNF/IT. M. lb. andCOLMAN WARD CUTLER, M. D., OF NETS JTOBK CITY. Light from its source spreads from center to circumference — not as the arrow flies, bul as the wave passes. The continually repeated cycle at the origin is imitated in all it> essentials at each surrounding particle, which, being thus made luminous, transmits in turn what it has received to others next removed. This is not the place to discuss al length the wave theory of light, but let it be remembered t lint the image on the retina is the result of purely mechanical processes into which the time element necessarily enters. Whatever the nature of the cycle at the origin, it has to do with a mass of matter controlled by elastic forces, hence its period is constant. The conditions at balf-cycle periods are such as may be represented by algebraic equals and opposites, compounding into zero if both are impressed on the same body at the same time. The passage of light through space is the transference of motion from one body to another, or to many others whose reactions bring or tend to bring the first to rest, and which are broughl to resl in turn by those on whom they act. The time element in this process of light propagation is also determined strictly in irdance with mechanical laws, and hence the spherical shell of a wave-surface is deformed or distorted by any change in the density or structure of the medium through which it passes At the outset, in a homogeneous medium, the wave-surfaces are spherical, and the light received by any body to which the wave has reached is measured by the area of wave-surface which it intercepts. This mean- that the body is, as it were, a buffer to the moving masses of which the medium is composed. If the recipient is at an equal distance from two such sources of light whose phases and cycles are similar, it will of course receive twice the light that it would from one. Now. the whole theory of transmission by waves implies that every separate point of u wave-front is itself, while the wave is passing, nothing other than an instantaneous source of light, and may he treated a- such, and that the results traceable to any one lumi- nous element i Fig. 57, I) are the same as may be obtained by the summation of results i rate the fact that h hen the center of a wave-surface Is behind the wave, it is a radiant ; when In front "t the u due to Bimilar condition- as they exist al -one- later period in every separate element, a, >>. c, d, etc., along the whole wave-surface. Thus it happens that any point. //, equally distant from tin- point-, I, and C, receives double the amount of lighl or energy from both theee point- that it doc- from either. REFRACTION AND REFLECTION. 103 A change in the form of the wave-fronl so that, as at a', ne recognizes the /'s as typical of focal distances, and the r as a radius, but f and f" are also radii, and their magnitudes measure the flatness of the incident and refracted waves; - is the curvature of a wave-surface, and u // is the coefficient of slowness for wave-travel in the medium thus indexed, while u" — ft' is the lag of the wave as it passes from one medium to another; and so OD until the whole physical theory is read from the necessary geometrical relations. Refraction and Reflection. — With SnelVslaw for a stepping-stone we now pass to the geometrical consideration of refraction and reflection. This 104 <;i\i:i;m. optical i>rix(ti>li:s. law for oearly a hundred year- was the expression merely of the results of experience in the observation of refracted light. It is now generalized and applied to both reflection and refraction. Its consistency with the irarc theory of light may be seen as follows: When a wave-surface whose section may he represented by a l> (Fig. 59) passes through d, the surface separating one medium from another in which (;il (J"1 |-,,- 59.— Showing that a wave-surface is not changed in its direction by passing through (d) an optical surface parallel to it. however the character of the medium may change a1 that surface, but that when th.- optica] surface [a') is inclined to the wave-surface, the latter must experience a change in its direc- tion dependent on its change of velocity in passing from one medium into the other. for any reason whatever lighl make- its way at a different rate of speed, if the wave-surface immediately before its passage is parallel to the surface sepa- rating the two media, it will he parallel to it immediately after its passage, because at no time have the circumstances governing its speed differed along the whole line of the wave-front, the change having taken place everywhere at the same in-taut. The length of section is immaterial so that it be straight. Its straightness as a measurable quantity is the arc divided by the radius, so whatever the curve for a section as small as you please, the above statement is practically true, neither end of the wave gains on the other and it continues to advance in a straight line. If the wave enter- a retarding medium whose surface, d', is not parallel to it- own. instead of making its way as it otherwise would to the position a", b l} the spread of the light-disturbance from particle to particle has cov- ered, say, a -mailer area in the new medium than in the old, and the limit of it- advance is along the common tangent of the circles whose radii are proportional to the time since they began to form in the new medium. Since the line '■' represents the velocity of propagation in the medium // and v" in the medium fi", the desired relation-, are easily established. Each is perpen- dicular to it- wave front and is consequently a radius or ray ; a", A, shows the place to which the wave would have advanced had the character of the medium ii"t changed at Locate the centers from which the waves come and to which they go, and easy to locate the center of the optical surface ; con- necting these centers, p' } p" } or //" and n with the point of incidence a I Fig. ), gives ns the three radii, each of course perpendicular to the surface to which it belongs, and consequently mutually inclined to each other as are those surfaces. Through the relations of these radii the law was discovered, through them it is most easily proved, and through them it is most frequently stated, angles of incidence, reflection, and refraction being defined as angle- made by the incident, reflected, or refracted ray (perpendicular) with the radius of the optical surface. The ability to transfer the attention from surfaces to rays, and to replace velocities by their reciprocals, is a great geometrical advantage, though it gives a show of artificiality to the whole theory of optical instruments as far as we have occasion to pursue it. If u, however accented, is taken to represent > Equation 1 may lie written sin i / /i / = sin i // fJ- // , (2) and Equation 2 is Snell's law. As here used, //, //', etc. represent the time needed for light to travel unit distance in the medium with which each is connected ; they might be called coefficients of slowness or coefficients of sine magnitude ; they are, in fact, called indices of refraction. The time needed for light to spread unit distance in ether — or in air, which is very nearly the same — is the standard of measurement, and is assumed to be 1. The actual value in seconds for ether, for air, or for other media is of no special import to us here; we need only the relative magni- tudes, which are known or easily obtained, and are represented by // appro- priately accented. When //. is equal to 1, it is often omitted from a product as a matter of brevity and convenience. In all the formulae here used it will be written for the sake of symmetry and clearness. With this much of physical explanation and the law of sines as the rule of the road, we may proceed to speak of rays and foci as of pencils and points, hoping that their true significance will not be forgotten, and believing that the little effort that is necessary to identify physical with geometrical relation- ships will more than pay for itself as a guard against error and as a mne- monic aid. Wc shall use the word refraction in its most general sense, including refraction and reflection. If exceptions to this usage occur, they will be noted. The first general problem that presents itself in the study of image-form- ing optical instruments is this : Given waves of circular section, what will be their curve in either medium after incidence on the spherical surface which separates it from another of different index '.' The problem may be solved by the aid of Fig. HO. .1. in which wave- at ah would converge upon the point p f } excepl that the optical surface changes their curvature, giving them a center at //'. In this particular case //, />. /-', n',;i" are known, ami />" \< sought, but the solution desired should enable us to determine the position of any one of the quantities when the others are given, h being the point where the optical surface meets the line connecting it- center with that of the incident wave. 106 GENERAL OPTICAL PRINCIPLES. At // the incident wave and the optical surface have a common tangent, and there is no change in the direction »>f the wave or of its radius; conse- quently, the center of the two waves will he on a line with the center of the optical surface. At any other point of incidence the law of sines applied to the two kimwn radii will indicate the third, and its cross witli the axis at p" will he approximately the center of wave curvature. The solution is as follow- : of refraction and reflection, showing the relative positions as expressed by to be the same for rays and normals as for the surfaces i" \\ hicb they belong. At ii the waves trallel to theoptii a \s any point common to optical and wave-surfaces; p' is the en hit i. i the Incident wave, p" of the refracted, and /.'" of the reflected wave. The values of radii, curvat and focal distances are ordinarily considered positive when the centers t" which thej appertain lit- to the righl real! positive. For the convenience of a one-letter notation draw Fig. 01 identical with I' ig. 60, hut represenl the radius of the refracting surface by r, the distance of any point /> from the center of the refracting surface by g appropriately accented, the distance of any point /> from -. < '. and g f , and whose vertex measures the angle of incidence, and another triangle whose sides are /■. <". and g", and whose vertex i- the angle of refraction. The angle between r and g may lie called <">. REFRACTION A .X I > REFLECTION. 107 From the well-known property of triangles conic these two equations (3) sin ; (/ sin <5 Dividing 3 by 4 to eliminate o, By Snell's law, Eq. "J, Therefore, 7 /,~,> or H-"g"e'= "'.'/'' ' sin i 2! sin & e' sin /' sin i" g'e" e'g"' sin /' sin /" (5) (7) It should be noticed hen 1 that when the point a (Fig. 61) is placed very near to li the pole of the optical surface, e is nearly equal in value to/, and at the limit, when a and h become identical, any e is exactly equal to the corresponding /. The value of/ at the instant when a and A coincide is the value thai gives accurately the curvature of the wave at h. If the wave is circular in section, //' determined for one point on its surface is determined for all. When the refracted wave has not a circular section, it is usual in practice cither to shut /" f Fig. 61.— A one-letter notation for case (.4) Fig. 60. off that portion of its surface which departs appreciably from a uniform curve, and assumes that all the rays cross at the limiting position of />". or to name for the focal point that position of//' which is nearest to the greatest number of rays at once. Some information may be obtained concerning the curve of the wave by substituting for e' and e" in Eq. 8 the value which each pos- sesses by virtue of its being opposite to the angle d in the triangle to which it belongs ; thus : e /2 = ^ + ; -2_2.7 / /-cosJ. (8) e /n = y>n + r 2 _ 2 g // r cos ( j_ (9) Squaring 7 and substituting the value <■ from {), " ' f2 g" 2 \ a'' 2 ^ r 8 -I'/r cos '5) =fi /2 g' 2 (g" 2 + r- - '! i- the aberration for the 108 GENERAL OPTICAL PRINCIPLES. angled (longitudinal spherical aberration), and there is no aberration tor such values of g' or g" as cause d to disappear. A- will be readily appreciated, any irregularity in the curvature of the refracted wave interferes with the point-to-point correspondence of the image t,, it- object. The optical surfaces of most instruments arc spherical, and many circumstances conspire to limit our use of these surfaces to that part which is so near the axis as to be practically without aberration, or to have only so much aberration as may be ignored or eliminated by compensatory error-: so in all first approximations p" in its limiting position is taken as the focus conjugate to />' ; and since the e's and the /'s are in this position identical, Eq. 7 may be written thus: (^ = 9'f-, or ^=/^C (11) ? g"r "' r g' Designating these segments by their terminal points, as in Fig. 60, the nature of the relation sought becomes apparent : f^J>l>\ : l>l>'\ (12 ) ft' p'n p" 'a In (li a /''i>") we have an anharmonic range in which the two foci are con- jugate to the center and tiie pole of the optical surface, and the cross ratio is; the ratio of wave velocity in the two media. It is worth while to study into this a little if necessary, for, besides furnishing the easiest possible method of remembering the relations of the foci to their surface, it shows that the relation- are reciprocal, and that the two foci, being given a surface of any curve, may be placed, or a curve corresponding to any place may he deter- mined in precisely the same way. Anv combination of lenses and mirrors may he replaced by an equiv- alent surface: this is of very general utility, and, moreover, in the theory of thin pencils the circle of least confusion is located between the first and second focus of the pencil by the harmonic variety of this relation, the ratio being, as in the case of the mirror, equal to — 1. (See p. 127.) Again, when g in Eq. 11 is replaced by it- equal (/ — r), we have the following : n" I ff — r \ f ft , f„_.' f , ' which, when reduced, as it easily can be, gives the most important formula in this part of the hook : (13) In as brief a treatise on geometrical optics as this mu a "word-sign" for the other. Et should never be written in any other form until it has become so familiar to the eye thai from anj aide an error of transcription would be discovered at a glance. It i- general in it- application for the local distances of axial pencils for a surface of : 1 1 1 \ circular curvature, plus or minus, between any media of whatever index. It mighl ju-t as well have been deduced from anj of the special cases pictured in Fig. 60, and the preceding applies and may be read equally well in connection with anyone ol these cases, p"' is used in this figure to indicate the position which p" assumes when fi" //'; that is, in all cases of reflection. Fig. 60, A, was chosen as the type by which all may be classed and remembered, because in it all the curvatures, all the local distances, and other magnitudes are positive quantities; and if Eq. \''> is remem- bered as belonging to the case where all the quantities are plus, no confusion need atise CARDINAL POINTS. 109 in interpreting apparent anomalies of sign when a numerical equation of this form presents itself. The discussion of Eq. 13 is much more simple than its derivation. It tin- optical surface is a plain-, r becomes infinite and the last member vanishes, and consequently — =£- or — = ■*— . which must be construed t<> mean that the conjugate foci of a f " f ' ll" f •> & plane refracting surface are on the same side of the surface and at distances whose ratio is the same as the indices for the two media. If any value represented by/',/", or r has a minus sign, it of course represents a distance to the Left of h. If/' or/" repre- sents an infinite value, the inference is that the wave surface is perfectly flat, that the rays are parallel. Only in one case can /*' and p." be replaced by quantities having different ~i_ r n-. That //'should equal -(/'would indicate a position of the wave that physical condi- tion.-, can only account for by the supposition that it is a reflected wave— that is, turned back into the medium whence it came — and consequently travelling with the same velocity as before. Therefore the numerical value of fi" must be the same as «'. And it can be stated in this connection that when the indices differ in sign their numerical values do not differ, and ( , I = — 1. This only happens in cases of reflection. It is not only unnecessary, but it is confusing, to make any distinction between problems of reflection and refraction other than what i- indicated by the signs of the refractive indices. The simplicity and generality of the conditions is such that the laws, the methods, the formulae, and their interpretations are the same for katoptrics as for dioptrics. Katoptrics is that part of the science of optics that deal- with the phe- nomena of reflection, especially from regular surfaces like mirrors. Dioptrics treats of the phenomena of refraction, and with the definitions we dismiss the distinction, except in such degree as it is shown by the signs of the indices. Eq. 13 is the open sesame to all of Optics that we require. When the quantities that are represented by //.' and //." are of unlike sign, they are equal and we are dealing with reflection. All other cases are refractive. The inverse situation is covered by the rule which tells us to treat all mirrors as optical surfaces between media whose indices are 1 and — 1. Cardinal Points, four in number, may be named in connection with a single optical surface (Fig. 62). They are //, the center of the surface, A. the Flo. 02.— Above, the first principal focus i> a radiant, and rays become parallel in (V 1 . Below, rays par- allel in >/j.' converge in u". to the second principal principal j»>i,tf. F 7 , the first principal focus, and /-'".the second principal focus. The Center. — Since concentric circles are parallel, the wave whose center of curvature before incidence i- ,/ will have /' for a center after incidence — i.e. the ray that passes through /< i- un refracted. It will be seen hereafter that the relative size of object ami image is the ral their respective distances from » : that they approach » together; that each i> inverted in passing through // ; and that when they meet at » the size of one, in term- of the other, i- numerically equal to the ratio of the velocities of the light wave- by which lid GENERAL OPTICAL PRINCIPLES. the respective images arc formed. It will be seen also that the center n is to the optical surface what the two Qodal points n' and n" are to the lens or the optical system. The principal point h is the point where the optical surface is pierced by the line connecting it- center with the radiant. Object and image approach A together. At // they are equal and congruent (see page L12), and to h of the optical surface correspond the two principal points, h' and fi". of the system. The principal loci. F' and F" . are the same for the surface as for the system. The first principal focus, /•". is the center of those waves which after incidence become plane. In other word-, V is the cross of rays that are made parallel by incidence on the optical surface. The second principal focus is the center of those waves that before tnci- denc i the surface were parallel ; or it may be stated thus: Rays previously parallel cross after incidence at the last principal focus. These foci are found by giving to the variables of Eq. 13 such values as will impose the required conditions. To find /•", substitute x for /" in Eq. 13 and solve for /. This is because the center of a plane wave or the focus of a parallel pencil is at infin- ity. If/" = 3o, — =0, and so disappears from the expression, and we have r— £-,-*> (14) the necessary result of the condition imposed. The second principal focus, F", is found in the same way, for when J v.. 0, and S"= J P L -r F "- t 15 ) To apply this, suppose light from air is incident on a convex glass surface whose radius is one-fifth meter (.20 M i. Replacing that by which in the preceding paragraphs // has been con- nected with p". The path <>f the light-wave being reversible, either config- uration may in theory play the part of object to the other as image. Their distances from each other and from the cardinal point- of the surface are determined by previous considerations. Their relative magnitudes are to be determined. The magnification of an object by it- image i- ordinarily of two kind-, longitudmal and transverse. With the longitudinal, which may be obtained, for example, by comparing (Fig. 65) <{ %' with q" s", we will not here con- cern ourselves. The following is an easy ge strical determination oi the transverse dimensions of object and image: Lei the line p f q' perpendicular 112 ( ; EN /•: h'AI. OPTICAL PBINCIPL ES. to the axis be represented by/, its conjugate by ./", minus because it is on the opposite side of the axis, and it is important to distinguish an inverted from .in uprighl image. From the point p' let two lines be drawn, one par- allel to the axis and one through F', the first principal focus, and let them he continued till they meet the optical surface. As these lines are rays, their i *' Fig. 65.— Image ami objecl : magnification determined by properties of the principal foci (Eq. 18). course after meeting the surface is determinate. That parallel to the axis will pass through the second principal i'oens F", and that from the first principal focus will be made parallel to the axis. Where these two refracted rays meet will he the focus conjugate to p f , and p" q" will in this ease be —j". The three horizontal lines of the figure are parallel. The two /'s are -within required limits perpendicular to them, hence the triangles on the left are all similar, and the triangles on the right are all similar; so we have these two equations from a comparison of the sides of similar triangles: il = F '~f = F " F (18) y, r , F" -j" From these two equations we may learn where an object must be placed in order that object ami image may be equal and cosensal. For such a condition -%- must lie equal to 1. This can only be the case in (18), where /'' and j" are both equal to nothing; therefore the only place is at the surface itself, and there object and image meet and arc of the -a me size. To find where object and image are equal in size and opposite iii sense, we put ■.,, -1. This condition is imposed upon (18), when / / lF' and when./" 2 F". ' By replacing /*" and /•"' by their equals from Equations 14 and 15, and letting u" V l y and/" each equal to /•, Equation 18 reduces to ^~= 'rr/ This may be construed to mean, thai when the two images meet, as they must, in the center of the optical surface, their dimensions arc proportional to the velocity of light in the media to which they respectively correspond. For refraction it will he seen, r. point i- coincident with the point of its image. The cross-ratio (see page 108) bj which tic- cardinal points of the mirror are connected with the conjugate foci being l . I » /'./"./") is an harmonic range, and, any three points being given, the fourth may he determined by the well-known formula: „ h I'll J"ll (19) 'I'lc graphic solution is convenient, as it may he done with a pencil and straight- edge only. It three consecutive elements are given, as /". /'../' I Fig. 66), connect these three points by Straight line- with any other point, of the axis a and the fourth line. Tins drawing will answer too tor all systems whose first and last media are in this ratio. Before proceeding to show thai other systems of more surfaces than one Fig 68. Tan a': tan a" /' :/" (relative to " Helmholtz's formula"). may, if their centers arc colinear, be treated much in the same way as single .surfaces, it i- necessary to prove Helmholtz's formula connecting the size 114 GENERAL OPTICAL PRINCIPLES. of each image with the inclination to the axis of any ray common to them all. Let /' a j" (Fig. 68] be the ray between two images. Assuming the figure t" be made up of two right-angle triangles, therefore. ks is evident from Fig. <>•'>, a h a It tan « tan « /" tan*' f" tan*" /'' > <„„,/" principal point, principal focus, principal plane, nodal point, ami so on. arc properly bo named tor a single surface, but lor a system of surfaces to use the ordinal adjective dm- i- sometimes misleading. Weshall use the term last principal point or (n l th principal point, and so on, giving if the ordinal adjective and the number of primes that corresponds to the medium to which it appertains. This is not so much an innovation a- a conscientious adhesion lo the -pirit ami method of the notation ami nomenclature in detail. Something i- gained if the accents on letters serve to locate the phenomena to which their existence is due. The ability to locate other cardinal point- a -et. in fact, lor each medium reached by waves that were parallel at incidence on tie- system may not be of any special importance, but it is or advantage to have characters systematically named ami accented. It enables us to read our record- aright and to locate easily the processes to which the characters refer. I'lc removal of the origin for tin- estimation of focal distances accounts for the appearance <,f /,' and h /// in the denominators of Eqs. 23 ami •_' i ' infra). The obscurity, CENTERED OPTICAL SYSTEMS. 115 if any, vanishes when it is remembered thai h and //"' as distances are, by convention, counted plus when measured into the system from the tirst and last surface respectively. /•"s and $'s, the surface foci, arc measured both right or both left, each from its surface while the 3"'s, the foci for the .system, arc measured both in the same direction as the /•"s and *'.s. This is the reason why in Eq. 23 /•" has been replaced by (&' - h') while in Eq. 2i, 4> /// has been replaced by (©'"-A"') We may now proceed to the consideration of three media separated bv f y f F' ti~~ ~^^^~^^ ^L ■"v be replaced by {(j)— d). <1, being the distance between the two surfaces (cK //), is obtained from Eq. 13 by the following substitution, and, being the only unknown quantity, its value is immediately forthcoming: By the same method is obtained -E. d'"-h'" F"-d (23) (24) 116 GENERAL OPTICAL PRINCIPLES. Principal Planes. — There are definite reasons for replacing the one prin- cipal point on the polo of the single surface by the two points, h' and h'", not necessarily on any surface. We may imagine a plane through each car- dinal point perpendicular to the axis and designated by the name of the point. On the principal plane, which is tangent to and within required limits is coincident with the single surface (Fig. 72), the end points of incident rays Figs. 72 and 73.— Principal points and planes as defined for the surface and for the system. are arranged in a configuration that is identical with the beginning points of refracted or reflected rays; and it will be remembered that conjugate images approach this plane together until their corresponding" points are united each to each and the two images become identical. No such single plane can be placed in any system of optical surfaces, hut two planes perpendicular to the axis may always be found such that the configuration of end points a' // // I Fig. T-'li of incident rays on one surface is congruent with a n+1 , 6 n+1 , and , the beginning points of reflected or refracted rays in the last or (>i + l)th mod in ii i, such also that when the first image moves toward one of these planes ami disappears in it, the final image moves also toward the second plane and disappears in it. A little consideration will convince the student that if ./, the middle image of the three index system (Fig. 74), be so placed that it as A //• A Fig. 74.— The cardinal points ol a three-index system Above, h and ij, Aral ant principal points ; •/, middle Image Below , r and n, tir-t and last centers ; n' anil //'". first and lasl nodal points ; 0, optical centi i an object produces two images (one by each surface) equal in size and cosensal, these two images will lie in planes which answer the above description. We THE OPTICAL CENTER. 117 shall call this middle image ./. From these planes along the axis conjugate foci of the system arc measured. Whatever transformations take place within the system are comparatively unimport- ant if only we may receive light emergent from one plane apparently unchanged since its entrance at the other. If also these planes arc so related that the ohjecl approaches one as its image approaches the other, until in size and sense alike each disappears in its plane, then the two principal plains are quite tit to replace the single plane of the single surface, and Fig. ":!. which we use here to illustrate the system, becomes exactly what Fig. 72 would become if pulled apart and separated by the distance between h' and //"': We now proceed to find the position of this middle image, indicating principal foci as nsnal by capital letters, other focal distances by -mall let- ter-. Of course the distance of the middle image from the F surface will be indicated by/", its distance from the surface by "". y f" 1 From Eg. 18, J = „•/// $// 25 Divide 25 bv 20, and j" $"- 9 >r J y _ F"$" — F y//~ F"4>"~"i", .„, (It" a" and ?_=2_. (26) jpV/ f" Tims it is seen that the middle image will have in the two surfaces con- jugates that are equal and cosensal if it divides the middle medium into parts proportional to the principal foci appertaining thereto. If d represents the distance between the surfaces and ./the place of the middle image, Jh d V" will be equal to /" = F „ ^„ . The conjugate focal distance Jh ' may be found by substituting this value for /" in Eq. 13. In like manner Eq. 13 applied to the <1> surface will give the value of (j)'" (1 (!>" for h'" from that of <' parallel. The optical center i- the name by which tin- point i- known, and to determine it- place we make use of Equation 22. By it the linear dimen- sion- of ;ii'- < nected with those of it- first and lasl image ; thus, it'j' t:u. «' p"Otftn«" i'"'j'" tan «'"• IIS GENERAL OPTICAL PRINCIPLES. We may drop out the middle term of this equation, and as the condition imposed is thai a' is equal to a'", the other tangents also disappear, giving „>y u'-y\ (28) the condition to which we must conform in Locating the three points. By the usual notation we use g to measure distance- from the first center, and j those from the second, and remember that — -/'/•'" ,/"/•", and fif l "$"=fi"$ / "; (29) which may be easily proved. Referring to Fig. 70, whore the distribution along the axis of the cardinal points of the two surfaces is shown in its relation to and its two images, we have two expressions for the relative size of eaeh pair : ./' £_ '■'" g" g"-F'' y ,„ _ >" (30) (31) Dropping out the middle terms and multiplying Eq. 30 by //' and Eq. 31 bv «"', (t'y _ n'F" O g"-F' n"' the optical center. tional to the principal foci of the two surface-, but this time we must use the principal foci for ray- that are parallel in the middle medium, whereas before we used the principal foci for rays that wen parallel outside the middle medium. NODAL POINTS. 119 In a three-index system the optical center, and in the lens, where the first and last media are the same, both middle image and optical center can be located geometrically, as in Fig. 75. The surface ends of any two parallel radii arc connected by a straight lint' ; its cross with the axis is the optical center of the lens. . The image of the optical center in each surface gives the nodal point cor- responding to that surface ; it may he found by Eq. 13 as above, remembering that 6F' , =9' F' + ( and #0" and that F / +

>■ F - Fig. 7f>.— Construction for finding the conjugate to any radiant when the cardinal points arc known. A is the axis of an optical surface; />', the axis of a system of surfaces. Cardinal planes are indicated by the usual letters, cardinal points are where those planes intersect the axes. To find the conjugate oi any radiant/ in the surface A, draw two rays, one parallel to the axis, one through the center ol the surface. The former after refraction must pas* through the principal focus: therefore its path is deter- mined. The direction of the latter is unchanged by refraction. Its cross with the first ray is the focus f" conjugate to /'. For a system the method is the same, except that for incident rays the surface and center are replaced bythe first principal plane and first nodal point. Refracted rays are drawn from the last principal plane and last nodal point. It will be noticed thai the second picture is identical w it li the first, except thai all the lines have parted cither at the surface or the center, and the diagram has been lengthened by the break an amount equal to n' n'". faces may be used equally well for systems; but every picture thus formed will be broken in two, some of its lines parting at the principal plane, some at the center. The two halves being separated by translation parallel to the axis, there will result a similar construction, except that the surface h takes on a finite thickness equal to h' h'", and the center n instead of being a point is stretched out into a line, reaching from n' to n"', and equal in length to h' h"'. It is hardly possible in an article as short as this musl be to include rigid demonstrations of everything necessary to its usefulness. Little, so far, has been omitted which was necessary to show both geometrical and functional 120 GENERAL OPTICAL PBINCIPLES. relations existing between the cardinal points of the optical system and the center, the pole, and the two foci of the single surface. The student who desires to pursue the matter in the same thorough manner must be referred to Helmholtz for whatever of proof is omitted from the remaining pages. By a continuation of the methods used above it can be proved that when the principal point- are located for any system of two surface-, and when the principal foci of the system are measured from these points; that when the Qodal points are placed, and §', §'", //', and ;/'" he usc-*l as above to indicate distances from them ; and when, as in Eq. 17, //' and u" are used to measure distances away from the center, with the principal loci as origins, — then not only Eq. 13, but also Eqs. 17 and is, apply equally well to the system as to the surface, if only allowance he made for the lost space between the prin- cipal planes and between nodal points. This fact i- of great practical utility, as it gives no restriction at all in cases where the thickness of the lens is small as compared with its focal length. In most of the cases where spectacles are usvd the thickness of the glass may he ignored. When we add to this statement the extension which i- warranted by fact that not only may surfaces he compounded into systems without change of properties, but these systems still further compounded, the one with the other, it will appear that for every -el of surfaces, however many in number, an equivalent set of eight points may he determined as follow-: The optical center, the middle image, the two principal points, the two no dal points, and the two foci. The following formulae give the places of the cardinal points where three media are concerned. They are applicable to media separated either by surfaces or systems, if only it he remembered to measure F ' lS "' r "' S ,1 J /••" iJj" ,,", /■"• $» I „,/ '"* u.'"9"i /■" ") J (37) From Fig. 75 it is easily proved that d and d are similarly divided by 0. We may therefore substitute d for o, // for n, and 35 for v in Equations o7, and so obtain the formula? for the position of the optical center as measured from the two surfaces. Principal Points. — h' and //" as linear magnitudes are positive when measured from /i and 37, the extremes of ■■ ,/' It'" /•'" l/>" ./' (38) PRINCIPAL FOCI. 121 _ Principal Foci. — &' and 3*'" arc considered positive when each principal point conies between it- focus and the other principal point: & F'W" *' (39) JP//Q/// F" " (40) From these last equations, by the substitution of the values of the F's and the $'», as obtained by Eqs. 14 and 15, are deduced the simplest expres- sions for the cardinal points of any system. They flow from the above equations without complication or difficulty, and are obtained by the ordinary processes of elimination. Expressed in terms of fi' ft" ft'" ,■ and p, they reduce to vulgar fractions having / i"(fi"'-ft")r+fi"(/i"-n') P -(fi'"-ii"W-p')d = N, 11 for a common denominator. This term, being constant for the system, may be calculated once for all, and so is abbreviated to N, there being no phys- ical significance here intended. It is merely an abbreviation borrowed from Helmholtz. These are the values : &' fi'fi"r p ,,_ li" u'"rp &'" = N p'(p»-p'" )rd N h ,„ - ?'"(/*' -I*")pd N = p'(j i "-(i'")rd + l i"iti'"-/i')rp N n ,„ = ?"'(?' -p")pd + fi"{,u'-p'")rP i H=d"-&'= fiz_ szz = d-Az_^z// ; W-p'){li»'-p''){r- P -d) N d-n'-i 1-J (43) (44) (45) Eqs. 39 to 45 may be used without restriction. These general formulae may be much simplified by the imposing of cer- tain conditions which often occur in practice. Thus, if the middle medium is very thin, d may be considered equal too. In t hat case // is also equal to o, and h, //, ./, //", and r t all coincide ; so the hist term in N disappears, and our system is practically described by the two values of 3' and W. The fir-t two terms only of their denominators being left, we write in full, ;i> follows : f-'r p 3« / ^///_ yU //) r+ ( /U //_ / ,/)p' »" = . ir r n {fi'"-p")r+(fi"-fi')p If both radii are now supposed alike, the middle medium drops out of the account, p'r 3-" ' = -' V 17 L22 GENERAL OPTICA I. PRINCIPLES. and we have a single optical surface between the firsl and third medium — a condition realized in the passage of light through the cornea and aqueous. A -till more important condition that may he imposed on a system of two surfaces is thai the firsl and Last media shall have the same index. This gives the leu- proper. The Lens. — It would seem the part of wisdom to confine the term "lens" to such combinations, and to use the word "system" lor others. In this way a distinction i- made which is in keeping with the derivation of the word and with ordinary mechanical constructions, and which is continually in evidence through the simplicity of the resulting formulas, while a lens that is used as a window between two different media is such only in name, and the name so used i- definitive only of a triviality. We shall use the word "lens" only for two-index systems. The crystalline lens of the eye is not excluded from this category, as the aqueous and vitreous are of the same refractive power. Reducing Kip 41 to 45 by letting- p" 1 u.' y we have the formulae charac- teristic of lenses : g ,/ = g,/// = p'li"rp (48) p-'dr (fi"-(i')d+fi"(p-r)' li'dp (fi"- t t')d + it"(p-r. (49) fl = d . (p"-p')(d + p-r) (5Q , {n"-p')d+pf'{p-r) Fig. 77. illustrative of the preceding paragraphs, shows the disposition along the a\i- of the cardinal points of several optical systems, a is a single optical surface, and to it corresponds the aphakic eve and the schematic eye of Listing, b is the general case of two surfaces separating three media, all of different indices. In this the nodal points and the principal points are not identical, c is a true lens as described above, in form resembling the crystalline. In it, as in defg, other lenses, principal points, and nodal points coincide, and it may be noted that, assuming u" > »' and d less than r p, positive lenses are thicker in the middle. Double convex and double concave lenses have their principal points between the curved surfaces. In plano-convex and plano-concave lenses A, A" 7 , and J all come ther on the curved surface. In the meniscus they pass out of the substance of the lens and arrange themselves in the medium farthest from the centers of curvauire. / corresponds to the human eye, /• to the eye with a spectacle lens before it. The continuity of a series of systems is seen by looking, for example, at system 6, and poting that the point 3 1 '" in the relevant formulas is such a function of /'"' and p thai one may be increased as the other is decreased without altering the place of 3 1 "' ; so thai wherever in a system of three media 3*'" happen- to be placed by making the compensatory changes in p and " . "'" may be broughl to We equal to y." without altering the places of the principal foci. In this way. without changing the disposition of the foci, /<"' may be varied until it i- equal to r, in which case h' will be equal to nothing. In other word-, the single surface may he treated as a system in which the third index of refraction is equal to the second, and whose rod surface has an infinite curvature, and whose center and surface are both coincident with the center of the firsl surface. Such a substitution of values may always be made in the use of Eqs. 17 to 50, where oj f the component systems is a single surface. The Diopter. — Consistent with any scheme thai measures the direction of light-propagation as positive, the curvature of the wave is considered posi- tive when it- center i- in front of it, for it- radiu- inu-t be then positive, and SO, THE DIOPTER. L23 whether mirror, refracting surface, or sys- tem, it> strength as an optical factor is esti- mated by the curve of the wave, the con- vergence of the rays that may be produced by it. The unit which is now universally and almost exclusively used iu the esti- mation of the strength of lenses is the diopter, suggested by Xagel and named by Monoyer. It is to the credit of ophthal- mologists that in their optical work inches are being fast forgotten. Lenses are thus described by giving to each the reciprocal of its focal length in meters, and placing before this number the sign -f- or - to denote whether it has a real or virtual focus for parallel rays. The convenience of this method is its chief recommendation, as combinations of lenses are subject to computation by simple addition in an all but universal standard of measurement, instead of requiring pencil and paper com- putations in terms that are none too rapidly becoming archaic. The focal length of a lens whose dioptric number is given is of course the reciprocal of that number in meters, or one hundred times that reciprocal in centimeters. In comparing the two systems it may be said of one that it designates the lenses by their f'oeal lengths in inches, the other gives to a lens its additive value in diopters. To reduce accurately from either system to the other, one divides 39.37 by the number of the lens. A sufficient approx- imation for all test-case examples is to use 40 as the dividend. Thus a glass of 8-inch focus is equal to ") diopters. A three-diopter lens lias a focal distance of one-third of a meter — that is, 33 cm. — or. if its old number in inches is desired, divide 40 by 3. It is approximately No. 13; accurately, it is 13.123, unless the method of calculation has proved superior to the method of it> original manufacture and measurement, which for ordinary spectacle lenses is quite likely to he tin- case. For all thin lenses the distance between the principal planes may he ignored, and the equa- tions that have been used for surfaces may he used without restriction; and in their use they admit of such simplification as comes from put- ting S / &'" §' %'". There are but three cardinal points to such a lens. The nii the medium in which j" is placed. We may say, consistently with the notation of this article, that Fig v.* — Virtinil [magi • by refrac- Fig - ,| Virtual focus of concave lens, tions, /'" by refractions. when the image i finds itself in a medi whose a nta are different from it- own, the image is virtual. Examples of real images are seen in Figs. 72, 73, and 78. Fig. 80 show- a concave lens with it- virtual focus al '•> /// . (AFDLXAL I'OIXTS OF THE EYE. 125 We take note here that the general forms of the lenses given in Fig. 77 may be described by the following terms: Double convex, double concave, plano-convex, plano-concave, concavo-convex, or convexo-concave; the last variety when thinnest on the edges is called a meniscus. Applying Eqs. 48 to oO to obtain the characteristic properties of this group, one easily proves that the principal points of the double convex and the double concave 1 variety are between the two surfaces; that in the piano- lenses they are both united on the curved surface ; that for the concavo-con- vex type they pass out of the substance of the lens on the side of the greater curvature. It will be found also that when radii, surfaces, and indices are so arranged that the strength of the lens is negative — that is, when the lens has a virtual focus <*F" falling on the left in the figure and 3 1 ' on the right — then h' and hi" are also transposed, each being found between the other and its own prin- cipal focus. With one exception the lenses that are thickest in the middle are of positive focal length, and all positive lenses whose index is greater than that of the surrounding medium are thicker in the middle than at the edges. The one exception of a minus lens that is thinner at the edges occurs when r is greater than p, when d is greater than the distance between the centers, and when //' {p — r) is algebraically less than (//' — fi f )d. Equation 49 will under such conditions give a minus value for "&'". The human eye, as has been said, is a centered system of optical sur- faces like that given in Fig. 77 (j). We copy here from Czapski's table of dimensions and constants, given for reference in his book on optical instruments, where figures collected from various sources by Helmholtz furnish what might be called a composite reproduction of the type, and where also are tabulated the results of care- ful measurements and calculations in a single case by Tscherning. Along the vertical line of Fig. 81 are the cardinal points and other points of interest as arranged on the axis of the eye. Between cornea and retina the spaces are correctly given on an enlarged scale of 2.5 to 1. All distances are in meters, so that when applied to use in the above formulae the strength of a lens or system will be expressed in the diopter, the familiar unit of the test- case. .0*49Oo|_ Ml Afc. 013700 1 Afe. ~outoo_ _fi 03IIOO. . OSbiOi . OUSOCL. TTc The cases in which practice suggests or renders useful the application of the above formulae are not infrequent. We mention only two: One a case of axial myopia in which a supposition that the dioptric system of the eye has remained the same, hut the retina has been displaced backward an amount which is easily calculated from the strength of the glass needed to give distinct distant vision. Suppose the size of the retinal image is required for the corrected eye. The correcting lens is usually made as thin as possible; hence its optical center and all the cardinal points except the two foci are at its geometrical center. F" is minus, and, measured along the axis, F' is plus; (/ is the distance of the correcting lens from the cornea added to 0.001 7oI>2, the distance of the cornea in front of //' of the eye. Both foci of the emmetropic eye may be obtained from the table, and thus the figures are all obtainable for getting principal points and nodal points for the complete system through the application of formula 36 to 41. 4 Co. Cm. FIG. 81.— Tile rar.lin.il points of the human eye, measured from the cornea From cornea to retina, en larged to a i- 126 GENERAL OPTICAL PRINCIPLES. Another interesting case occurs when' the Lens has been removed and a strong plus. glass is worn. The nodal points of the glass may be calculated without difficulty, <>r, it used for reading, a plano-convex, with the flat side in front, will be acceptable to the patient, and its nodal points arc on the convex surface. The surface of the cornea is the principal poinl of the eye, and its curvature read from the ophthalmometer locates its center, which is the nodal point for the aphakic eye, or this center may be assumed to be like the average and supplied from Fig. 81. It can be hardly thought necessary to guide the student farther,as he 1ms now all the points of the component systems which tire required to give the cardinal points of the equivalent or resultant system, and these being found, the magnification is forthcoming by Eq. 18 or Eq. 2(>. Astigmatic Surfaces and Pencils. — We pass now to a very brief consideration of astigmatic surfaces and pencils. We have thus far assumed that the optical surfaces were spherical — that is to say, surfaces of revolution about their common axis, and whose principal sections were circular. It happens that such is not always the case. Imperfections of the cornea or lens give for the surfaces of the eye itself imperfect approaches to sphericity ; and even if that were not so, a displacement of any center or radiant focus from the axis of the system produces the same change in the transmitted or reflected pencil that would result from imperfect curvature of the sur- face. For the small pencils with which we deal there is only one form of astig- matism. It is that which would be given to a pencil of light by the optical action of a toric surface. A sphere is the surface developed by the revolution of a circle about one of its diameters. A torus is developed by the revolution of a circle about any line that is in the same plane, but not a diameter. Roughly speaking, when the axial line is a cord the torus is shaped like an apple with a dimple in its blossom end equal to that in its stem end. When the axial line is not a cord, the torus is like an anchor ring. When the line is at an infinite distance from the circle the toric surface is a cylinder. The toric lenses in use are supposed to be such as might be sliced from a toric surface by a plane parallel to its axis of development. Such a lens is centered optically when both its centers, the center of the circle and the cen- ter about which in its development the circle revolves, are on the axis of the system. it will need but little consideration to convince the reader that in two different sections of such a surface the problems relative to the transmission of light will be exactly similar to those which we have just considered as true for any plane whatever of the spherical surface. A plane section of the toric surface may be taken perpendicular to the circumference of the developing circle, or coincident with that circumference, and in either ease it will be a circular section. In one case it will be the sec- tion of least, and in the other the section of greatest, curvature, with foci cor- respondinglj shorter and longer than in other sections ; and in each case may the optical c litions be described and determined by the same laws and for- mula? a- those previously considered lor a spherical surface, which is a sur- face of circular section. The sectii f the toric surface through it- two centers, both of which we suppose to be on the axis of our optical system, may take place through a meridian not coincident with the section of greatest or least curvature, and then consecutive ray- from any axial point will not be reunited by this sur- face "ii tin- axis, l>nt near it. The result i- that an axial pencil directly inci- dent on such a surface ha- the characteristics that are portrayed by Fig. 82, showing the general form of the pencil from A.ubert, and the distribution of ASTIGMATISM. 127 its component rays as in a diagram by Edward Jackson from Norris and Oliver's System of Diseases of tJu Eye. The point along the axis that can be mosi satisfactorily utilized a- a focal point i- at F in the figure. It is the place where the rays are collected into thf smallest bundle. It i- called "the circle of least confusion," and its place between /*', and F, divides that distance in such ratio that it is a fourth Fig. 82.— Showing the distribution of rays and focal lines in an astigmatic pencil i h FF ' F, i = — 1. harmonic to F x and F r Consequently, it is determined by the same formulae and constructions that arc used to locate the conjugate foci in a spherical mirror (see pp. 108 and 113). Astigmatism is usually an anomaly and not a desideratum. It is meas- ured and discussed in terms of the diopter, which have proved equally use- ful whether applied to pencils or lenses. The amount of astigmatism is the strength of a lens which under ordinary optical conditions would change the convergence of the meridian of lea>t to that of greatest curvature, or rive eersa. The correcting lens must be essen- tially a toric, and one also whose focal anomaly is exactly equal and opposite to that of the pencil to be corrected. For simplicity the cylinder is usually chosen, and, having only one finite focus, it is designated by the dioptric value of the correction required. In correcting the anomalies of refraction and accommodation it is not in general possible to use a simple lens, either cylinder or sphere. One gives thi cylinder necessary to make either of the extreme foci coincident with the other, and then adds whatever of spherical correction is required. The par- ticular combination of cylinder and sphere that is used is more a matter of commercial than of physiological interest. The astigmatism that has been described as produced by a toric lens is the only kind that has been successfully and systematically corrected. It is for "thin pencils" the only kind that exists, and tor pencil- as large as may enter the pupil it is the only kind that merits attention, aberration being so well known by its own name as to be considered, if at all, under a separate head. The classification of astigmatism into "simple" " compound" " myopic" "hyperopia" and so on may have it< clinical advantage-, but it seems ti- the writer to be of very doubtful propriety. We deal only with one kind "f astigmatism. It may have its existence in a myopic eye, a paper-weight, or in the glass door of a Gothic house, but a nomenclature that takes cognizance of such facts i- confusing to the novice unless he clearly understands that the astigmatism and it- method of correction is the same in every case. For those who find it convenient to classify astigmatism by it- associated anomalies it may be stated that when the retina of the eve at resl fall- behind the posterior focal line, the condition i- what i- called " COW1 p0U nd myopic astigmatism;" when it falls on the posterior focal line, il is called "simple myopic astigmatism;" when it fall- between the two focal lines, il is called •■ mi. n or 22, a pair each of both kinds, plus and minus, the cylin- ders usually piano-cylinders, the sphericals double convex or double con- cave. Optic Axis ; I/ine of Vision ; I,me of Fixation ; I/ine of Sight. — We have spoken of the eye as a centered system, and such it is in type. Its principal points, its nodal points, its center of motion, as well as the cardinal points of the lens, are usually all on one line or nearly so. This line is called the optic axis. It is approximately the axis of symmetry for the whole organ. It is sometimes the ease that the macula, the center of the most acute.' perceptive power, is directly in this line, but oftener it is not. When the optic axis passes through the macula, it is the line of vision as well, meaning by the line of vision or the line of sight the line on which the object must be placed in order that the visual act should be most advantageously performed. I fader these circumstances also the opl i' # axis is the line of fixation, for it is the line passing through the center of motion and indicative of the eye's position or aim. An excentric position of the macula lutea is so common as to be the ride rather than the exception. It i- usually toward the outer side of the optic axis. ( tonsequently, the line of vision is no longer coincident with that axis, but crosses it w itli a -light " fault " at the nodal points, and the line of fixa- tion connecting the center of moti >f the eye with the object on which it is trained has now a position which differs from the optic axis almost as much as the line of vision. The angle OMA (Fig. 83) is taken as the measure of this lack of sym- metry due to the excentricity of the macula. It is called the angle gamma, y. It is reck d as plus when the optic axis falls outside of the visual axis. Another peculiarity <>\' construction musl be considered in connection with the form and position of the cornea. It i- convenient, and in some measure consistent with existing conditions, to look upon the cornea as ellipsoidal rather than spherical in its contour. Its horizontal section it the curve were completed would occupy a position in the average emmetropic eye something like thai pictured in Fig. 84. Here it is seen thai the corneal major axis does not coincide either with the visual axis or the optic axis. The lack of symmetry thus pictured is usually measured bv tlic angle which the major axis of the cornea make- with the visual axis. This angle is known a- a, th< angh alpha, and is reckoned plus when the MIRRORS. 129 vi-ual :ixis pierces the cornea on its nasal side. In high myopia the angle a is often negative (see also p. 96). Fig. 83.— OMA = The angle gamma. Fig. 84.— The angle alpha. Mirrors. — In the eve itself are no plane surfaces, and no surfaces whose chief function is comparable to that of the mirror; but such surfaces musl be considered as being intrinsic parts of many instruments. The mirror-like action of the dioptric surfaces of the eye is made use of in various methods of investigation. A mirror being only a special ease of single optical surface where // = — u" y it may be most satisfactorily discussed in connection with previous studies by making the substitution of // for — ft" in the general formula? 13 and 18. Substituting and reducing, we have i- + i-=2. (51) /" f As has been previously mentioned, this formula is suggestive of the harmonic relation for which a construction lias already been given (Figs. 66 and 67). Whichever side of the surface is used, the principal focus is halfway between the center and the surface. It is found from Eq. 13 in the usual way. It is evident from the formula or from the graphic construction that image and object are always on the same side of the principal focus : also that they are always separated by the surface or the center, never by both; also, wherever the object, the image that is on the same side of the principal focus a> the reflecting surface is a virtual image. The relation between the size of object and image is precisely the same as for dioptric surfaces, and may be determined either by Eq. 18 or 21. We have but one more presenl application for Eq. 13, and thai is for the special case where the surface, either dioptric or katoptric, is plane. In such case /■ = <», the second member disappears, and £/ = £ L30 GENERAL OPTICAL PRINCIPLES. which may be construed as saying thai the foci conjugate to a plane optical surface vary as their respective indices. Make this a reflecting surface again by putting ,"-" = — f*', and we find thai foci conjugare to a plane mirror arc of equal length ami of opposite sense j thus: 1 - ] . Substituting * tor /" or V" in Eq. IS, we find that for plane surfaces, whether katoptric or dioptric, 4^= ±1, (54) showing that in reflection or refraction the image is equal in size to the object. The ambiguity of sign enter- the equation on account of the double interpre- tation which may he given to the expression for infinity. It must l>e remembered thai the conditions to which these formulae have been applied, and to which alone tiny are considered applicable, are such as exist for centered surfaces and pencils of light whose rays make very small angles with each other and with the axis of the system. The Prism. — The prism enter- a system optically through the decenter- ing of one or more of its surfaces. The prismatic lens in it- simplicity dif- fers from the ordinary lens in no other way, and the prismatic element in the lens i- measured by the angle between the two lines that contain the cardinal points of the two surfaces. To qualities which the prismatic glass possesses by virtue of it- curved surfaces must he added those that are due to the non- coincidence of the two axes, and these are best studied in the case of the plane prism. The action of n prismatic lens as used in ophthalmology is the added action of the simple lens and the plane prism. The plane prism is made np of two plane optical surfaces inclined to each other at an angle less than 180°. 'flic firsl and third media are usually alike. These conditions cannot he sidered analogous to any previously discussed, as on one or both planes the pencil is oblique ; neither is it possible to look upon both planes l !-. 35 Refraction of light in tin- principal section of a plane prism. :i- centered on any finite axis. Consequently, we have to begin again with tiie law ofSnell, ami we confine ourselves to refraction in a principal section. The apex or edgt of the prism i- the intersection of the two planes form- ing it- sides or faces. A principal section is a section of the prism by a plane perpendicular to the edge. A base-apex line is the line of intersection of either side with :i principal section, from Snell's l:i\\ we know that a ray of lighl which before incidence is confined to a plane <>/ principal section will pa-- PJRISMS. L31 through the prism without passing oul of thai plane. Such plane is pictured in Fig. 85, where angles made with the normals to the first surface arc desig- nated by n, those made with the second surface by C\ and where the primes show in what medium the light-ray making the angle is situated. [f /.' is the refracting angle of the prism and I> the total angular devia- tion caused in any ray passing through the prism, the following relations are easily established : l> " I ty'—y". (55) M = + i>-R. (57) Applying Eq. 2 to the angles in question, gives fi' sin $'=(i" sin ', (59) V»"=i2--0", (60) and //'sin{(i? D) <>'[ u"smR-'. (61) Hence, by easy trigonometry, sin (R+D) cos <;/- cos i II- J>< sin <./ " ' sin /.* cos o"-cos R sin 0" ) . (62) When the prisms are thin, as in most spectacle lenses, the angles /.' and M + D may be substituted for their sines, and 1 for their cosines, giving D = J2 //^cosi^_ 1 |. (63) l fl f cos O f > and this is still further simplified in D={ti"-fi')R, (64) bv limiting the angle of incidence to one so small that COS V _-\ COS I .-' When the light-ray passes symmetrically through the prism, as in Fig. 86, x may be substituted for " and ", giving 2 D ■ — =sin t>!) /,' which is useful, because it expresses the action of the prism on light which Fig. 86.— Refraction a1 position of minimum deviation passes through in its position of minimum deviation, a term which defines itself. 132 GENERAL OPTICAL PRINCIPLES. The deviation at position of perpendicular incidence or perpendicular exit is given by D = sin- 1 f nii\-i2. A simple transposition of Go gives . iZ + D sin — [iff _ 2 2 (66) (67) the formula for getting the index of refraction from the deviation and refract- ing angle. Total Reflection. — There is one special condition that comes to our notice gcnerallv in connection with reflection and refraction at plane sur- faces. We may take as illustration Fig. 87, and ask guidance of Snell's law v r Fig. 87.— Concerning total reflection. when the wave whose normal /•, incident from the denser medium (//"), makes with the limiting surface an angle whose sine, multiplied by ,, is greater !'■ than 1. The path that Snell's law would seem to indicate for the refracted wave would he an impossible path, for there is no angle whose sine is greater than 1. Under such conditions refraction does not take place. There is do break in the continuity of the phenomena, for when the angle a" i," i- so great that ' - -in <>>" 1 ; then sin (j/ = 1, and the refracted ray, r , / i- parallel t<> the surface. The wave-front, in other words, is perpendicular to the optical surface, and neither recede- nor approaches it. \ -till greater increase of the angle <>" would so increase <'' that its gen- eral direction would be into, instead of out from, (;>"). The angle would have a minus -inc. Imt it- numerical value could he nothing other than /'", since the medium is {[*")) and this is the relation characteristic of reflection. Under such conditions all the [ighl that is not destroyed is reflected, and the phe- nomenon is known a- total reflection. The prism i- of use in ophthalmology chiefly on account of its causing a deviation in tin- path of light, and thus furnishing an instrumenl which may he w~c(\ either a- cause of. or compensation for, slighi anomalies of the posi- tion of the eye itself. The practical application to Buch purposes i- given THE METER ANGLE. |:; elsewhere. In thai application it is accessary to take cognizance of its value as used to cause deviation of light, and thus an apparent displacement of any object through it. The relation between the refracting angle and the deviation produced being such, prisms have until recently been described by their refracting angles as Pr. 1°, Pr. 2°, and so on. By Eq. 65 it will be seen that the deviation produced by any prism of ordinary glass, D = (1.54 — 1) R, is very nearly one-half the refracting angle of the prism ; and since one-half a degree is about the smallest increment which ophthalmologists have found useful, the scale is a very convenient one, and in spite of criticisms is still much in use. Its only fault is that the numbers on the glasses do not correspond to the values for which they are used. To remedy this defect it has been proposed to number prisms by the angular deviation in degrees, replacing the degree-mark by a small <\ to avoid eon- fusion, thus Pr. l d , Pr. 2 d . This is the Deviation-angle System of Jackson. The unit in this system is about double the value of the unit of the Refraet- ing-a ngle Si/stem . To obviate the necessity of making any material change in the size of the working unit, it was proposed to give to each prism the value of its angular deviation in terms of the radian, the only unit of angle that is recognized in works on analysis and mathematical philosophy. One one-hundredth of this, the radian angle, which, in accordance with "C. G. S." (Centimeter- Gramme-Second) nomenclature, is a cenirad, is so near the unit of the Refract- ing-angle System as to be practically indistinguishable from it. This is the Centrad System of Dennett. The Refracting-angle System and the Centrad System so nearly coincide that for glass of any ordinary index some number be- tween and 35 will be identical for the two systems, and the others of the scale will be so near as to admit of interchange under ordinary circumstances. Centrads are prescribed thus: Pr. l v , Pr. 2 V . The Prism-diopter Scale of Prentice does not differ much from the Centrad Scale, and does not diner appreciably from FlG - ®-^™ ^\?^;{] of >"' i — u ">' it in the numbers that are most used. It gives to every prism the value of the tangent of the deviation in hundredth-, of the radius. Centrads and the prism diopters are compared in Fig. 88. The same fault may be found with the Prism-diopter Scale as with the Refracting- angle Scale — namely, the number on the glass is ;i transcendental function of tin' value for which the ulass is used. Within the Hunts of common use the three scales .ire alike, and the choice is one of symbol and sentiment only. Prism diopters are described thus : Pr. 1^ Pr. 2 A , and so on. To Pnntice i- due also the suggested change of the ° to d for the degree deviation. and to A for the tangent deviation. The author has extended the symbolism to the centrad system by inverting the triangle for it. There remains only the Meter-angle System, it having been suggested that the "Meter Angle" of Xagel be adopted as a unit for prism nomenclature. The Meter Angle. — The meter directed to a point in that plane one meter's distance from the center of rotation. The value of this angle depends, of course, on the interocular distance, which must need- be conven- tionalized if it is used for purposes of prism notation. An interocular dis- tance of .06 makes the meter angle equal to •"» . Though a little narrow tor an adult, it is perhaps a- good a distance as any to assume. The advantage 134 GENERAL OPTICAL PRINCIPLES. of this unit is supposed to consisl in this, thai for any point of fixation con- vergence and accommodation are expressed in the same terms, the inclination of the axis to the median line being the same in meter angles as the accom- modation in diopter-. The writer is not aware that the meter angle is in actual use as a prism unit. 1 1 > relation to convergence may be seen in Fig. 89, and the following notation has been suggested : I'r. L m , Pr. '2'". Fig. 89. The meter angle. Table I. gives the deviation in degrees corresponding to all the different -\ stems of prism notation : Table I. — Showing the Value in Degrees of Deviation of Prism belonging to the Other Systems? ** • 5 • - If 1 ~ " x P •6 cS u G - Deviation. T '— - - 7 Deviation. Meter-an- gle. Deviation. Pr. 1° = 0° 32' 20" 1 V e 34' 22" 0°34'22+ lm = l°43' 6" 1 2° = 1° 4' 50" 3°=1° 37' 20" 4° = 2° L'20" ..V 1° 8' 45" L°43' 7" 2° 17' 30" 3* l A 1° 9' 1°43' 2° 17' 2 m = 3°26'12 // 3 m = 5° 9' 18" 4"> = 6°52'24" ! For interocular distance of .06. 5° = 2° 4i" 8" :. v 2° 51' 53" 5 A 2° 52' 5m = 8 o 30 / 5// J 6° = 3° 14' 50" 6^ 3 26' IV 6* 3° 26' 7 3 17' 20" :" 4° 0'38" 7^ 4° go_^o 20' 2" 8 V = 4° 33' in" > A 4° 34' 9° = 4°51' 10" 9 V 5°. 9' 23" 9* 5° 12' 10°- .v 23' 10" 10^ 5° 1 in A 5° 4:;' 11° 5° 58' 20" I] 1 6° L8' 8" 11^ 6° 17' 1»=1°50' 1 12° = 6° 32' l:; 7 V 50" 14° = 7° 38' 12 V i:; v 6 52' .".1" 7 26' 53" 8° 1' 16" 12^ i:; A 1I A 6° 51' 7° 24' 1 >8' 2* = 3° 40' 43" 3 m = .-.°:;iK 11" I" 1 7 0- Jl'"j:;" , For interocular distance of .064. 15 8° L1'32" I5 N - 35' 39" l.-r 8° 32' 5 m = 9°12' 3" J Accomttiodation i^ that function of the eye that makes clear vision possible at varying distances. This adjustment for all distances between the far point, punctwm remotum, and the near point, punetum proximum, is accomplished by the action of the ciliary muscle in changing the form of the lens. The theory of this process, which has been generally accepted, is that of 1 [elmholtz. The ciliary muscle may be considered as made up of two parts — an outer, formed of longitudinal fibers which arise at the junction of the cornea and sclera, and pass backward to a diffuse attachment in the outer layers of the choroid, called the tensor choroidea or muscle of Briicke; and an inner portion, formed of fibers which have an approximately circular course, e:dled compressor lentisor Mailer's muscle. When the ciliary muscle contracts, the choroid and ciliary processes are drawn forward, and by the contraction 1 This table is taken from Dennett's article on " Prisms" in a System of Diseases of tlu Eye, edited by Norris and Oliver, vol. ii. p. I I- ACCOMMODA '//ox l:;: of circular fibers the circumference of the ciliary processes is narrowed, the zonula or suspensory ligament of the lens relaxed, and the lens, being released from the tension which this has exerted on its capsule, tends to assume a more convex shape. This hypothesis has no1 been seriously disputed until Tscherning, following in the footsteps of Thomas Young, developed a theon which, as it becomes more generally understood, may in pari prove a danger- ous rival to that of Helmholtz. Briefly, Tscherning asserts that the accommodation does not depend on a relaxation of the zonula of Zinn, but on its tension through the agency of the ciliary muscle, whereby the peripheral portion of the lens is flattened and the curve of the anterior surface from an approximately spherical approaches a hyperboloid form. The theories of Helmholtz and Tscherning are illustrated by Fig. 90. Fn.. '.'ii.— a, accommodation according to Helmholtz. The dotted line represents the thicker form assumed by the lens when the traction of the zonula is diminished by the contraction of the ciliary muscle. B, accommodation according to Tscherning. The unbroken lines show the lens at rest. The dotted lines show the change occurring during accommodation, supposed to be due to the traction of the zonula being increased by the contraction of the ciliary muscle. Ii will be seen thai the increased dioptric ]«ower«if the lens viiav in- obtained either by relaxation of the zonula or by contraction. Tscher- ning believes that the changes which he has observed in the lens during accommodation prove that the latter theory is correct, while Hess {Graefes Arch., xlii. 1, S. 288; Ibid, xliii. 3, S. 17/ 1 opposes it strongly. As regards the change in the lens itself, Tscherning's view seems abundantly proven by numerous experiments. 1 The action of the ciliary muscle is still undetermined. The older description, as given above, is supported by the diagrams according to [wanoff, but these results have not Keen corroborated in recent times, although they appear in some of the besl text-books. Tscherning believes thai the inner portion of the muscle retracts, having its more fixed attachment posteriorly in the choroid, which is steadied by the tension of the vitreous, this being increased during accommodation by the backward traction of the lens. This retraction of the oblique fibers of Midler's muscle, which is probably not as purely a circular muscle as bas heretofore been described, makes trac- tion on the zonula and produces the changes in the lens. The iris as a diaphragm cuts off the peripheral parts of the lens. SO that whichever view is taken ofthe mechan- ism of accommodation the optical conditions remain practically the same. By accommodation is meanl the muscular effort, the change in the shape of the lens, .and the effect produced on vision. The muscular effort is -ell- evident. The change in the pupillary portion of the lens is ~een from the changes which the reflexes called the images of Purkinjt undergo during accommodation. These images are catoptric — thai is, formed by reflection from the cornea, the anterior and the posterior surfaces of the lens. In the 1 Cr/ellit/.er : " Die Tscherningsehe Accommodationstheorie," A rchiv f. Ophth., Bd. xlii., iv. Abtheilung. ! Graefe and Saemisch : Handbuch der Augenheilkunde, Bd. i. p. 276. 136 GEXERAL OPTICAL PRINCIPLES. pupillary space pictured in Fig. 91 are seen the reflections of two bright squares, one above another : a is reflected from the surface of the cornea, b from anterior surface of lens, c from posterior surface of lens. They are best a b ( , B Fig. 91. — A, reflections during distant vision; 7?, during near vision; a, from the cornea ; 6, from the anterior surfat f lens; c, from posterior surface < if lens. It is seen that the reflections from the anterior surface of the lens become smaller, showing that that surface becomes more convex during accommoda- tion. C, reflection of a candle flame; a, from cornea, sharply defined; b, from anterior surface of lens, large and blurred ; c, from posterior surface of lens, small and inverted. seen in a dark room when a bright light is thrown on the eye from the side opposite the observer. During accommodation the reflex of the anterior surface of the lens be- comes smaller, which indicates an increase in convexity. In some eyes the image changes its position in a manner to indicate a slight advancement of the surface (Helmholtz), but this is not constant (Tscherning). The posterior surface of the lens becomes slightly more convex, but does not change its position. The pupil contracts during accommodation. According to Tscher- ning, the portion of the iris between the pupillary border and the periphery retires a little, corresponding to the flattening of the peripheral portion of the lens which he has proven takes place. It has been stated that the tension of the anterior chamber diminishes during accommodation. Foerster (1864) observed that in patients with small keratoceles the protrusion diminished or disappeared during accommodation, to reappear when this was relaxed. When the accommodation is relaxed the eve is adjusted for a far point. When the greatest accommodative effort compatible with clear vision is made, the adjustment is for the near point. Range of Accommodation. — Accommodation is measured by its effect on the vision, and the effect may be described either in terms of distance traversed between the far and near points, as measured from the eye (range of accommodation), or in diopters, expressing the increase of the refractive power of the Lens (amplitude <>r power of accommodation). The additional strength which the lens gains may be considered as a separate lens placed in front of the crystalline. The focal distance of such a lens being .1, the distance of the far point from the eye R, and of the near point /', the range of accommodation would be A = P — B, and, as tli<' refractive power of a lens is the inverse of its local distance, the refractive power of the lens which we assume to represent accommodation would be 1= 1 ' A P /; The application of this to emmetropia is 1111 A P oc /•' the far point being at infinity. PRESBYOPIA. 137 The power of accommodation is measured by the strength of a lens suf- ficient to give the rays leaving the near point the direction in the vitreous which they would have if without it they came from infinity, or in emnie- tropia the accommodation is measured by the dioptric value of the near point. For example, an emmetrope whose near point was at 10 cm. would have 10 diopters of accommodation ; thus ; i—L-l~L-ioj>. A .10 cc .10 A myope with a far point at 50 cm. (2 diopters of myopia) would have an accommoda- tive ability of 8 diopters ; thus : i-=- - = 10 2)-2 D = 8D. A .10 .50 In hyperopia only convergent rays are focussed on the retina, and the far point is a virtual focus behind the eye. It has therefore a negative value. We may best not alter the formula, but remember that a negative sign in its last denominator makes that fraction additive, as seen in the following example, where a person whose hypermetropia is 2 D, and whose near point is 10. cm., is shown to have an accommodative power of 12 D: \ = — - (-^— ] = — + — = 10 D + 2 D = 12 D. A .10 V-.50/ .10 .50 Practically, the accommodation in hyperopia equals the sum of the iens required to bring vision to infinity with that representing the dioptric value of the near distance. It will be seen from what has preceded that the measurement of the far point is equivalent to the determination of the static refraction of the eye. The near point is the nearest point at which very small type can be seen most distinctly, and is usually measured by Jaeger's test type. Relative Accommodation. — Ordinarily, accommodation and convergence are exerted together, the eyes being directed to the point for which vision is adjusted, but a considerable latitude or independence of these functions in their relations to each other is possible. If, for instance, an emmetrope fixes at a point 3 •"> cm. from the eye, the corresponding accommodation would be 3 D, but a certain amount of relaxation of accommodation and of additional power is possible with the same convergence. This relative accommodation varies for each point of fixation. The normal relations have been tabulated by Donders. 1 The practical applications are numerous. A lack of unity between accommodation and convergence is seen in the normal eye at the near point. The function of converg- ence being stronger than that of accommodation, the absolute near point is attained at a sacrifice of binocular vision, convergence over-acting, and thus reinforcing accommo- dation. In hyperopia the accommodation required is greater than the convergence, and the same tendency of the two functions to reinforce each other offers a stimulus to the latter which may result in convergent strabismus. In myopia less accommodation is required; accordingly there is less incentive to converge, and insufficiency of converg- ence or even divergence may occur. Presbyopia. — The power of accommodation diminishes progressively from the earliest youth. As a result, the near point recedes from the rye, until at about the age of forty in emmetropia it reaches the distance <>i' '-"-' cm., and the strength of accommodation has become abouf L5 / ; . Near 1 Accommodation mid Refraction of the Eye, \>. 111. 138 G ENEBA L OPTH . I L PBINi 7/7, ES. vision then is rendered difficult, and from this time on convex glasses must be used to bring the near point nearer and to compensate for the diminishing power of accommodation. The cause of this change is a physiological sclero- sis of the crystalline lens, which renders it less elastic in response to the force of the ciliary muscle. The table (Table 11.) and accompanying curve, de- - Distance of Pin Distance of K in meters. Ampli- tude of Presby- opia in < 111 meters. .1. 0.07 30 14. D 15 0.08 00 12. 20 0.10 00 10. 25 o.l -1 00 8.5 30 el 1 00 7. 35 0.18 00 5.5 40 0.22 ' 4..". 0. 4:. 0.28 30 3.5 1. r,o 0.4 X 2.5 2. :,:, 0.66 1. H.0.25) 1.75 3. (in 2 2.(H.0.5) 1. 4. 65 4. L.33 1 1. 0.75) 0.5 4.75 7«i -1. -0.8 (H. 1.25) 0.25 •>..> lb 0.5 -0.5 (H. 1.75) 0. 6.25 80 ii 1 i> 1 i II. 2.5) n. 7. 10 IS 2 : s So jf 60 e r 70 ?f & ' II \P f 8 7 6 s « 3 2 r 7*— /J -2 -3 J. -f Table II.. with the accompanying curve < Fig. 92), show s the relations of age to accommodation and static refractiou. The table is taken from Xagel, 1 and is slightly modified. The curve is modified by Landolt from bonders. vised by Donders, shows the decrease in the amplitude of accommodation as well as the change in the static refraction, beginning at about the age of fifty-five, by which an acquired hyperopia takes place; the curve, y> p, repre- sents the changes in the near point ; the curve r r, the far point. V- has been said, presbyopia begins at the time when near vision becomes difficult. This period varies with the refraction of the eye, for the reason that the strength of the accommodation required to bring the near point to a comfortable distance depends on the positi f the far point. Thus in myopia the far point is nearer the eye than in hyperopia, and the same strength of accommodation will continue the range of useful vision for near work at it- proper distance later in life ; that is to say, presbyopia is postponed in myopia ami anticipated in hyperopia as <• pared with emmetropia. Ii will lie -ecu thai a myo] I' •"■ 1> will reach the age of sixty without dis- comfort, while a hyperoj f the same degree would be able to overcome his hyperopia ami to bring the near point to the reading distance, at the latest, up to twenty-five years. It is important to re mber that the accommodation cannot he sustained at its maximum. There must always be a reserved power, as in any other continuous work, ami that is why the near point is said to he at lii' cm., allowing 0.5 D 1 D reserve above the accommodation required tor the average reading distance. working distance is decidedly arbitrary, depending on the kind of work .lone or tin- hal.it of the individual a- regards the distance the work is held from the eyes ami on the visual acuity, lor if this is diminished, the work must lie brought nearer in order to obtain larger images, ami the accommodation must be aided accordingly. Visual Acuity. Vision i- measured by tin- size of the smallest object which c:in he recognized at a fixed distance in the mosl favorable lighl with the best optica] adjustment. The size of the objeel i- expressed l>\ the visual angle formed he line- that pass through it- extremities, through the nodal points of the eye, to the inverted image mi the retina. The size of the image 1 Graefe und Saemisch : Handbucli der Augenheilk., Bd. vi. p. 466. VISUAL ACUITY. 139 on the retina varies as the distance of the posterior nodal poinl from the retina, which distance Is greatesl in myopia and leasl in hypermetropia. Axial ametropia is referred to, as that is the commonest form. When the ametropia i- corrected by ;i leu- placed at the anterior focus of the eye. the retinal image i- the same size a- if the eye were emmetropic. A stronger lens is needed tor the correction of myopia the farther the lens is placed from the eye. and a weaker lens suffices for hypermetropia if removed from the eye. Differently stated, this i- : a concave lens loses strength and a convex lens gains strength if removed from the eye, which explain- the tendency of presbyopes to slide their glasses down the nose as the presbyopia increases. It is obvious that to attain the highest visual acuity for a great distance the eye must he placed in a condition to see to the best advantage; that is to say, the ametropia must he corrected lor infinity, consequently the glas> that gives the highest visual acuity is the measure of the static retraction. The distance usually chosen for the examination of vision i- 6 m. So great a distance is taken because it i- desirable to measure acuity uninfluenced by the effect of accommodation, and rays of light that enter the eye from any point on an object 6 m. away, however wide the pupil, are practically parallel and meet on the retina. Snellen's type are so devised that each letter subtends an angle of five minutes, each part of a letter and each space being one-fifth of the whole in linear measurement. A visual angle of five minutes has been assumed as representing the average of a great many measurements of the eye- of indi- vidual- of all ages, and Snellen acknowledges that a great many young per- sons have a greater visual acuity. It has been said above that visual acuity is measured by the ability to recognize an object at a given distance. Tin- means that the part- of which it is composed can be differentiated : each part of one of Snellen'- letter- subtend- an angle of one minute VV VV (Fig. 93). ... J JPj The perception of a single object, however, would ^■CZ ^hh _ • i i» ifi x j- i" • • ' 't. • •! 'iv ii Fig. 93. — Two of Snellen's not be a reliable test ot vision, as its visibility would test-type, depend on the intensity of the light by which it was seen, and would be, in some measure, independent of it- size and the dis- tance ; for instance, a fixed star is visible, although its apparent size is almosl infinitely small and it- image -mailer than one of the perceptive elements of the retina. Two star-, however, cannot be distinguished as separate unless they are about sixty seconds apart ; that i-, unless the distance between their imago on the retina equals at least the breadth of a perceptive element. If the distance were -mailer, both images would fall upon the same or upon adjacent element-. In the first case both would produce a -ingle sensation, and in the second case there would be two sensations, but upon adjacent ele- ment-, so thai it could not be told whether there were two points of light or one which fell upon both elements. From the fad that the diameter of the cone- in the macula corresponds quite closely to the smallest distances between the images of two objects that can be recognized as two, 1 the conclusion has been drawn that the cones are the perceptive elements. 2 ' According to Kolliker, the cones in the macula lutea vary from 0.0045 nun. to 0.00">4 nun. in diameter, while a visual angle of 60" covers on the retina a space of 1 138 mm. and one of 73" a space of 0.00526 mm. • Helmholtz: Handbuck der Phygiologisehen Optik, Zweite Auflagi 140 GENERAL OPTICAL PRINCIPLES. Snellen's letters are arranged in lines, over each of which are Roman numerals indicating the distance, P. at which the letters of that line appear under an angle of five minutes or the distance at which they can be read by an eve of normal vision. The distance at which they can be read by the eye that is being tested is d. The formula, then, for visual acuity is V- .. As examinations arc ordinarily made at a tixed distance of about six meters, " d " is constant, the value of the fractional expression being varied with the value of the " D" which designates the smallest legible letters, thus V is normal vision. V = — indicates that what the patient ought to see at sixty oO meters he can see at only six meters, an acuity of <>. 1. It is best, however, to leave the fraction unreduced, thus recording the exact distance at which the test wa< made. If vision is inferior to — , the test types may be brought bu o nearer, and the distance recorded at which the largest is read, as — . If this is not enough, the distance may be noted at which the fingers of the out- stretched hand can be counted against a dark background, or, still farther, only the movements of the hand may be seen, and finally light perception only, at varying distances, or, simply, the differentiation of light from dark- ness (L. P.) may be all there is to record. A better system than that of Snellen is one devised by Monoyer, in which tbe lines progress in tenths from 1. to 0.1. The regularity of the interval is a decided advantage, and has been utilized by Dennett with the modification that the size of every letter in each line has been so chosen as to ensure its uniform visibility. For the illiterate, characters may be used which can be described without being named, or Burchardt's series of dots Pig. 94.— Test-type for the , , rril * ..i t^> • *-cc *. illiterate. may be used, lhe most common are the hi s in different posi- tions (Fig. 94). Guillery proposed to measure the visual acu- ity simply by the use of a black dot on a white ground. I5y comparison with the letters of Snellen he found that such a dot seen at an angle of 50" would correspond to the nor- mal visual acuity; at 5 in. it would have a diameter of L.2 mm. An acuity of one-half would be shown by the ability to see a dot of double the area at the same distance. The dots are placed in various parts of squares and are to be localized by the patient. 1 Entoptic Phenomena. — Objects in the eye in front of the sensitive layer of the retina intercept light that passes through the pupil and throw shadows which under certain conditions can be perceived. Since Listing- tire ( saminati f objects in our owe eye- has been called entoptic observation. II* a clear sky is looked at through a pin-hole in a dark card placed near the anterior focus of the eye — the rays thus reaching the retina parallel — or if* a flame al a distance of 5 m. is seen through a strong convex glass held two or three inches from the eye, a bright disk of light will be seen formed by circles of diffusion, upon which various objects arc visible : (1) The traces of the lid- on the cornea formed by half closing the eyes. These horizontal lines remain an instanl after the pressure has ceased, and in some cases show a more lasting effeel of constriction, leading to an irritable condition called " tarsal asthenopia." The tears and drops of mucus are seen following the movements of the lid-. (2) The lens or some tt inircii, 1S4">. i, .1. Bull: Tram. Eighth Internal Ophth. Cong., Edinb., 1894. m 3 ENTOPTIC PHENOMENA. Ill the radiating star-shaped figure of the lens and numerous small round objects like hyaline globules may be seen. These increase with age until the senile changeSj the beginning of cataract, may also become apparent to the possessor in this manner (Donders). (3) In the vitreous there are always floating bodies, cells, and fibers, which as m/uscce volitantes cause alarm to the nervous observer till he is assured of their insignificance. (4) A very interesting application of the entopic method is the observation of the retinal vessels (PnrUinje). They may be seen in three ways : [<() In a darkened room a candle is held at a short distance from the eye which regards the distance. The vessels come into view as dark lines on a yellowish background. They seem to move when the candle is moved. (b) On looking through a stenopaic opening at the sky, if the opening is kept in motion, the vessels are distinctly seen, even to the smallest around the macula. (c) If a strong light is focussed on the sclera as far as possible from the cornea, and moved slightly from side to side, the same phenomena occur. The explanation given by Heinrich Muller (1855) is that the shadow of the retinal vessels falls on the sensitive layer of the retina. In the last experiment Muller measured the movement of a vessel projected on a surface at a known distance, and the movement of the focus on the sclera which pro- duced this excursion, and calculated the distance behind the retinal vessel at which the sensitive layer must lie, his result coinciding very closely with the actual distance between the vessels and the layer of rods and cones. Kb'nig and Zumft 1 have recently attempted to apply this principle to the analysis of color vision, and have claimed that different colors are seen at different levels, violet being perceived by the most anterior portion of the sensitive layer, red by the most posterior. Considerable doubt has been raised, however, by Koster 2 as to the accuracy of these statements. 1 Sitzungsberichte der koniglich. preuss. Akademie der Wissenschaft. zu Berlin : Mai, 1894, xxiv. 2 Grae/^s Archiv, xli, i, S. 1. EXAMINATION OF THE PATIENT AND EXTERNAL EXAMINATION OF THE EYE; FUNCTIONAL TESTING. By G. E. DE SCHWEINITZ, A. M., M. D., OF PHILADELPHIA. The value of case-records is greatly enhanced if a systematic method of examination is pursued with each patient. The following order of examina- tion, based upon the one employed by S. Weir Mitchell in the Infirmary for Nervous Diseases, Philadelphia, is arranged for this purpose: Name ami residence. Age, sex, race, married, single, or widowed. Family history: hereditary tendencies; general and ocular health of parents, brothers, sisters, etc. Personal history: children, their general and ocular health ; miscarriages; meno- pause; former illnesses; syphilis and gonorrhea ; injuries. Occupation: relation of work to present indisposition. Habits: brain-use; tobacco; alcohol; narcotics; sexual. Date ami mode of onset ami supposed cause of present trouble ; outline of its course, Organs of digestion : teeth; tongue; stomach; bowels. Organs of respiration : nose; throat: Lungs. < Organs of circulation : heart ; pulse ; blood. Kidneys: examination of urine. Abdominal organs : liver ; spleen. Organs of generation: menses; leucorrhoea; uterine disease. Nervous system: intelligence; evidences of hysteria ; hallucinations; sleep; ver- tigo; gail : station; tendon- and muscle-jerks; paralysis; tremor; pain; subjective Bensations; convulsions ; headaches and their position. Eyes: previous attacks of inflammation; injuries; infections; ocular palsy or squint ; amblyopia ; previous use of glasses ; ability to use eyes. Direcl inspection and examination of eyes : inspection of the skull and orbits (sym- metry or asymmetry) ; lids; ciliary borders ; puncta lacrymalia; upper and lower cul- de-sacs; conjunctiva'; caruncles; cornese (oblique illumination); irides (mobility and color); anterior chambers (depth and character of contents) ; vision; accommodation; balance of external eye-muscles ; mobility of globe ; tension; light sense; color sense; field- of vision; held of fixation; ophthalmoscope; ophthalmometer; retinoscope; refraction. Necessarily the examiner will modify the thoroughness of his investiga- tions according to the character of each ease. Direct Inspection of the Eye and its Appendages.— The lids should be examined for distended superficial veins, edema, tumors, tor ex- ample, enlargement of the Meibomian -lands, and for anomalies ; their edges lor inllai ation, parasites, misplaced cilia, and small morbid growths; the pimcta for permeability, deviation or retraction from the globe, pressure a< tie same time being made over the lachrymal sac in order to express from it, through the puncta, any contained Quid; the caruncles and plicae for swell- ing, foreign bodies, irritation by incurved cilia, and -mall morbid growths, for instance, polyps or angiomas; the conjunctival cul-de-sacs for abnormal I 12 BLOOD-VESSELS OF THE CONJUNCTIVA. 143 secretion, granulations, foreign bodies, concretions and disturbance of the vascular supply, the examination being carried well tip into the upper fornix after thorough eversion of the lid. In order to evert the lid the patient should rotate the eye strongly down- ward, while the surgeon seizes gently the central eyelashes of the upper lid between the index finger and thumb of his left hand, and draws the lid downward and away from the globe, placing at the same time the poinl of the thumb of his right hand above the tarsal cartilage of the li.~)~> < '. (!»o.!»!)° 1'. -i. <■. about "J < '. lower than thai of the rectum, — and in inflamed eyes noted nil average increase of 0.98 C. The highest conjunctival temperature is found in acute iritis, bu1 even then does not equal the normal body-tem- peral lire. 1 [rekiva of Ophthalmology 1893, wii. |>. 151, THE WIDTH OF THE CORNEA. 145 Inspection of the Cornea. — This will reveal inflammation, ulcera- tion, opacities, the track of former blood-vessels, exudates upon its posterior surface, and foreign bodies. Slight irregularities may be detected by placing the patient before a window, while his eyes are made to follow the uplifted finger held about a foot from his face and moved in various directions ; the image of the window-bars reflected from the cornea will be broken as it crosses the spot of inequality. In the same manner abnormalities in the curve of the cornea may be roughly ascertained, because if the curve is nor- mal the reflection does not change, at least in the central portion of the cornea ; if the curve is abnormal or the surface of the cornea irregular, there is corresponding distortion in the size or shape of the reflection. A more accurate method is to employ a keratoscope, or Pladdo's disk, as it is called. This instrument consists of a disk shaped like a target, upon which are drawn concentric black circles, a sight-hole being in the center. The patient is placed with his back to the window, while the surgeon holds the instrument 30 cm. in front of the eye, and, looking through the central aperture, observes the reflections of the circles from the cornea. If these are broken or distorted, the indications of irregu- larity in the surface are present (Fig. 96). Any irregularity on the surface of the cornea is quickly detected by the method of kerat&metry, especially with the oph- thalmometer of Javal andSchiotz (see page Fig. %.— Placido's disk or keratoscope. Fig. 97.— Priest lev Smith's keratometer. 197), the reflections of the targets being greatly distorted as they cross the point of irregularity. Abrasions and ulcers, even when minute, may be differentiated by drop- ping into the eye a concentrated alkaline solution of fluorescin (Griibler's fluo- rescin '2 per cent., carbonate of soda 3.5 per cent.), which colors greenish- yellow that portion of the cornea deprived of it> epithelium, while the healthy epithelium, or even that epithelium which is -imply roughened and opaque, as in keratitis, remains unaffected. A minute foreign body may thus he located if situated in the centre of an abrasion, because it appears as :i black dm sur- rounded by a green area. So, also, may the progress of a corneal ulcer be studied, the color test differentiating sharply that portion of the ulceration which i> still active from that which is covered with new-formed epithelium. The "Width of the Cornea. — This may he measured approximately by 146 EXTERNAL EXAMINATION OF THE EYE. holding before it a rule marked in millimeters and noting the number of spaces its width occupies, or, more accurately, by employing Priestley Smith's kera- tometer. This instrument consists of a scale situated between two plano-convex Lenses. The surgeon places his eye al the principal focus of the combination, and, holding the scale before the patient's eye, observes that the cornea sub- tends i>n the scale exactly its width I Fig. 97). The average horizontal diam- eter of the normal cornea is 11.0 mm. (Priestley Smith). The Sensibility of the Cornea. — This may be tested by gently touch- ing the surface of this membrane with a wisp of cotton twisted to a fine point. [f sensation is intact, the touch will instantly be followed by the reflex action of winking. As a control the opposite eye may be similarly examined, if the cornea is found insensitive, the forehead and face should he examined for areas of anaesthesia cither with the point of a moderately blunt pin or with an esthesiometer. Thermic as well as tactile sensibility should be investigated. Oblique Illumination. — The surgeon places the patient two feet from the source of illumination and focusses a beam of light with a two-inch or three-inch lens upon the cornea, at the same time observing the surface under Fig. 98 Method of oblique illumination. examination through a leu- of the same focal distance, which act- as a mag- nifier, held between the thumb and fore linger, the disengaged fingers being utilized to elevate the upper lid i Fig. 98). The distance of the lens must be varied slightly to bring the various tissue- — the cornea, iris, or crystalline leu- — within its focus, the patient being required to look up, down, and to either side while the anterior surfaces and media of the eye are illuminated. To deteci a foreign body the light should be directed at an acute angle, but it' tiie pole of the lens is to be examined the light should be thrown perpen- dicularly into the pupil, the -ui-cuii placing his eye in the same direction without interfering with the light. By this method minute abrasions, foreign bodies, nebula', and. in short, all corneal changes, may be examined. The cha- racter of the aqueous humor, the depth of the anterior chamber, the surface of the iris, .-\ nechiae, atrophic liber-, -mall tumors, ami persisting pupillary mem- brane are readil) studied, and, finally, opacities in the anterior capsule and axis of the lens can be investigated, and b\ focussing deeply even the anterior layers of the vitreous. Tin- routine examination should never be omitted. Recent!) Dr. Edward .lack-on ha- designed a binocular magnifying lens THE PUPIL. 1 17 lor examination of the eye by oblique illumination, which is :i material aid. Two lenses are placed side by side, and so joined that the visual line of the righl eye (tierces the right lens near its optical center, while the visual line of the left eve pierces the left lens near its optical center. This gives each eye an undistorted field all around the point of fixation, and these fields can be combined in full binocular vision. In place of this lens a cornea/ loupe may be employed. This i- a lens, properly mounted, by which the cornea is strongly magnified. A corneal microscope, or a specially prepared lens of high power, permits the study of minute changes in this membrane, and is utilized for the examinati >f traces of former vascularization, and by its help even the circulation of bl 1 in the vessels constituting a pannus may be studied. The Color of the Iris.— Blue and gray are the predominating hue- in the irides of the inhabitants of northern countries; brown occur- next in frequency, while the various admixtures produce yellow and green -hades. Perfectly black irides are never seen, but dark irides. taking the whole population of the world, are the most frequent in occurrence. With rare exceptions the color of the iris of all new-born children is of a light grayish- blue. The stromal pigment is developed subsequently, and the color of the iris does not become fixed, so to speak, until about the third month. Slight differences in shade between the two irides are not uncommon. More rarely, even in health, the irides differ in color (chromatic asymmetry), one being brown or greenish, the other blue or gray. Under these condition- one iris usually corresponds in color with the irides of one parent, and the remaining iris with those of the other parent. Instead of uniform pigmenta- tion a single triangular patch or several irregular spots of dark color may appear upon one or both irides ( piebald irides). When these spots are small they have sometimes been mistaken for foreign bodies. While chromatic asymmetry is perfectly compatible with health, it is stated to be more com- mon in patients with neuropathic tendencies — for example, in chorea and epilepsy. In 25 of 50 cases of chorea of childhood (Sydenham's chorea) ex- amined by the author the irides were equal in color and shade ; in the remain- ing 25 there were slight differences in shade or tone. In only 1 of these 25 was there any true asymmetry of color. In some instances of chromatic asymmetry there is liability to disease, especially to cataract, on the pan of the lighter eye. This susceptibility may be present in several members of the same family. Discoloration from disease causes one iris to be green, while it- fellow remains blue. This indicates iritis or cyclitis. It is often an early symp- tom of inflammation of the iris, and should lie looked for in every inflamed eye. The Pupil. — The size of the pupil in health varies with exposure to light and with accommodation and convergence. It i- also influenced by age, the color of the iris, and the character of the refraction. Other thin-- being equal, the pupil is generally smaller in old age, in blue eye-, and in eye- with hyperopic refraction, while it is larger in youth, dark eyes, and eyes with myopic refraction. There is no physiological standard on which to base a measurement, but with accommodation at iv-t the diameter of the pupil varies from 2.11 to 5.82 mm., the average diameter, according to Woinow, being 4.14 iniii. Under similar illumination the pupils should be round and of equal size, although a large Dumber of measurements — for instance, those made among healthy military recruits — indicate that slight differences in the width of the pupil- are compatible with health. 148 FUNCTIONAL TESTING. Measurement of the Pupil. — The pupil can be measured approxi- mately by holding before it a rule marked in millimeters and noting the number of spaces its width occupies. The chief objection to this method is, as Edward Jackson points out, that the distance subtended on the rule is less than the diameter of the pupil, in proportion as the distance from the observer's eve is less to the rule than to the pupil. For the purpose of accurate measurement a number of instruments have been devised, known as pupillometers. A simple and useful device is one which consists of a scale of cir- cles held close to the observed eye, the scale being fig. 99.— simple pupiiiometer. slowly rotated until that circle which matches the pupil in size is reached (Fig. 99). Priestley Smith's keratometer ( Fig. !»7) can also be employed. The Pupil-reactions and Methods of Testing- Them. — A uniform light should be employed and the character of the light should be stated. As Turner insists, the light employed for testing the sensitiveness of the retina or visual center should not be more intense than that to which the eye is usually accustomed. Therefore, except under certain circumstances, exami- nations made by reflecting light into the eye with a mirror or by passing a flame in front of the eye are not accurate. It is much to be regretted that in recorded examinations such loose statements as "pupils dilated," "pupils contracted," "pupils medium-sized," have been so much used. Mobility of the Iris. — The reflex mobility of the pupil ' is tested to ascertain the presence of attachments between the iris and the lens (synechia 1 ), or immobility from atrophy of the iris, or to examine the sensitiveness to light of the retina or visual center. (a) The patient, placed before a window in diffuse daylight, with one eye carefully excluded, is directed to look into the distance with the exposed eye. which is then shaded, when, in the absence of abnormalities, a consider- able dilatation of the pupil will occur. On removal of the covering hand or card, contraction to the same size as that which existed before the test was applied takes place. This is the direct reflex action of thepupil, and is brought about by a muscular contraction of the sphincter of the iris following the stimulation of the optic nerve. (h) If during this examination the other pupil, which has been shaded by a card or covering hand, i- observed, it will be found acting in unison with it- fellow. This i- the consensual or indirect reflex action of the pupil. The iii- response to light-stimulus should also be tested with both eyes open and exposed in the same source of illumination. The eye-, should then be covered and exposed alternately and the pupil-reactions noted. Under normal con- ditions the pupils should be equal, not only with both eyes open, but with one eye shaded. (c) If the patient is required to look into the distance and then quickly direct his eye- at a near object for example, the point of a pencil held at a distance of about 10 cm. — pupillary contraction occiii's under the infliieiic f accommodation and convergence ; that is, the sphincter of the iris contracts in association with the ciliary muscle and the internal recti. This is the associated action of the pupils (convergence-reaction). Accommodation in- 1 It is customary to speak of the action or reaction of the pupil, although really the mo- bility of the iris ifi ascertained. For convenience : " mobility of the iris" is Bynonymous with " pupil-reaction." THE PUPIL IN DISEASE. 149 creases pupillary contraction, but this docs not take place under the influence of accommodation unassociated with convergence. It does occur with con- vergence without the act of accommodation. (d) A second reflex action of the iris, the other being its contraction under the stimulus of a beam of light (direct light-reaction, paragraph a), consists of a dilatation of the pupil when some cutaneous nerve is stimulated, especially one in the skin of the neck. This is the skin reflex (pain-reaction), and may be tested by pinching the skin of the neck, or, better, by using a farad ic brush. (e) Finally, the reaction of the iris to the mydriatics and myotics may be tried, especially that produced by cocain, which in the normal eye should cause nearly full mydriasis and widening of the palpebral fissure from stimulation of the sympathetic. (For the physiology of pupil-phenomena see page 96.) Abnormal Pupillary Reactions, or the Pupil in Disease. 1 — When about to investigate pupil-reactions six possibilities, as William McEwen points out, should suggest themselves to the examiner — namely, (a) The action of drugs ; (b) ocular disease or optical defects ; (c) spinal or sympathetic lesions ; (d) localized cerebral lesions in special centers or tracts ; (e) abeyance of brain-function ; (/) cerebral irritation. For the convenience of ascertain- ing in what portion of the path of the pupil-reflex the lesion is situated Magnus 2 has divided it into the following three portions: 1. The Centripetal Part, including the Optic Nerve, Chiasms, Tracts, and Connecting Fibers to the Cortex. — If there is interruption of the conducting power of one optic nerve — for example, the right — illumination of the pupillary area on that side fails to elicit either the direct or the indirect reflex action of the pupil. On the other hand, illumination of the left eye causes its own pupil to contract (direct reflex), as well as the pupil of the right or affected eye (indirect reflex). Lesions affecting the chiasm and the tract are accompanied by hemianopsia (see page 481) and the special pupillary phenomena which belong to this condition, while lesions in the optical pathway between the corpora quadrigemina and the cortex, although accompanied by probable changes in the visual field, are unassociated with pupillary disturbances. 2. The Part of the Reflex Ring which carries the light Impulse from the Corpora Quad- rigemina to the Oculo-motor Nuclei (Meynert's Fibers). — If both sides are affected, neither pupil reacts to the impulse of light falling on either eye, but there is normal reaction to accommodation and convergence. (See Argyll-Robertson symptom, below.) 3. The Centrifugal Portion of the Reflex Ring {the Nucleus of the Sphincter of the Iris, the Third Nerve, and the Termination of the Third Nerve in the Iris).— If the right nucleus is affected, the direct light-reflex action of the right pupil is abolished, and also its indirect reflex. A beam of light directed into the left eye is followed by pupil-reaction in that eye (direct reflex). Pupil-reaction in that eye also follows light stimulus of the oppo- site or right eye (indirect reflex), but is somewhat lessened in degree. The pupils react normally to accommodation and convergence, and are unequal, the right being the wider. If the trunk of the right oculo-motor is atfectcd, there is pupillary immobility under the influence of light directed into the right eve, and also when it is directed into the left eye, as well as loss of accommodation upon the right side. Light falling into the left eye produces on this side a normal reaction which is also manifested if the light is directed into the opposite eye. The pupils are unequal, the right being the larger. Similar conditions arise if the peripheral fibers of the oculo-motor at their termination in the iris are affected upon one side. We have now to consider a little more in detail : 1. Dilatation of the Pupil (Mydriasis). — This occur- in ocular diseas< — for instance, glaucoma — in cases of non-conductivity of light (optic-nerve atrophy), in orbital disease, and under the influence of mydriatic drugs. It is further seen in fright, emotion, anemia, in depressed nervous tone, neurasthenia, aortic insufficiency, and irri- 1 The following paragraphs are abstracted from the author's chapter on " Diseases of the Optic, Oculo-motor, Pathetic, and Abducens Nerves," in .1 Text-Book q) Nt American Authors, edited by I'". X. Dercum, ls'."~>. pp. T'.i 1-sn:;. '-' Klin. Monatsbl.f. Augenkeilk., xxvi. p. 255. 150 FUNCTIONAL TESTING. tation of the cervical sympathetic. It is noticed in vomiting, forced respiration, and anemia of the brain — for example, syncope and is said to be present in persons of low mental development. In disease of the nervous system dilatation of the pupil, when of cerebral origin, indicates extensive lesion; when of spinal origin, irritation of the part (McEwen). Systematic writers have divided dilatation of the pupil into irritation-mydriasis, caused by irritation of the pupil-dilating center or fibers, and ptirnfy/ic mydriasis, caused by paralysis of the pupil-contracting center or fibers, or by failure of the stimulus to be conducted from the retina to the center. The former is apt to be -ecu in hyperemia and irritation of the cervical portion of the spinal cord, in spinal meningitis, in cases of tumor of the spinal curd, and also, under certain circumstances, in tumor of the cerebral contents, in psychical excitement ir example, acute mania -and in tabes dorsal is and progressive paralysis of the insane. The latter, which is also known as iridoplegia, is found in disease at the base of the brain affecting the center of the third nerve, in pressure of the cerebrum when in great amount, as from hemorrhage, tumors, advanced thrombosis of the sinuses, or large - : also in the late stages of HieningO-encephalitis. It is said to be present iu acute dementia when there is edema of the cortex, and i.s (bund in cerebral softening. Hemorrhage into the centrum ovale and cerebral peduncles also produces mydriasis McEwen I. •_'. Contraction of the Pupil (Myosis). — This appear- in congestion of the iris, paralysis of the sympathetic and also of the fifth nerve, in certain fevers, in plethora, venous obstruction, mitral disease, and under the influence of myotics. If the myosis i- of cerebral origin, it indicates an irritative stage of the affection ; if of spinal origin, a depression, paralysis, or even destruction of the part (McEwen). matic writers divide contraction of the pupil into irritation-myosis, caused by irri- tation of the pupil-contracting center or fibers, and paralytic myosis, caused by a paral- ysis of the pupil-dilating center or fibers, or by a combination of both. Irritation-myosis, as just noted, is found in the inflammatory affections of the brain and its meninges — e.g. meningitis, abscess (al first the myosis is on same side as le- sion), and beginning sinus-disease. According to the rule previously given, myosis may change to dilatation if the products of disease become excessive ; hence the serious prog- nostic import of mydriasis under these circumstances. .Myosis is seen in the early - of cerebral tumor, in small hemorrhages into the cerebellum, and at the onset of cerebral apoplexy. Berthold, quoted by Swanzy, uses myosis as a diagnostic symptom between apoplexy and embolism. McEwen points out that the convulsions arising from meningo-encephalitis are accompanied by myosis. while those due to epilepsy are usually associated with mydriasis. Apoplexy of, or pressure upon, the pons is associated with myosis. Paralytic myosis [spinal myosis) occurs in lesions of the cord above the dorsal verte- bra. It is especially noteworthy in tabes dorsalis. At first the pupil reacts to light and convergence, but later exhibits the Argyll- Robertson phenomenon (or reflex irido- plegia); that i-. it responds only slightly or nol at all to the ught-impulse, but the associated action of the iris — or, in other words, the contraction of the pupil in accom- modation and convergent — is preserved. The lesion under these circumstances is prob- ably in the libers which pass from the proximal end of the optic nerve to the oculo- motor nuclei. Turner contend- that a single lesion in the fore part of the oculo-motor nuclei in the Sylvian gray matter is the cause of both myosis and reflex iridoplegia. Paralytic myosis is also met with in paralysis of the insane, pseudo-dementia paralytica of syphilitic origin, bulbar palsy when complicated with progressive muscular atrophy or sclerosis of the brain and spinal cord. and. according to Mills, in some forms of multiple neuritis. The iris reacts peculiarly to mydriatics, which dilate this type of pupil only partially, and their effeel is for a long time manifest. Cocain, however, readily expand- the -mall pupil of reflex iridoplegia (Heddseus). Myotics contract it »"/ maximum. Unilateral reflex iridoplegia, or that condition when one pupil is unaffected by vary- ing degrees of illumination of both eyes, but reacts to accommodation, the unaffected pupil responding to separate light stimulus of either eye, may exisl with or without mydriasis, and usually is wider than its fellow. It i- seen in tabes dorsalis and syphilitic cases. It i- probably due to lesion in the sphincter nucleus. It should be distinguished from unilateral reflex blindness see ' 1. p. 1 19 . The reverse of the Argyll-Robertaon symptom has been observed, and indicates disease in a special part of the oculo-motor nucleus. Unequal pupils anisocoriaj arc rarely -ecu in health, although it is stated by one I wanow) that among I'M healthy military recruits the right pupil was TESTING ACUTENES8 OF VISION. Ill larger in 49 and the left in 53, equal width being found in only 12. [f there is recent wide dilatation of one pupil and do disease of the eye, the instillation of a mydriatic may be suspected. Unequal pupils occur in eyes with widely dissimilar refraction if one eye is blind, in aneurysm, dental disease, traumatism, and in diseases of the nervous system. If the disease is cerebral, unequal pupils denote unilateral or focal disease. They arc not uncommon in tal>es, disseminated sclerosis, and paralytic dementia. Varying inequality of the pupils, or a mydriasis now occurring on the one side and now on the other, i-. according to Von G-raefe, a serious premonitory symptom of insanity. Special Pupillary Phenomena. — The hemiopic pupillary inaction i- referred to on page 480. The cerebral <;,,•/,.,- reflex of the pupil (Haab's reflex consists of a marked bilateral pupillary contraction which takes place if the patient >its in a dark- ened room and directs without change of accommodation or convergence hi- attention to a bright object already present within the compass of tin- field of vision. Harold Giflbrd has described an orbicularis pupillary reaction; that is, a contrac- tion of tlie pupil which takes place when a forcible effort is made to close the lids. The discoverer explains tin- as the result of an overflow stimulus, attempted closure of the lids exciting in the nucleus of the orbicularis fibers of the facial an activity which is transferred to the pupil-contracting center. The test is of use in determining whether the pupil sphincter is paralyzed. Paradoxical Pupil-reactions.— Dilatation of the pupil under the influence of light-stimulus, and contraction when it has been -haded, have been described in cases of meningitis. A good deal of doubt has been cast upon this type of pupil-reaction. 1 Hippus, which is a normal phenomenon for a few seconds after light-stimulus to the retina and optic nerve, consists of a rhythmical contraction and dilatation of the pupil occurring without alteration of illumination or fixation. It is seen in cerebro- spinal sclerosis, disseminated sclerosis, neurasthenia, hysteria, psychical disturbances. epilepsy, and acute meningitis in its early stages. 2 Testing Acuteness of Vision. — For the purpose of determining acuity of sight test-types are employed, in which the letters arc of various sizes and are constructed according- to the methods described on page 138. Inasmuch as many good eyes possess a vision of five-fourths of the standard angle, Dr. James Wallace of Philadelphia and Dr. Culver of Al- bany have arranged a scries of test-types in which, instead of an tingle of five minutes, one of four minutes has been substituted as the basis of each letter. Dr. Randall points out that the order of the letter- should be adjusted so as to bring the confusion-letters in the same alternation. It i- preferable to have large letters at the top of the card, do particular advantage accruing from the inverted arrangement. The color of the card is of importance, a cream color verging on the India tint giving the best definition through lessening of irradiation (Randall). White letter- on a black background are also employed. When it is desired to test the acuity of sight, the patient is placed 6 meters from the type-card, in a well-lighted room, and each eye is tried separately. If the letter- of No. 6 2G feet, approximately) are read, vision is Qormal or 1, but if at the same distance no smaller letter- than those numbered is 60 feet) can be discerned, vision is .1. It is usual to express these results accord- ing to the formula. V= — , in which V stands for visual acuteness, d for the distance for the distance at which the type should be read, s, ( that in these instance- the vision would be recorded {j and T ,; -. or in feet -^- , — — (see also page I I"). X A I j A Any other distance may be chosen, provided it does nol place the patient For a full accounl of this condition see Gaz hebdom., No. 62, 1896. - The author de-ires to acknowledge much indebtedness u< Swanzy's chapter on " Hie Motions of the Pupil" in the preparation of the section devoted t<> the pupil. 1 52 FUNCTIONAL TESTING. closer to the test-card than '•) meters, at which close range the function of ac- commodation would introduce an element of inaccuracy. Thus, the scale made 15 use of by De Wecker and elaborated by Oliver assumes -jj- ( — ?==., approxi- mately), instead of | as ]. In like manner, a 4-meter distance may be util- ized, as lias been done l>y Edward Jackson. Rays coming from letters at <>, 5, or 4 m. have so little divergence when they reach the eve that they are usually considered parallel; hence if the patient sees distinctly at this distance, his vision is perfect at the longest range. In point of fact, however, as Frederick K. Smith has insisted, there is an appreciable divergence of rays from the distances mentioned, equivalent respectively to ^, ^, and J diopter lens. In the final adjustment of glasses this divergence should he recognized. For the purpose of a control test, and also for determining the visual acuity of illiterate persons, cards are employed on which a number of black dots and disks of various sizes are placed, which should be counted at dif- ferent distances. Among the best known of these are Burchardt's "inter- national tests/' For the same reason Edward Jackson has designed a visual test which is an incomplete square, the incomplete side being turned successively in different directions (see also page 140). A useful test for children may be constructed by printing on a card small pictures of well- known objects which in size shall approximately conform to the standard angle. Such a series has been published by Dr. Wolffberg of Breslau. If the patient fails to decipher the largest letter at the distance employed, he should be moved closer to the card. Thus, he may be unable to read the type uumbered 60 at 6 m., but may discern this at 4 m., I=^o Gr yV°^ nor " mal. Still further depreciation of visual acuity is recorded by requiring the subject to count the outstretched fingers at various distances (^, 1, or 2 m.), V = counting lingers at the distance measured. When the ability to distin- guish form (qualitative light-perception) no longer exists, the perception of light should be tried by alternately screening and shading the eye, or by illu- minating the eye with light reflected from a mirror or focussed through a magnifier. I/ight-sense. — Having determined the acuity of vision by means of the test-letters, the examiner has ascertained the form-sense, and may proceed to ,i~y l-'n;. ion— l'hfitoinetrr <>f !•'<"> rst it iKiicIisi. investigate a -croud subdivision of the sense of sight, the light-sense, which is the power possessed by the retina, or center of vision, of appreciating vari- ations in the intensity of the Bource of illumination. An instrument called a photometer is employed for this purpose, :m.), and the latter light-minimum ( L. M.i. Other instruments have been invented by Forster, Landolt, and \l. Wal- lace Henry. 1 By means of Forster's photometer (Fig. 100) the lowest limit of illumination with which an object is still visible (the minimum stimulus) is ascertained. The following description is taken from Fuchs : "A box, A, blackened on the inside, bears on its anterior wall two apertures for the two eyes, . i Special Tests. — In order to obviate the change which occurs in the color of yarns, etc. the color-sense may be investigated by the spectroscope, which, however, is not convenient for office-work. The changeable colors, which arc colored mixtures like those of wools, may be produced by passing polar- ized lighl through a quartz plate and again through a Nicol-prism. The following account, condensed from Carl Weiland's ' description of the Javal-ophthalmometer as a chrommometer, gives the essential points of instruments constructed for this purpose, and of his own happy modification of the ophthalmometer : In the color-measurer of Rose the light is passed through a Nicol-prism first, and then by a diaphragm through a double refracting prism, from where it enters firsl a quartz plate cut at right angles to its optic axis, and finally a second Nicol-prism. Two circles of complementary color.- are thus produced, which change continually when the upper quartz and Nicol-prism are rotated, but always remain complementary to each other. Konig's ophthalmo-leukoscope is like Hose's instrument, except that the first Nicol-prism is wanting and that quartz plates of' different thickness — 5, Id, or 15 mm. — are used, according to the degree of color-saturation required. In Chibret's chromato-photo-optometer the quartz plate is cut parallel to its optic axis, and the change in colors is obtained by inclining the plate at different angles to the line of vision. As these instruments are expensive, Weiland has devised a chroma- tometer which lie describes as follows : The color attachment to .(aval's keratometer consists "of a straight metal tube, about I' inches in diameter, reaching from the place where the patient's cornea usually is to about the beginning of the barrel of the telescope, and so fastened to the head-rest thai its axis coincides witli the axis of the instrument. At the front part of this color- tube (here i< a plane glass plate behind which a Nicol-prism is fastened in a cork. From this prism the polarized light passes by a round diaphragm through a quartz plate, cut at right angles to its axis and about 5 mm. thick. "fhe patient, looking with the Javal through this tube, will see two large color- fields partially overlapping each other. These color-fields are of complementary hues, while the place of overlapping shows white; provided, of course, that white light as reflected from a white surface, like a piece of white paper, is employed in this experi- ment. II' now the arc of Javal be rotated, while the color-tube remains in the same position, the colors will change continually, but always remain complementary, return- ing, however, to their original hues after the arc has been rotated through 90°. "• For the purpose of examination, place the patient's eye at the ocular of the in- strument, after you have first looked in yourself and given to the new color-tube such a position that blue and yeliow appear, because thus most color-blind persons will recog- nize two different colors. Now ask the patient whether the two colors are exactly alike or at least shades of the same color. If he answers No, turn the barrel of the Java! slowly through 'J0°, telling the patient to stop you as soon as the two colors are the same. Il he bas g I color-sense he will always see two different colors, but if he is color-blind, he will find that in a certain position of the arc the two colors will appear alike, or at least as much alike as if they were shades of the same color. These colors will usuallj be green and rose for a green-blind person, while the red-blind person gen- erally selects a more bluish-green and a rose with much more red in it. This suffices lo prove that the case is color-blind." Pseud o-isochromatic Tests. — According to Mauthner, certain colors which the normal eye differentiates appear to the color-blind person "falsely of the same color"— i. e. pseudo-isochromatic. At one time the color-blind subject will describe a- alike a row of colors which are not so ; at another time, when the tesl relate-; to the recognition of letters or signs on a colored ground, he will not see them, especially when the color of the ground and the letters (figures, signs, etc.) arc pseudo-isochromatic and equally clear. Daae ha- placed ii| ,i card on which are fastened ten horizontal rows of variously colored wools one row \\ Inch contains only red wools, one which coii- 1 Archives oj Ophthalmoloyy, xxiv., 1895, p. 349. MOBILITY OF THE EYES. tains only green, and one which contains only purple. I n the other seven rows the various colors arc placed next to each other. The color-blind person designates row s a- of the same color when thi> is not the case and the reverse. A test of this character, according to Mauthner, is a positivt pseudo-isochro- matic test, because it depends upon the positive expressions of the patient in regard to color similarity. Of the negative pseudo-isoehromatic tests — negative because, according to Mauthner, they depend upon the fact that the color-blind person does not read figures or letters which are drawn upon a pseudo-isoehromatic ground — the plates of Stilling may be mentioned (see page <><)4). Pseudo-isoehromatic powders have also been prepared by Mauthner for the same purpose. Simultaneous contrast tests based upon experiments with colored shadows are not satisfactory in practical work. Meyer's discovery thai if a gray ring or border is placed upon a colored — for example, red — piece of paper, and then covered with tissue-paper, it will appear to the normal eye in the complementary color — that is, green — has been utilized for practical work, particularly in the letters devised by Pfliiger. These consist of black or gray letters upon a colored around. The letters are then covered by tissue-paper and appear in the complementary color. Lantern-tests are sometimes employed, and are of great value in the examination of railroad employes (see page 604). Accommodation is measured in practical work by finding the nearesl point at which fine print can be clearly deciphered. The type- most fre- quently adopted are those known as Snellen's 0.5 or Jaeger's 1. Frequently, however, the types in common use are very badly printed and constructed. The letters should be so arranged that they subtend the standard angle of five minutes at a given distance; for example, 25 cm., 50 cm., etc. Ordina- rily, these letters are arranged upon suitable cards. Excellent series have been published by Schweigger, by James Wallace, and by Charles A. Oliver. In order to study the phenomena of accommodation the studenl should record — (1) The nearest point of perfectly distinct vision attainable with the smallest readable type, or the punctum proximum (abbreviated j>. p, or simply //). (2) The far point of distinct vision, or the punctum remotum (abbreviated p. r, or simply r). (3) The range, amplitude of accommodation, or the ex- pression of the amount of accommodative effort of which the eye is capable. This is expressed in the number of that convex lens placed close to the cornea whose focal length equals the distance from the near point to the cornea, and which give- rays a direction as if they had come from the far point ; thus, if the near point be at I<> cm., the lens which expresses the amplitude of accom- modation is + 10 I). 10. A convenient measure is a stick marked 10 on one side in inches and fractions of an inch, on the other side in milli- meters and centimeters ; on the edge the amplitude of accommodation is expressed in diopters. (4) The region or the space in which the range of accommodation is available. (5) Relative accommodation, or that independent portion of this function which can be exercised without alteration in a given amount of convergence, and is divided into a negative portion, or that portion which is already in use, and a j»>si/ir<' portion, or that portion which is not in use. If the patient is unable to read the line tesl print at any distance, a convex leu- should be placed before the eye and the near (point and far poinl recorded with its aid (see also page 134). Mobility of the Byes. — This i- tested by causing the patient t<> follow with his eyes, the head remaining stationary, the movements of the uplifted 156 Fl r N( "/VO.V. I /. TESTING. finger, which i- directed to the right, to the left, upward, and downward. Both eyes must be observed, and note made of any lagging in their move- ments or of the failure of either eye to turn into the nasal or temporal eanthus. At the same time, the relation of the movements of the upper lid to those of the eyeball is recorded. The attention of the patient must be centered upon the moving finger, and allowance should be made for the imperfect mobility of highly myopic eyes. Anv asymmetry of the skull, or difference in the level of the two orbital margins, may be observed, because such conditions are not infrequently associated with ametropic eyes, especially when the two <'\es possess great inequality in refractive conditions. Investigation of the Balance of the External Bye-mnscles. — Under normal conditions perfect equilibrium of the external eve-muscles is present, but preponderance, for example, of the power of the external recti, or vice versd, produces a tendency to divergence or convergence, which, however, is overcome, with the preservation of binocular single vision, in spite of the disturbed equipoise. This condition was named by Von Graefe dynamic stra- bismus, it is frequently designated insufficiency of the ocular muscles. Dis- turbance of the normal balance (imbalance, as it is now called) creates a tend- ency for the visual lines to depart from parallelism, or the various phorias of placed before one ey< — f'«>r example, the right — i. e. with its base toward the nose. II" the Images are on the same level, no de- viating tendency is present. II' the right image rises higher than the other, the visual line of the right eve tends to be lower than that of its fellow, and there is insufficiency of the vertical muscles. That prism, placed with it~ base down before the left eye, which restores the images to the horizontal level measures the degree of deviation. (5) Produce vertical diplopia, and tot the functions of the lateral muscles at the ordinary working distance, or 30 cm. For this purpose it is customary to employ the equilibrium test of Von Graefe, in which a card, having upon it a large dot through which a fine line is drawn, is held 25 or 30 cm. from the eyes, diplopia being induced by means of a prism of 10° or 15°, base up or down, before one eye. A more accurate test-object is a small dot and fine line, or a single word printed in fine type, requiring accurate fixation and a sustained effort of accommodation. If, the prism being placed base down before the right eye, the images stand exactly one above the other, equilibrium is evident; if the upper image (image of the right cyel stands to the left of the lower image, there is crossed lateral deviation ; and that prism, placed before the left eye with its base toward the nose, which restores the image to a vertical line measures the tendency to divergence, exophoria, or insufficiency of the internal recti. If the upper image stands to the right of the lower, there is homonymous lateral deviation ; and the prism placed before the left eye, with its base toward the temple, which restores the images to a vertical line, measures the tendency to convergence, esophoria, or insufficiency of the external recti. (6) Ascertain the power of adduction (prism-convergence), abduction (prism-divergence), and sursumduction (sursumvergence) by finding the strongest prism which the lateral and vertical muscles can overcome. 1 Beginning with adduction, find the strongest prism placed before one eve, with its base toward the temple, through which the flame still remains single. The test should begin with a weak prism, the strength of which is gradually increased until the limit is ascertained. This varies from 30° to 50°. In this test, if diplopia occurs when, for example, the strength of the prism reaches 20°, single vision may not return until the prism has been reduced, for instance, to 10°. The space between the greatest and least power of adduction has been described as the " region of diplopia" (Reeves, Lippincott, Gould i. In like manner abduction is tested, the prism now being turned with its base toward the nose ; (>° to 8° of prism should be overcome. The ratio be- tween adduction and abduction should be 6 to 1 (Stevens) — i. e. if adduction is 48°, abduction should be 8°, but, according to Risley, in carefully corrected or emmetropic eyes the ratio is 3 to 1. Sursumduction, or the power of uniting the image of the candle flame seen through a prism placed with its base downward before one eye with the image of the same object as -ecu by the other eye, is ascertained by beginning the trial with a weak prism, } r ° or 1°, and gradually increasing ii- strength. The limit i~ usually ■'> , but may be as high a- 8 or 10°. If the eyes of the patient under examination are ametropic, the proper 'The words "power of adduction," etc arc here used with the significance ordinarilj attached to them. For another consideration of this matter tin- student Bhould read the para- graphs relating to the same Bubject in I »r. I taane's discussion of " Tin- Anomalies of the < Ocular Muscles," p. 503. 158 II \\< 'TIOXA L TKSTlSli. correcting lenses should be placed before them, and the examination for the various forms of insufficiency made through this glass. It is, moreover, ex- ceedingly important that the correcting glass should be accurately centered ; otherwise, in a lens of considerable thickness, a prismatic effect would he produced which would utterly preclude accurate determination of the mus- cular condition-, especially of the vertical muscles, where the search for fractions of* a degree of deviation is sometimes necessary. It' the muscular examinations have been undertaken as part of a routine preliminary investi- gation of an eye, they should be repeated after the refraction has been accu- rately determined, and, if anomalous, corrected. Practically, all of the examinations for muscular errors can be made with a -erics of prisms and a trial frame, hut they are facilitated by the use of certain instruments of precision, especially some form of FJerschel or re- volving prism, the one devised by Uisley being the best (Fig. 101). The latter consists of two prisms, superimposed with their bases in opposite directions, constituting a total value of 45°. They are mounted in a cell which has a deli- cately milled edge, and fits in the ordinary trial frame. The milled edge permits convenient turning in the frame, so that the base or apex of the prisms can he readily placed in any desired direction. The prisms are caused to rotate in opposite directions by means of a milled screw- head projecting from the front of the cell. With this rotary prism the strength of the abducting, adducting, and supra- and infraducting muscles can he measured. If the rotary prism is placed before the left eye with the zero mark vertical, and the screw turned to the right or left, it will cause the base of the resulting Fig. 101.— Risley's rotary prism. phorometer. prism to he either inward or outward, that i-, toward the QOSe or temple, :i- may be desired ; or it may be placed with the zer ark horizontal and the base turned upward or downward. All examinations for muscular defects BALANCE <)/' THE EXTERNAL EYE-MUSCLES. 159 may be accurately ascertained with Dr. Gr. T. Stevens's well-known phorom- eter, which is illustrated in Fig. 1*>'2. One of the simplest tests of the ocular muscle.- is the obtuse-angled prism of Maddox. This is composed of "two weak prisms of '■> . united by their bases. On looking through the line thus Conned al a distant plane, two false images of it are seen, one higher and one lower than the real image seen by the other eve, the position of which, to the right or the left of the line between the false images, indicates the equilibrium of the eye. A faint hand of light, of the same breadth as the two false images, is seen extended between them" (Fig. 103). The answers of the patient may be materially assisted by placing a red glass before one eye and thus tinting the real image. I {'this stands directly in the center between the two false images, all forms of insufficiency are eliminated; if it stands to the right or to the left, there is insufficiency of the ts for insufficiency of oblique muscles Savage : i.insuffi- : M u- obliqut 7. insuffi: ■. n: 5 1 1 It ml. .1 :i ?buqu< Fig. 103.— Position of the Fig. 104.— Tests images as seen through the ciency of left super- . obtuse-angled prism of insufficiency of right superior oblique ; l, insufficiency of right inferior Maddox (Randall). oblique : 5, equilibrium of oblique muscles. external or of the internal recti ; if it stands above or below the center, or is fused with the upper or the lower image, there is insufficiency of the superior or inferior recti. Insufficiency of the oblique muscles (cyclophoria), according to Savage, may be detected "by placing a Maddox-prism, with its axis vertical, before one eye (the other being covered), which regards a horizontal line on a card 18 in. distant. This line appears to he two, each parallel with the other. The other eye is now uncovered, and a third line is -ecu between the other two. with which it should he parallel. Want of harmony in the oblique muscles is shown by want of parallelism of the middle with tl ther two lines, the right end of the middle line pointing toward the bottom and the left end toward the top line, or vice versd, depending upon the nature o\ the indi- vidual case " ' ( Fig. 104). 1 Much doub the phenomenon L894. ,i has been cast upon the accuracy of this test by V. B. Eaton, who considers a physiologic one. Consult Journal of the American Medkal I .Sept, 160 FUNCTIONAL TESTING. The rod-Jest, also designed by Maddox, depends upon tlie property of transparent cylinders t<> cause apparent elongation of an object viewed through them, so that a point of light becomes a line of light so dissimilar from the test-light that the images are not united. It may be suitably employed by having mounted in a cell which will tit in the trial frame a transparent glass rod colored red, | in. long, and about the thickness of the ordinary stirring-rod used by chemists, or a series of glass rods placed ulie above the other ( Fig. 105). The examination for horizontal deviation is thus described : " Seat the patient at (J m. from a small flame, placed against a dark background, and put the rod horizontally before one eye. If the line passes through the flame, there is orthophoria (equipoise) as far as the horizontal movements of the eyes are concerned. Should the line lie to either side of the flame, as in most people it will, there is either latent convergence or latent divergence : the former, if the line is on the same side as the rod (homonymous diplopia); the latter, if to the other side (crossed diplopia)" (Fig. 106). .1 R Fig. 105. -Maddox-multiple-rod. i i. -i for horizontal deviation; the rod is before the righl eye: .1 the line ■ through th rthophoria ; B, the line passes to the right of the flame latentconvei or ■ Bophoria ; C, the line passes to the left of the flame latent divergence, or exophoria In order to teal the vertical deviation, the rod is placed vertically before 'he eye: a horizontal line of light appears, and the patient is asked if the line passes directly through the flame or if it appear- above or below it. The following ride, quoted from Maddux, will suffice to indicate the "hyper- phoria" eye : " [fthe (lame i- lowest, there is a tendency to upward deviation of the naked eye ; if the line ie lowest, of the eye before which the roil i- placed" ' ( Fig. 107). ■ Dr Swan M Burnetl substitutes for the Maddox-rod a 6 I ». cylinder. POWER OF CONVERGENCE. 161 The measurement of the extent of the deviation may be made in the ordi- nary way byn'nding that prism, placed before the naked eye (preferably with therotary prism of Risley), which brings the line and flame together. In order to avoid the awkwardness of the phraseology " insufficiency of the internal recti," etc., and at the same time more accurately to describe the Fig. 107.— Maddox's rod-test for vertical deviation ; the rod is before the right eye : .1, the line passes through the flame — orthophoria ; B, the line passes below the flame; the upper image belongs to tin- left eyi — right hyperphoria; C, the line passes above the flame; the upper image belongs to the right eye —left hyperphoria. muscular anomalies, the following terminology has been introduced by Dr. George T. Stevens, and has received a deservedly wide acceptation : The condition in which all adjustments are made by muscles in a state of physio- logical equilibrium is called orthophoria. Disturbances of equilibrium are known as heierophoria, or insufficiencies of the ocular muscles. The deviating tendencies of beterophoria may exist in as many directions as there are forces to induce irregular tensions. The following system of terms is applied to the various tendencies of the visual lines : I. Generic Terms. — Orthophoria: A tending of the visual lines in parallelism. Heterophoria : A tending of these lines in some other way. II. Specific Terms. — Heterophoria may be divided into — 1. Emphoria : A tending of the visual lines inward; 2. Exophoria : A tending of the lines outward : 3. Hyperphoria right or left) : A tending of the right or left visual line in a direction above its fellow. This term does not imply that the line to which it is referred is too high, but that it is higher than the other, without indicating which may be at fault. III. Compound Terms. — Tendencies in oblique directions may be expressed as hyperesophoria, a tending upward and inward ; or hyperexophoria, a tending upward and outward. The designation " right" or " left*' must be applied to these terms. Power of Convergence. — In order to determine the maximum of convergence an instrument known a- an ophthcUmo-dynamometer may lie em- ployed. The one devised by Landoll consists of a metallic cylinder, blackened on the outside, placed over a candle flame. The cylinder contains a vertical -lit 0.3 mm. wide, covered l>v ground g;las<. The luminous vertical line thus produced is the objeel of fixation. Beneath the cylinder i- attached a tape measure graduated on one side in centimeters, and <>n the other in the cor- responding number of meter-angles. The fixation objeel is gradually ap- proached in the median line toward the patient, until that point where double 162 FUNCTIONAL TESTING. vision occurs is reached, or the nearest poinl (pimctum proximum) of con- vergence, and the distance in centimeters read from one side of the tape, and the corresponding maximum of convergence in meter-angles on the other. The minimum of convergence may also be ascertained with the instrument, bul when this is negativt it is determined by finding the strongest abducting prism which will not cause diplopia while the patient is fixing a candle flame at ii in. It' the number of the prism is divided by 7, the quotient will ap- proximately give in meter-angles the amount of deviation of each eve when the prism i- placed before one. The amplitude of convergence is equivalent to the difference between the maximum and minimum of convergence. 1 The Field of Vision. — When the visual axis of one eye is directed to a stationary point, not only is the object thus "fixed" visible, hut all other objects contained within a given -pace, which is large or small in proportion to the distance of the fixation point from the eye. This space is the field of vision (conveniently abbreviated V. F.), and the objects within it imprint their images upon the peripheral portions of the retina, or those which arc independent of the macula lutea. In contradistinction to visual acuity and refraction, which pertain to the macula in the act of direct vision, the function of sight capable of being performed by the rest of the retina is called indirect vision. The limits of the visual field may be roughly ascertained in the following manner : Place the patient with his back to the source of light, and have him ti\ the eye under examination, the other being covered, upon the center of the face of the observer, or upon the eye of the observer, which is directly opposite his own at a distance of 2 ft. Then let the surgeon move his fingers in various directions midway between himself and the patient on a plane with hi- own face, until the limits of indirect vision are determined, controlling at the same time the extent and direction of the movements by his own field of vision. Instead of using fingers as the test-object, the author, in common with many surgeons, is accustomed to employ a black rod 1v Jeffries (Fig. L08). In like manner, a campimeter may be employed, the one designed by De Wecker being a useful model. It may be understood by reference to Fig. 109. The patient's eye regards the cross in the center of a black vertical .-- >-- i" """ __- .-- -, \ V » ' v • i +■ ,' \ 1 \ \ / 1 I ■**. *,, s — — r 1 . 1 ! X. [_ White Blue.... Red Fig. 108. — Limits of the normal field for white, blue, and red, transcribed upon a blackboard (after Norris). Fig. li ►'.». — ( 'ampimeter of I »e Wicker. table while the test-object is moved from the periphery toward the center, and the outermost limit of its recognition is marked on the radiating line which it follows. When each line has thus been traversed, the points are joined by a continuous line, and a graphic representation of the visual Held results. The field of vision may also be examined on a flat surface at a greater distance than 2o to 30 cm., after the manner proposed by Bjerrum. The examinations are made at a distance of 2 m. on a large black screen 2 m. in breadth, which can be let down from the ceiling to the floor. At this dis- tance the blind spot (see p. 169), instead of measuring about 2.V cm., as on an ordinary perimeter, measures 20 cm. in diameter, and everything else is in the same proportion. The test-objects used by Bjerrum are small circular disks of ivory fixed on the ends of long dull-black rods. They vary from 10 to 1 mm. in diameter. The examination is begun in the ordinary way at 30 cm. with the 10-mm. disk, and then continued at 2 meters' distance with a 3-mm. disk. In the first case the visual angle approximately is 2 . and in the second -V. The normal boundaries in the firsl instance have been given ; in the second they are 35° outward, o0° inward, 28° downward, and 25 upward. The method is valuable for finding sector-shaped defect-, irregular limitation-, and especially seotomata (see p. 169). 1 Beyond 15" measurements on a flat surface cease to be accurate, because the object i- too far away from the eye ; rays perpendicular to the visual line 1 Dr. Joseph E. Willets I Aimtds <;/' Ophthalmology and Otology, 1896, vol. v.. No. 3, has constructed a prismatic perimeter in which a Dumber of prisms or cones are arranged, which trun-init or refract rays of light to that part <>(' tin- retina corresponding t" tli' degrees in the present perimetrical chart. ror full details the reader i- referred to the article.) 164 FUNCTIONAL TESTING. coming from a peripheral object would be parallel to the blackboard, and could not arise from it or any object passed across its surface. The accurate investigation of the functions of the periphery of the retina requires the use of an instrument called a perimeter, for which we arc chiefly indebted to A.ubert and Forster. This instrument consists essentially of an arc(or a semicircle) of wood or metal marked in degrees which rotates around a centra] pivot, which at the same time is the fixing point of the patient's eye, placed 30 cm. distant — i e. at the center of curvature of the perimeter arc. The test-object, 1 or 1 1 cm. in diameter, affixed upon a carrier, is '-- Perimel imination may be made with the carrier which moveB along the semi- circle, orth i maybe carried along this by means of dark disks attached to a long handle, each disk containing in its center the test-object. The patient's chin is placed in the curved chin-rest ; the notched end of the uprigbl i>ar is brougnl in contacl with the face, directly beneath the eye to be tied, which attentively fixes the center of the semicircle. The other eye should be covered, ■ neatly adjusted bandage 1 be n cord charl is inserted at the back of the instrument, in Ivory vernier the examiner is enabled to mark exactly with a pencil the point on the corresponding to the position on ; rcle al which the patient Bees the test-ODject. The then joined by a continuous line, and a map of the Held is obtained. moved from without inward along the arc, and the point noted in each me- ridian at intervals of 30 . where it is recognized. Usually the examination is begun with the are in the horizontal position, which is then moved from this meridian to the nexl (e.g. up and out), and so on until the whole field has been investigated. Generally it is sufficient to examine eight meridians Fig, II-., The result is transcribed upon a ••hart, prepared by having ruled upon it radial lines to correspond to the various positions of the arc, and concentric circles to note the decrees. THE EI ELD OE VISION. 165 Tlir numbering of the meridians on the numerous charts which have been published is far from uniform, as may be -ecu by examining the accompany- ing diagrams ( Figs. 111,112,113). Noyes and Knapp, 1 in order to secure uniform n rds of the visual field, have advised the designation of the meridians accord- ing to the method employed by Ilelm- holtz in his study of the movements of the eye — viz. "to take as the zero point the left end of the horizontal meridian of each eye, and to count from left to right as the hands of a watch viewed by a person under examination move. 0° accordingly marks the temporal end of the horizontal meridian of the left and the nasal end of the same meridian of the right eye; 180° marks the nasal end of the horizontal meridian of the left and the temporal end of the same meridian of the right eve." 2 Since the Aubert-Fiirster instruments appeared the perimeter has under- gone numerous modifications and the market is supplied with a host of models. The most practical and time-saving instruments are the so-called Fig. 11L— Visual-field chart according to Forster. Fig. 112. — Chart for Mcllardy's registering perimeter. Fig. 113.— Chart for perimeter (Fig. 110). self-registering perimeters, especially those designed by Stevens, McHardy, and Priestley Smith. A useful model for bedside examinations ig the hand perimeter of Schweigger. The size qfthi visual field varies considerably within normal limit-, being influenced by the character of the light, which should illuminate with equal intensity all portions of the perimeter are in each position ; by the size of the test-object, which should be not less than ] and not greater than '2 cm. in width ; by the attention of the patient, whose eye should accurately regard fixation during the measurement ; and by the patient's physical and mental condition. Indue prolongation of the examination produces retinal tire and 1 Archives of Ophthalmology, vol. xv. p. 207. [nstead of having the patient fix his eye npon the central pivot, it may be directed upon :i porcelain button on a bar placed 15° from the center to the left it' the righl • amined, and vice versa if the left i^ under observation., This plan originally suggested by Forster, makes the optic-nerve entrance, and not the macula, the i entre i >f the visual field. L66 FUNCTIONAL TESTIXU. corresponding contraction of the visual field. The extent of the field of vision is also somewhat under the influence of the size of the pupil and the state of refraction, being larger in eyes with widely dilated pupils or with hyperopic refraction, and smaller in eyes with contracted pupils or with myopic refraction. Enlargement of the visual field may be ooted during accommodation for the near point and when the patient wears concave glasses ' i Mauthner). The average physiological limits of the form-field, or, what is practically the same thing, the field when this has been measured with a square of white l.V cm. in width, an — outward, 90 ; outward and upward, 70°; upward, 50 : upward and inward,-",:) ; inward, 60°; inward and downward, 55° ; downward, 72 ; downward and outward, 85°. These limits, which form a good working field, arc somewhat exceeded by the mean limits resulting from the examination of a number of normal eyes, as recorded by Forster, Landolt, and Baas.' The last-named author finds the average result of ten observers as follows: Outward, 99° ; upward, 65°; inward, 63' : downward, 76°. Figures indicating a "minimal field," or "smallest physiological field," have been recorded, varying from 90° i Forster) to 50 (Treitelj outward ; 55-21° upward ; 60-40° inward ; 70-40° downward. Certainly, in the judgment of the author, the smaller of these limits cannot be regarded as physiological, and the greater is about equal to the average working field already given. A- we ordinarily measure the visual field, the measurement represents the relative visual field, in contradistinction, as Baas points out, to the absolute visual field. The former records the limits for a test-object of definite size ; the latter the maximal expansion which it is possible to obtain. The fig- ures then given are the relative visual field (test-object 1-2 cm.), and trans- scribed upon a chart produce Fig. 114. Examination of this chart shows that the field of vision is not circular, being greatest outward and below, and most restricted inward and above. This restriction depends partly upon anatomical reasons — i. e. the v<.\ixv of the orbit, the lids, and the nose inter- fere with vision, and partly upon physiological reasons — i. e. the per- cipienl layers of the retina extend farther forward on the nasal than on the temporal side, or, as Landolt expresses it, the outer pint of the retina is less used than the inner, and its functions, therefore, are less developed. Hence, as each portion of the field corresponds to the opposite portion of the retina, the inner part is smaller than the (.liter. To avoid the influence of the physical obstacles afforded by the cranial bones, the eye should be made to li\ an object iii each meridian •"><> i g L14.— Various limit- of the form-field: a, I .. ragi . b, average working field . ;-t physiological field. 1 Convex glasses should exercise :i contracting influence ; indeed, Berlin, quoted by Baas, found .i ring-shaped defect in the peripheral visual field if measured through strong convex placed ome distance from tin rfie ten • Baa , Butz, bonders, Drott, Hegg, Landolt, Reich, Schon, Stober, - ■ B D Stuttgart, 1896, p i ! I'OLOli-FIKlJ). L67 Fig. 115.— Binocular field of vision (Moser). in the direction opposite to that under measurement or else suitable rotation of the head should be made. Binocular Field of Vision. — The field of vision for each eve having been defined, it remains to point out that the field of vision which pertains to the two eves, or that portion in which binocular vision is possible, consti- tutes only the area where the central and inner parts overlap. This is evident from the diagram. The continuous line /, bounds the field of vision of the left eye, and the dotted line R the visual field of the right eye. The central white area corresponds to the portion common to both eyes, or to that area in which all objects are seen at the same time with both eyes ; the shaded areas correspond to the portions in which binocular vision is wanting. In the middle of the white area lies the fixation point,/, and on each side of it the blind spots of the right and left eye, r and / (Fig. 115). Having thus determined the limits and continuity of the visual field, the functions of the peripheral parts of the retina in regard to perception of colors, acuity of vision, and appreciation of light should be investi- gated. Color-field. — The color-field is examined in the manner described in connection with the general visual field, the squares of white in the instru- ment being replaced by pieces of colored paper 1 to 2 cm. in diameter. The order in which the colors are recognized from without inward is — (1) blue, (2) yellow 7 , (3) orange, (4) red, (5) green, (6) violet. In prac- tical work blue, red, and green are the colors employed. Non- saturated colors are not correctly recognized when the test-object is first m'cm. Thus, yellow at first appears white; orange, yellow ; red, brown ; green, white, gray, or gray-blue; and violet, blue. The investigation of this zone of imperfect color-perception is important in various patholog- ical conditions, especially in the study of the visual fields of hysteria and of disseminated sclerosis. The physiological extent of the color-fields, like that of the general field, is subject to variations within normal limits, which are represented by the figuresin the following columns, hi each left-hand column are the figures denoting the extent of an average color-field mapped with 1 cm. square object, while in each right-hand column are the averages of the results of ten observers recorded by Baas, the Bize of the t « -t -« >1 >i« '»-65 ( Outward and upward 60 15 "10 I p W ard 40-45 33-39 27-34 Upward ami inward 45 30 25 [nward 45-50 30-39 2o-33 [nward and downward 50 35 2"i Downward 58 62 45-50 30 13 I downward and outward ■"> ■ )) ''' These, when transcribed upon a chart, are represented in Fig. 116. A.s may have been inferred, the extent of the color-field is greatly governed l,v the size of the test-object. According to < towers, 1 who has recently reopened this subject, with a sufficiently large area of color it will he found that all the color-fields differ in extent very little from the fields for white. Green alone seems to fall short of the edge of the white field by aboul 5°. The extent of the color-field is further governed by the character of the light, the nature and saturation of the color, the contrast in luminous intensity between the colored test-object and the background. To quote from Ward Holden : Other conditions being the same, the field becomes larger as the saturation, the intensity, or the size of the color is increased ; and the field is larger the less the contrast in luminous intensity between test-object and background. The Acuity of Vision of the Peripheral Parts of the Retina.— This diminishes from the macula to the periphery. It may be tested with small squares of Mack paper, separated from each other by their own width, by noting the point in each meridian where they are recognized as separate objects. The tests of Landolt and Ito are 6, 5, -'5, and '1 mm. black quadrants on a white ground. Groenouw employs as a test-object to be passed along the perimeter arc black points on a white ground of .',, \, I, 2, and 4 mm. in diameter. The result obtained is called " visual acutenessfor a point." 2 The results have the form of a horizontal oval nearly parallel to the limits of the visual field. The Light-sense of the Periphery of the Retina. — This may bo tested conveniently with Ward Holden's tests, which are thus described by the author : One card has a 1-niiii, black point on one side, and a 15-mm. quadrant of light gray, having ± of the intensity of white, on the other. With a peri- meter of 30 cm. radius the black point and gray patch arc each seen by a normal eye outward, \-> ; upward, 30° j inward, 35° ; downward, 35°. The second card has a 3-mm. black point on one side, and a darker gray patch, having .; the intensity of white, on the other. Each is seen on the perimeter arc, outward. To : upward, 15 ; inward. 55° J downward, 55°. Card 2 will reveal slight disturbances of light-sense near the periphery, and card 1 in the intermediate and central zone-. Groenouw's and Holden's tests are declared by their author- to he re delicate than color-tests, or at least equally bo, while they possess the advantage of being more intelligible to tin- patient. According to the experiments of Landolt, the perception of light is the niosl constant function of the healthy retina, and remain- marly the same throughout it- surface, while the color- and form-sense rapidly lessen toward the periphery. Progressive diminution of light-sense, however, from center to periphery will be found it test-objects of varying luminous intensity with / 'i,, idh. Soc. I' K. t vmI. \\ p, ] •_'. (For further particulars the reader is referred to llii- most ini'-n -tit ; remarks, the employment of a jingle point as :i test object affords information in. i bo mm li "i the form-sense as of the I i ^ 1 1 t--ti i-«-. FIELD OF FIXATION. 169 the illumination of ordinary daylight arc employed. For practical purposes in cases of very defective vision an idea of the retina'.- sensibility to light may be obtained by passing a candle flame along the arm of the perimeter as a test-object, while a second candle flame is made the point of fixation.' The most frequent departures from those limits of the visual field assumed to be normal are general or concentric contraction ; contraction limited especiallv to one or the other side ; peripheral defects in the form of re- entering angles; absence of one segment or quadrant; and absence of the entire right or left half of the field (see page 472). Scotomas. — In addition to these defects, search should be made for dark areas within the limits of the visual Held, or scotomas. These are distinguished as positive when they are perceived by the patient in his visual field, and nega- tive when within the confines of a portion of the visual field the image of an external object is not perceived, but the affected area is not discovered until the field is examined. Negative scotomas are further divided into absolute and relative. Within an absolute scotoma all perception of light is wanting, while within the confines of a relative scotoma the perception of light is merely diminished. The latter are color scotomas, usually for red and green. Scotomas are further subdivided, according to their situation and form, into centred, paracentral, ring, and peripheral. In every normal eye there is a jihysioloe/ieal scotoma which may be re- garded as the type of an absolute scotoma corresponding to the position of the optic-nerve entrance, which usually may be found 15° to the outer side of and 3° below the point of fixation, the distance from fixation being greater in hyperopic than in myopic eyes. This is known as Mariotte's blind spot. Usually the form of the blind spot is not round, but a vertical oval, its upper and lower end being somewhat drawn out to correspond to the larger retinal vessels. Its size depends upon the distance from the cornea. In Landolt's experiments on his own eye at a distance of 35 cm. from the cornea to the plane of projection the mean height of the blind spot was 52 mm. and its breadth 44 mm. The blind spot is much enlarged under certain conditions ; for example, by retained marrow-sheath or by papillitis. For the detection of scotomata small test-objects, white, gray, or colored, l cm. square, are employed, which are moved in different directions from the point which the eye under observation attentively fixes, and the spot marked where the object begins to disappear or change its color. The arm of the perimeter is usually marked near the center in half degrees for this purpose. All examinations around the center of the field of vision, and hence the ex- aminations for scotomata, are readily made upon a blackboard. Berry urges that the ordinary test for scotomata be supplemented by making an examina- tion of the particular area of the field at a distance of 2 m. or more, so as to obtain a larger projection of the blind portion, and to be able to work with small retinal images without necessitating the use of very small objects. Field of Fixation. — This includes all points which the eye under observation can successively fix, the head being perfectly stationary. Various methods for determining the limits of the field of fixation have been employed ; for example, watching the image of a candle flame on the center of the cornea 1 Readers interested in the acuity of vision of the peripheral parts of the retina and testa for the light-sense of the retinal periphery arc referred to the excellenl papers on this subject byGroenouw [Archival of Ophthalmology, \.\ii., L893,p.502) : Ward Bolden [bid., xxiii . p. 10 ; and Karl Baas [loc. cii., pp. 55! 57). In the last-named publication the literature of the entire subjeel is reviewed. 17(1 FUNCTIONAL TESTING. as the eye follows the test-light moved along the perimeter arc until the limit (.!' movement is reached. This method, suitable to amblyopic eyes, is not so accurate as one which requires the patienl to distinguish letters. The patient is seated before the perimeter, with the semicircle horizontal, precisely as if his visual field was to be examined, and the eye under observation (the head being perfectly rigid") is made to followa word composed of test-letters repre- senting the minimum acuteness of vision, and the point where vision ceases to lie distinct marked in successive meridians. 1 Landolt's measurements of* the field of fixation undei normal conditions are as follows: Outward, 45- 50 : inward. 15 : upward, 35-40 : downward, 60 . l>r. (I. T. Stevens determines the rotations of the eyes with a special instrument called a tropometer. According to his measurements, the most favorable rotations an — Outward, 50°; inward, ")5° ; upward, 33° ; down- ward. 50 . i See also p. 499.) Tension. — This term indicates the intraocular resistance, and is clini- cally demonstrable by palpating the globe with the finger-tips. The middle and ring fingers are placed upon the brow of the patient, the tips of the index fingers upon the eyeball, and gentle to-and-fro pressure made, the eyes being directed downward. This pressure must be made in such manner as not to push the ball into the orbit ; otherwise no information of its true resistance is obtained. The tension of one eye must always be compared with that of its fellow, and in any doubtful case the results may be contrasted with those obtained by examining an eye known to be normal in another patient of similar age. Normal tension is expressed by the sign Tn, and the departures from it by the symbols '.', 1, 2, + 3, and — ?, — 1, —2,-3: the plus signs indicate increased, and the minus signs decreased, resistance. In physiologi- cal experiments various kinds of apparatus, constructed upon the principle of the manometer, are employed, and for clinical purposes instruments known as tonometers have been devised. In practical work, however, sufficiently accu- rate data are obtainable by a careful use of the educated finger-tips. Protopsis, or protrusion of the eye, may be caused by orbital diseases, tenotomy, paralysis of the ocular muscles, and Graves's disease; while en- largement of the ball is the result of various conditions residing within the globe — myopia, intraocular tumor, and staphyloma. If the cause is uni- lateral, the resulting condition is asymmetrical and the two eyes may be compared by observing the relative positions of the apices of the cornea? with each other :ind with the line of the brows. 'I he eyeball is apparently shrunken (enophthalmos) in some cases of ptosis and in wasting of the orbital fat. and is diminished in size in high grades of hyperopia and congenital failures of development. As Nettle- ship ha- pointed out, the amount of exposed sclera decides the apparent pro- trusion or recession of the eyeball. Position of the Eyes. — Instead of presenting parallel visual axes, one eye maybe deviated i n ward, out ward, downward, or upward, constituting one of the various 'ypc- of strabismus, a condition which may or may not be associated with diplopia. ■ v Wood has devised a useful tot for this purpose: Trans. Ophthalmolog. Section A. M. L896, 262 THE OPHTHALMOSCOPE AND ITS USE; THE NORMAL EYE-GROUND. By B. ALEX. RANDALL, A. M., M. I)., OF PHILADELPHIA. Ophthalmoscopy is the visual exploration of the eve, and is more strictly limited to the study by transmitted light. Its utilization has inau- gurated a new era in ophthalmology, from which most of its scientific devel- opment dates ; but general medicine has been and is greatly concerned in the information thus gained. The ophthalmoscope ought to be in daily use in the hands of every physician, and it will be when the erroneous impression has been removed that its use is difficult to learn. A half-hour's good instruction can give any intelligent person command of its technique and a dozen illustrations of its various revelations ; and moderate practice alone, with loyal adhesion to the cardinal rules, will then serve to widen almost fid maximum the field of its employment. Compared with medical micros- copy, its technique is very simple, although reasonable persistence in the face of difficulties may be less easy when dealing with a patient than in the quiet conditions of laboratory work. The beginner must not expect to succeed at once under adverse conditions which would try or even battle the expert : the study of a patient in bed is comparatively hard, even with an electric-light ophthalmoscope, and when intractable or otherwise difficult his examination may prove beyond the power of any one ; yet it is to such very practical utilization that the physician may at once unreasonably desire to put the new accomplishment. Restricted at first to easy conditions, the aft may be prac- tised with few failures and rapidly growing comprehension ; the infinite variations which fall within the physiological limits will be gradually learned and cease to be frequent enigmas, and the physician, made duly self-confidenl by his success, will not too easily accept defeat when difficulties have to be surmounted. Learning that real cause only need disturb him, he will seek the ground of his difficulties in the narrow group of requirements ; and when these have all been met can feel assured that he has located, if not overcome, the obstacles, and learned as much, perhaps, as the circumstances would permit to any one. The Ophthalmoscope. — The ophthalmoscope, augen-spiegel <»!' the Germans, is a mirror for throwing light into the eve. Elaborate and costly forms have been devised in numberless variety, intended to meet almosf every possible requirement in the way which the designer think- I x~1 : but it nm-t not be forgotten that any one can in a moment improvise an instrument better adapted sometime- to the needs of the ease before him than an\ which he could find in the -hop-, and competent for a considerable group of cases. A bit of looking-glass with a hole scratched in its silvering, two or three 171 L72 THE OPHTHALMOSCOPE AND ITS USE. microscope-slides held together in the fingers, or three or four cover-glasses in the end of a splil stick — improvisations of the original Helmholtz-mirror — can reveal the commencing changes at the macula of renal disease which might easily escape the user of the most high-priced ophthalmoscope. But this "weak-light" instrument is an over-refinement for the majority of eases: the condensed illumination of a perforated concave mirror is more generally use- ful, and the brow-mirror of the otologist and laryngologist may revert to its earlier use. when Etuete first employed it for ophthalmoscopy. Yet an instrument designed for wide diversity of ophthalmoscopic work, and convenient in size and construction, is naturally to be preferred. The original ophthalmoscope of Helmholtz is practically unknown to most modern Pig i it. -i >phthalm< scope <.f Helmholtz: the concave s)ia>l>- /; i- sel al the Bide of the handle, ", with di>ks of lenses b) centering at its ■ hole. In front "f this a triangular case projects, car- rying three thin glass plates at an angle of 56 t< i the line of Bight, by means of which the light is reflected ino ■ the i eye. 118 -Loring's ophthalmoscope, with tilting mirror, complete disk of lenses from Lto 8 and to • 7, and supplemental quadrant containing 0. i and L6 D. This affords 66 glasses or combinations from ) 28 to —24 D. oculists, and it- surpassing value in some directions has been eclipsed l>v less cumbersome rival- (Fig. 117). The convex mirror of Zehender, on which the lighl is concentrated l.\ a len-. has as completely passed away, and almost every ophthalmoscopisl of to-day utilizes, with scant or no recognition, the perforated mirror of Ruete. Behind this is generally placed the revolving disk of lenses added by the optician Reko ingle, double, or even treble — and upon these fundamental elements have been rung changes more numer- ous than eonld be here recorded. 8 • of the besl of these arrangements worthy of being credited to the designer we owe to the lamented Dr. Edward < i. Loring. The i lifications of his later instrumenl (Fig. 1 18) are all ques- tionable gains al the cost of undoubted loss, and are almosl as numerous as OPTICAL PRINCIPLES OF THE INSTRUMENT. 17:; the individual users. That of the writer (Fig. 1 I'M aims at unusual com- pleteness of the series of lenses, cylindrical as well as spherical, brought seriatim to the sight-hole withoul removing the instrument from the eye, and boasts a minimum deviation from the dimensions, weight, and balance of the best "Loring." Dr. Edward Jackson's admirable use of slides of lenses (Fig. 120) forms the simplest of "refraction-ophthalmoscopes," most warmly to be commended to the non-expert; while ( Ymper's chain of lenses (Fig. 121) or Morton's modification of it otters a most ingenious solution of the difficulty of bringing a wide series of uncombined glasses close behind the sight-hole of the tilted mirror. For the practitioner who is willing to make but small outlay the simple Liebreich mirror, with its clip to hold its few lenses, will prove fairly satisfactory. Optical Principles of the Instru- ment. — These need concern its user little at first. Rule-of-thumb methods will suffice for the great majority of cases, and the minutue of the dioptrics Fig. 119.— Randall's modified Loring ophthalmoscope, in which the "quadrant" i> moved by tin- <■.>._: below, so that every glass can in- brought to the sight-hole without removing the instrument from the eye. A disk of concave cylinders 0.5 to l. Is eccentrically mounted, so that each can he brought at any desired inclination of its axis into combination with any spherical. Itgives51 spherical lenses or com- binations Tin- mirror can l»- detached to substitute a weak-light, plane, or more concave mirror, or left off, uncovering the 6 mm. breadth of tie- lenses when the instrument is used as an optometer. The disk of cylinders can be left off as drawn, or attached to any firm of ophthalmoscope. of the eye, upon which depend such questions as the amplification of the erect image and the height or depth of objects, involve formula-- from which most oculists shrink. We will consider only the manifest facts, easily ob- served and verified, which go to make up the possibilities and limitations of the instrument, and will consider the refraction and accommodation of the eye only so far as they force themselves upon the attention of the ophthalraoscopist. The eye is a camera obscura, provided with a complex lens-system capable of changing focus and armed with a diaphragm — the iris — which varies the size of it- central opening — the pupil — limiting the amount of light which • ■liter- and the optical imperfections of the image. This pupil generally 174 THE ol'IITUM.Moso )/>/■: a.X/) ITS USE. appears Mack because the light entering it is reflected back, alter partial ab- sorption, in exactly the direction from which it came. As the observer's head i- ii"i generally a source of light, but an obstacle, cutting oil' all illumination from ttiat direction, hiseye receives none of the returning rays. If the pupil be wide, however, and the retinal sur- face less than the focal distance behind it. as i~ common in children and in ani- mals, it i~ not difficult lo obtain a red Fig 120 ' i hthalmoscope, « iili tw<> superposed Blides ol ming Bingly 01 com hlned behind the Bight hole of the tilting mirror. r combinal n to 18 D.. with great convenience, and is exceedingly Bimple and thin Mice naosl other ophthalmoscopes, the i licate concave glasses, and white t" murk convex, makii combinations unlikely. i ( ouper's ophthalmoscope, wit □ i ndless chain coming singly close bt ric tilting mirror, which rotates i left when tin left eye is to be examined, in '"" - modification the lenses are free in the i in i. and moved by the sprocket acting below. h 71 hind i the Moi 1 1 ;m reflex from within the eye. Ophthalmoscopy aims to secure uniformly this result, by bo reflecting a beam of light that the observer's eye is always in position to receive the returning rays, and not only tool. tain a diffused glare from the pupil, but to see numberless details within. For this a number DIR1AT METHOD OF OI>l ITI 1 A LMOSf < >l> ) 175 of optical conditions have to be met, depending not only upon the refraction of the eye in general, bul upon that of the observed eye in particular, and involving- even the conditions of the observer's eye. To these we first must turn. By the law of the conjugate foci of lenses, light from within the illumi- nated eve emerges in parallel rays it' the eye be emmetropic, divergent if hyperopic, convergent if it be myopic. To make such rays furnish a clear image of the interior two methods are in vogue, and various optical apparatus is needful for each. The simpler method is known as the "direct/' or that of the "upright image," in contrast to the "indirect," which gives an " inverted image." Direct Method of Ophthalmoscopy. — In this method the mirror is placed before the observer's eye, so as to throw light through the pupil of the observed eye, and the two are brought close together ( Fig. 122). If the ob- served eye be emmetropic, parallel rays pass from it into the observer's, and if this be also emmetropic, a clear image is obtained without further aid. If B" "B" Fig. 122.— Diagram of the direct method with the formation of an upright image: rays from the source ^'". etc., according to the distance of projection. the observed eye be hyperopic, myopia or accommodation in the observing eye may neutralize it and permit of seeing clearly ; if not exactly thus adjusted, a convex lens must be introduced to render parallel the divergent rays. If, on the contrary, the eye be myopic, the observer must employ a concave glass to Wring the convergent rays to parallelism, unless himself hyperopic enough to be focussed for such convergence. 'Thus it is requi- site that there shall be a series of concave and convex lenses at command, which may be skilfully used as required in order to afford clear views in all conditions of refraction. But this, while inconvenient in some respects, constitutes one of the great advantages of the direct method ; for the lens thus required to give a sharp image of the retinal details becomes, under proper conditions, the measure oj the ametropia. That this should be accurate assumes thai the observer must be emmetropic or allow for his error of refraction, and make no accommodative effort that would change it from this basis. The lens thus used musl be prop erly placed before the observed eye. It ought to be about 13 mm. from the cornea, at the anterior focus of the lens-system, and it should be tilted little if 176 THE OPHTHALMOSCOPE AND ITS USE. at all, since thi< has a distorting effect. The ophthalmoscope should be so constructed as to givea considerable series of glasses coming seriatim to the sight-hole, which should nol be too small nor tunnel-like from thickness of the instrumenl ; ami a> the \\gh\ must be taken from the side <>t' the patient's head, the mirror should incline in the needed direction, leaving the rest of thi' ophthalmoscope straight. fhc tidd of view open to the direct method is never larger than the pupil, and grows steadily smaller as one draws farther away from the ob- served eye. So the advantage of a dilated pupil is evident : although an expert can approach SO close, locate so well the image presented, and pro- ceeding from it to each other desired part of the eye-ground, can build up from thi- -cries of glimpses so satisfactory a mosaic, that he may explore with ease through a •"'> mm. pupil when a tyro might find difficulty even were the pupil dilated to f 25—30 em., and the emerging ray-, unless already strongly convergent, are intercepted with tlic convex leu- held some 5 cm. in front, so that they are brought to a focus near by. Here a real inverted image is formed in the air (Fig. 123), and thi-. ami not the eye-ground it-elf, i- studied by the observer, generally with the help of a convex lens to magnify it. The principle is the same as that of tin- compound microscope, while the direct method is like the use of a simple leu-, the lens-system of the observed eye serving to magnify all the details of it- own interior. The myopic observer may often dispense with any mag- nifier back of hi- minor, and if the observed eye he very myopic, it forms the requisite image Dear enough in front to obviate the need for an object- glass. Here, then, the mere c ;ave mirror may serve all needs, and in circumstances where the satisfactory nse of the direct method i- very difficult. In thi- method i h depends upon the clearness of the object-lens held Dear the observed eye; and one of ample size and of material, like pebble, 1 The cupping "i glaucoma was mistaken for prominence by the earlier observers. MENSURATION OF FUND US-DE TAILS. 177 not easily scratched, has distinct advantage. A protecting mounting is often useful. The reflection from the pole of the cornea is Less troublesome than when contrasted with the weaker illumination of the direct method ; but the reflections from the front and hack surfaces of the objective Lens compel a little tilting of it to throw them out of the way. An element of astigmatic distortion is thus introduced which must be allowed for. A round optic disk may be made to appear oval, the longer diameter corresponding with the least inclined diameter of the lens. When the eye is astigmatic a similar distortion of the disk appears, which may be modified by tilting the lens ; hut irrespective of this, to-and-fro movement of the lens corrects and reverses the apparent lengthening of the nerve-head, ■which reveals whether it is anatomically or only optically elongated. Fig. 123.— Diagram of the indirect method Riving an inverted image : rays from the source of light L, converged toward the observed eye Obd by the concave mirror M, are intercepted by the leni- (>hj, and after coming to a focus diverge again and fight up the fundus. From a part of the illuminated fundus A B rays pass out of the pupil to be again intercepted by the lens O and form an inverted real image at its anterior focus A' B'. This real image is viewed by "the observer's eye behind the sight-hole of tfie mirror with the aid of a magnifying-lens Oc, and is seen enlarged, as at A'' B". Size of the Image and Mensuration of Fundus-Details. — The problems as to the amplifications afforded by the upright and by the inverted image and the mensuration of objects in the fundus are complex and varia- ble. Even in the " reduced eye" many other factors must be determined in order to permit of precise statement of the result. Suffice it here to say that in the emmetropic eye the upright image, when projected to 10 inches, is about sixteen-fold the linear size of the retinal surface seen ; and an optic disk 1.5 mm. in diameter will seem 24 mm. broad when projected to 25 cm. An easy test of this is to hold a quarter-dollar or shilling before the one eye while the other views the disk, and find the point where the images seem of equal size : this distance will vary little from 10 inches. In hyperopia the enlargement is less, in myopia more, the myopic eve having virtually an extra magnifying lens in it as contrasted with the emmetropic, and still more the hyperopia The indirect method affords about one-third as much amplification as the direct, increasing as the object-glass is weakened and the ocular strengthened. Hence myopia gives smaller and hyperopia larger images by this method. Another interesting point, still more practical, is the mensuration of the axial lengthening or shortening as afforded by prominence- or depressions of the eye-ground. Having determined the refraction at the general retinal level, the ability (aside from astigmatic condition-) to see some object with stronger convex or weaker concave Lenses marks its protrusion above that level, and the following table shows the amount of elevation calculated for the "reduced emmetropic eye:" 12 ITS THE OPHTHALMOSCOPE AND ITS USE. Lengthening or Shortening of the Eye in Axial Ametropia (Landolt). Myopia. Iiur Axial Length. ii\ peropia. Decri Axial length 22.824 () 22.824 0.5 0.16 22.98 0.5 0.16 22.67 1 0.32 23.1 1 1 0.31 22.51 2 • 2 0.62 22.20 3 1.01 23.83 3 0.92 21.90 4 1.37 24,19 4 1.21 21.61 5 1.74 24.56 5 1.50 21.32 . 2.52 25.34 6 1.7(3 21.06 10 3.80 ■luy.i 7 2.03 20.79 15 6.28 29.10 8 2.28 20.54 20 9.31 32.13 10 2.78 20.04 < >n the contrary, the need of stronger concave or weaker convex lenses to bring the objecl sharply to view demonstrates its depression below the general level, as also shown in the table. The prominence of a swollen optic nerve- head or of a tumor-mass may thus be measured, and comparison will show the variations of it- advance or recession. So, too, a glaucomatous or other cupping of the nerve or the staphylomatous bulging in a coloboma may be exactly determined, when at first glance it may have seemed doubtful whether the ill-focussed surface was raised or depressed. The same table holds ap- proximately for general conditions of axial shortening or lengthening, with the proviso that emmetropia (or any other refraction) may exist with different axial lengths it' only the power of the refractive media be adjusted to such lengths. The axis of 23.8 nun., which may be assumed for the average adult emmetropic eye, has grown from some 16 mm. in infancy; and while a diopter or so of congenital hyperopia may possibly have been outgrown, the eye may be said to have changed its length and its refraction exactly pari "passu? As the other diameter- of the globe are generally approxi- mately the same as the axis, and the corneal diameter i- about one-half as great, a correction can lie thus gained, perhaps, when in an eye not show- ing typically myopic of hyperopic deformity we wish to estimate from the refraction it- exact length and the position of objects not on the retinal level within, as may he desired in case of operation for the removal of a foreign body in the vitreous. (See also page 201.) The mensuration of objects or distances on or near the retinal level can generally best lie given in terms of the cardinal object- there presented for comparison — e.g. "broad a- the retinal vein,*' ''two disk-diameters out," etc. The actual size can easily he then estimated with a- close approxima- tion a- would he possible with the complicated apparatus devised for actual measurement. Examination of the Media. — Previous to the employment of either method of examination of the fundus it is generally advisable to investigate the media lying in front of it both by focussed incident light (oblique illumi- nation, see page I 16) ami by transmitted light. For the latter it suffices to illuminate the eye with the concave mirror from eighl or ten inches away, when any opacity in cornea, lens, or vitreous will appear as a dark silhouette against the reddish background. Magnifica- tion of tin- by a convex leu- behind the mirror enhance- the delicacy of the test, and often brings to view minute details otherwise invisible. Beginning .-it some 25 cm. away with a I I >. lens, the surgeon can study each eye, I tot 1 1 looking straighl forward and in oblique positions ; and then, approaching closer and using stronger leu-.-. In- can focus at will upon the cornea, lens- 1 Randal] : / \n„,. Ophih. Soc, v. 1890, p. 657. .1 UTO-OPHTHALMOSCOPY. 179 layers, anterior or posterior capsule, or the various depths of the vitreous, until at the closest range the strongest available amplification may be utilized. Foreign bodies escaping every other effort at their detection are thus readily seen, and opacities or vascularities of the cornea form striking objects. The preliminary observation from a distance has a great advantage also in the determination of refractive errors, for little or no eye-ground detail comes sharply to view, except in hyperopia or marked myopia : in the latter. slight movement of the eye or head will show that the image is inverted. Irregularities of refraction also become thus readily manifest, flattened facets left by loss of substance appearing like blisters in a window-pane to distort the detail- seen through them and give the image as in high hyperopia. The condition known as (tonicity of the cornea or lens may thus appear to give a dark center or surrounding zone, although the tissues be perfectly trans- parent ; and if the observer draw back a meter or more and use a long-focus or plane mirror, every eye will give shadows in the pupil with slight rotations of the mirror, and the method becomes what is known as the shadow-test or retinoscopy, our most delicate means of estimating the refraction (see page 202). Notable differences of eye-ground level are conspicuous when studied from a distance of 20 or 30 cm., and this constitutes the best way of studying detachments of the retina, vitreous opacities, and intraocular tumors. Admirable, too, is this method for learning the position of opacities, since the movements of the eye are about a fixed center of rotation back of the pos- terior pole of the lens ; and every visible object anterior to this will seem to move in the direction of the gaze, and everything posterior in the opposite direction, the rapidity and extent of the excursion indicating by parallax its distance from that center. Auto-ophthalmoscopy. — A word may also be said as to auto-ophthal- moscopy, although its value is limited. Several methods may be employed, but the simplest is that of Coccius, to hold the plane skiascopy-mirror be- tween the eye and the shaded light, so that the light falls into the pupil through the ample sight-hole, while the emergent rays are caught by the margin of the opening and reflected back to the macula (Fig- 124). Upon the Fig. 12-t. — To illustrate auto-ophthalmosi dark background behind the lamp the observer will then project the image of the small illuminated area, and with a little care the disk can be found and studied and the vessels followed out a long way in any direction except close to the macula. The picture is not a mere suggestion, like the Purkinje image, but can be drawn in good detail ; and he who i- working up eye- ground sketches, and has no other model at hand, can thus often freshen his impressions of form or color at the momenl when he most needs them. The inability to see the macular vessels is compensated by the endoscopic methods of bringing them into view (Fig. 134), either by the convex mirror of Avres or the pin-hole of Mandcl~tainm. Illumination is, first and last, the most important element of success in all these measures. A steady and ample source of li-ht of fairly uniform lso THE OPHTHALMOSCOPE AND ITS USE. color is therefore essential. Daylight is undoubtedly the truest illumination under which to study conditions where faint gradations of color arc at times all-important ; yet even within the hours when it is obtainable it varies greatly in any consultation room. It> use may be ignored except as a matter of curiosity or in some leukemic conditions, when it may be noteworthy if the fundus look- as yellow under it as the normal eye doe- by Lamplight. An Argand gas-burner, so mounted upon a hinged bracket or an adjustable stand that it may be shifted to any desirable position, is almost always ob- tainable or may be substituted by any good oil lamp. A second chimney, of glass or isinglass, will shut off much radiant heat from the observer, and still more from the patient nearer by ; while an opaque chimney of iron or asbes- tos with a vertically oval opening about 3 to 5 cm. will be found useful in restricting the light to the desired direction, leaving everything else in shadow. With this precaution the ophthalmoscopic room need not be very dark, although strong rays of daylight should be excluded by shutters or -hade- ; and it i- very well to have several blackish surfaces conveniently placed to form fixation points for the patient's gaze during examination. The eyes may be thus kept steady, while the dark surface affords nothing to call forth accommodative strain or pupillary contraction. Either of these may prove serious obstacles to some of our measures, and it is worthy of much care to avoid them. The test and glare are trying even to well eyes, and must be mercifully and judiciously tempered for over-sensitive eases if we would obtain full suc- cess and avoid actual injury. Here the use of the plane or weak-light mirror may have decided value, or the reduction of the light by turning it down or narrowing the aperture through which it shines. If gas-fixtures are used, it is very desirable to so arrange them that the light may be near the patient or the observer a- desired, and with a range of 4 to (i m. for skiascopy — a need best met by having a bracket at each end of the room, one being also used for illumination of the test-type. It is inadvisable to have the light too close to the patient, and much heat reflected by the mirror and directly radiated from the flame may be -pared him by putting the burner a foot or more back of his head. It is important, too, that the light shall be as nearly as possible behind the head, so as to avoid needless rotation of the mirror; but it must not he cut olf by the patient's head when the macula or temporal retina is being studied. It will be found that if it is far enough to the side to illumi- nate the lid-margins at the outer canthus, it will meet all conditions. Mode- rate tilting of the mirror will then suffice to throw the light into the eye. and the instrument can be brought so close that it touches the brow and eyelashes of the patient without having the light (ait off. Position of Surgeon and Patient. — One of the cardinal errors of the beginner is in not getting close enough : the field of view is thus rest rieted, the corneal reflex more disturbing, and refractive errors unduly distorting or blurring to the detail-. In highly ametropic eves great differences in the required lens depend upon its distance from the anterior focal point of the eyi — some 13 nun. from the corneal pole; and in high myopia a satisfactory view can sometimes be obtained only when the observer's brow is actually touching that .if the patient. This presupposes the condition, essential in in- --t cases, that the observer use hi- right eye for the patient's right and hold the ophthalmoscope in hi- right hand, and nice rcrsu. The convenience, or even the possibility, of doing this depends in part upon the seating of patient and observer, and the face-to-face position usual abroad i- nut at all the best. It is better that the observer's chair should be POSITIOX OF si' IK ; EOS ASD VATIEST. 181 close beside the patient's, with the scats fully overlapping; and then, unless very discrepant in height, each may -it erect and at ease. A child is often of better height standing by the ophthalmoscopies seat, and, on the other hand, satisfactory studies can be most hastily made when the observer stands bv the sitting or standing patient. If the light be on a swinging bracket, it can be instantly swung from one side to the other, while the ophthalmoscopic transfers himself and his seat to thai side for the study of that eye. Each will learn the position most satisfactory to himself, and habitually adopt it. but a constrained pose is to be deprecated as imperilling accuracy and thoroughness. Children often tend to nod forward if quiet, or, on the con- trary, to wriggle and turn, so as to need some steadying : the free hand may do good service, therefore, in lightly grasping the occiput, while the thumb rests in the concha, controlling any rotation (Figs. 125, 126). Limited by the pupil into which it is thrown, the beam of light utilized Fig. 125.— Position of examiner and patient for direct ophthalmoscopy, with seats overlapping ;nil>strr<>rs. Reflections. — To the beginner these are very annoying. He hardb approaches sufficiently close to the eye. hi- fundus-illumination i- rarely the best, and the brilliant comealreflex seems to occupy mosl of the pupillary sj and frequently is regarded as the whitish optic disk for which he is instructed first to look. In a narrow pupil thi- reflection from the cornea (and to an 182 THE OPHTHALMOSCOPE AND ITS USE. extent generally unperceived those also from the fro nt and back surfaces of the lens] is ever an obstacle which the expert cannot wholly ignore, and may at times find insurmountable. Generally he can look to the inner side of it or through its margin, and approach so near that its perception is slight. A small sight-hole also reduces its annoyance by increasing the fundus- illuminatioD and cutting off some of the ray- reflected from the cornea. Reflections are present at all the boundaries between the media, but only those upon the retina are apt to be noticed when not specially sought. In childhood, particularly, the whole retina is often covered, especially along the larger vessels, with shimmering, " watered-silk" reflections, which shift with each motion of the mirror, and by the reversed direction of their movement -how that they are formed by concave surfaces where the prominence over the vessels passes into the general retinal level. Of the same nature is the more definite reflex-streak parallel to the nasal side of the disk, to which be the same OUl its local [ can use l lie hweinitz). I'M. 126 Position ol i icaminerand patient for indirect ophthalmoscopy: the seating can as for < t the examiner sits a foot or more away, holds theobjeel Lens at al distance In front oi thi obsi i • ■ 'I i y< teadying ii by resting the other fingers on the face, am ■ ye and band, without change of the lamp, to examine either eye of the patient (De Sc Weiss has called attention as being prodromal of myopia (see page 187, Fig. 132), and the bright streak so-called light-reflex) always to be seen along the retinal vessels, especially the arteries, has been thus explained. In the macular region a halo can often be -ecu by the indirect method, generally horizontally oval, and having a diameter two or more times that oi the disk. Thi- i- less easily -ecu in the upright image, unless a strongly concave mirror be used ; and unless the ring of reflecting mirror just around the sight-hole be centered exactly with the pupil, only a portion of it will be visible. So, too, as to the little reflection from the fovea centralis, which is apt to be crescentic or coi a-shaped unless the mirror is exactly centered. Then the tiny concavity reflects the entire ring of brightness surrounding the night-hole, while the 'enter of its floor gives back a central point of light. Like ino-t retinal reflections, these are besl seen when the surface is a little beyond the focus, and are more apt to aid than disturb, since they serve to locate the points deserving minute scrutiny, and arc lost as the retinal struc- t Hi.- are precisely ft icussed. LOCATION OF OPACITIES. 183 Opacities of the Media. — These are al times prohibitory of study of what lies beyond them, ami unless their presence and character be perceived they may prove very harassing or misleading by suggesting partial obscuration of the fundus details, retinal lesions, or refractive errors. I >i it due employmenl of focal illumination and the lighting of the fundus from a little distance will rarely fail to reveal the real difficulty and serve to locate it exactly. Againsl the red field of the illuminated pupil every such opacity will show dark in proportion to its lack of transparency : with a magnifying lens behind the mirror most minute and faint objects may he discerned readily. Not only real opacities, hut also irregularities of surface, such as conicity of the cornea or lens, flattened facets, or plications a- of the capsule, can be thus revealed, and the resultant impairment of vision correctly interpreted. Most difficult of all are the cases of turbidity of the media, since there are often no formed elements to give definition to the opacity, which merely obscures the view. Where the aqueous humor is at fault the altered appearance of the iris often furnishes the clue; but a discolored lens or a turbid vitreous can at times puzzle the most expert and permit of diagnosis only by exclusion. Location of Opacities. — This is of frequent importance. When far hack near the retina the anterior position of opacities can generally be appreciated, if not estimated, by parallax, as compared with the movement of the retinal vessels ; hut the expert easily measures in the erect image by the interposition of convex lenses how much forward an object lies. Near emmetropia each diopter gives a difference of 0.3 mm. — theoretically increasing to the myopic side, decreasing in hyperopia (e. g. + 6 D. 1.77 mm. ; — 6 D. = 2.13 mm., Nagel). Anterior opacities, on the other hand, are generally referred to the pupillary margin, and by their motion relative to it in movements of the eye their distance hack or front is determined. The center of corneal curva- ture, which is near the posterior pole of the lens, may also he used, as pointed out by Jackson : the image of the mirror can always be seen in the line of this point, and any motion in reference to it determined. As previously stated, the rotation-center of the globe is the cardinal point of reference (p. 17!'). Refractive Errors. — These can markedly complicate the diagnosis it' the observer be not well posted. It is often surprising how much can he discerned in an unfocussed eye-ground, not only when hyperopia allows a clear view of details from a distance <>r to an observer who does not relax his accommo- dation, hut even when considerable myopia or astigmatism precludes sharp- ness of definition. To the indirect method these case- offer small difficulty: moving the objective lens a little to or from the eye compensates for large axial variations, while a little tilting of it make- or correct- astigmatism as great as is often met. Yet even to the direct method more is revealed than might he expected, and careful focussing is called for to decide whether all the distortion or blur present is really due to the refractive error. Much anatomical anomaly or pathological lesion can he concealed by the imper- fection of the view; and minor changes in nerve, choroid, and retina are thus habitually passed over unseen or ignored by ophthalmoscopists of long ex- perience. The habit of sketching tin- findings in the examinations ha- here one of it- prime functions ; and the use of stereotyped forms on which to till in detail- is to he condemned, at leasl for the beginner. Each drawing, how- ever rude and imperfect, should portray with all possible precision the apparent form of the disk, the trend of its vessels, and the condition- of its margins ; since the minute observation here called for may prove unexpectedly valuable in these very cases, and begets an exactness of perception essential \s\ THE OPHTHALMOSCOPE AND ITS USE. and invaluable both in refraction-measurement and in the clinical observation of diseased conditions. Differences of Level in the Eye-ground. — These are always to be ex- pected. The normal disk lias a prominence which justifies its name of papilla, although its center is often excavated nearly to the level of the cribriform lamina. The excentric location of the disk commonly exaggerates the greater protrusion of the nasal side, and its major vessels are decidedly prominent. This promi- nence may be much increased by edema and inflammatory infiltration, while the lower level of the outer margin and adjacent posterior pole grows deeper with the atrophic changes and stretching of " posterior staphyloma." This phrase, like that of "conns," is often employed as to conditions not strictly fulfilling its primary meaning; but the opposite view, that bulging at this point due to inflammatory softening does not take place, meets daily refuta- tion. These points must always be taken into consideration, not only in relation to the present refraction of the eye, but also as to its past and future. In the direct examination, then, we measure the direction of the rays of light, which, emerging from the observed eye, form u sharp image on the observer's retina. But this relation is affected by the observer's refraction as well as the patient's. Only upon an emmetropic eye will parallel rays be exactly focussed ; and any interposed lens needed to make sharp the image measures the momentary ametropia of the patient ± that of the observer. But it is only the refraction at the moment which is measured, and this may be very far from the static refraction which we desire. The ophthalmoscopist must learn what is his true static refraction, and as far as possible relax always to this condition. The author believes every one can learn so to do, although fatigue, headache, or improper conditions will at times preclude util- ization of the faculty. If the examiner does not, any fixed allowance for his unrelaxed accommodation is so utterly vague as to be of little value. Those who habitually use mydriatics to the total paralysis of accommodation, and accept in their measurements nothing as "near enough" to right which can possibly he improved upon, learn that total relaxation and total paralysis are identical in almost all eases, and that the "tone" of accommodation of which Ponders wrote decreases under scrutiny to the vanishing-point. The Normal Fundus. — The prime feature and landmark of the eye- ground is the nerve-head, with its branching central artery and vein. This lie- some 15° to the nasal side, and a little higher than the posterior pole of the globe, and appears ;i> a whitish disk from which the vessels ramify in the fundus (Fig. 127). It is surrounded by the red choroid, which usually defines sharply it- margin ; and the frequenl massing of choroid pigment here may give ;i gray or black edge, which is occasionally half as broad as the disk. The opening through the choroid is normally smaller than that of the sclera, and hides all trace of tin-; hut at time-, without recognizable absorption of the choroid or its pigment, a ring of white scleral tissue (scleral ring) can be -^m, partial or complete, within the choroidal ring. (See Plate 1.) Consisting of the nerve-fibers which enter to the retinal level and then disperse, the disk often presents :i slight prominence or papilla, in the center of which the diverging tissues forma porus <>j)/i<-ns. This may be incon- spicuous, especially in early life; hut i- ;it time- both wide and deep, one edge or perhaps all steep or overhanging, while pari of it i> usually shelving. The mos! conspicuous feature is the group of branching vessels. Both artery and vein may come to tin' summil of the papilla before dividing, but com- monly both branch in the bottom of the porvs, while occasionally only the Plate i The normal fundus. THE NORMAL FUNDUS. 185 subdivisions in bewildering number emerge from the nerve-head. Little difficulty should be experienced in distinguishing the broader, darker veins with their crimson tint from the scarlet arteries, which arc near the color of the background ; but the smaller branches differ less until they cease to be differentiable. On the larger veins and on all the arteries distinguishable as such, a bright streak of reflection ("light-reflex") marks the central convex- ity and shifts slightly with variations of the light. The branching is usually dichotomous, giving an upper and a Lowerartery, which again divides into a temporal and a nasal branch, while the veins /•VV- ;_ - Fio. 127.— Normal optic nerve-head, as seen with the ophthalmoscope and in section under the micro- scope, each x 15 diameters. The slight papillary elevation, with its central porus, the central vessels, and the beginning of their ramification in the flher-layer of the retina, the sharp-cu1 margin of retinal and choroidal pigmentation outlining the disk and slightly emphasized as a choroid ring, are well shown. prcs,. lit fair parallelism. Small vessels, not always visibly arising from the central, generally pass outward toward the macula ; and at this margin especially, independent cilio-retinal vessels, not always of small size, are fre- quently met. The branches pass from the disk with sinuous curving sweep, as a rule, and with slowly diminishing caliber extend toward the periphery. On the disk, especially as they curve down into the excavation, the veins often present visible pulsation, and in rarer cases of disproportionate pressure the arteries also empty and fill, particularly in glaucoma ; crossing and entwining of vein and artery are com n (Figs. 128, 129), bul it i- extremely rare for L86 THE OPHTHALMOSCOPE AND TTS USE. vein to cross vein, or artery artery. Anastomosis of the vessels, almost always on the disk, is also of the raresl occurrence (Fig. L30). Entwined retinal vessels. Twisting of a retinal vein around the accompanying artery on their way to the region supplied is not unusual— generally about the margin of the disk: such a ■ •f an artery, as the superior temporal in (1), is rarer, as is also the' recurrent turnof the upper nil vein to twist around the upper nasal artery in (2). The rear limit of the nerve-head i- the eribrifoivn lamina, at which the optic nerve-fibers lose their sheaths ami enter the eye as naked axis-cvlinders. Pig tnosing veins and aberrant artery. This varies in depth, bul can generally be distinguished, especially at the porus; :md a deep excavation generally has as it- bottom this mottled sieve-tissue. Till: .XOh'MM. I CXI) IS. 187 *?« I 1 1 K ^0ut l>\ a dlio-retinal vessel arising at the edge of the disk from the short ciliary vessels or communicating with the choroidal system (Fig. Fig. 135.— Choroido-retinal aberrant artery. L35). Tortuosity of vessels may be mere exaggeration of their normal sinu- osities ; hut at times, especially in strained hyperopic eves, they may have the marked curves, vertical a< well as lateral, usual in neuro-retinitis. Single loops may lie across the disk or adjacent retina (Fig. 136) or protrude into the vitreous, or the single strand of the persistent hyaloid artery, generally devoid of hi I. extends forward, in rare instances reaching or branching upon the po-tcrior capsule of the lens. Small cystic outgrowths, especially to the nasal side, may mark a more atrophic stage of its condition (Figs. 137, 138). Pio 181 'I tortuoiu \. i''i'.. 187. Persistent hyaloid artery. Supernumerary depressions of the disk with emerging vessels ar< casion- ally Been : more often there is a colobomatous gap, due to incomplete closure CONGENITAL ANOMALIES. 191 of the fetal cleft. This, which is normally open l>ut for the sixth or seventh week, may be held open, probably by intra-uterine inflammation, and give rise to most various and extreme malformations. The disk may be alone coloboma- tous and -how a depression, oftenesl downward, of dark aspect and apparently Fig. 138.— Cystic outgrowth on disk. Fig. 139.— Fibrous outgrowth on disk. immeasurable depth (Fig. 140), or the white sheath may be plainly seen beneath the gap. Sometimes the sheath alone is involved, and the disk, superficially normal, shows a peculiar greenish coloration near one margin that can be traced into its depths. Oftener the choroid shows a defect, usually downward, at times Fig. 110.— Coloboma of nerve and sheath. involving nerve and sheath, and perhaps extending broadly as far forward as can be seen (Fig. 141), while coloboma of iris or lens, or both, mark- the greater extension (in time as well as area). Difficult of explanation are those rarer cases in which the defecl is outward, inward, or even upward, where the fetal deft can hardly be supposed to have had influence. Gap of the retina alone, true persistence of the fetal cleft itself, has hardly ever been 192 THE OPHTHALMOSCOPE AND TTS USE. described: some representative of retinal structure is usually present, when perhaps not even a vessel marks choroidal tissue, and the lack or stretching of scleral tissue forms a considerable staphylomatous concavity. Areas of defed at or near the macula (Fig. 1 1_) are probably not related to the fetal cleft, latt mark mere atrophy and non-development resulting from fetal in- flammation — a process that may leave strands, knobs, or falciform folds of membrane protruding into the vitreous chamber, and is doubtless responsible tor the persistence or perversion of most of that for which the faulty pre- natal development is held accountable. Fig. 141.— Huge coloboma of choroid, involving the nerve-head and extending to iris. ('mnis was the name early given to the atrophic choroidal changes at the nerve-margin, which s etimes present a form suggestive of a cone. Oftener it i- a crescent embracing the outer half of the disk — at times the nasal or other margin — in some cases annular, though generally broadest out. With this is generally associated an ectasia or staphyloma posticum, due to coincident atrophy or yielding of the sclera. Noted at first exclusively with myopia, many writers have denied the kin-hip of the crescents seen in other refractive conditions ; and there is little doubt that several groups of condi- tions ought to he differentiated, just a- there are high myopias in the illit- erate who sclera] insertion has general or only occasional truth, the crescent most commonly begins at the outer margin as a region of altered color, Fig. 142.— Coloboma of macula. doubtless inflammatory. Pigment is absorbed, to be deposited in most eases at the outer margin of the crescent, and as the atrophy advances the area increases in size, usually by the demarkation of another crescent beyond. Fig. 143.— Distorted myopic disk with scleral ring, atrophic and semiatrophlc conus, aberrant arter; Three or four ere-eent- al once may be thus shown in one eye in different stages of atrophic change. Rarely the process retrogrades and n cre» i nl of altered color return- to the normal. Actual development of a large myopic 13 1!>4 THE ol'IlTHAI.Moscori; a\/> its USE. crescent may never have been fully observed, lor in most cases it and the advance of the myopic stretching can he stopped by atropine and alterative tonics : and some of us feel that our lull duty has not been done in a case that Fig. 144.— Underlying conus below, up to emergence of vessels. does progress. Yet clinical study has been long and extended, and definite enough to bridge any gaps and show the usual identity of the processes; and strong anatomical evidence to the contrary could alone disprove it. Pig. 1 15.— Retained marrow Bheatta ; huge ana Burrounding disk. Probably another matter i- presented l>v the condition called "congenital conus?' tl conus downward" or "underlying conus." It has the form of a crescenl of whitish color, apparently extending in inula- the margin of the nerve, generally below, although also noted in or nut or at times even above. It i- probably akin to coloboma of the nerve-sheath, although not merging < 'ONG EN1 T. {LA NOM. I LIES. 195 into this condition, seeming to underlie the upper layers of the nerve-head and to extend in at time- as far as the central vessels. Most like the "scleral ring-." normally or morbidly revealed, it yet presents recognizable differences, which seems to mark dissimilarity of nature. Where it is marked, full acute- ness of vision can rarely be attained ; and the usual presence of notable astigmatism and the frequency of aberrant vessels passing through it point to it as a congenita] delect (Fig. 144). An interesting anomaly, sometimes most striking in appearance, is fur- nished by marrow-sheaths on the retinal fibers. Enstead of being lost outside of the hi mi mi, these elements are met in patches at or near the disk, of white fringed aspect, partly burying the retinal vessels under their opacity. The Fig. 146.— Small isolated marrow-sheath patch up and out near macula. rule in the rabbit and other animals, this is an exception in man, and may constitute a huge broadening of the blind spot (Fig. 145). If extensive, they are apt to extend outward in the line of the major upper and lower temporal vessels, forming a crescentic white patch, within which the macula is seen decentered out. At the nerve they are apt to overlie the margin and to cast a greenish shadow inward ; which is, of course, more marked if there be any atrophy of the nerve. They may easily be mistaken for snowy patches oi' infiltration, such as the "snow-banks" of albuminuric or other retinitis, although generally far more fibrillar in their snowy whiteness; but the dif- ferentiation is not easy when they form small isolated patches unconnected with the disk (Fig. 146). Vision, except in the broadened blind -pot, may be absolutely unaffected (see also p. 472j. METHODS OF DETERMINING THE REFRACTION OF THE EYE: OPHTHALMOMETRY; OPHTHALMOSCOPY, SKIASCOPY, OPTOMETRY; THE USE OP MYDRIATICS. By EDWARD JACKSON, A.M., M. D., OF rilll.AKKI.I'III \. Ophthalmometry, more properly called Keratometry, is the measure- ment nt' the curvature of the cornea and the astigmatism due to the differences in that curvature in different directions. The ophthalmometer consists essen- tially of a telescope furnished, in connection with its object-lens, with some arrangemenl for doubling the images formed by it. In the ophthalmometer of Helmholtz and that of Leroy and Dubois this doubling is effected by covering one-half of the object-lens by a piece of plate glass inclined in one direction, and the other half with a piece inclined in the opposite direction. The separation of the two images produced by this arrangement is the same at whatever distance the object is placed. In the ophthalmometer of Java! and Schiotz the doubling is effected by a double prism, and the separation of the two images is only constant at a con- stant distance. To make sure that the images formed by the instrument shall always have this constant distance cross-hairs are placed within the barrel of the tele-cope. In using the instrument these cross-hairs must be in focus when the images are fociissed ; that is, the images must be formed at the plane of the cross-hairs. To effeel this the eye-piece is so adjusted as to accurately focus the cross-hairs for the observer's eve, and then the images are focussed by moving the telescope to or from the eye under examination until they become distinct with the cross-hairs. The curvaturt <>i Hi< cornea is measured by determining how large an object i- required to give a reflection from the cornea just equal to the separa- tion of the doubled images. Knowing the size of the object, the size of its reflected image, and the distance of the object from the eye, the radius of curvature of the cornea i- ascertained by a simple calculation. With the ophthalmometer of .(aval — to which alone, as of most practical value, we -hall refer -the distance of the object i- always practically the same. It is deter- mined by the distance from which the image of the corneal reflection will be f ' i 1 1 1 < < I at t he cr< '---hair-. The size of the corneal reflection i- also constant, being the extent to which the doubling prism separates the two images at the con-taut distance. This being the case, the size of the object and the curvature (or radius of curva- ture) of tin' cornea are inversely proportioned to one another, so that a scale can be calculated upon which a certain size of object will correspond to a METHOD OF USING THE OPHTH A LM< >M ETEB. 197 certain radius of curvature of the cornea. Such a scale lias been calculated and laid off upon the arm of the ophthalmometer. Along with it is placed a scale of diopters of refracting power, corresponding in an average eve to the different lengths of the radius of corneal curvature. The instrument is shown in Fig. 147. The most striking part of it is the great metal disk which shades the surgeon from the light, and has on it- margin figures to indicate the direction in which the arm is turned. Through the center of this disk projects the telescope, and just below it the arm, placed horizontally, is shown, with the two mires upon it, the fixed mire to the ri<>4it, the movable mire to the left. On the right of the picture is the head-rest, with adjustable chin-support, and four electric lamps attached to illuminate the mires when good daylight from a space of open sky is not available. The telescope is mounted in a collar which allows it to be freely revolved on its Fig. 147.— Javal-Schiotz ophthalmometer. axis, carrying with it the graduated arm and mires, allowing the curvature to be measured in any meridian of the cornea. Unimportant variation- as to the disk (which is in some models omitted), form of arm, method of illum- inating, etc are suggested by different writers, but the essential features of the instrument are those above indicated. Method of Using the Ophthalmometer. — To use the ophthalmome- ter the instrument should be placed where strong light will fall upon the mires. The patient's face, which should be in comparative shadow, is placed in the head-rest, one eye covered with a metal shade and the other directed into the barrel of the telescope. The surgeon, glancing along the telescope, sees that it is turned toward the patient's eye. Then by the large s< pa-sing through one foot of the tripod he adjusts the height of the tele-cope, and by moving the whole tripod back and forth focusses the corneal in] within the instrument. What he sees is the doubled reflection of the disk and mires, one image of each mire | A and B, Fig. 1 18) being close togi ther. The movable mire is then shifted back or forth along the arm until the cA^c 198 DETERMINING THE REFRACTION OF THE EYE. of its central image just touches the edge of the central image of the other mire (1, Fig. L49). It will be noticed thai each mire is crossed by a black line parallel to the arm. If the cornea is astigmatic, these lines on the adjoining images of the two mires appear continuous only when the arm is turned in the direction of on,- of the principal meridians of astigmatism. In other positions they seem relatively displaced. The telescope is now rotated on its axis until the direc- tion of the arm i- found in which the lines on the two mires correspond. The mire- are then broughi so that their images are quite accurately in con- tact, and the index on the movable mire indicates upon the scale on the arm the radius ,,f curvature of the cornea, and corresponding refraction in one of the principal meridians. The tele-cope i- next rotated until the arm stands at right angles to its former position. If astigmatism be present, it will be found that in this position the mires either separate or overlap. If they overlap, as in Fig. 149, Pigs, i 18, 1 19.— Mires or targets of ophthalmometer. 3, the number of steps of overlapping indicates the number of diopters of astigmatism. If in this second position the mires separate, as in 12, Fig. 149, they must again be broughi in contact and then rotated hack to the former direction, in which they will now overlap and so indicate the amount of astigmatism. If during the examination the patient looks away from the telescope, so tli.it some portion of the cornea other than the center is presented, the refrac- tion of this other pari of the cornea will he indicated, differing, perhaps greatly, from thai of the central portion of the cornea. Commonly, the first position in which the mires are broughi in contact will he with the arm horizontal. Bui if it is found that in this position the black line- upon them do not correspond, do not come opposite one another, the instrument musi be rotated either way until these become continuous one with the other. The position of the patient during the examination should he made as comfortable as possible by having the heighl of the instrumenl or of the patient's chair freely adjustable, and the examination musi he completed quickly before the patienl ha- become tired or restless. Ophthalmometry is of special value in cases of aphakia. In other cases the corneal astigmatism which it gives suggests approximately the meridians and amount of the total astigma- tism. Objective Methods for the Measurement of Refraction. — Rays of lighi to he focussed on the retina musi enter the eye with a certain degree of divergence or convergence tor each degree of ametropia. Rays coming THE OPHTHALMOSCOPE— DIRECT METHOD. 199 from any point of the retina and passing oul of the rye travel the same paths in the opposite direction, and Leave the eye correspondingly convergent or divergent. The retraction of the eve may be determined l>v ascertaining what divergence or convergence must be given to rays in order that they shall be focussed on the retina. Methods that do this arc subjective methods for meas- uring refraction. Or we may take the rays from the retina and ascertain the degree of convergence or divergence which they have <>n emerging from the eye. Methods of doing this arc objective methods for the determination of refraction. The Ophthalmoscope. — 1. The Direct Method. — The retina of the patient being illuminated by the ophthalmoscope, rays proceeding from it enter the eye of the surgeon and are focussed on his retina. If the surgeon is emmetropic parallel rays will be focussed on his retina, and the lens necessary to focus there the rays coming from the patient's retina is the lens necessary to make those rays parallel — i. e. the lens which corrects the patient's ametropia. To determine which lens does this the surgeon watches the finest visible details of the fundus of the patient's eye. When the focussing is imperfect, these details are blurred ; when perfect, they are seen clearly. Suppose a case of hyperopia, illustrated in Fig. 150, in which P represents the eye of the Fig. 150. — Eye of patient and surgeon measuring H. patient, and S the eye of the surgeon. The rays from the patient's retina leave his eye divergent, and are directed to focus back of the surgeon'- retina. By trial the convex lens, L, is found, which, rendering the rays parallel (see the dotted lines), causes them to be focussed on the surgeon's retina. This lens, L, which renders parallel the rays coming out of the patient's eye, is the correcting lens, the lens which Mould make parallel rays from some distant object convergent enough to focus them upon the patient's retina. i- ii,. l.i- Rays in myopia. In myopia (illustrated in Fig. 151 i the rays emerge from the patient's eye convergent. A concave lens, /,, i- required to render them parallel, so that they can be focussed on the surgeon's retina ; and this concave lens is the cor- 200 DETERMINING THE REFRACTION OF Till-: EYE. recting lens which, placed in the same position, would render the parallel rays coming from some distanl objecl sufficiently divergent to be focussed on the patient'- retina. [f the patient's eye is emmetropic, the rays emerge from it parallel, and require no lens to secure their perfect focussing upon the surgeon's retina. What has been said of other forms of ametropia holds for regular astig- matism : only the ametropia differs in different meridians, and its correction in any one meridian affects the distinctness of lines in the fundus running- at right angles to that meridian. Thus in an eye where the hyperopia in the horizontal meridian requires a 1 D. convex lens for its correction, and the hyperopia in the vertical meridian requires a 21). convex lens for its correc- tion, the I 1 >. convex lens renders clear the vessels which run horizontally, and a 2 I >. convex lens i- required to render clear the vertical vessels; the difference between the two lenses, 1 I)., is the amount of astigmatism present. In the practical use of the ophthalmoscope to measure retraction the chief difficulty is due to the influence of accommodation in the eye of either the patient or the surgeon. In any case the effect of accommodation is the same as the effect of a convex lens, partly correcting hyperopia and diminishing its apparent amount ; or adding to myopia, and to that extent increasing its appa- rent amount. Accommodation in the surgeon's eye is guarded against by practice. Yet always in young eyes, particularly when tired or irritated, there i< a chance of some accommodation being present. In the patient's eye accommodation is reduced to the minimum by making the ophthalmoscopic examination in a thoroughly dark room of sufficient size, with the gaze fixed on blank space to encourage the complete relaxation of the ciliary muscle. Using these precautions, the influence of accommodation is still to l>e guarded against by choosing, as most nearly correct, the strongest convex or the weakesl concave lens with which the details of the fundus are clearly visible. In determining astigmatism one should first seek the strongest convex or weakesl concave lens with which the vessels running in any one direction are still clearly -ecu. This lens will give the hyperopia or myopia present in the meridian at right angle- to those vessels. These vessels run in one of the principal meridians of astigmatism, the other being at right angles to this. Having determined the direction of the meridians and the lens required by one of them, the next point i- to find what lens renders clear the vessels run- ning at righl angles to those seen clearly with the first lens. The difference between the two lenses gives the degree of astigmatism. A not In r source of error in measuring refraction with the ophthalmoscope Hi- in the differences in the refractii f the same eye through different parts of the dioptric media. Thu- the refraction at the centre is never the same a- the refraction at the margin of the widely-dilated pupil, [n some eyes without ;i mydriatic the pupil dilated in the dark room shows a very different refraction at it- margin from that ai it- center. The refraction at the center of the pupil is commonly what i- of importance, and the error which might occur by measuring refraction through the edge of the pupil must l>e guarded against. \jain. the refracti f the eye varies at different part- of the retina. In a perfectly spherical eye the refraction at the macula is least hyperopic or most myopic. The refraction of the anterior parts of the retina and choroid may be highly hyperopic, even in eye- quite myopic at the macula. Then, too, the depth of the fundus may vary in other ways, a- from posterior staphyloma or cupping or swelling of the optic nerve entrance. THE OPHTHALMOSCOPE— INDIRECT MEZlHOp. 201 It is therefore important to select for the measurement of refraction the details «>t' a certain part of the fundus, generally as Dear the macula as pos- sible. For astigmatism the examiner should take as test lines the vessels run- ning from the disk to the macula, with their lateral branches. The large vessels as they pass upward and downward from the optic disk are particularly liable t<> protrude into the vitreous, and thus give an appearance of* astigma- tism when none is really present. The pigment-layer of the retina and the vessels are usually the parts the retraction of which is measured; but the attention may be fixed upon anv other detail seen within the eye. In glaucoma the refraction of* the bottom of the cup may be compared with the refraction at the margin of the cup, or in optic neuritis the summit of the swelling may have its refraction compared with that of the retina beyond the swelling. J5y its refraction the surgeon may seek to locate an opacity in the vitreous. The distances in front of the plane of emmetropia indicated by a certain hyperopia, and the distances behind that plane indicated by an equal myopia, are shown in the following table, calculated for the average eye, hav- ing an antero-posterior axis of 22.824 mm. (see also page ITS). iopters. H. Diminution. M. Increase. Diopters. H. Diminution. M. Increase 1 0.31 0.32 7 2.ii:; 2.52 •j 0.62 0.66 8 2.28 2.93 3 0.92 1.01 9 2.53 3.35 4 1.21 1.37 10 2.78 3.80 5 1.50 1.74 15 3.91 6.28 6 1.76 2.13 20 4.90 9.31 2. Indirect Method. — In using the ophthalmoscope by the indirect method rays coming from the retina are focussed by the object lens to form a real inverted image between that lens and the surgeon's eye. When they emerge from the eye parallel, this image is formed at the principal focus of the object lens. When they emerge divergent, as in hyperopia, the image in- formed farther from the lens. When they emerge convergent, as in myopia, it is formed close to the lens. By ascertaining the exact distance of the image from the object lens one may determine the refraction of the eye. This has been attempted by placing a screen where the inverted image is most distinct, and measuring its distance from the object lens, but this method is not of practical value. A modification of this, the Schrrridt-JRimpler method, instead of the screen has a source of light of peculiar form, enabling the surgeon to judge when it i- accurately focussed. To use it the object lens is placed exactly its focal distance from the principal plane of the eye, and by trial the surgeon finds what distance the ophthalmoscopic mirror must be held from the lens to give the most distinct view of the image of the source of light upon the fundus. This is obtained when the focus of the mirror coincide- with the focus of the object lens; and a scale attached to the lens gives for each position of this image the amount of hyperopia or myopia to which it corresponds. Fig. 152 represents the course of the rays in this method, the solid lines indicating the rays reflected from the ophthalmoscopic mirror and entering the eye. and the broken lines, the rays coming from the patient's retina to the eye of the surgeon. By the indirect method the nearer to the eye the object lens is held the -mailer i- the inverted image in myopia, and the larger it i- in hyperopia. The change of size due to the change of distant 1' the lens in froni of the patient's eye varies with the degree of ametropia. Hence the presence and kind of ametropia of high degree can be recognized by varying the dis- 202 DETERMINING THE REFRACTION OF THE EYE. tance of the lens from the eye. In hyperopia the withdrawal of the lens from the eve make- the image smaller, in myopia it makes it larger. la PlG. 152.- Course of rays in Schmidt-Rimpler's method. astigmatism such withdrawal makes the disk relatively larger in the direction of the meridian of greatest refraction, and relatively smaller in the meridian of least refraction. This change in the form of the disk is an evidence of astigmatism, most noticeable in high mixed astigmatism. Skiascopy ; Retinoscopy ; The Shadow-test. — The method of de- termining refraction with the ophthalmoscope by the position of the inverted image is of little practical value, because of the difficulty of ascertaining the exact position of that image and its nearness to the eye. Skiascopy is essen- tially a method of determining the distance of the inverted image from the pa- tient's eve with great accuracy. Fig. 153 represents an eye in front of which Fig. 153.— Eye with convex lens placed before it. i- placed a convex lens, causing the rays from a point, /'. of the retina to he focussed at /.' .• tin- lens, L, may he regarded as composed of two lenses, // and //' — // strong enough t<> render parallel the rays emerging from the eye, and L" able to take parallel ray- and focus them at /.'. By subtracting tin- strength of /." from that of L. it i- easy to get //, the correcting lens. Suppose L to have a strength of 5 JD., and R to be 1 m. (the focal distance of a I I>. lens) from /,. /." will be I D.. and 5 — 1 I D., the strength of V required to a irrecl the byper< >pia. The strength of /," to he deducted from t li.it of /, is found by determining the distance of /•' from the leu-, h. Fig, 154, representing the patient's eye (myopic) focussing the rays from .1 nt C and from /»' at />. it will he noticed that if tie- Burgeon's eye be placed m .Y. nearer the patient's eye than D } the ray reaching it fr I comes through the upper part of the pupil, so that .1 will appear al a in that direction, lint if the surgeon's eye he placed at .V, beyond C />. the point .1 will appear to he located in the lower part of SKIASCOPY; Iti: n.Xoscoi'Y; THE SHADOW-TEST. 203 the pupil inward a', the ray from .1 reaching the surgeon's eye from that direction. In the same way, from N, B will appear in the lower pari of the pupil, and from .Y\ in the upper part of the pupil. Fig. 154. — Showing how the rays cross, and so change their relative positions at the plane of reversal, I> < '. This reversal in the apparent position of any given points of the retina occurs at the distance of Cand D. Closer to the eye the point really above appears above ; the retina is seen in an erect image. Farther from the eye, the point really above appears below, and the point really below appears above; the retina is seen in the inverted image. The change from the erect to the inverted image occurs at the point for which the patient's eye is focussed, either by its own myopic refraction or a lens placed before it ; which point is, therefore, called the point of reverse/. The position of the point of reversal is determined with practical accuracy by observing the apparent direction of movement of light and shade in the pupil. The light is thrown on the eye with a mirror, usually a special form of the ophthalmoscope mirror, which may be either plane or concave. If plane, it should have a small sight-hole, 2 or 2^ mm. in diameter, with its margin free from reflections. By turning the mirror slightly in different directions the light reflected from it on the patient's face, and also the portion entering his eye and falling on the retina, are made to move correspondingly. The movement of light and shade as it appears in the pupil is now watched. When the apparent movement is in the same direction as the real movement of the light on the retina, the erect image is being watched, and the surgeon's eye must be inside of the point of reversal, as at N (Fig. 154). When the apparent movement in the pupil is the opposite of the real movement of light on the retina, an inverted image is being watched and the surgeon's eye is beyond the point of reversal, as at X'. By studying these opposite move- ments on the two sides of the point of reversal that point is located. With a certain movement of the mirror there is always the same move- ment of the light on the face whether the mirror be plane or concave. Thus, when the mirror is made to face upward the light moves upward across the patient's face. If the mirror is turned down, the light moves down across the patient's face. With the plane mirror the light on the retina always moves in the same direction as the light on the fact — in the same direction, or with the mirror. Willi the concave mirror the light on the retina always moves in the direction opposite to that of the light on the face — always moves against the mirror (Fig. loo). The reason for this is that with the plane mirror the light enters the eye as though coining from an image (called the immediate source of light) as far behind the mirror :i- the real or original source is in front; but with the concave mirror the immediate source — the point from which the light seems to come to the eye — is a small inverted image of the original soura of light, formed in fronl ol the mirror. Hence, with the plane mirror, if the lighl in the pupil appear- to move vilh the mirror — with the lighl on the fact — the surgeon know- that the point 204 DETERMINING THE REFRACTION OF THE EYE. of reversal is not between him and the patient. But when, with the same mirror, the apparenl movement of light in the pupil is against the mirror — in the opposite direction to the movement of light <>n the fact — ho knows that the point <>t' reversal is between him and the patient — that he is beyond the point of reversal and looking at the inverted image. ( >n the other hand, when with the concave mirror the Light in the pupil appears to move with the mirror — with the light on the face — the surgeon knows that this is the opposite of the real movement of light pn the patient's retina, and that, there- fore, he is watching an inverted image. But if with the concave mirror the light in the pupil appears to move against the mirror — against the light on the face — knowing this to be the direction of the real movement of light on Fig. 155.— Course of rays in skiascopy with concave mirror: A A, one position of mirror giving imme- diate source of light at I, and illuminating retina toward a ; i: />'. another position of mirror with imme- diate source of light at /'. and retina illuminated toward b, the retina, he knows he is watching an erect image, the point of reversal being somewhere behind him. Rate of Movement, Form, and Brightness of the Light-area. — Besides the direction of the movement of light and shadow, the brightness and form and rate of movement of the illuminated area in the pupil are of practical importance. At the point of reversal a single point of the retina appears to occupy the whole area of the pupil. As the point of reversal is departed from, more and more of the retina is >cvn in the pupil. Hence, near to the point of reversal a slight movement of the light-area on the retina will appear to carry the light entirely across the pupil — the light and shadow move in the pupil swiftly. But at a greater distance from the point of reversal they move slower. The apparent form of the light-area in the pupil is also modified by the nearness of the surgeon to the point of reversal. The actual form of the light-area on the retina is commonly circular. This circle appears greatly magnified when the surgeon is near the point of reversal, and only a >mail pan of its margin can be seen in the pupil at one time, the boundary between lighl and shade appearing al st a straight line. While faraway from the point of reversal, especially if the surgeon be near the pupil, the whole area of retinal illumination may be seen in the pupil as a complete circle. More important -till in determining the apparent form of the light-area are regular astigmatism, alienation, and irregular astigmatism, to be presently con- sidered. The brightness of the light-area in the pupil depend- on the concentration of the lioht thrown into the eye and the extent to which the retina is magni- fied. The immediate Bource of lighl being commonly near the mirror, the light i- most concentrated on the retina when the mirror is held near the point of reversal. Bui just al the point of reversal the magnification of the PRACTICAL APPLICATION OF SKIASCOPY. retina makes the illumination appear feeble, so thai the brighesl area of light in the pupil is obtained about 1 or '1 D. from the point of reversal. Practical Application of Skiascopy. — The room should be thor- oughly darkened, and the source of light shaded with an opaque chimney having a circular opening opposite the brightest part of the flame. For the plane mirror the source of light should be so arranged that it can be brought quite close to the mirror and moved with the mirror to or from the patient's eye, and the opening in the shade should be 5 or 10 mm. in diameter. For the concave mirror the flame is to be hack of the patient's head. generally as far from the mirror as possible; and if a .-hade is used, the opening should be 10 to 20 mm. in diameter. When not otherwise stated, the following description refers to skiascopy with the plane mirror. It may be applied to the concave mirror by reversing the significance of the direction of movement of the light in the pupil : 1. Hyperopia. — Without a lens the light moves across the pupil with the light on the face. The convex lens, L (Fig. 153), strong enough to overcome the hyperopia and to give a point of reversal. R, is placed before the eye. The surgeon, then varying his distance from the patient's eye, tries the move- ment of light and shadow alternately from within R, where the movement is with, and from beyond R, where the movement is against, the light on the face. The position of the point of reversal is thus determined. Its distance from the patient's eye is then measured or estimated. This is the focal dis- tance of the over-correcting effect of the lens L, which over-correcting effect, subtracted from the whole strength of the lens, leaves the strength required to correct the hyperopia. Suppose a 5 D. convex lens placed before the eye gives movement with the light on the face at 20 in. (51 cm.), and against the light on the face at 30 in. (76 cm.), the point of reversal taken as midway is at about the focal distance of a 1.5 diopter lens; the over-correcting effect of theoD. lens equals 5. - 1.5 = 3.5 D. — the strength of the lens required to correct the hyperopia. In making the final determination of the refraction, if the freedom of the eye from astigmatism and aberration allows the movement of light and shadow to be easily watched at a greater distance, a weaker lens, giving a point of reversal farther from the eye. may be used. But if there be much irregular astigmatism or aberration, the determination can be more correctly made with a point of reversal still closer to the eye. 2. Myopia. — From the myopic eye the rays emerge already convergent to meet in a point of reversal that can lie determined without the use of any lens, except in myopia of very low degree. Commonly, however, it i- too close to the eye for accuracy, and a concave lens partly correcting the myopia should lie placed before the eye, and the remaining myopia measured ami added to the strength of the concave lens for the total myopia. F<»r example, in a case of myopia of 10 P.. a concave 9 D. lens being placed before the eve, the point of reversal i- round at 1 in. This corresponds to myopia of 1 1>.. whirl'], added to '.» I>., the strength of the lens, gives L0 D., the total myopia. In the case ot \.rv low myopia, as only 0.25 !>.. a convex 1 1 >. lens i- placed before the eye, and the point of reversal found in this case at ::i in. (78.5 cm.), indicating 1.25D. ot' myopia. From this, by subtracting 1 D., the strength of tin- lens, we gel 0.25D., the myopia originally present. :;. Emmetropia \- shown when the convex lens placed befor* a point ot' reversal jusi at it- focal distance. 206 DETERMINING THE REFRACTION OF THE EYE. 1. Regular Astigmatism. — In regular astigmatism the ray- coming from the retina emerge from the cornea with different degrees of divergence or convergence in different meridians. For the two principal meridians there are. therefore, always the two separate points of reversal, their distance apart indicating the amounl of astigmatism. When in such an eve a point of reversal is found, it is soon discovered that it is a point of reversal only for the movement in one direction. The surgeon's eye, placed at this point, sees the retina magnified enormously in the direction of the one meridian, and magnified much less in the other prin- cipal meridian. This makes the light-area in the pupil appear elongated in the direction of the first meridian, giving it a band-like appearance, shown in Fig. 156. To make this hand-like appearance most distinct, the immediate source of light should he at the point of reversal for the other meridian. With the plane Fig. 156.— Band-like appear- m j 1Tor the surgeon must place his eve at the point ance in shadow tesl ° tr ' ' of reversal nearest the eye, where he will get move- ment undistinguishable in one meridian, and with the light on the face in the other. The original source of light is then to be pushed away from the mirror, its reflection (the immediate* source) retreating correspondingly behind the mirror until it reaches the point of reversal for the other principal meridian. The direction of the band-like appearance is to he carefully noted as the direction of the principal meridian of greatest refraction — the direction for the axis of a convex cylinder that would correct the astigmatism. The direction of the other principal meridian, the direction for the axis of a con- cave cylinder to correct the astigmatism, will he at right angles to this. With the concave mirror the surgeon's eye should he placed at the point of reversal that is the farthest from the eye and the original source of light brought closely to the mirror, causing its conjugate image (the immediate source of light) to go farther from the mirror and closer to the patient's eye, until it reaches the nearer point of reversal, and the hand-like appearance appear- mosl distincl in the meridian of least refraction. In this position the hand cannot he seen to move in the direction of its length, but at right angles it also move- with the light on the face. 1 laving determined the direction of the principal meridians of astigmatism, the hyperopia or myopia in each is to he measured separately, just as hyper- opia or myopia would he measured in any other case, with the light as near the plane mirror a- possible or as far away as convenient from the concave mirror. fhe difference of refraction between the two meridians is the amount of astigmatism. When it has been determined, a cylindrical lens correcting it should he placed with the proper spherical lens before the eye, and the tesl applied to ascertain if the correction is really complete. Aberration. — In most eyes the refraction at the edge of the dilated pupil is more myopic or less hyperopic than at the center. In this form, called positivt aberration, the point of reversal for the edge of the pupil i- nearer the eye than the point of reversal for the center, and from the latter point movement of lighi against the light on the face i- to be noticed in the edge ..I' the pupil. This light in the edge is brighter than the light at the center of the pupil, and great care nin-t be taken to avoid error on this account. \\ I h ii the center of the pupil i- the mure myopic it is called negativt aberra- tion, fhe circular distribution of aberration largely determines the shape of SUBJECTIVE METHODS OF TESTING REFRACTION. 207 light and shadow in the pupil, making it more circular when otherwise it would be of different shape, as in regular astigmatism. When aberration is present the point of reversal for the margin of the pupil may be close t<> the surgeon's eye, while the point of reversal for the center is far from it. In this ease the movement of the light in the center of the pupil will be slow, while in the margin it will be swift. The light-area then appears to swing around a fixed center, and assumes an angular shape, shown in Fig. 157. This i- the appearance presented in conical cornea where the cen- ter of the pupil is more myopic than the margin. Irregular Astigmatism. — The differences of re- fraction due to the lens-changes preceding cataract, or the irregularities of the cornea following phlycten- ular keratitis, break up the liffht and shadow in the FlG - 157.— Angular apjpear- ., . . ,, . L , ° „. ance m liiu'li aberration, pupil into small irregular areas, the surgeon must find which of these areas is most likely to be of use for eye-work, and measure the refraction in it. To do this it may be necessary, on account of the small- no- of the area, to come quite close to the patient's eye. Here a small source of light and a small sight-hole in the mirror are of great importance. Subjective Methods of Testing Refraction. — To determine what lens is required to bring perfectly to a focus the rays entering the eye we may resort to tests based upon a single point of light. Thomson's ametrometer consists of two small gas-flames, one fixed and the other movable along a graduated arm, which can be revolved about the first as a center. The dis- tance of the two flames apart when their diffusion-areas appear to just touch each other gives the degree of ametropia in the meridian parallel to the grad- uated arm. Hotz uses two small holes in a disk placed in front of a window or lamp-flame. To the patient having astigmatism each of the points of light so obtained appears elongated, and by turning the disk so that these elongated image- lie in the same line, an index enables the surgeon to read off the direc- tion of the principal meridians of astigmatism. The simple optometer consists essentially of a convex lens which i- placed close to the eye, and a graduated arm extending from it on which moves a card bearing test-type. In emmetropia the type can be seen distinctly only as far as the focal distance of the lens. In hyperopia it i- read to a greater distance, and in myopia only to a lesser distance, corresponding to the degree of the ametropia. Either of the above subjective methods maybe found of service where others are not available; but they are not commonly used, and by the sub- jective method of determining refraction is commonly meant the method with trial-lenses and test-letter-. The trial case contains a sufficient series of spherical and cylindrical lenses, with trial-frames in which they can be placed before the eye, prisms, solid, pin-hole, and -lit disks, and colored glasses. By combining two or more lenses together a very few convex and concave lenses can be made to answer for any case of ametropia, but where many cases are to lie tested con- venience and economy of time demand a fairly complete sel of lens* 5. Hiis may include pair- of convex and concave lenses, with 0.12 P. intervals t<> 1.5 D., 0.25 I), interval- to I I)., and 0.50 I >. interval- to 8 1 >., for both spherical- and cylindrical-. Then for the -pherical-, 1 I >. Intervals to 20 I >.. with, perhaps, 25 D. and 30 D. added. The prisms may run by 1 -centred interval- to 10, with the 12, 15, 2<>, and 30 centred prisms in addition. :><>* DETERMINING THE REFRACTION OF THE EYE. To use the trial-lenses, test-letters suited to the distance adopted are to be hung in a strong light, cither natural or artificial, the latter being preferable because it can be made more uniform. The test-card should always have one or two lines of letters .-mailer than those intended to be read at the distance adopted. Thus for »> in. there should be a line of 5-m. letters. Some pa- tient- have visual acuteness greater than ^. Use of the Trial Case. — The pinhole disk furnishes a ready means of distinguishing between imperfect vision due to ametropia and imperfect vision due to other causes. In the former case the placing the pin-hole opening before the eve lessens the diffusion-areas upon the retina and improves vis- ion ; it' the imperfection of vision is not due to ametropia, the pin-hole disk rather makes it worse. The slit is used in discovering astigmatism of moderate or high degree and the direction of its principal meridians. In astigmatism the diffusion- areas on the retina are wider in the direction of one principal meridian than in the direction of the other. The slit limits them at right angles to its length, but not in the direction of its length. When, therefore, it is placed before the eve, turned in one direction, it cuts down the diffusion-area in its larger dimension, giving the greatest improvement of vision. At right angles to thi< it limits the diffusion-area in the other direction, in which it isalready raosl limited, and gives the least improvement of vision. These directions of the principal meridians of the astigmatism being found, the slit may be turned in the direction of one meridian and spherical lenses tried until one is found correcting the ametropia in this meridian, and giving the best vision obtainable through the slit. The same is done for the other meridian, and in this way the correcting lenses, both spherical and cylindrical, may be deter- mined. This test has practical value as an approximate and confirmatory test. In the ordinary use of test-hnses each eye is tested separately, the other being covered by a solid disk or ground glass. When accommodation is absent the aim is to find the lenses which give the best vision. Some idea of the ametropia is given by previous objective tests and the acuteness of vision without a lens. The concave or convex lens expected to correct it approxi- mately i- placed before the eye and the vision with it noted. Then weak- additional convex or concave lenses are held in the hand in front of this, trying firsl the one, then the other. If the first lens has been convex, and the additional convex spherical further improves vision, a convex lens cor- respondingly stronger i- substituted. The trial is then repeated, and this is continued until a lens is found which can neither be increased nor diminished in strength without lessening the acuteness of vision. If the eye i- free from astigmatism, this is the lens desired ; but to test BUCh freedom from astigmatism cylindrical lenses should be tried. The cylindrical lens is to be held in front of the spherical lens selected, and its ;i\i- turned in different direction-, a- vertical, horizontal, and oblique to the right ami to the left. For this purpose the astigmatic lens, convex in one meridian and equally concave iii the meridian perpendicular thereto, is prefer- able to either the con\c\ . .f concave cylinder. Such astigmatic lenses should be included in the trial case. Having ascertained thai in Borne one direction the cylindrical lens im- proves vision, BUCh a lens LS to be placed in the trial-frame, cither with the spherical lens already there or with one slightly weaker if the cylindrical lens i- of the same kind, or a slightl) stronger if the cylinder is of the opposite kind. Thus, if tl 'iginal spherical lens was 2 !>.. and 1 I >. is the MYDRIATICS. 209 cylinder to be combined with it, the spherical should be changed to 1.5 I >. If it is preferred t<> use a — 1 I), cylinder, the spherical lens should be changed to 2.5 I>. After this the cylinder is to be slightly turned, first t" one side and then to the other, the patient being required to indicate when the turning makes his vision worse. This i> repeated until it is pretty cer- tain just what direction of the cylinder-axis gives the best vision. Then weak convex and concave spherical lenses arc to he tried in front of the combined spherical and cylindrical lenses, to see if either will .-till further improve the vision, and these are followed with the astigmatic lens and a new- trial of the direction for the axis. This routine is to he repeated until any change in any factor of the combination impairs the acuteness of vision. The combination thus arrived at is the correcting lens of the eve for the distance at which the test is made. It' this distance he 4 or (5 m., 0.25 or 0.17 I), must he subtracted from the convex or added to the concave spherical lens to make it the perfect correction for truly parallel rays from more dis- tant objects. The same process is repeated for the second eye. When the power of accommodation is present, the aim must he to find the strongest convex or the weakest concave spherical lens that gives the besl vision. Cylindrical lenses will be tried as above, preferably before attempt- ing the final determination with the spherical lens. The determination of the spherical lens is best effected by testing both eyes at once and beginning with convex lenses that are too strong or concave lenses that are too weak to permit of the best vision. Then, if convex, before removing such glasses the next weaker lenses should be placed before the eyes. In this way what- ever relaxation of accommodation has been secured under the first lenses is preserved. If vision is yet not perfect, a still weaker lens is substituted in the same way, and so on until the best vision of which both eyes are capable is obtained. The eyes are then to be tested separately by covering each of them alter- nately. If it is found that only one eye has attained to its best vision, the lens before the other eye is to be still further weakened until it, too, has obtained its best vision. The lenses thus chosen will be found to correct the total hyperopia in the majority of even young persons. In myopia the spherical lenses are to be made successively stronger, and when the best vision is obtained the eyes are to be toted separately by alter- nate covering. MYDRIATICS. The drugs atropin, duboisin, hyoscyamin, hyoscin, daturin, ami scopol- amin, alkaloid- obtained from members of the Solanacese, and bomatro- pin. a derivative of atropin, constitute the true mydriatic-. Applied to the eye. they produce dilatation of the pupil and paralysis of the accommoda- tion, which after a time, varying with the drug and the amount of it em- ployed, entirely pa— es away. In some cases the dilatation of the pupil is of use in the determination of refraction, since it render- easier the use of the ophthalmoscope, skiascopy, and the test-lenses. But the chief value of these drug- in this connection lies in their action as cycloplegics. By paralyzing the ciliary muscle they eliminate the influence of accommodation. In healthy eye- a -ingle drop of ! of the following solutions is usu- ally sufficient to accomplish this: atropin, 1 : 100, duboisin, hyoscyamin, or scopolamin, 1 : 250. Of homatropin hydrobromate a single drop of even a saturated solution will not paralyze the accommodation. It musl I" used by repeated instillations of a 2 to I per cent* solution at shoii intervals. An) of the other drugs will prove effective in weaker solutions if the instillal 1 1 210 DETERMINING THE REFRACTION OF THE EYE. are repeated. In practice it is customary to prescribe either atropin, dubois- in, or hyoscyamin in solutions of the strength named, to be instilled at the patient's home three times a day for one or more days. The repeated instil- lations are necessary to guard against their possibly imperfect character. Homatropin should be instilled by the surgeon or a trained assistant, and the instillations repeated every five or ten minutes until from four to six have been made ; and after its use the determination of the refraction should be completed within one or two hours, as it often begins to lose its control of the ciliary muscle soon after that time. In the choice of the mydriatic homatropin has the advantage of greater brevity of action. The accommodation completely recovers from its effect, usually within forty-eight hours, while after atropin two or three weeks are required before it is quite recovered, and after the use of the other drugs named from one to two weeks must elapse. Scopolamin, 1 : 500, is an effi- cient mydriatic, u^ed by making two instillations one hour apart. Accommo- dation will completely return in six days. Even weaker solutions may be efficacious. In using these drugs certain alarming intoxicating effects must be borne in mind. While in the amount mentioned most people do not experience these, in exceptional cases a single drop of one of the solutions mentioned, except of homatropin, may cause severe symptoms of intoxication. These are— dryness and redness of the throat and skin, with delirium and inco- ordination of movement, especially inability to walk. The patient is not usually much disturbed, but his friends may be greatly alarmed, although from any such dose these symptoms are quite unattended by danger. On their appearance the use of the drug must be suspended, the patient kept quiet, given water freely, and, if decidedly delirious, small doses of an opiate. Homatropin is much the least likely to produce such symptoms, and duboisin, hyoscyamin, and scopolamin (which may be but different names for the same drug) are the most likely to produce them. In the eyes of a few persons these mydriatics produce marked conjunctival irritation or in- flammation, and the homatropin solutions mentioned always produce a tem- porary hyperemia of the conjunctival and pericorneal vessels during the period of absorption. Cocain, a drug of an entirely different class, possessing little or no power to paralyze the ciliary muscle, may be useful to dilate the pupil in persons over fifty years of age whose pupils are small and whose power of accommo- dation i- not sufficient to interfere with tests for refraction. A single instilla- lion of a 2 pel - cent, solution is followed after thirty minutes or an hour by decided enlargement of the pupil, yet with very little inconvenience and no danger. All drugs which cause dilatation of the pupil, except cocain, are danger- ous in ey<- presenting the essential changes of glaucoma, since they may pro- duce a glaucomatous outbreak, lint if such a revelation of the presence of glaucoma IS promptly met by the proper treatment, it can hardly be regarded a- unfortunate for the patient. No eye in which this accident can occur is likely long to escape glaucoma, and without the mydriatic the advent of this disease mighl lie so insidious as to escape detection until irreparable damage had been done. Whether mydriatics should be used in the great mass of refraction cases is a debated question. That with their use the determination of refraction can be more certainly exact cannot be doubted. The question is as to (1ENERAL PLAN OF EXAMINATION. 211 whether the increased certainty and accuracy are worth the discomfort and loss of time from ordinary occupations that the mydriatic causes. In deciding this question the desires of the patient and the appreciation of exactness in his work on the part of the surgeon will be the determining factors. Table of the DiJ'cmit Mydriatics. u w qi fsolu- monly which utions a no- effect. be ins to e. a o Name of druj; and salt com- 3-p S °e -cgu "32 s?.s jU monly used. >o'3j, ■C o 3 cc ^-~" « 3 XI XI TJ * :-7. elat in ■ con y changes in the choroid, including increased redness, or alteration of color by edema or atrophy ; and, secondary to the changes in the choroid, by opaci- 214 NORMAL AND ABNORMAL REFRACTION. ties in the vitreous and the crystalline lens, and softening of the sclera with local bulging | posterior staphyloma). The progressive changes in refraction, to be discussed under Myopia, arc also symptoms of eye-strain. Acute or chronic conjunctivitis may arise from the same cause. This may amount to a slight exaggeration of the irritation fell when the eyes are tired, or it may develop into a chronic catarrhal con- junctivitis, practically incurable even by removal of the original cause. When the conjunctivitis is severe, corneal disease may be associated with it, and if chronic it is apt to be attended with changes in the lids, marginal blepharitis, styes, etc. Eczema of the lids and neighboring parts has also been ascribed to eye-strain and relieved by wearing glasses. The symptoms manifested outside of the eye and its appendages are — Headache. — This i- often spoken of a- reflex, hut is better regarded as due to aerve-exhaustion. It is commonly frontal, in some cases extending to the occipul or throughout the whole head. Sometimes it is strictly limited to one sid( — hemicrania. It may he directly associated with the use of the eyes, or be apparently constant, or may occur at certain times, apparently not determined by any particular eye-work, and yet in the latter case may be as completely cured by the careful relief of eve-strain as when more evidently connected with eye-work. The headache of eye-strain is not mi generis. It has the same characters a- headache arising from entirely different causes. In many instances it is (tartly due to eye-strain and partly to the other causes. If the other causes can be discovered and removed, it may he cured without the wearing of glasses or any reduction in eye-work. More fre- quently it is cured by the correction of ametropia or faulty habits of using the eyes. Sometimes, when removal of one factor has given temporary relief, hut the headache return-, the discovery and removal of the other factor may be necessary to make the relief permanent. Neuralgic pains in other portions of the body or attacks of migraine may arise from eve-strain. Anorexia, nausea, vomiting, palpitation of the heart, and similar disturbances may he due to eye— train. Nervousness, which the patient -peak- of as an intolerable desire to cry out or do some violent act, Liability to keep quiet after prolonged eye-work, peevishness and irritability of temper, are among its manifestations. For the rarer forms of disturbance the therapeutic test by relief from the -train will be necessary to establish the diagnosis. Eye-strain may cause certain motor disturbances, as twitching of the lids, tonic blepharospasm, and in rare cases choreiform movements or epileptiform seizures, or it may We the most substantial cause of hysterical manifestations. With these, as with headache, eye-strain is usually but one of two or more factors. Hyperopia. — Hyperopia, Hypermetropia, or Far-sightednesSf is the error / I [g i & The course ■ i raya in a hyperopic eye. of refraction which arises when /A* retina is situated in front oj the principal focus of tTu dioptric surfaces. Fig. 158 represents a hyperopic eye able to focus parallel rays at / behind HYPEROPIA. 215 the retina and / the lens which, turning the rays toward r, the virtual "far point" of the eye, causes them to !>e focussed on the retina and corrects the hyperopia. The hyperopic eye is adjusted for convergent rays, and these are not encountered in nature. Without accommodation it sees indistinctly at all distances. By the exertion of accommodation it sees clearly, hut only by the exertion of accommodation exceeding (by the amount of its hyperopia) that required of the emmetropic eye; and, having to use some accommodation constantly, it is deprived of the periods of rest which come to the emmetropic eye when tixed on distant objects. The greater amount of accommodation required of it causes the hyperopic eye to sutler earlier from the diminution of accommodation by age, and afterward the further loss of accommodation deprives it of distinct distant vision. We have from hyperopia Liability to eye-strain and indistinctness of vision, either of which may become an indica- tion for correction of the defect by convex lenses. Causes, Varieties, and Course. — Hyperopia is due in the majority of cases to antero-posterior shortening of the eyeball, axial hyperopia. This is caused not so often by a flattening of the globe as by a diminution in all its diameters. The other causes for it are — flattening of the curvature of the cornea or crystalline lens, hyperopia of curvature, and removal of the crys- talline lens (accidental or operative), or its congenital absence or dislocation — aphakial hyperopia. It is possible to conceive also of hyperopia due to a low index of refraction of the crystalline lens — index-hyperopia. At birth nearly all eyes are hyperopic. It is possible that during the first years of life there is some general tendency for hyperopia to diminish, although this is not proven (see p. 178). On the other hand, from early adult life to old age there is a general tendency for hyperopia to slowly increase, due to the gradual increase in size of the crystalline lens. As Priestley Smith has shown, the lens, like other structures of epithelial origin, continues to increase so long as it continues healthy, increasing one-third in bulk between twenty-five and sixty-five years of age. Increase in the size of the lens, supposing it to keep the same shape, causes an equal increase in its focal distance and a correspond- ing increase of hyperopia. This is independent of the apparent Increase due to the failure of accommodation, and continues after all power of accommoda- tion has been lost. The varieties of hyperopia recognized in practical work arc based on the relations of hyperopia to the accommodation. They can lie best illustrated by an example: Suppose a case of hyperopia of 1<> I>. in which the total accommodation is only . of accommodation which can lie relaxed or exerted, and which, therefore, can lie used t" COrrecl an equal amount of hyperopia, but which hyperopia can be left uncorrected at will. This part of the hyperopia which can be corrected or not by the accom- modation is called facultative hyperopia. The absolute hyperopia and the facultative, added together, give the manifest hyperopia. The mai hyperopia, with the latent hyperopia, together constitute the total hyperopia. 216 NORMAL AND ABNORMAL REFRACTION The relations of these different varieties or parts of the hyperopia may be better understood bv the following diagram : Total accommodation. Involuntary V Voluntary A. Latenl II. Facultative II. Absolute 1 [. Manifest 1 1. Total hyperopia. The subject may be -till further illustrated by considering whal happens when successive convex lenses are placed before an eye with ;i hyperopia of I" D., and a total accommodation <>f 8 I >. Without any lens the vision of -ucli an eve is imperfect. A weak convex lens improves it, and the im- provement continues as the strength of the lens is increased up to '1 I)., which correct- the absolute hyperopia, and. with all the power of accommo- dation added to it, focusses parallel rays on the retina, giving good distant vision. A- the convex lens is made stronger the vision i> not further im- proved, hut the best vision is obtained with less exertion of accommodation. Thus, with a 1 I >. lens it is necessary to exert only !i D. of accommodation, and with a 7 I ). lens only •'> I >. of accommodation. 'Phis continues until all the manifest hyperopia i- corrected by an 8 D. lens, the vision remaining clear with only 2 1 ). of accommodation. If, however, a still stronger lens is placed before the eye, the accommodation being able to relax no farther, the 2 I), of aeco odation, plus the leu-, gives an over-correction, blurring dis- tant vision. The portion of the accommodation which cannot be relaxed has been indicated in the above diagram as involuntary, and the part that can be relaxed or exerted at will is voluntary accommodation. By the use of a mydriatic the total accommodation, both voluntary and involuntary, is relaxed and the total hyperopia revealed. A-bsolute hyperopia only occurs after the power of accommodation for objects at a distance from the eye has fallen below the amount of hyperopia. In early life it i- only seen in hyperopia of the highest degree. After middle age, the power of accommodation being lost, it appears in all hyperopic eves, and when the accommodation is entirely gone all hyperopia is absolute. Latent hyperopia may not he present. Many persons with strong accommo- dation are able to relax it entirely when looking at distant objects through convex lenses. In other eyes it i- constantly present, and in still others is presenl only part of the time. The inability to relax the accommodation is often spoken of as spasm oj accommodation. Such spasm is most likely to or. ai i' w hen the eye- a re irritated or fatigued. The facultative hyperopia, lying between the latent and the absolute, varies with these, decreasing as either of them increases, and on the whole tending to diminish with age along with the diminishing accommodation. In measuring refraction without a mydriatic the important point is to get as much of the hyperopia manifest as possible, and to do this the two eye- must be tested toe-ether, as recommended on page 209. Willi reference to these dill'eivnt varietio it i- essentia] always to hear in mind ihat their relations to each other are not fixed — thai there is no constant ratio between the manifest and the latent hyperopia at any particular age or for the individual. The proportion- may vary from day to day, <>r even from minute to minute. Symptoms. — Since hyperopia may be corrected by accommodation, only the highest degrees give rise to symptoms in early childhood. The earliest symptom is convergent squint, arising with the effort of accommodation. This HYPEROPIA. Ill effort being great, the nervous impulse overflows, causing additional muscular contraction- in muscles closely associated with that of accommodation, and especially excessive contraction of the internal recti muscles. Convergenl squint of this kind is apt to begin before six years of age, and is mosl commonly associated with hyperopia of high, but not the highest, degree. Squint occurs where the hyperopia can be corrected by greal exertion of the accommodation. When this is too difficult imperfect vision is accepted. Such imperfect vision may be noticed by a careful observer in early childhood, but commonly is not detected until the child begins to read. It is then found that to increase the size of the imperfect retinal images the book is held very close to the eyes, as in myopia. This practice in early childhood quite as frequently indicates high hyperopia. ruder the influence of school-work lower grades of the delect begin to cause eye-strain. This often shows itself in local congestion and inflammation of the conjunctiva and lids, conjunctivitis, styes, photophobia, and frequent winking on account of the conjunctival irritation. In later childhood begins the liability to headache ; young children rarely complain of ocular headache. During school-life even the lower grades of hyperopia are liable to cause eye- strain, but afterward, most eyes being used to better advantage and not being so severely taxed, the low degrees of defect are less likely to cause trouble, although headaches established during childhood may be continued, and periods of poor health may cause the development of eye-strain. As the time approaches when even emmetropic eyes sutler from presbyopia, hyperopic eyes manifest the same symptoms earlier, in proportion to the degree of hyperopia. These symptoms are — failure of the vision for near-work, particularly in the latter part of the day or when tired or working by poor light : print has to be held farther from the eyes in order to be read, and conjunctival irritation and inflammation again occur, often in repeated acute attacks that are ascribed to "cold." Still later, as the power of accommo- dation falls so low that it can no longer correct the hyperopia, indistinctness of vision is developed. Treatment. — While any departure of the refraction of the eye from the emmetropic standard constitutes an error or an anomaly of refraction, it- is only when under the conditions of work imposed upon the eye such an error or anomaly causes interference with vision or strain, that the refraction is to be considered abnormal. Treatment, therefore, is not indicated by the mere existence of hyperopia, but by the fact that the hyperopia has caused symp- toms, or is likely to cause them, under conditions of work to which the eyes are about to be subjected. Many hyperopic eyes, therefore, do not require the aid of correcting lenses, but when symptoms arise that may with prob- ability be ascribed in part to this error of refraction the correcting lenses should be used. How they are to be determined lias been sufficiently indicated in the pre- ceding section (page IDS). The general rule should be to give the full correction — that is, the lens which makes the hyperopic eye similar to the emmetropic eye, enabling it to focus parallel rays on the retina without any exertion of accommodation, and to focus divergent rays with the least effort of accommodation. To this general ride certain objections are offered which inn-t he carefully considered, and certain exception- W llich must he recognized. It i- urged that if some eyes continue normal with uncorrected hyperopia, other- may continue normal with their hyperopia but partly corrected, and that the ride should lie to give the weake-t glass thai will allow the USC of the eye- with comfort. But it is impossible, except by trial, to know that 218 NORMAL AND ABNORMAL BEFRACTLON. any incomplete correction will be sufficient in the particular case. The full correction promises the greatest degree <>r the greatest probability of relief after the eye has once become accustomed to it. The inconvenience <>f wear- ing glasses is the same with a partial as with a full correction ; therefore, if the patient must wear glasses at all, he oughl to have from them the greatest benefit or the greatest certainty of benefit obtainable. The second objection to divine the full correcting lens is that if a portion of the hyperopia is latent — and it is often incorrectly assumed that this is so in nearly all cases — the wearing of the lull correction renders distant vision indistinct. If the latent part of the hyperopia were a fixed amount, this objection would have more practical weight. As it is, one cannot correct the manifest hyperopia of to-day and be sure that the same lens will not over- correct it to-morrow. As long as latent hyperopia is allowed it will vary, and. at certain times, lead to blurring of distant vision unless a very wide margin is left for such variation. On the other hand, it is only necessary to wear constantly the full correcting lenses to render the total hyperopia mani- fest. Sometimes this is accomplished in a few minutes or a few days; in other cases it may take week.-, but if the glasses are a true correction and are steadily worn, it can always he brought about. This manifestation of total hyperopia is doubted by some ophthalmologists, partly because of the failure of patients to wear their glasses constantly or always to look through them when worn, hut chiefly on account of the inaccuracy of supposing that the correcting leu- for a limited distance, 15 or 20 feet, is a true correction for greater distances. Such a lens causes a very perceptible blurring at greater distances, very annoying to persons accustomed to distinct vision, and never to be overcome by any amount of persistence in wearing glasses. The person who under a mydriatic sees perfectly at 4 m. with a 1 I), convex lens never will see perfectly at a longer distance with that lens — never will accept such a leu- with satisfaction, not because of any "spasm of accommodation," but because it is not his correcting lens for parallel rays ; it is 0.25 D. too strong. (See also page 209.) A third objection is that even if finally accepted the full correction is harder to becom< accustomed to than a partial correction. This seems plausible, but experience indicates that it is not the case unless the partial correction i- so incomplete a- to give a very diminished assistance to the eye. It appears to be easier for an eye to learn to relax its accommodation entirely than to learn the new partial relaxation that a partial correction of the hyper- opia renders necessary. Some surgeons claim it is best to arrive at full cor- rection by successively increasing partial corrections, due full correction may at first cause the greater trouble, but this is at its maximum during the first two up three day-, and after that it rapidly diminishes ; it is certainly less in the aggregate than is entailed l>\ ;i series of increasingly stronger glasses, which, moreover, cause greater expense. The wearing of correcting lenses should be constant. This should be the rule iii hyperopia, although not so essential as in myopia and astig- matism. Some indication- ;i- to the constancy with which glasses should be woin may be drawn from the symptoms. Headache, particularly if continu- ous or occurring without apparent connection with any particular use of the eyes, is very much more likely to be relieved when the lenses are worn con- tinuously. The -at in' i- true of chronic conjunctivitis and marginal blepharitis and of inflammatory change- within the eye. Where there is headache or irritation directly following special use of the eyes, a- in reading or sewing, which quickly passes away when -iieh eye-work i- suspended, it i- likely that MYOPIA. 219 relief will be afforded by using the correcting lenses only during the periods of such work. It is often necessary to have the glasses worn continually at first, until the headache or chronic inflammation has been entirely cured and the eyes have learned the habit of relaxing accommodative effort when not working. After this it may be quite enough to use the glasses only when the accommo- dation will he especially taxed. Again, many children have trouble from hyperopia, requiring the use of correcting lenses during school-life, who, when they leave school, can lav aside glasses and continue free from any symptoms of eye-strain. Exceptions to the prescribing of a full correction are made — first, in young persons with good accommodation and high degrees of hyperopia and with comparatively trifling symptoms, occurring only when the eyes are especially taxed; second, in cases in which it is impossible to persuade the patient to submit to some present inconvenience in the hope of future benefit. Under these circumstances the only thing to do is to give a very incomplete correc- tion at first and increase the strength of the lenses slightly at short intervals. Patients who take this attitude are generally in a position to bear the increased expense, and if it is explained that the first glasses are only for temporary use and are to be changed after short intervals, perhaps changed several times at such intervals, the partial correction may be resorted to. Deficiency of convergence or marked exophoria may also be considered as an indication for not completely correcting hyperopia. In cases of convergent squint the constant wearing of the full correction is always to be tried. Apart from the wearing of correcting lenses, there is no treatment for hyperopia ; but the symptoms that arise from it may be relieved by diminished use of the eyes, especially for near work, or by im- provement of general health, and by the influences and remedies that bring it about. Myopia.— Myopia, Brachymetropia, Short-sight, or Near-sightedness, is the error of refraction existing when the retina is situated hack of the principal focus of tin- dioptric surfaces, and rays of light to be focussrd upon if must enter flu eye divergent from some comparatively near point. Fig. 159 represents a myopic eye focussing parallel rays at/in the vitreous, / Fig. 159. — The course of rays in a myopic eye. and requiring the lens /, which will cause them to diverge from /■, the far point of the eye, in order that they shall be focussed on the retina. Causes, Tendency, and Varieties. — Myopia may occur as the result of a simple congenital tendency to the formation of too Ion- an eyeball or too great curvature of its dioptric surfaces, but the great mass of myopic eyes must be regarded as pathological. They exhibit distinct, and often very grave, Lesions of the ocular tissues, to which the myopia may lie secondary, but which it tends to aggravate. The sclera i- distended by a normal intraocular pressure of 25 or 30 mm. of mercury. This pressure preserves the form of the eyeball and the proper 220 NORMAL AND ABNORMAL REFRACTION. relation of the dioptric surfaces to each other and to the retina. The normal sclera resists this pressure without yielding. Acute disease, .diathetic impair- ment "1' general nutrition, a local inflammatory process starting with con- gestion of the choroid ('nun eye-strain, or a congenital nutritive deficiency lower- the resisting power of the tissue, leaving it unable to withstand the in- traocular pressure. Distention then occur.-, commonly near the posterior pole of the eye, causing elongation of the antero-posterior axis of the eyeball. When such distention is started, anything tending to increase intraocular tension or to diminish the resisting power of the sclera favors it. Different writers attach different degrees of importance to the various possible factors. Some believe a diathetic vice of nutrition essential to the production of myopia : some regard external pressure, dependent largely upon the form of the orbits and the width between them, as most important ; some consider inflam- matory changes within the eye as the chief cause of distention ; some ascribe an important influence to accommodation, and others to excessive convergence. The writer recognizes the possible influence of all these factors, but believes excessive convergence is by far of the greatest practical importance. It is universally recognized that prolonged near work favors the occurrence and increase of myopia. Such near work causes physiological hyperemia, often exaggerated by poor light or excessive minuteness of the objects looked at ; faulty position of the head, leading to venous congestion of the eves ; con- finement indoors to a sedentary occupation, which impairs nutrition ; strain of accommodation ; and excessive convergence which, sooner or later, increasing myopia renders necessary. When the eye has become myopic its elongation makes convergence abnor- mally difficult, and the continued use of the eye for near work, because it cannot he used for distinct distant vision, increases the amount of convergence required of it. With weakened sclera, with increased pressure of the extra- ocular muscles from increased convergence-effort, and the pressure abnormally continuous, the tendency is for distention to increase. Myopia tends to be progressive. Probably all cases of myopia are at the start progressive. Some myopias cease to increase when the requirements of excessive near work made temporarily or during school-life are relaxed. Others become stationary from increasing rigidity and resisting power of the sclera which seem to come nor- mally with increasing age. Still other cases continue progressive until conver- gence becomes too difficult to he sustained, when the more defective eye is per- mitted to deviate, and divergent squint, either intermittent or constant, is estab- lished. After this, the muscular pressure of convergence ceasing, the myopia ceases to increase. In a lew cases, however, the sclera is so thinned, its resist- ing power so low, thai distention continues until the intraocular changes pro- duce blindness. To these the term malignant myopia is properly applied. Myopia reaches much higher degrees than hyperopia, and the high myopias constitute a larger proportion of the cases; myopia of over 20 I >. i- as common ;i- hyperopia of 1 I >. In Bpeaking of degrees of myopia we may designate as low myopia that oi less than 2.5 I>., where some accommodation is habitually employed for near work. Moderate myopia LS from 2.5 D. too I)., where near work can he done without accommodation. High myopia ranges from 5 to lo I)., in which work 1- besl done at the far point of distinct vision. Very high myopia i- above Hi I>., and is usually accompanied by greal alteration in the shape of the eyeball ami changes in it- coats. Symptoms and Complications. — Myopia renders indistinct all objects situated beyond the tin- point of the eye. Such indistinctness is not always MYOPIA. 221 noticed if it begins in early childhood or comes the ease, there is no temptation to get an increased effect by looking ob- liquely through the lens. Some persons object to the diminished retinal images caused by strong concave lenses, and prefer very much weaker lenses. If one weak enough to entail no strain when looking through it obliquely answers the purpose without any risk of excessive convergence, it may be wiser to give it. Occasionally, too, the full correction may be given for dis- tant vision, and something deducted (1 or 2 D.) from the glass for near work, until the habit of accommodating normally for near objects has been formed. Patients should be warned of the dangers of looking obliquely through con- cave glasses. Besides using correcting lenses, the myope must learn to keep his near work as far from his eyes as possible. The lenses are chiefly useful by enabling him to have a greater working distance, and no benefit as regards the progress of the myopia or the health of the eye can be expected unless the opportunity to diminish the strain of convergence is utilized. As an aid to a greater working distance, good light and the avoidance <>)' reading very fine print or prolonged looking at other minute objects must be attended to. ('are must be taken to avoid protracted near work. It should be interrupted by frequent intervals, during which the convergence may be allowed to relax and the eve- to fix on some distant object. The po-itioti of' the head is also important, particularly in young persons. Reading while lying down or in a bent posture, causing pressure on the veins of the neck, favors ocular con- gestion, and should especially be avoided. Use of the eyes during periods of impaired nutrition, as from acute disease, during greal physical exhaustion, etc., may also be dangerous. Outdoor life, besides demanding distant rather than near vision, act- l>v improving general nutrition. When choroid;'! con- gestion i- marked, the influence of complete rest of the eyes for ■ »me days under the influence of a mydriatic may promptly check a process that t< rids 224 NORMAL AND ABNORMAL UEFRACTLON. to soften and rapidly distend the sclera. When increase of myopia does occur thf lenses should be promptly changed accordingly. The operative treatment of myopia by removal of the crystalline lens by discission, followed by extraction it' the patient's age makes it necessary, is claimed nol only to improve vision by removal of high myopia, making com- paratively weak glasses necessary, but also to exert an influence in checking the progress of the myopia, and actually to cause a diminution in the antero- posterior axis <>(' the eyeball. In the judgment of the writer it is not proper to resori to it in any ease where the progress of the myopia can he arrested by the wearing of correcting lenses and ordinary hygienic precautions. But where glasses cannot be comfortably worn or with them the myopia continues distinctly progressive, it is proper to extract the crystalline lens. This ope- ration may also he resorted to in cases of high myopia in one eye and in myopia with commencing lens opacity. In such eyes cataract often remains incomplete for many years, and grows no easier of extraction — it may even become more difficult to remove because of the larger nucleus when ripe than when the opacity begins to interfere with vision. The reduction in myopia by extraction of the lens varies in different eyes, usually between If) and 20 D. Generally, it will not he exactly corrected by the removal of the lens ; glasses for both near and distant vision will be required, accommodation being lost with the removal of the lens. Astigmatism. — Its Nature and the Vision of Astigmatic Eyes. — Astigmatism is always an ametropia of curvature. If is a defect in which rays front a single /mint do not after refraction tend to meet at a single point. In irregular astigmatism the curvature is irregular and the refraction differs in the different parts of the pupil. In regular astigmatism the refraction is the same in different parts of the pupil, lint differs at the same point in different directions. This depends upon inequality of curvature of the dioptric surfaces in the different directions. A familar illustration of the kind of surface causing it is found in the curve of the edge of a watch. The curve in the plane parallel to the face of the watch is weaker than the curve in the plane perpendicular to the face. The inequality of curvature causes the rays to be refracted more strongly in the directi f the stronger curve, and in that plane to come to a focus before they have reached a focus in the plane of the weaker curve. Instead of being focussed to a single point, they are focussed successively to two lines at right angles to each other and separated by a certain interval. In most cases of regular astigmatism the fault depends chiefly upon inequality of curvature in the cornea, although there is usually also some inequality in curvature in the crystalline lens. It is common to speak as though the astigmatism were due entirely to the corneal curvature, but it should lie remembered that this is only exceptionally the case. In considering the refraction of the astigmatic eye it i> only necessary to follow tip' course of the rays as regards two meridians, called the principal meridians —viz. the meridian of greatest curvature or greatest refraction, and the meridian of least curvature or least refraction. In regular astigmatism these are always perpendicular to each other. In some eyes they are not perpendicular, but in such eyes the astigmatism i^ not regular, or if a part of it he regular, there i- present also some irregular astigmatism, which can- not !.!■ corrected by an} lens. (See page 206.) When the refraction has been corrected in the principal meridians all of the regular astigmatism, all the astigmatism that is corrigible, is corrected lor all meridians. The focussing of lighl l>\ the astigmatic eye may be illustrated by Fig. ASTIGMATISM. 225 161, in which the circle represents the cornea as seen from the front; aa represents the principal meridian of greatesl refraction, and b l> the principal meridian of least refraction. By the vertical curvature all rays entering the upper half of the cornea arc brought down to the level of the central ray when tbey reach the point/, and all rays entering the lower half of the cornea are brought up to the central ray at the same point. At/ all the rays have Fig. 161.— Illustrating the refraction of the rays in the principal meridians. been brought to the level of the central ray, but they have not been focussed to a point, for in the meridian of least refraction, b b, they have been less turned from their original course, and therefore from side to side arc -till spread out the distance//. Not until they have travelled on to the point shows them running at right angles to the focal lines mi the retina, so that they overlap the spaces on either side, giving the greatest blurring ) and 'J shows them running obliquely, so that the overlapping causes blurring, l)iit le-- than that for .">. All lines looked at by the astigmatic eye are seen in one of these ways at any given time. The eye may, by change of accommo- dation, so vary its refractive power as to bring first one and then another focal line upon the retina, making the lines clear at first in one direction and then in the other. Symptoms of Astigmatism. — Generally lines can he seen clearly only when they run in some one direction, and this direction is that of one of the principal meridians. This necessarily occasions a certain indistinctness of vision, which i- peculiar in that, when tested by the test-letters, some of these on account of the direction of their characteristic lines are more blurred than others. The patient may mix-all several of the letters of a certain size, and yet recognize other- of bul half that size. In general, the indistinctness due to astigmatism is not more than half as great as that produced by myopia or hyperopia of equal amount. It has been stated that the astigmatic eye seeks to overcome indistinctness of vision by unequal contraction of different parts of the ciliary muscle, causing unequal convexity of the crystalline lens in different meridians. It ha- not been certainly prosed that this occurs. But the indistinctness may be partly overcome by rapid changes from one state of accommodation to another, causing first tl ie focal line and then the other to fall upon the retina in such quick succession that their impressions may aid in a single mental perception. Either use of the accommodation leads to eye-strain with all it- possible manifestations — pain, congestion or inflammation of the eye and its appendages, headache, and other manifestations of disturbance of the general uervous system. In childhood the difficulty of the imperfect images hinders the development of the power- of visual perception, and even of the general mental processes, [ndistinctness of vision, though present from early life, may - -what diminish as the patient learns to use his eyes, hut increases again when age ha- caused the impairment or complete loss of accommoda- tion. High astigmatism, especially myopic, with the greatest defect in the vertical meridian, i- quite a- likely to cause partial closure of the lids, with secondary disturbances of the cornea, as is myopia. Varieties. — Astigmatism with the ruh is astigmatism with the meridian of greatest refraction vertical or nearly so, as it is in a large majority of cases. Astigmatism against the ruh mean- that the meridian of greatest refraction i- horizontal or nearly -o. The number of cases of this kind is comparatively small, hiit they grow more frequenl alter middle life. The astigmatism that follows cataract extraction, iridectomy, and similar corneal sections is usually of this kind, because 3uch sections are generally made in the upper margin of the cornea, and their influence is to flatten the cornea in the meridian per- pendicular to their length. Astigmatism against the rule has also been noted a- a forerunner of glaucoma. ASTIGMATISM. 227 Oblique astigmatism means that the direction of the principal meridians departs much from the vertical and horizontal, and approaches rather to 15 and 135 degrees. Some writer- believe thai astigmatism against the rule and oblique astigmatism are mosl likely to cause inconvenience, or to cause more inconvenience than astigmatism with the rule of equal amount. This may be explained by the fact that only line- parallel to the principal meridians can be perfectly focussed on the retina, and that the greatest number of lines looked at are either vertical or horizontal. \\ hile the amount of astigmatism and the direction of it- principal me- ridian-are independent of the position of the retina, the relation of the retina to the focal lino determines the variety under which astigmatism i- classified ; thus, in Fig. 163, suppose c represents the cornea, the -olid lines represent Fig. 163.— Figure illustrating varieties of astigmatism. rays as refracted in the vertical meridian, and the broken lines the rays as refracted horizontally, / to be the position of the anterior focal line, and g the position of the posterior focal line. When the retina passes through /the defect is called simple hyperopic astigmatism — hyperopic because a- regards the meridian of least refraction and the focal line g the eye i> hyperopic — simple because it can be corrected by the simple cylindrical lens which cor- rects the meridian of least refraction. When the retina is situated at A the astigmatism is called compound hyperopic. The eye is hyperopic for both meridians, for both focal lines, and it can be corrected only by a compound cylindrical or sphero-cylindrical lens. When the retina passes through g the defect i- simph myopic astigmatism, the eye being myopic for the meridian of greatest refraction and the focal line/', and capable of correction by a simple cylinder correcting the meridian of greatest i'e fraction. When the retina is at m the astigmatism is compound myopic, the eye being myopic for both focal line- and meridians, and it- ametropia i- only corrected by a compound cylindrical or sphero-cylindrical lens. When the retina i- situated between /and g the eye i- hyperopic for g and the meridian of least refraction, and myopic for / and the meridian of greatest refraction; the astigmatism i- called mixed, and requires for the correction of the ametropia a lens convex in one meridian and concave in the other. It is evident that simple increase in the antero-posterior axis of the eyeball by distention will cause the same case of astigmatism to pa-- from compound hyperopic to simple, then to mixed, afterward to simple, and finally to compound myopic. In case of astigmatism becoming myopic these changes successively occur in the course of the progressive distention of the eyeball (see also pages 127 ami 128). Correction of Astigmatism. — This is effected when ray-. Instead of being focussed to two focal line-, are focussed to a single point. I'hc corre tion of the ametropia present requires that for parallel ray- tin- point shall fall upon the retina, lint the astigmatism may be fully corrected, although a certain 228 NORMAL AND ABNORMAL REFRACTION. amount of other ametropia (hyperopia or myopia) remains uncorrected. Astigmatism i- corrected by any cylindrical lens <>r combination of lenses that makes up for the difference of refraction in the two principal meridians. Thus a convex cylinder with its curve parallel to the meridian of least refrac- tion, and equal in strength to the difference between the two principal me- ridians, will correct any case of astigmatism. A concave cylinder with its curve parallel to the meridian of greatest refraction, and strong enough to make the difference between the two meridians, will correct it equally well. Or a convex cylinder correcting a part of the astigmatism may lie placed with it- curve in the direction of the meridian of least refraction, and a concave cylinder strong enough to correct the remainder of the astigmatism with its curve parallel to the meridian of greatest refraction. In general, any case of astigmatism may he corrected by one of three combinations of lenses. Take, lor instance, a hyperopic astigmatism in which the horizontal meridian is hyperopic 4 I)., and the vertical meridian hyperopic 2 I). The astigmatism may he corrected (1) by a convex 2 D. cylindrical lens placed with its curve horizontal (axis vertical), and the addi- tional hyperopia corrected by combining with this a convex 2 D. spherical lens. This astigmatism may he corrected (2) by a concave 2 I), cylindrical lens placed with its curve vertical (axis horizontal). This woidd have 1 the effect of increasing the hyperopia of the vertical meridian, and to correct the hyperopia a convex 1 I), spherical lens would he required. It would also be possible (3) to correct the astigmatism with a convex 4 I), cylinder with its curve horizontal (axis vertical) and a convex 2 D. cylinder with its curve vertical (axis horizontal). The one cylinder would bring the posterior focal line on the retina without affecting the anterior focal line, and the other cylinder would bring the anterior focal line on the retina without affecting the posterior line. In this way hoth focal lines, brought to the same distance from the cornea, would become a single point, and the astigmatism would be corrected, and with it also the hyperopia. For the one case of astigmatism any of the following lenses might he chosen, the correction being optically as good with one as with another : (1) I- 2D. sph. O 2 D. cyl. axis 90° (vertical) ; (2) tD.sph.C 2D. cvl. axis 180° (horizontal); (3) 2 I), cyl. axis 180 = I I >. cyl. axis !'0°. Looking at these, it will he seen that (1) has on the whole the weakest surfaces. It is theoretically possible with it to get ihc thinnest lens and the one having usually the least aberration. It is also the lens most commonly -elected in testing the eye with trial glasses, ami the one most frequently prescribed. It will he observed that (2) ha- one convex and one concave surface. The spherical surface ha- to he stronger than that of (1), and therefore causes more aberration; hut this j^ a matter of very little importance. It i- of greater importance that b) placing the concave surface toward the eye and the convex surface away from it something of a periscopic effeel can he obtained by this second leu- allowing the eye to he turned in different directions without causing so much obliquity of the visual axis to the lens surfaces. On this accounl (2) will prove on the whole the most satisfactory fir ;i large proporl ion of cases. With reference to (3), it will he noted that it include- two cylindrical sur- faces with their axes exactly perpendicular. Such a lens is very hard to ASTIGMA TISM. 229 grind sufficiently accurate for practical purposes, and impossible to grind with theoretic accuracy. Its surface-, too, are stronger, and therefore cause inure aberration. On every account this form of lens, the crossed cylinder, is to be avoided. It lias rarely Keen used except for mixed astigmatism, where it gives weaker surfaces than either of the sphero-cylindrical lenses. But this doe- not compensate for the increased expense and necessary inaccuracy of crossed cylinders, and it is better never to employ them. The following formulas will illustrate this subject a- regards mixed astigmatism : (1) - 1 D. sph. O-h 2 D. cyl. axis 90° ; (2) + 1 D. sph. O -2D. cyl. axis 180° ; (3) + 1 D. cyl. axis 90° O - 1 I). cyl. axis 180°. In compound myopic astigmatism the same thing holds, as the following equivalent formulas will indicate : (1 ) - 2 D. sph. O - 2 D. cyl. axis 1 80° ; (2) -4D. sph. O - 2 D. cyl. axis 90° ; (3) -4D. cyl. axis 180°O-2D. cyl. axis 90°. In simple astigmatism the correetion for the better meridian is <> ; and one element of formulas (2) and (3) becomes 0, so that the two become alike. In simple hyperopic astigmatism we would have the following: (1 ) or (3) + 2 D. cyl. axis 90° ; (2) - 2 D. sph. 0-2D. cyl. axis 180° ; from which one may choose the simple cylinder, which is the cheapest lens, or the sphero-cylindrical lens, which gives the better periscopic effect. In simple myopic astigmatism the formulas are thus : (1) or (3) -2D. cyl. axis 180°; (2) - 2 I), sph. O + 2 D. cyl. axis 90°. "Wearing 1 Glasses for Astigmatism. — -The whole treatment of astig- matism consists in the wearing.of glasses. Since astigmatism interferes with distinctness of vision at all distances, and since it entails, when uncorrected, a use of the accommodation entirely different from that of emmetropic, hyperopic, or myopic eyes, it is important that the lenses correcting it should be worn constantly. This is essential in all cases at first. Sometimes a patient, by wearing glasses constantly acquires the habit of using the accom- modatioi rmally and can continue to so use it by sacrificing something ol distinctness of vision on laying aside his correcting lenses at times when the eyes are not to be especially taxed. Such persons, after the con-taut use of cylinders for some time, are able to do without using them constantly when the eye- are not employed on work requiring distinct vision. [n general, however, a patient having much astigmatism maybe warned that he will always require the help of correcting lenses. Cylindrical lenses, contrary to what is sometimes expected, are often dif- ficult to become accustomed to, especially if they are strong, if the patient is advanced in years, and if the axes of the cylinder- before the two eye- inti-t be turned in different direction-. Strong cylinders are never satisfactory at 230 NORMAL AND ABNORMAL REFRACTION. first. With sonic persons, especially when past middle life, the difficulty of becoming accustomed to them is so great that they are very likely to give up the attempt. This should he carefully considered before ordering glasses. Any cylindrical lens changes somewhat the shape of the retinal images and, therefore, the apparent shape of objects looked at. When the axes are turned in different directions the distortion of the retinal images, corresponding to the directions of the axes, differs in the two eyes, so that it becomes difficult to fuse the two impressions they make and secure binocular vision. These unpleasant effects may he diminished by wearing for a time an incomplete correction of the astigmatism or by bringing the lenses particularly close to the eye-. Aberration. — A spherical lens does not perfectly focus the rays passing through it. In general it acts toward the edge as a stronger lens. This may lie illustrated by the following diagram, which shows the course of the parallel rays as refracted by a convex spherical surface (Fig. 164). The rays passing through the center are focussed at/, the principal focus of the lens, and those passing through the margin are focussed closer to the lens. The unequal distribution of light in the circle of diffusion, its concentration to a i re, L64. figure illustrating spherical aberration. ring at the edge and a point at the center of that circle, may he studied with a strong convex lens focussing light upon a card. In the human eve the periphery of the crystalline lens is more convex than the center, and acts, therefore, as a stronger lens than the center, just as in the ordinary spherical lens. The periphery of the cornea, on the other hand, is always more or less flattened. Within the pupil, in the majority of eyes, the increased convexity of the crystalline lens predominates, so that they present a stronger refraction, higher myopia or lower hyperopia, at the periphery of the pupil than at its center. This condition the writer has called 'positivi aberration. When the opposite occurs the refraction is Stronger, the myopia higher or the hyperopia lower at the center of the pupil than near it- margin, constituting negative aberration. Aherration [day- an important pail in skiascopy, determining the form and size oi the lighl area in the pupil, causing reversal of the movement of lighl in tin' periphery (in positive aberration) to he perceived closer to the eye than the vement of lighl at the center, where it is of more practical importance. W hen aberration is confined chiefly to the extreme periphery of the pupil, where it is -Inn off b) the pupillary contraction in a strong light or during near work, it ha- no influence on the working power i>{' the eye. When it begins near the center of the pupil, causing the eye to be more hyperopic when the pupil i- contracted by a strong light or tor close work than when more dilated, it ha- an important influence in producing eye-strain, and may AXISOMF/ritOPIA. 231 be a cause of error in the selection of lenses. An eve with positive aberra- tion will often select with the undilated pupil a convex lens 0.25 I >. stronger, or a concave 0.*25 I), weaker, than it will accept while the eye i> fully under the mydriatic. Aberration is to be recognized by skiascopy and considered in the choice of lenses. It cannot be exactly corrected by any particular lens, but is some- times an indication for the wearing of a stronger lens than one which will allow of perfect distant vision, such a lens being found in these cases decidedly more helpful. High negative aberration is sometimes diw to increased refractive power in the nucleus of the lens — incipient senile cataract — or to conical cornea. Irregular astigmatism is recognized by skiascopy, causing appearances represented in Fig. 165 A and B. Traumatism or disease of the cornea, leaving irregularities of its surfaces (Fig. 165, .1), tissue-changes in the lens preceding cataract (Fig. 165, B), and occasionally faulty development of the cornea or lens 1 , cause irregularities of refraction that prevent the perfect focussing of light to a point by the dioptric media. Such defects are not capable of correction by lenses. The eye, however, often presents within the area of the pupil small areas in which the refraction is comparatively uniform, which areas may be corrected by some combination of lenses, and the vision and comfort of the Fig. 165.— Appearances of irregular astigmatism recognized by skiascopy. patient thus be greatly improved. The practical thing to do is to study these cases carefullv by ophthalmometry and skiascopy, and to correct the mosl regular portion of the cornea. In a few cases, where no lens can render much service, it may be worth while to try a stenopaic spectacle. This is an Opaque disk in front of the eye with a narrow slit or, more commonly, a single pin-hole opening in it. Such an apparatus often gives a noticeable improvement of vision, but it is rarely found very serviceable because it interfere- with the visual field. Anisometropia.— Some inequality in the refraction of the two eyes is the rule, and occasionally this is such as to render one eye hyperopie and the other mvopic, or one astigmatic, while the other is i'wc from astigmatism. Such a difference constitutes arkisometropia. The importance oi the dif- ference depends entirely on its degree, and nol on whether it amounts to a difference in the kind of ametropia. The general rule when the difference is not great i- t<> give each eye its exact correction. If the difference between the two correcting lenses is very great, they affeel the size of the retinal images, so that bi :ular vision be- comes difficult. When one leu- i- much stronger than the other. looking through the periphery produces a correspondingly differenl prismal Causing object- to be -ecu double, of the etTofl to ll-e the illKCJ.- falling OH the two retina- causes -train of the extraocular muscles. 232 NORMAL AND ABNORMAL REFRACTION. For the above reasons the full correction of anisometropia cannot always be practised. It is generally safe to prescribe the correcting lenses for both eyes when these differ less than 1 1>. [f they differ not more than '2 D., they will generally be accepted, although this cannot always be assumed. If they differ more than l' D., the patient will find it very difficult or impossible to use them for satisfactory binocular vision, although a few persons will prefer to have anisometropia of ■"> or I I), fully corrected. When the difference of refraction cannot he fully nut by difference of glasses, the rule is to correct the better eve and to allow- the worse eye the full correction of its astigmatism, with a spherical lens equal to that of the better eye or a little stronger. Sometimes if both eye- have good vision, but cannot work together, one may be corrected for distant vision and the other given a leu- that will adapt it for near seeing. Congenital anisometropia often gives little trouble, but anisometropia coming on from change in the refraction, as in progressive myopia, i- likely to be very annoying. The similar effect produced by glasses not accurately suited to the eyes is also very annoying. Acquired anisometropia, particularly from 0.5 to 2 I)., is especially liable to give rise to squint, and its correction is indicated to preserve or restore binocular vision. Presbyopia. 1 — The failure of accommodation with age leads finally to complete inability to change the optical condition of the eye, so that only rays of a certain convergence or divergence can be focussed upon the retina. In the great majority of eye-, which are hyperopic, this renders necessary the use of convex lenses for near vision. For this purpose the need of lenses i- felt —the eve is presbyopic— as soon as the power of accommodation has diminished so that it is unequal to the task of keeping the crystalline lens convex enough to focus rays accurately on the retina when the eye is engaged in ordinary near work. When this occurs either symptoms of strain, such as congestion and pain in the eye, conjunctivitis, or headache, arise, or after the effort has been sustained for some time the ciliary muscles suddenly relax and all near objects become blurred. If the eyes are now rested for a minute, the power of distinct near vision returns, but if the near vision is continued, it again fail-, and, persisting in the attempt, such failures become more and more frequenl until the effort is given up. The failure is first for object- at the shortest distance from the eye, as -mall objects or line print that needs to be broughl close in order to be seen. Objects that may be held farther away, or the same object in a strong lighi which will render it distinguishable at a greater distance, may still be clearly seen, the patient noticing only that he requires good lighl and has to hold thin-- farther from the eyes than formerly. Presbyopia i> caused first by the increasing rigidity of the crystalline lens, which limit- its tendency to become more convex when the tension of the suspensory ligament is removed by contraction of the ciliary muscle. Subsequently the ciliary muscle also becomes weakened or undergoes atrophy, and the power of accommodation is completely lost. Presbyopia i- relieved by supplementing the insufficient focussing power of th,. crystalline lens by a convex lens of the necessary strength placed before the eye. In choosing such a lens it i- to be borne in mind that we have to enable the eye not only to see clearly at the required di-tance for an instant, but to sustain distinct vision at that distance over periods of continuous use. The maximum contraction of ,i gele is always one that cannot be long sus- tained ; hence the leu- giving the patient a near point where he wishes to 1 For additional consideration of ilii- Bubjecl Bee page 137. PRESBYOPIA. 233 work will be insufficient for continuous work. With most persons only two-thirds of the accommodation can be long kept up. A few can sustain three-fourths of it, bul others, particularly young persons suffering from weakness of accommodation, can comfortably sustain only one-half of the full amount. In correcting presbyopia, then, we not only find the near point of distinct vision, but from that near point and the refraction of the eye calculate the total power of accommodation. Then assuming that two-thirds of this accommodative power is available for continuous work, the difference be- tween that available accommodation and the accommodation required for the sort of near work to be done is the strength of lens that should be given to correct the presbyopia. This may be illustrated by examples of different errors of refraction. Suppose, first, a case of presbyopia in emmetropic eyes. The nearesl point of distinct vision being 18 inches (45.5 cm.), corresponding to 2.25 D. of accommodation, two-thirds of this, which may be assumed as available for near work, equals 1.5 D. Now, if the patient wishes to use the eyes for ordinary reading, writing, sewing, etc. at a distance of b'> inches (33 cm.), where 3D. of focussing power will be required, 3. — 1.5 I). 1.5 I), will be the strength of the convex lens that should be given to supplement accom- modation — to correct the presbyopia. If the patient has been wearing such a lens or one nearly as strong, and still shows evidence of undue strain of the eyes for near work, it may be that he cannot sustain two-thirds of his total accommodation, but requires the presbyopic correction to be made some- what stronger, as 1.75 -or 2 D. On the other hand, if such a patient has been reading without any lens and without much inconvenience, it may be assumed that he can sustain more than two-thirds of his total accommodation, and therefore a weaker lens, as the 1 or 1.25 D., may be given. Suppose in another case the patient has hyperopia of 2D., and a near point of distinct vision of 1<> inches (40 cm.), corresponding to 2.5 D. of focussing power, to which is added the 2D. needed to correct the hyperopia, making 4.5 D. of total accommodation. Two-thirds of this accommodation, or •'] D., would only correct his hyperopia, and leave 1 D. to adapt the eye for near vision at a distance of 1 m. If such a patient is to work at 13 inches (33 cm.), where 3D. of focussing power is needed, he will require the help of a lens equal to 3 D., — 1 D., or 2D. The increased use for accom- modation will cause the hyperopic eye to suffer earlier from presbyopia if it has not the help of correcting lenses for the hyperopia. It will also be noted that with a certain near point the hyperopic eye requires a stronger supple- mentary lens, since that near point represents, with a greater amount of accommodation, a greater need for it. The lens required in the above case might be found by correcting the hyperopia with a 2 D. convex lens, when it would be found that the near point was at !) inches (23 cm.) I 1.5 D. of accom- modation), and that two-thirds of this accommodation. 3D., would be suf- ficient for work at 13 inches (.'}.'» cm.). Hence no further correction for presbyopia would be required, the correction of the hyperopia causing the presbyopia to disappear. By myopia the need for a presbyopic correction is postponed and dimin- ished. Thus, an eye with myopia of ."» D. will be able to work at 13 inches (33 cm.) without any lens and without accommodation, and tor that kind of work will never suffer from presbyopia. Take another case, where the myopia is 1 I), and the near point found at 22 inches (57 cm. |, corresponding to 1 .75 1 >. of focussing power ; subtracting from thi^ 1 1 >. of myopia leaves 0.75 1 >. as the 234 NORMAL AND ABNORMAL REFRACTION. total accommodation. Of this two-thirds, or 0.5 D., being available for near work, is to be added to the 1 D. of myopia, making 1.5 D. of available focussing power, and for work to be done at 13 inches there will be need in addition for a convex lens of 1.5 D. That is, in myopia of 1 L)., with only 0.75 D. of accommodation, the same help is required as in emmetropia with accommodation of 2.25 D. With myopia, as with hyperopia, the total accom- modation may also he found by first correcting the myopia and then taking the near point. In astigmatism the accommodation can only be accurately determined by taking the near point after the correction of the astigmatism, and the amount of convex spherical to be added for near work on account of presbyopia will then be determined as though the eye had been originally emmetropic. Some- times in giving lenses for presbyopia with astigmatism, while the concave cylinder is better for distance, the convex cylinder with its axis turned at right angles is better for near work. Suppose a ease of simple myopic astig- matism requires for its correction — 1.5 D., cylinder axis 180°, and with this correction before the eye the near point is 18 inches (46 em.), the accom- modation 2.25 I). The spherical to be added for near work at 13 inches (."18 cm.) would be 1.5 D., and a convex 1.5 D. spherical, combined with the concave 1.5 IX, cylinder axis 180°, is the optical equivalent of the convex 1.5 IX, cylinder axis J)0°. For distant vision such an eye may be given — 1.5 I)., cylinder axis 180°, and for near vision f 1.5 I)., cylinder axis 90°. Course. — Presbyopia usually begins between the ages of forty and fifty. With hyperopia, which may have given no earlier evidence of its presence, it begins younger ; with myopia, later or not at all. Even with emmetropic eyes the increasing rigidity of the lens may require the use of convex glasses before the age of forty, and with a few the need of a presbyobic correction is deferred until after the age of fifty. In all cases after it has begun presbyopia is progressive. The power of accommodation continues to diminish until it is entirely lost, and such dimi- nution causes the necessity for increasing the strength of the supplementary lenses — the presbyopic correction. Generally, the lenses should be changed often enough to have a difference of not more than 0.75 D., or about once every two or three years from forty-five to fifty-five. Most patients require the same correction for presbyopia for both eyes. In a lew cases this is not so, the accommodation failing faster in one eye than in the other, and re- quiring a correspondingly stronger supplementary lens. In such cases the eye- should be repeatedly tested to make sure that there is actually a differ- ence between them, and the tests repeated at short intervals. The Mounting of Glasses. — Lenses are commonly supported before the eyes by spectacle or eye-glass I pince-nez) frames. The former have the advan- tage of more rigidly fixing the position of the lens before the eve. The latter are more readily removable when the lenses are not required for eon-tan t use. The proper adjustment of the frames is a matter of much importance, since the right lens in the wrong position doe- not have its proper effect, and may be entirely unsatisfactory (see pages 236—240). The Period of Adaptation. — Weak lenses, less than 1 I>.. may prove satisfactory and comfortable from the -tart or within a few days after begin- ning to wear them. Children may become accustomed to even strong lenses in a very few days. Correcting lenses will generally be accepted without complaint when the eye is kepi tor some time under the influence of a mydriatic. Hut. apart from these exceptions, lenses are rarely accepted with entire comforl at first. THE PERIOD OF ADAPTATION. 235 The period of adaptation during which the first discomfort diminishes and passes away may last from two to six weeks, or even longer; during this period convex lenses are Likely to cause blurring of distant vision, concaves render near work noticeably more fatiguing, and cylinders cause distortion of objects and an indefinite discomfort. These unpleasant effects may from the start he more than balanced by the benefits experienced, yet it is prudent in all cases to warn the patient that some weeks must elapse before the glasses can be expected to do their best. With such a warning most people encounter the necessary difficulties without loss of confidence. But if permitted to put on the glasses expecting immediate satisfaction, they become disappointed, lose faith in the prescriber, and are likely to refuse to give them a fair trial. The good of the patient and the reputation of the surgeon both demand that a careful explanation of the period of adaptation should be given when the glasses are prescribed. SPECTACLES AND THEIR ADJUSTMENT. By R. .J. PHILLIPS, M. I)., OF PHILADELPHIA. A spectacle-lens should be so placed that, in use, the line of sight passes through the optical center perpendicular to the plane in which the glass lies. These simple conditions would be extremely easy to satisfy were it not for the tact that the organ of vision must of necessity be extremely active and mobile. The eyeball may, in fact, be rolled in its socket about 60° in every direction from a point immediately in its front, while movements of the head, or even of the entire body, are constantly called in requisition as greater range of vision is required. These facts destroy at once the possi- bility of so placing a glass that its center may be coincident with, and its plane be perpendicular to, the line of sight under all circumstances. Only a glass fastened to the eye and moving with it could fulfil these conditions. Though the glass cannot be attached to the eye, it can be and is attached to the head, which, as has been noted, is nearly constantly in motion, seconding the activity of the eyes. The necessity of looking through the center of the glass limits for the wearer the range of the eyes in their sockets, and increases in a corresponding degree the excursions made by the head. This augmented head-motion, which can he noticed in almost all wearers of glasses, arises partly also from the effort to bring the plane of the lenses perpendicular to the line of sight. The only exception to these statements is in the case of a person who i- wearing a glass which under-correct s his ametropia, and who looks through it obliquely in order to increase its refractive effect. The more exactly the glass and frame are fitted to the requirements of the case, the le— of this auxiliary head-movement will he required ; some increase in it must, however, he accepted as one of the concomitants of wearing spectacles. When a person with glasses raises his head continually, markedly elevates <>r de- presses hi- chin, or forcibly twists hi- spectacle frame in his fingers, he is instinctively seeking to correel faulty refraction or faulty frame-fitting. Spectacle- are ordered to he worn either constantly, or for near work only, or for distant vision only. It will he readily understood that the circumstances under which near work i- usually done admit of the most exact adjustment of the glass. S\\c\\ work i- usually held in the hands or occupies a desk or bench having a fixed position relative to the workman. It is below the level of hi- eye- and within reach of his hand-, and only slight excursions of the eyes arc required in it- performance. As the line of sighl is directed down- ward, the •' near" glass [n, Fig. 166) must he placed below the level of the eye ; at least its optical center must be so placed. It must face strongly down- ward in order to bring it- plane perpendicular to the line of sight (6). It should face slightly inward for the same purpose, since the visual axes converge in near vision. Tin- convergence necessitates, further, that the optical center- of the glasses -hall he placed from I to li nun. nearer together A DJ I T STM ENT OF SPEt "/'. I ( 7. /;- /. ENSES. 237 Fig. 166.— Showing position of lenses before eye. than are the centers of the pupils, since the visual axes would otherwise pass t<> their inner sides. If an isosceles triangle is constructed with the inter- pupillary distance as its base, and the visual axes, directed toward a near object, as its remaining sides, it will he apparent that the farther from the eyes a pair of glasses stand and the nearer to the eyes the work is situated, the less should he the distance between the optical centers of the glasses. The pre- cise distance between optical centers which any given case may require may thus be determined. In " distant" vision the gaze may be directed toward any point of the hori- zon or firmament, and yet, practically, the relation of the line of sight to the face, and consequently to glasses at- tached to the face, does not vary greatly. A distant object would have to change its position considerably in order to move through rive degrees of one's field of view. Hence rapid changes in the direction of the line of sight are seldom required. Ample time is afforded for whatever adjust- ments of the head and trunk may be necessary. Distant vision usually takes place, therefore, with the visual axes directed forward perpendicular to the plane of the face (a, Fig. 166). When glasses are ordered for this use alone they should have optical centers separated by the same interval as that between the pupils (since they will not be used during convergence), and should face directly forward, lying in a plane parallel to the general plane of the face (d, Fig. 166). The optical centers of the lenses should stand at the same height as the pupils. In the greater number of cases the spectacles prescribed are intended for constant use — that is, the wearer will need them as well in viewing distant objects as in work near at hand. It is evident that to place the lenses in the exact position desirable for either of these purposes would render their use awkward for the other, in the height of the optical centers as well as in their distance from each other, and in the facing of the glass, we are therefore forced to place "constant" glasses in a position intermediate between that best for distant vision and that best for near work. This intermediate posi- tion is selected, not at all because these glasses are used at an intermediate distance, but because from tin- position they may be readily shifted, at leasl approximately, by a motion of the head into either of the other positions. The distance between the optical centers of "near" glasses should be from I to a kind of tripod, its points of support being the top of each ear and the bridge of the nose. It is not possible to make an indif- ferently selected point on the bridge of the nose serve as the support of spectacles. Nearly always it will be found that there is one particular point at which they tend to rest. In adapting spectacles to any given face, there- fore, the problem is to bring the optical centers to the position previously determined that they should occupy with reference to the eyes, while at the same time their support is placed at this best adapted point on the crest of the uose. The spectacle bridge known as the "saddle" bridge is the only one which allows of unlimited variation in the relation of these two points. In fitting a frame to the face the curved portion of the bridge between a and A. Fig. 167, should be adapted to the bones of the nose at the point at Fig. L67. Saddle bridge. Fig. ltis.— Saddle bridge. which it i- supported. Having once received the proper shape, this portion of the bridge should not be altered, as its only function is to furnish a firm, equally pressing support for the"arms"c and '/, by means of which the centers of the glasses may lie carried higher or lower on the face or the dis- tance between them varied. These variations are accomplished by alterations in the ; 1 1 1 •_; b • - of the wire at a and />. The length of the arms c and 0 mm. 5 mm. n/> .'hum. out 20 mm. base. The direction in which the front of a spectacle faces dependson the angle which it forms with the side piece- or temples. II' these latter are inclined METHODS OF TKSTISO LENSES. 239 toward the bottom of the frame, the glasses when in use will face downward. It should be remembered that hook temples arc simply hooks. They cannot, with comfort, be made to exert the force of a spring or a clamp upon the skin. They should touch the skin throughout the greatest possible portion of their extent, so as to distribute the weight they carry, and should not be allowed to press unequally owing to inequalities of the surface. Their proper form i- a straight line from the hinge of the frame to the top of the ear, where a sharp curve joins that portion which is accurately fitted to the back of the ear, with which it is in contact. In eye-glasses ! pince-nez) the same adaptability to differently proportioned faces is found in the "offset guard," which in spectacle- is attained by means of the " saddle bridge." The nose-pieces of these guards should be accurately moulded in every case to the sides of the nose at the point where they obtain the best bearing surface. Fixed points of support for the lenses are thus ob- tained. The height of the lenses before the eyes will now depend on the point of attachment of the " arm " of the guard to the nose-pieces. In Fig. 169, for abed e y Fig. 169.— Guards of eye-glasses. example, the guard marked b will carry the lenses higher than the one marked e. The direction in which the lenses face is controlled by the size of the angle in the arm of the guard. Thus, in the figure, at a the arm has a right angle and will render the plane of the lenses nearly vertical ; that is, the latter will face directly forward, while at b the angle is greater than a right angle, and the glasses will face more downward. The distance of the glasses from the eyes depends upon the length of this arm of the guard. The longer it is, the farther forward the glasses will be held; d and g, in the figure, have longer arms than a or b. Variations in the distance between the centers of the lenses may to a limited extent be pro- cured by an arm which is bent so that its free end doe- not lie in the same plane as the nose-piece. If greater latitude is required it must be procured by variation in the transverse diameter of the lens used, or by alteration of the length of the "stud" which connects the lens with the guard. Methods of Testing Lenses. — Toensure accuracy and comfort, spec- tacles, before being worn, should invariably be critically examined a- to the strength of the lenses and the fit of the frame. The most convenient method of determining the strength of lenses is the well-known one of neutralization by means of the test-case lenses of known strength. In practising this manceuver the len- is held about a foot before the eye and an object several yards away is sighted. < >n moving the lens slowly across the line of sight the object seen through it appears to move also. In the case of convex lenses this apparent movement is in a direction contrary to the motion imparted to the lens, or, in the language of the refraction room, i- •• against it." With concave lenses the apparenl movement of the object i- ill the same direction a- the movement of the lens, Or " with it." I f a convex and a concave lens of equal strength are held together, all this apparent ra ment ceases ; they " neutralize " each other. The surgeon is, therefore, able 240 SPECTACLES ANT) THEIR ADJ ISTMENT. to quickly discover the strength of an unknown spherical lens by trying it with lenses of the opposite sign until that one is found which fa uses all move- ment rotated about it- optic axis (a, Fig. 1 7. This appearance is, therefore, presented in two positions of the cylindrical lens. In one position the vertical line marks the axis of the cylinder; in the other the line is at a right angle to the axis. To locate the axis an object presenting crossed lines, as at c, Fig. 171, is selected; the lens is so held that each line appears unbroken and is first moved horizontally, then vertically. The line across which motion is apparent marks the axis of the cylinder. The cylindrical lens of the opposite sign which neutralizes this Fig. L70. — Method of testing cylindrical lenses. Fig. 171.— Method of testing sphero-cylindrical and prismatic lenses. motion discloses the strength of the cylinder under examination. Care must l»e taken that the axes of the two coincide. In a sphero-cylindrical lens the cylindrical element is recognized by its causing on rotation an apparent obliquity of a portion of a vertical line, just ;>- did the simple cylinder. On viewing the crossed lines, c, however, and moving the lens first horizontally, then vertically, apparent motion of the objecl i> imparled in both directions, hut in one it is more rapid than in the other. In neutralizing, the least rapid movement may he firsl obliterated by means of a spherical lens. This gives the strength of the sphere in the com- bination. Holding these two together, one proceeds to neutralize the cylin- drical element by means of a cylinder of opposite sign, precisely as though no sphere were present. < )n rotating :i />rixni>i/i<- lens about one's line of sight an apparent dis- placement of ;i vertical line takes place, a- at '/, Fig. 171. When the line is continuous it marks the base-apex line of the prism. At right angles to this is the meridian of maximum displacement. The prism being held ;ti one meter's distance from the object, each centimeter of apparent displacement of the line shows one centrad of strength in the prism. The <>/>lirti/ center of a lens is located l>v using crossed line-, a- al <■, Fig. 171, except that lor this purpose the lens is held within about a foot and the line- should hi' tine. When each of the lines is continuous their crossing point marks the optical center. The distance between centers being found correct and a final inspection disclosing no flaws or scratches in the glass, no bends of the frame, or want of symmetry between it- two sides, the spectacles are ready for the wearer. DISEASES OF THE EYELIDS. By 15. L. MILLIKIN, M. D., OF CLEVELAND, OHIO. Congenital Anomalies. — Partial or complete absence of the eyelids (ablepharia) is occasionally met with as a congenital defect. It may occur in one or both eyes. Lagophthalmos is a defect in which the eyelids arc wanting and the orbit is divested of any covering for the globe. An abnormal shortness of the lids, which prevents their fully covering the eyeball, has been similarly, and perhaps more correctly, so designated by many authors. Cryptophthalmos is a condition in which the eyeball is completely con- cealed by the skin, which is stretched over the orbital cavity. Sometimes the eyeball is absent. Under the latter circumstances, however, the name is not an accurate one. Cleft-eyelid (coloboma palpebral) is a congenital defect in which there is a fissure of the lid, usually triangular, with the base toward the ciliary margin. The fissure may exist in either the upper or lower lid, theformer being the usual seat. It has also been reported in the upper and lower lids on each side. The cleft involves the entire thickness of the eyelid and is rounded off at its margins. It occurs oftener with cases of hare-lip than with anomalies of the eyeball itself. Symblepharon is a condition of union, either partial or complete, between the eyeball and the lid-. Another unusual congenital anomaly is a union between the margins of the lid-borders (ankyloblepharon). This attachment may be thread-like or involve a considerable intermarginal surface. The external angle- of the lids may be adherent, producing the defect known as blepharophimosis, result- ing in a shortening of the palpebral opening. Ectropion is an eversion of the edges of the eyelids, frequently accompa- nied by enlargement of the eyeball. Entropion is an inversion of the edges of the lid-, and is usually asso- ciated with the incurving of the lashes — a condition known as distichiasis. Epicanthus is an unusual congenital anomaly caused by a fold of skin which stretches across the inner palpebral space connecting the eyebrow with the bridge of the nose, the fold thus covering all the structures located at the inner canthus. It is generally bilateral, and gives rise to. or i- associated with. ;i Battening of tin- bridge of the nose. Slight degrees of it may exist in children at birth, and with the development of the nasal bones tin- deformity gradually passes away. Associated with epicanthus may be microphthalmos (sometimes only apparent on account of the diminished palpebral opening), strabismus, droop- ing of the upper lid, ami anomalies of the lachrymal passagi Epicanthus may be remedied by an operation in which the redundant i a 211 242 DISEASES or THE EYELIDS. skin is removed from the bridge of the aose and the edges of the wound brought together with sutures. Congenital ptosis is :i drooping of the upper lid over the eyeball. It may be on one side or bilateral, and never amounts to complete closure of the lids. In thi- condition there is inability to raise the eyelid except by wrink- ling the forehead through the action of the occipito-frontalis muscle. The anomaly is not infrequently associated with other malformations, as epican- thus, paralysis of the eye-muscles, etc. It may be corrected by operative procedures, described on page 557. Erythema of the lids is a form of hyperemia of the skin, usually due to external irritation, such as burns, traumatism, and poisoning, or it may be indicative of some systemic disturbance. It is often well marked in inflam- matory condition- of the eye. Treatment will depend largely upon the cause, the erythema often dis- appearing with the cure of the primary lesion. Locally, soothing lotions, lead-water or extract of hamamelis, will be all that is required. Erysipelas is rarely, if ever, a primary affection of the lids. It usually develops from a similar lesion of the lace. The danger in this disease is that it may involve the deeper tissues of the orbit, affecting the retina or the optic nerve, and thus eventuate in blindness. In severe eases it may produce sloughing of the eyelids, with consequent deformity. The disease is cha- racterized by great swelling, increased tension of the lids, smooth and brawny skin, deep redness, and the formation of vesicles or abscesses. Tlu' treatment, both local and general, must be such as is usually adopted for erysipelas in other portions of the body. Abscess of the lid (phlegmon) is characterized by an acute swelling of the eyelid, somewhat localized, indurated in the central portion, accompanied by much redness of the skin, heat, throbbing pain, malaise, and fever. The swelling is frequently very marked, the skin toward the height of the inflam- matory stage in the severer cases often presenting a brawny appearance. Abscesses resull from external injuries, from disease of the orbital walls, or they may arise from infectious causes or occur during illness — e. v marked edema, redness, beat, pain, localized hardness or induration, the lasl indicating the point of infection. In malignanl pustule, as in erysipelas, there may be very exten- HORDEOLUM. 243 sive sloughing of the eyelid, producing at times a condition of lagophthalmos. A.fter sloughing of the lids the ciliary margins alone may remain intact on account of the rich vascular supply. There is usually marked general de- pression, with fever. By absorption of the anthrax poison into the deeper tissues orbital cellulitis, or even meningitis, may ensue with fatal results. Treatment. — This must be governed by general surgical principles. As soon as there is any evidence of pus the swelling should be freely opened, with one or more deep incisions, in order to prevent infiltration and possible involvement of the deeper structures of the orbit. The incision, followed by hot poultices or by compresses of absorbent cotton or gauze, wrung out of hot bichlorid-of-mercury solution, 1 to 2<)(><) or 1 to 5000, will be very efficient. The administration of iron and quinin, tonics, stimulants, and good diet i- of decided value. In cases of extensive sloughing of the skin of the lids marked lagoph- thalmos and ectropion can be prevented by fastening the remaining marginal portion of the lid to its fellow by two or three stitches The granular sur- face may then be treated with repeated skin-grafts applied according to the Thiersch-method. If this method cannot be followed, then the proper plas- tic operative procedures for these deformities must be undertaken, as indicated on page 555. Ulcers of the lids may be due to contusions, burns, and various injuries, as well as to lupus, scrofula, syphilis, and herpes. The symptoms will vary with the cause ; likewise the treatment. Hordeolum (Stye). — According to the location, hordeolum may be hordeolum externum or hordeolum internum. Hordeolum externum is an acute inflammation of one or more of the glands of the hair-follicles. Horde- olum internum is an acute inflammation of the Meibomian glands. In other words, hordeolum or stye is a circumscribed inflammatory process, and is due- to infection of the sebaceous glands or connective tissues of the lid, usually associated with the staphylococcus pyogenes aureus or albus. Symptoms. — These are rapid edema of the lids, redness and tenderness coming on after a short time — a day or two — often quite severe pain, and sometimes fever and general disturbance. A hard lump or point of indu- ration is felt at the seat of inflammation. Within a few days the color of the tissue over the stye changes from a red to a yellow hue, and the abscess "points." If allowed to take its course, the abscess-sac ruptures, the pus escapes, and the symptoms rapidly abate In hordeolum internum "pointing" of the absees> takes place on the inside of the lid through the palpebral conjunctiva ; in hordeolum externum, near the margin of the lid through the skin. The latter variety is much the more common. Styes usually oceiii' in persons subject to blepharitis, the chronic inflamma- tion of the latter affection affording good soil for acute infectious inflammation of the solitary glands. The infectious character is well indicated by the fad that persons arc very liable to successive attacks of styes, which occur, in many cases, at frequenl intervals over a period of months. Young persons are generally the subjects of this disease, especially if they arc scrofulous, anemic, or poorly nourished. These two varieties of hordeolum presenl essentially the same clinical picture. With both there is inflammation of the sebaceous glands, and they are analogous to acne in the skin. The marked swelling of the former, as distinguished from the hitter, i- due to the anatomical character of the ti- in which the inflammation takes place. 244 DISEASES OF THE EYELIDS. Treatment. — In the early stage an attempt may be made to abort the development of a stye by the application of cold or very hot packs, or by touching the month of* the gland involved with the sharpened point of a stick of nitrate of silver. [f unsuccessful in this/' pointing" of the abscess should be encouraged by warm fomentations or properly applied poultices. Early opening of the stye is important. A.s soon as there is an indication of softening in the center of the induration a free incision should be made into the tumor in order to evacuate the contents and to prevent the extension of the necrotic process. Care should be taken that the incision is made parallel to the fibers of the orbicularis muscle, so that no deformity may remain. Subsidence of the symptoms is rapid after evacuation of the contents of the abscess. Between the attacks treatment should be directed toward improving the general health and alleviating the inflammation of the lid-margins; refrac- tive errors, which may cause styes, should be corrected. Sulphid of calcium has some repute. Bxanthematous Eruptions of the I/ids. — Ulcer of the lids, due to variola or small-pox, is of not infrequent occurrence. The parts attacked are the hair-follicles and sudorific follicles and glands. The results of severe attacks are pitting, cicatricial contraction of the lids, with ectropion and loss of the eyelashes, which, when permanent, produces the condition called madarosis. Treatment is directed toward limiting as much as possible the ulcerative process. Protecting the pustules by (lusting with a dry powder, such as starch and zinc oxid, in equal parts, or touching the ulcerated portion with a sharpened stick of nitrate of silver, has been advantageously employed. Vaccine Blepharitis ( Vaccine Ophthalmia, Vaccinia of the Eyelids). — This occasionally occurs from infection from a vaccination idcer. It usually affects the borders of the lids, and is characterized by the rapid for- mation of an ulcer of the lid-margin, accompanied by much redness, swell- ing of the lids and of the preauricular and submaxillary glands, together with general fever, malaise, etc. In the early stage the vesicles appear with pitted center, but later the pustules are quite characteristic. In the last stages of the ulceration they resemble syphilitic ulcers, and must be differen- tiated from these by the history and progress of the case. Associated with the disease of the lid, marked conjunctivitis occurs, often simulating a diphtheritic membrane. Treatment is directed toward allaying the early inflammatory symptoms, and later touching the ulcers with a '2 or 3 per cent, solution of silver nitrate. Aseptic washes to keep the eye clean should also be used. Kczetna appears either on the eyelids alone or is associated with general eczema of the face. It occur- also from the irritative secretions in chronic conjunctivitis, or in children as the result of rubbing the secretions from the eye upon the lids. It is most frequent in scrofulous or badly nourished children. Eczema is caused in adults by epiphora, ectropion, etc., the tears running over the cheeks excoriating the surface, [n these cases the Lesions .ire usually found on the lower lid. Treatment must be directed primarily to the cause. Locally, zinc oint- ment or Hebra's diachylon ointment, spread on lint or muslin and applied constantly, is satisfactory. Painting the -kin with a 2 to 10 per cent, solu- tion of nitrate of silver has been found to be very serviceable ; only the latter in strong solution blackens the -kin on exposure to light. Its action, how- ever, in moist or ulcerative eczema, i~ very effective. Herpes zoster ophthalmicus i> the term applied to that variety of n lev ii A urns. 245 herpes zoster which attacks the skiii of the eyelids and other areas supplied by the first division of the trigeminus nerve. The disease is characterized by the formation of vesicles over the terminal portion of the nerve. The attack is preceded by severe neuralgic pain over this area, succeeded by tin' formation of vesicles over the forehead, the eyelids, the nose, cheek, and the upper lip, the disposition of the vesicles depending upon whether the firsl or s( \\^\ division of the trigeminus is affected. The third division is rarely affected. The vesicles first contain a clear, limpid fluid, but rapidly become cloudy and purulent, and finally dry into crusts. On removal of the latter, deep ulcers are found. After healing, permanent scars remain, which, by their peculiar grouping, indicate the nature of the attack. Not infrequently the cornea is affected, which greatly complicates the case. These ulcers of the cornea may result in permanent opacities. Iritis and cyclitis are not uncommon, especially if the nasal branch is affected ; indeed, there may be a destructive inflammation of the whole eye (ophthalmitis). Palsy of the ocular muscles and atrophy of the optic nerve may follow herpes. The cause of herpes zoster is obscure, but it is an inflammatory affection of the trigeminus. Persistent neuralgia may remain after an attack of herpes. Treatment. — This is symptomatic. The vesicles should not be opened, but these should be dusted over with a drying powder (rice starch) and the ulcers allowed to heal beneath the crusts. Removal of the latter is productive of much pain. Internally morphin, quinin, and iron, according to indica- tions, must be given. Keratitis and iritis require the usual measures elsewhere described. ~Bleph.a.ritis(Blcpharitix ma rc/hudis, Blepharitis ciliaris, Blepharo-adenitis, Blepharitis ulcerosa, Psoropldhalmia, Lippitudo ulcerosa, Tinea tarsi, Sycosis tarsi). — On account of the peculiar anatomical structure of the margin of the eyelid this region is subject to a variety of diseases, with somewhat character- istic symptoms, forming a group by themselves. Rich in vascular and glandular structures, the edges of the lids are the seat of marked inflamma- tory disturbances, the more especially as they are greatly exposed to external irritation. Therefore disorders of the margins of the lids are among the most common of all diseases of the eye. In intensity of inflammation there are all degrees, ranging from a mere red fringe of the lids to a disorganization of their borders. Two principal varieties of marginal blepharitis have been described, according to the symptoms — (1) squamous or simple blepharitis, and ('2) ulcerated blepharitis. (1) Simple Blepharitis (Blepharitis squamosa). — In this variety the margins of the lids are bordered with a red fringe, fine bran-like scales ap- pearing at the roots of the cilia and between them, which drop off if the ey< - are rubbed. There is also a tendency for the cilia to fall out if disturbed : they grow again perfectly. When the scales arc removed the skin beneath is found to be hypercinic, but not moist or ulcerated. In another variety instead of the scales there is a wax-like secretion which adheres to the lashes, gluing them together, but on its removal there is no evidence of ulceration beneath, the tissues appearing simply red and hy- pereinic. (2) Ulcerated Blepharitis. — In this variety there are hyperemia, red- ness, shedding of lashes, and crusts. When the crusts are removed by wash- ing an ulcerative process is evident beneath them. Many yellowish-white points appear, from the center of each of which protrudes a cilium. Upon 246 DISEASES OF THE EYELIDS. pulling out the lash there is often found adhering to the root a small rounded drop of pus. Si ill deeper is found a small ulcerated base extending into the hair-follicle. The cilia are readily removed on the slightest traction. As the disease progresses the hair-follicles are successively involved in the ulcerative process, until, not infrequently, the entire series of cilia is destroyed, leaving cicatrices with their attendant and consequent deformity. When the cilium has fallen out a new one takes its place, of a different color, more or less stunted in its growth, and in a malposition the result of cica- tricial contraction of the ulcerated hair-follicles. The lashes thus become more and more stunted and misplaced or entirely destroyed. By the cicatricial contraction the lashes may be turned backward so as to touch the eyeball, giving rise to a condition of trichiasis, or the entire line of lashes may be destroyed, leaving the lid bald — madarosis. Another result of the ulcerative process may be the gradual eversion of the lower eyelid, due to the cicatricial contraction, which pulls the conjunctiva forward upon the lid-border, the lid itself falling away from the eyeball and permitting the tears to run over, in turn increasing the irritation (lippitudo, or " blear- eye "). The final result is an ectropion. Hypertrophy of the body of the lid not infrequently ensues, due to the long-continued inflammation, and pro- duces drooping of the upper lid (hypertrophic blepharitis). It may be seen, therefore, that blepharitis ulcerosa is a much more serious condition than blepharitis squamosa. The patient sutlers little inconvenience as the result of the disease in the milder forms, and consults a physician more on account of the disfigurement than from any great annoyance. In the more pronounced forms the sensi- tiveness to light, the irritation, the sticking of the lids in the morning, etc. are real discomforts. Patients are unable to use the eyes for close work with comfort, and when the lashes are greatly displaced, with the resulting corneal irritation, they become almost helpless. Etiology. — The causes of blepharitis are twofold — viz. local and general. The heal causes are external irritations due to vitiated air, smoke, injuries, and chronic conjunctivitis, especially if associated with excessive lachryma- tion, inflammation of the laehrymo-nasal passages, and disease of the rhino- pharynx. Abnormal shortness of the lids may excite the affection (Fuchs). Among the general causes are the exanthemata, scrofula, anemia, tuberculosis, syphilis, or malnutrition from any cause. Stubborn varieties may depend upon eczema, eczema seborrhoeicum, and seborrhea, and acne of the surrounding facial areas. Staphylococci are found in the pustules, and occasionally the tricophyton fungus {/>. tricophy- tiea). The demodex fotticulorum has also been seen in the lid-margin. Re- fractive errors unquestionably play an important rdle in the causation of marginal blepharitis, :i- well as in other irritative and inflammatory lid- diseases ; but they have not yet been accorded their due weight as causative factors in these affections. Correction of these errors by proper glasses will alone very often relieve ;i patient from troublesome blepharitis, which other methods seem powerless to effect. Pathology- — In blepharitis the inflammatory process involves chiefly the cilia and glands. In squamous blepharitis scales are produced on tin- lid-margins and the cilia fall out. These grow thinner and shorter .Hid li -- pigmented, and, ;i- the epidermis is casl off, they entirely liiil to grow. In blepharitis ulcerosa the epithelium and often the papillae are destroyed .it the -eat of u Ice ra t ioi i, and if the ulcerative process extends deeply into the SYPHILIS OF THE EYELIDS. 247 tis-iu's of the hair-follicles, thecilia are permanently destroyed and cicatricial contractions take place. Prognosis. — Blepharitis is essentially a chronic disease. It may la-t for years and not infrequently for a lifetime. In young persons it may disappear spontaneously as they grow older, while in other cases it persists in spite of all treatment. It is essential that treatment should be vigorous to prevenl permanent lesions. Treatment. — The treatment must have reference to both general and local conditions, as well as to the causes. Faulty states of the general health should be corrected by appropriate means. Excessive use of the eyes should be prohibited, refractive errors should be examined, and proper glasses pre- scribed. Chronic conjunctivitis, so generally present in these cases, should be relieved, and any obstruction to the free discharge of the tears through the proper channel should be removed. For the milder forms of blepharitis the non-irritating ointments give the most satisfactory results. After carefully removing the scales and crusts with warm water by gently washing them off, an ointment should be well rubbed into the roots of the lashes and along the margin of the lids, usually night and morning. For this purpose a 1 per cent, ointment of white pre- cipitate, as being especially mild, has been much used. The yellow and red oxids of mercury are also favorite prescriptions in the proportion of one-half to two grains to the dram of vaselin or simple cerate. A 5 per cent, solu- tion of chloral hydrate, alternating with a salve of pyrogallol (1 :8)and a 2 to 3 per cent, sulphur ointment, have been well recommended. In the severer cases associated with deposits of hard and strongly adherent crusts, which glue the lashes together, the use of a solution of five grains of carbonate of sodium to the ounce of water is most effective in removing them. It is important not to irritate the bases of the ulcers too much by violent means of removing the crusts. A pledget of absorbent cotton, moist- ened with the above solution, enables the patient or surgeon to remove the crusts effectually and without force. After the margins of the lids and cilia have been cleared of crusts the various ointments can be applied thoroughly to the diseased structures. In case of ulceration touching the ulcers with a five- to twenty-grain solution of nitrate of silver, or with a sharpened point of a silver-nitrate stick, acts most favorably. Where abscesses occur the cilia should be epilated with proper forceps, in order to give the remedies an opportunity of acting upon the diseased structures. No hesitation need be exercised about removing the cilia, for new hairs will replace those removed, even if they are repeatedly pulled out. When the disease has resulted in extensive cicatricial disturbances, as trichiasis, etc., proper operative measures alone are to be recommended. For the condition of madarosis no treatment avails. Phthiriasis (blepharitis pediculosd) is an affection resembling blepharitis, and is associated with it. The ciliary margins presenf a dark appearance, which is due to the presence of the nit- of the pediculus pubis. ( Hose exami- nation with a magnifying-glass of the borders of the lid will reveal the bases of the .'ilia full of the black eggs of the lice, and generally many individual lice clinging to the la-he-. Rubbing mercurial ointment into the margin- oi the lids destroys the lice and their eggs. Syphilis of the eyelids i< a somewhal rare affection. Ib>v< ver, nol only is the primary ulcer mef with in this situation, bul also secondary a tertiary lesions. Both sofl and indurated chancres occur on the -! in of the lids. The former i- an ulcer with a ragged edge and with a tendency to 248 DISK A.s/;s OF Till: EYELIDS. spread. It appears without history of injury or other cause. The hard, indurated base of the ulcer in the other ease is sullicieiitlv indicative of its nature, and in due time secondary manifestations of the disease are likely to appear. Nol infrequently the lids, along with other portions of the skin, are the seai of secondary eruptions. During the third stage, occasionally, ulcers and gummata appear in the lids, the latter often presenting a striking similarity to chalazia. These sometimes develop rapidly and undergo extensive ulcera- tive changes, producing ectropion, lagophthalmos, etc. Treatment must include the proper constitutional remedies, while the extension of the ulcerative process must be combated by the use of the cau- tery (nitrate of silver) and propel- washes, or with compresses moistened with bichlorid-of-mercury solution. Tumors and Hypertrophies. — Many benign growths occur in the eyelids, important on account of the disfigurement which they produce. A mono; these arc papillomata, or warts, which grow on the lids and their borders. Occasionally, from irritation, these growths may assume an epitheli- omatous type and prove serious. Their early removal, with cauterization of their bases, should he practised. Angioma (nevus) occurs on the lids or their margins as a congenital growth. A nevus appears as a bright-red -pot, not elevated, and usually is located near the margin of the lid. Its tendency is to increase in area some- what rapidly. The cavernous variety is usually elevated, sometimes gives a pulsatile sensation, and consists of greatly enlarged vessels. It disappears under pressure and becomes much enlarged when the patient stoops over. Some- times there may be a bruit present if the orbit as well as the lids is involved or if the dilatation of the vessels is extreme. The conjunctiva may also par- ticipate in the diseased process. A phlebolith in a varix of the conjunctival veins has been reported by Swan M. Burnett. Small Devi may be excised or cauterized with nitric acid or with the electro-cautery by means of the platinum point. Electrolysis may likewise be employed with advantage. In the larger varieties the growth may be cauterized at numerous points at a little distance from one another, as the cicatricial contraction of the -cars will cut off the vascular supply between. As little scar as possible should be aimed at, and frequent sittings may be advisable. bare forms of benign growths are fibroma, adenoma, papilloma, enchon- droma, neuroma, and lipoma. The last-named growth may produce a form of ptosis — the so-called ptosis lipomatosus. All of these growths should be re- moved if they produce any disturbing effects, and this is, as a rule, not diffi- cult of accomplishment. Cutaneous horns sometimes attain a considerable size. They arise from the skin of the lids, often near the margin, and sometimes involve a large proportion of the lid-area, 'flic excrescence is slow in its development and attains a horn-like hardness, especially toward its extremity. The growth should be cm off and a plastic operation replace the l< >>i cutaneous tissue. Xanthelasma (xanthoma, mtiligoidea) occur- in the form of rounded spots of various sizes on the surface of the skin of the eyelids. The patches are often situated on the eyelids near the inner angle, vary in size, and -how a tendency to increase in numbers. They have a peculiar dark-yellow color, which is their prominent feature. They give rise to no discomfort. They occur mostly in women of advanced years. CHALAZION. 249 The yellow or brownish-yellow patches may lie either on the surface of tlic skin (xanthelasma planum) or rise above it (xanthelasma tuberosum). These new growths of tissue are found to contain cells with granules or glob- ules of oil. Brown or yellow molecules ofpigmenl lie singly or in clusters in the cells and walls of the lymphatic vessels. Ablation may be practised on account of the disfiguremenl they produce. Chalazion (Meibomian cyst, tarsal tumor, cystic tumor, tarsal cyst) occurs as a round tumor of variable size, giving the feeling of a shot beneath the finger. The skin over it is freely movable, but the growth has a firm attach- ment to the tarsus beneath. Etiology. — The cause of chalazion is not well understood. Generally it occurs in persons subject to inflammatory disturbances of the lid-margins, frequently successive glands being attacked, one alter another, until most of the Meibomian glands of one or more lids have been involved. Refractive errors seem to be an important element in many bad cases of chalazion, especially of the recurring type. Fig. 172.-Vertical section of chalazion (Meibomian cyst); X 10, glycerin: 1, stratified epithelium •continued over the surface : 2, connective tissue outside tumor ; 3, capsule of fibrous tissue from which septa pass inward, dividing the cyst into lobules : 4. epithelial cells inside capsule : 5, fatty material occu- pying center of lobules, the (Alter layers being more opaque pollock). Pathology. — Chalazion may be solitary or several chalazia may occur in the lid, and the lower and upper lids of both eyes may be the seat of the growths. They originate in the Meibomian glands, and develop from an obstructive inflammation of the duct of these glands, which prevents the excretion of the sebaceous material. This accumulation aids in the development of an inflam- matory action involving the gland and its surrounding tissue. The result is a tumor of considerable size, the contents of which, undergoing a fatty de- generation, become soft, and till the sac with a gelatinous mass of granulation tissue containing giant-cells or with pus (Fig. 172). The process is very sim- ilar to the formation of an atheroma, except that the inflammatory changes are more marked. Then- i< no true cyst-wall. If allowed to take its course, the chalazion develops outward, toward the -kin (external chalai or involves the conjunctiva (internal chalazion). It frequently perforate- the latter, extensive granulations springing up on the under surface of the lid, often resembling a neoplasm. Usually a catarrhal conjunctivitis, which infect- the Meibomian glands, precede- the chalazion. Symptoms. — These vary somewhal in the acuti and chronic vari In the former the tumor may develop rapidly, with indications of much inflammation and with - • pain and tenderness. It resembl - 2.-.I » DISEASES OF THE EYELIDS. except that the tumor is more circumscribed and does not " point." The chronic variety grows slowly and causes no uneasiness, to the patient, except the feeling of weight in the lid which it gives (Fig. 17.°>). Should the growth perforate the conjunctiva, there may result some conjunctival and corneal irri- tation, due to the rubbing of the granulations upon these membranes. An acute chalazion is liable to be confounded with a stye, the diffuse appearance and "pointing" of the latter, however, serving to distinguish it. The chronic variety has been mistaken for small malignant growths and sebaceous cysts. The firm attachment of the chalazion to the tarsus should serve to differentiate it from a cyst. Sarcomata, when small, are difficult to diagnose, and some- times a microscopic examination becomes necessary to determine the true nature of the growth. PlG. 17U. —Chalazion. (From a patient in the out-patient department of the Western Reserve University, Medical Department.) Treatment. — The only satisfactory treatment for chalazion is surgical. Some relief, perhaps, may be afforded in the acute variety by frequent hot pack-, followed by the use of the yellow-oxid-of-mercury ointment. The proper surgical procedure for its removal is described on page 546. Sarcoma, as a primary growth, develops in the connective tissue of the lid-, ami occur- usually in children. In the early stage of its growth the skin moves freely over the tumor, but this rapidly invades the overlying tissues, which break down and become ulcerated. Sarcoma of the eyelids, of the small spindle-celled variety, may resull from traumatism. It sometimes resembles a chalazion, but careful examination is likely to show a deeper coloring, with diffuse swelling. Microscopical examination alone will some- times determine the true nature of the trouble. Primary sarcoma of the eyelid may arise from any of the subepithelial CARCINOMA OF THE LIDS. 25 1 tissues, and may be of the spindle-, large <>r small round-, or mixed-celled variety. Pigmentation (({'cells or cells and stroma is sometimes seen (melano- sarcoma). W. II. Wilmer, who has described a melanotic giant-celled sarcoma, has analyzed •">•"> eases, and finds that 4<> per cent, were spindle- celled, 43 per cent, round-celled, 17 percent, mixed, and 11 per cent, pre- sented myxomatous element.-. An early excision of the growth alone offers any hope of protection against a fatal outcome of the trouble. Even after thorough removal return of the growth occurs in 40 per cent, of the cases (Wilmer). Carcinoma. — The most usual type of carcinoma of the lid is the epitheli- omatous ulcer, commonly called "rodent or Jacob's ulcer." The border of the lid is the favorite starting-point for the growth, which occurs in elderly persons. It usually begins as a small pimple covered with a crust, and its Fig. 174.— Rodent nicer besinninqr in the left lower eyelid. (From a patient in land, Ohio, under the eare of Dr. Dudley 1'. Allen.) 'harity Hospital, Cleve- growth i- often exceedingly slow. As time goes on it gradually develops into a flat ulcer, with indurated, ragged, and elevated edges, attended with only a -light secretion. Eventually it may involve the lid-, eyeball, and adja- cent structures (Fig. 171). Rodent ulcer may he mi-taken for a syphilitic ulcer, l>ut generally the age of the patient, the -low growth of the tumor, and the therapeutic test with iodid of potassium, which rapidly relieves a syphilitic ulcer, suffices to differentiate the epithelial growth from the latter affection. It i- distinguished from lupus, because this disease occurs usually in young subjects, because of the greater inflai atory action of lupus, and because other portions of the body are at the same time similarly affected. Pathology. — Ordinary epithelioma of the eyelid presents no diff! from epithelioma of the -kin elsewhere. From the greatly thickened epider- mis irregular outgrowths penetrate into the subepithelial structures. Epithelial DISEASES OF THE EYELIDS. cell-nests may also lie in this layer, together with " epithelial pearls." The surrounding tissue is usually very vascular and infiltrated with round and epithelial cells. The growth may originate from the epidermis or from the epithelial lining of the sebaceous or sweat-glands; rarely from Meibomian glands. At times it appears as a raised ulcer with infiltrated edges. The growth may be ver^ -low, and cicatrization take place in the center a> the ulceration progresses at the edges. It' the ulcerative process is an elaborate one and extends into the deeper as well as surrounding tissues, a "rodent ulcer*' results. The stroma of these epitheliomata is always more or less infiltrated with round-cell- and presents the appearance of granulation-tissue. Rare forms of cancer of the lid-structures having their point of origin in the Meibomian or in Krause's glands may be denominated glandular carci- nomata, in contradistinction to the ordinary epitheliomata and rodent ulcers. Treatment. — Radical measures alone give any promise of permanent relict' in carcipomata. An early operation for their removal should be per- formed and the exposed surface covered with suitable skin-flaps. In the later stages palliative measures to aid in limiting the rapidity of the growth may he used. To further this end caustic, chloracetic acid, scraping with a curette, or the actual cautery may be employed. As milder measures aristol, chlorate of potassium, and injections of pyoktanin have been recommended. Not infrequently in the advanced cases it may be necessary to remove the eyeball, together with the orbital and periorbital tissues. I^upus Vulgaris. — Associated with lupus of the lace or nose the eyelids may beco the seat of this affection. The ulcers are formed by several points of infection coalescing and producing ragged, soft edges, which exude an offensive secretion. The disease frequently inflicts much damage to the lid-tissue, eventuating in marked cicatricial contraction and deformity. The history of the case, together with the fact that the face and nose are involved in the same disease, will serve to distinguish lupus from the syphilitic ulcer, for which it is likely to be mistaken. Treatment. — ( lauterization by means of caustic paste or the actual cautery gives the 1m -t results in the early stage of the disease. The ulcers may also be curetted. When the ulcers arc large sxcision may be practised, with the proper plastic operation for covering the denuded surface of the eyelids. I^epra. — Leprosy of the eyelids is very frequent in countries where the general disease is prevalent. Tubercular growths form in the region of the brows and cilia, producing loss of the lashes and eyebrows. Anesthetic patches of a color slightly different from the surrounding skin, with entropion and ectropion, are frequently developed. Elephantiasis Arabum i- characterized by a chronic hypertrophy of the skin and subcutaneous tissue. The lids reach enormous proportions, and from their mere weight prevent the patient from opening the eyes. The upper Md- .lie the ones usually affected. Elephantiasis occurs congen- itally or may result from an injury. According as the hypertrophy affects the lymphatics or the blood-vessels the name- of elephantiasis lymphangiec- imlis ;md elephantiasis telangiectodes have been assigned. Removal of the excessive growth of tissue sufficient to enable the patient to open the eyes offers the most hope of relief. Tarsitis is usually a chronic inflammation of the tarsus characterized by thickening of tin- body. Acute tarsitis, with sloughing of the tissues, has been described. There is often found associated with conjunctivitis ami blepharitis a thickening of the tarsus, especially in scrofulous subjects. Syphilitic tarsitis is the mosl frequent variety of the disease, and in this /;/. /,77/. I ROSPASM. 253 affection the thickening of the lids is often very marked, giving rise to much deformity. It usually occurs in the third stage of syphilis, and assumes the gummatous type of the disease; more rarely an acute form appear-. The symptoms of tarsi tis are gradual thickening of the lid, without marked inflammatory disturbance, and the consequent inconvenience to the patient of the bulk of the eyelid, which may droop over the globe. If the lower lid is the seat of the disease, the weight of the lid sometime- pulls it away from the eyeball, producing an ectropion. In severe eases an atrophy of the tarsus may ensue after the subsidence of the inflammation (Fig. 175). Fig. 175.— Syphilitic tarsitis. patient undei the Hospital.) •initz in the Philadelphia Treatment. — The remedies appropriate to blepharitis should be used locally, and any constitutional disturbance corrected by proper means. In tarsitis syphilitica treatment suitable for the specific disease should be insti- tuted. Recovery i- -low, but generally perfect. Blepharospasm i- characterized by a cramp-like contraction of some or of all of the tibei'- of the orbicularis muscle. A frequent condition in many persons is the contraction of a few fibers "t the orbicularis muscle in either the upper or lower lid, which is very annoy- ing. The twitching of the muscle may readily be seen by an observer. This condition i- usually indicative of some local irritation of the eye- or the lid.-, and i- of do great import. A more serious and uncomfortable phase of the difficulty is cramp o\ the entire muscle, when the eyelids close tightly and violently. There are two 254 DISEASES OF THE EYELIDS. varieties <>t' blepharospasm — the clonic and the tonic spasms. In the former the spasm is of momentary duration, and consists of a series of forcible uncon- trollable "Winkings;" in the latter there is a violent closure of the lids, which remain tightly shut for some minutes or for days or months, and the patienl i- rendered practically blind by the inability to use the eyes. Blind- in-- has occasionally resulted, manifest when the patient has become able to open the eyes, either with or without grave ophthalmoscopic changes. Blepharospasm may be either a symptomatic condition or an essential disease. Children especially are prone to have slight more or less frequent "blinking" attacks or nictitation, especially when using their eyes in school- work. They are generally found to have slight conjunctivitis or an asthe- nopic condition due to refractive error. Not infrequently associated with this i- a choreic or spasmodic affection of the facial muscles. Blepharospasm i- essentially due to reflex irritation of the fibers of the trigeminus, and hence occurs in follicular conjunctivitis, with foreign bodies in the eye ( when the spasms may be mine), with blepharitis, refractive errors, and muscular insuf- ficiencies. Depending upon the cause, the attacks are monocular or binocular, the latter form prevailing in all severe cases, the attacks being usually more severe on one side. In hysterical subjects the attacks come on without any known cause, the eyes close tightly, the spasm is persistent, and the patient is rendered helpless. In adults as well as in children the facial muscles may twitch as actively as the orbicularis. In elderly people the spasm is often associated with tie or with chronic conjunctivitis. Treatment. — The treatment of blepharospasm depends upon the cause. In case of local irritation removal of the foreign body, relief of conjunc- tivitis, blepharitis, or other local inflammation, correction of refractive errors, and gymnastic exercise for insufficiency of the eye-muscles are the essen- tial point- to be considered. The general health should be looked into, and tonics, especially iron, quinin, and strychnin, should be exhibited, care being taken that the latter does not aggravate the trouble. Antispasmodics, as conium and gelsemium, pushed to their physiological tolerance, may be of benefit. In many cases medication seems to have no beneficial effect. In some patients pressure on certain points seems to relieve temporarily the difficulty. The patient discovers these and learns to control, in a measure, the orbicularis spasm by pressing upon the point. This point may be situated on the fore- head or in some other portion of the head. In such cases galvanism, or, in very bad cases, hypodermic injections of morphin in these regions, may be tried. Complete rest from work, with change of climate, sea-bathing, or mountain-climbing, have sometimes proved efficacious when other means have failed. Ptosis (blepharoptosis, blcpharoplegia) i> a term properly applied to a drooping of the eyelid due to paralysis of the levator palpebrarum muscle. In addition t" true ptosis there i- a more or less marked degree of drooping of the lid expose the eyeball. This often is the case in tarsitis, hypertrophic blepharitis, granular conjunctivitis, ami tumors of various sorts occurring in the substance of the lid. Bu1 ptosis proper is due either to paralysis <>f the oculo-motor nerve or to a fault in the develop- ment of the levator muscle it-elf. The affection may be a congenital or an acquired one. In the congenital cases the ptosis may be associated with other congenital malformations of the lid-, eye, or orbit. In some cases of unilateral congenital ptosis, usually on LAGOPHTHALMOS. 255 the left side, while the eyelid cannol be raised voluntarily, it is raised when the jaw is moved during eating, or there i> contraction of the levator in asso- ciation with the external pterygoid. Not infrequently ptosis is the result of injury to the muscle-fibers or to the supraorbital branch of the oculo-motor (Fig. 176). Paralysis of the eye-muscles is frequently associated with ptosis, and it may be found in certain eases of hemiplegia or from lesion of the cortical center. In bilateral ptosis the peculiar pose of the head, which is thrown back to enable the patient to look under the drooping lids, is strikingly characteristic. Treatment. — The cause must determine the proper procedure. Medicinal measures must be instituted if the palsies are of syphilitic, rheumatic, or of Fig. 176.— Traumatic ptosis with cystic tumor of orbit. (Western Reserve University, Medical Depart- ment.) other origin which is amenable to medicinal agents. The surgical treatment is described elsewhere (see page 557). I,agOphthalmos manifests itself by an inability of the eyelids to do-,.. the degree of this immobility varying as the cause is a paralytic or a non- paralytic one. The non-paralytic causes art — shortening of the eyelids, which may be congenital or due to loss of tissue of the lids from burn-, ulceration, gangrene, etc. ; ectropion ; loss of reflex sensibility in the eyeball and protrusion of the globes, so that the lids are unable to cover them, as in exophthalmic goiter, orbital tumors, etc. The most marked cases are caused by paralysis of the orbicularis muscle, usually associated with facial paralysis. The distressing symp< - of lagoph- thalmos arise in connection with the cornea, which i- exposed to external irritations and suffers the loss of the lubricating and protecting action <>f the lids. The exposed portions of the cornea and conjunctiva become chronically inflamed, and ulceration and even blindness may be the result. Treatment should have in view, primarily, the protection of the eyeball from external irritation. Patients are likely to suffer most while isleep from inability to close the lids bv voluntary action. Hence in bad es the lids 256 DISEASES OF THE EYELIDS. should be closed with adhesive plaster, a compress and bandage, <>r by other suitable mean-. Relief should be directed to the cause of the affection in the paralytic variety, and the operation of tarsorrhaphy (page 547) may be re- quired. Symblepharon is an abnormal adhesion of the eyelid to the eyeball. It may be congenital, but is usually the result of injuries, especially burns from acid-, lime, or hot metal (Fig. 177). It occurs always when the con- junctival structure is destroyed in its sulcus and when the palpebral and bulbar conjunctiva' are cauterized in approximate positions. It also results from purulent and granular conjunctivitis, pemphigus, etc. Not infrequently the lid-margins become strongly adherent to the cornea by cicatricial bands or the entire body of the lid may be adherent i Fig. 17.S). Fig. 177.— Symblepharon due to burn hot metal. (Prom a patient in Western Reserve t'niversity, Medical Department, i Ankyloblepharon has the same causes as symblepharon, and likewise may be congenital or acquired. It consists of a union between the margins of the upper and lower lid-, and may be 'partial or complete. In the acquired variety burn- are the most common cause. Biepharophimosis is an agglutination of the eyelid- at the outer angle of the eye. ean-cd usually by eliroiiie eoiijti net ivi t i- or ulceration at the com- missure. The adhesions cause shorteningof the palpebral opening. Treatment. — These condition-, generally due to a similar cause, require like treatment. In case of injury, burn-, etc. care should be exercised to keep tin' lid- well separated from each other a- well a- from the eyeball. In case of extensive burn- of both the bulbar and palpebral conjunctiva no method will prevenl the lid and the eyeball from becoming adherent, with the formation of a more or less complete symblepharon. When the deformity has occurred suitable Burgical measures should lie employed for its correction (see page 5 18). ENTROPION. 257 Trichiasis is a term used to describe thai condition of the lids where the eyelashes are turned backward so as to rub against the eyeball. A single cilium or the entire row of lashes may be inverted. The most frequent cause of trichiasis is trachoma. The entire conjunctiva] surface being, as a rule, involved in chronic trachoma, the resulting cicatricial contraction affects the entire border of the lid and occasionally develops more or less complete trichiasis. The more localized affection i- likely to be due to burns, blepharitis, injuries, operation-, etc. The result of the lashes turn- ing in is marked irritation of the cornea, which often results in ulcers : thick- ening of the epithelial covering, somewhat simulating pannus ; constant lach- rymation ; and, in long-continued cases, permanent impairment of vision. Distichiasis is a term applied to that affection where there arc double Fig. 178. — Complete symblepharon due to burn. (From a case in Western Reserve University, Medical Department. rows of lashes, one row being directed properly, while the other is turned backward against the eyeball. Some authors consider distichiasis -imply one step in the development of trichiasis and assign the term to the congenital affection alone. The causes of the two affections are the same. Treatment. — Should a single lash or a small number of lashes turn in, temporary relief i> afforded by ( pilation of the cilia which are at fault. The lashes grow again, however, and this operation must be frequently repeated. Patient- can often remove the lashes themselves with a pair of cilium fore For permanent relief electrolysis or some other operative procedure must be employed i see page 5 16). Entropion is a turning inward against the eyeball of the external lid- margin. Not only the lashes bul the skin of the palpebral margin is rolled back againsl the eye. Two varieties of this affection have been described, the spasmodic and the organic. The former results from the over-acti m of the orbicularis muscle due to the reflex irritati f conjunctivitis, kerat etc. En elderly people it not infrequently results from operations when eye ha- Keen kept bandaged too long. The organic type results from chronic 17 258 DISEASES OF THE EYELIDS. trachoma, diphtheritic conjunctivitis, burns, injuries, etc., which lead to cica- tricial contraction of the conjunctiva. The effecl upon the cornea may be serious on account of the production of ulcers, opacities, etc. Treatment. — Spasmodic entropion is generally relieved by the disappear- ance of the conjunctivitis, keratitis, or foreign substance which has caused it. Early removal of the bandage is necessary when the entropion occurs after cataract operation.-. Strips of adhesive plaster applied to the lid-margin by one extremity and by the other to the cheek, or collodion painted over the lid. or strips of gauze fixed with collodion applied in the same manner as the adhesive strip-, serve a most useful purpose in case of spasmodic ectropion. The s< rr<-fim has been used with advantage by fixing a fold of the skin, thus pulling the lid-margin away from the eyeball. The chronic types of entropion require careful surgical treatment. The operations are described on page 548. Ectropion i- a rolling outward of the eyelids, so that the conjunctival portion is exposed to view. This eversion may be partial or complete. It may also be spasmodic or muscular and chronic or or- ganic. In the former case it is due to the over-action of the peripheral fibers of the orbicularis muscle. The lower lid sometimes shows a tendency to droop, particu- larly in elderly people and in persons affected with facial palsy. The tears thus run over the cheeks and occasion additional irritation. The causes of organic ectropion are those which produce a cicatricial shorten- ing in the length of the eye- lids, as chronic blepharitis, lupus, necrosis of the orbit or malar hone, abscesses, burns, and injuries ( Fig. 1 79). The eve beinir more or less exposed, the cornea suf- fers from external irritant-. Treatment. — No1 infrequently the excessive lachrymation which occurs in ectropion may be cured by slitting up the canaliculus and passing probes through the naso-lachrymal duet. Associated inflammation of the cornea and conjunctiva should receive attention. The severer chronic forms of the affec- tion require operative measures for their relief (see page 551 ). Seborrhea is characterized by a secretion on the margin of the lids cither of an oily fluid or of :i sebaceous material, which dries, forming crusts or scales along the cilia. Generally, seborrhea of the face, scalp, or other portions of the body i- an accompanying affection. It not infrequently occurs in young persons about the age >>\' puberty. Conjunctivitis and marginal blepharitis are frequenl concomitants. Treatment mu-t be directed to the improvement of the general health. Removal of the crusts and the application of mercurial or sulphur ointments, together with measures suited to conj stivitis and blepharitis, are required. Fig. 179.— Case ■ ! ectropion (From a patient in On- Charity Hospital.) CHBOMIDBOSIS. Milium. — Milia arc accumulations of sebum in closed sebaceous glands. These growths arc about the size of a milletseed, from which they take their name. They present a yellowish-white appearance, and are slightly elevated above the surrounding skin, giving the feeling of a pinhead under the finger. They usually indicate improper care of the skin, and occur in persons with some disturbance of digestion, constipation, etc. Treatment. — Hot applications, frequently repeated, together with suitable remedies for indigestion or constipation, will prove beneficial. After removal of the milium with a knife-point or needle, hot packs and mild ointment-, well rubbed in, will afford relief. Molluscum contagiosum (molluscum sebaceum) occurs in the lids in the form of small rounded tumors which originate from the sebaceous glands. They attain the size of a pea, have an umbilicated appearance due to the ori- fice of the gland on the summit of the growth, and have a wax-like color. The material from the growths is contagious. The disease not infrequently occurs among children in asylums and schools in the nature of an epidemic. The contagious nature of the disease is supposed to be due to a parasite, and the aifection is allied in character to contagious epitheliomata. The parasite is believed by some author- to belong to the class Coccidia, and to inhabit the epithelial cells and cause the formation of these small prominent epi- thelial growths. The coccidia multiply in the cells of the epithelial pro- jections; these are then cast off and accumulate as a mass of epithelial detritus. According to H. Muetze, the molluscum corpuscles are the prod- uct of a degeneration of the epithelial cells caused by the contagium, the nature of which is uncertain ; but the corpuscles themselves are not parasites. Treatment consists of opening each molluscum and scraping out it.- con- tents. Cauterizing the sac with nitrate of silver may also be employed. Hphidrosis (hyperidrosis) is a rare affection of the lid- characterized by profuse secretion from the sweat-glands. It is associated with excessive sweating of other portions of the lace or body, and has been noticed in cases of unilateral facial sweating. Its cause is not understood. It may produce excoriations, especially at the angles of the eyes and in the skin-fold-. Treatment must be directed to the excoriations of the -kin and to the cause if it can be discovered. Chromidrosis I sometimes called seborrhcea nigricans 1 ) is the formation of various colored secretions on the eyelids, the oily-like fluid giving a bluish or blackish color to the affected skin. It usually occurs on the lower lid. The discoloration can readily be removed by wiping. Some author- believe that it i- always an evidence of malingering, as it most frequently occur- in hysterical patients, particularly young women. In rare instances it i- genuine. It may be caused bv a deposit of dust upon a cutaneous surface affected with seborrhea. Treatment should be directed toward the relief of any general disturb- ance of the health. The discoloration may be removed with some oily sub- stance; lead-water and glycerin have been recommended. Sebaceous cysts arc small rounded bodies of the size of a pea or of a hazelnut which occur in the thicker portion- of the skin of the eyelids, especially in the superior or external orbital portion of the lid | Fig. They develop from the sebaceous follicles of the skin, and contain (•eon-, oily- like material, and frequently fine hairs. They have well-formed 1 For ;i full account of thi> affection see a paper by I>r. .1. K. Mitchell in the Phila. Jwrn., 1898, L 117-119. 260 />/,v/;j.s/;,s OF THE EYELIDS. cyst-walls, which enables the surgeon to dissect them out without great diffi- culty, this being the proper method of treatment. JF' ^ ^^ *% Fig. 180.— Sebaceous tumor of the eyelid. (From a patient in the Western Reserve University, " Medical Department.) Dermoid cysts likewise occur in the same region and should be removed in like manner. Cysticercus has been observed a few times under the skin of the eye- lid-, having the appearance of a sebaceous cyst, only the contents are fluid. On opening the tumor the remains of the parasite are discovered. THE EYEBROWS. The eyebrows may he the seat of eczema or of seborrhea, and are a favorite situation for the developmenl of sebaceous and dermoid cysts. Occasionally these growths extend some distance into the orbit, where by pressure they may produce a depression in the underlying hone. DISEASES OF THE LACHRYMAL APPARATUS. By SAMUEL THEOBALD, M. 1)., OF BALTIMORE. In treating of diseases of the lachrymal apparatus it is convenient to con- sider, first, those affections which have to do with the lachrymal gland and its ducts, and, second, those of the drainage apparatus, including the puncta, the canaliculi, the lachrymal sac, and the nasal duct. The lachrymal gland, prob- ably owing to its protected position and its multiple ducts, is, comparatively speaking, rarely the seat of disease, while, on the other hand, disease of the drainage apparatus, doubtless because of its intimate anatomical and patho- logical relationship to the nasal passages, is of very frequent occurrence. DISEASES OF THE LACHRYMAL GLAND. Dacryoadenitis, or inflammation of the lachrymal gland, occurs as an acute and as a chronic affection. Both varieties are rare, though it seems not improbable that acute inflammation of the gland is sometimes mistaken for cellulitis of the orbit, from which it is not always easy to differentiate it. Etiology. — It occurs more frequently in children than in adults, and oftener in women than in men. It has been known to assume an epidemic character, and Galezowski reports having met with an unusual number of cases during an epidemic of mumps. Other causes to which it has been ascribed are traumatism, " cold," rheumatism, gout, struma, syphilis, septic absorption, and the extension of inflammation from the conjunctiva and cornea. It is usually unilateral, but not infrequently both glands arc involved. Symptoms. — Acute dacryoadenitis gives rise to severe pain, which may be accompanied by elevation of temperature, cerebral excitement, sleepless- ness, and delirium. The lids, especially the upper lid, are greatly swollen, and there is marked chemosLs of the conjunctiva. The eyeball may be dis- placed and its movements restricted and rendered painful through the enlarge- ment of the gland. Palpation of the exquisitely sensitive gland is difficult because of the edema of the lids, and eversion of the lid, to permit of it- inspection, is out of the question. The general appearance of the eye is not unlike that which characterizes purulent conjunctivitis (S. ( '. Ayres). Suppu- ration may supervene within a few days, the pus making its way through the integument of the lid or into the conjunctival cul-de-sac, or the inflammation may subside without the formation of pus. in chronic dacryoadenitis the characteristic enlargement of the gland may be recognized by palpation, and sometimes by simple inspection. By everting the upper lid the swollen gland may be brought into view as a red, tongue- shaped, nodular mass ( Hirschberg). The gland Is usually sensitive to pre* but the pain, swelling of the lids, and conjunctival chemosis are much pronounced than in the acute variety of the disease. A.s in the latter, there may be marked displacement of the eyeball, usually downward and inward, 261 262 DISEASES OF Till-: LACHRYMAL APPARATUS. ;iii<1 this may give rise to diplopia. In rare instances non-suppurative dacryo- adenitis {mumps of the lachrymal gland, Hirschberg) is bilateral. Treatment. — The treatmenl of acute dacryoadenftis, if the ease is seen at the outsel of the attack, should consist in Leeching, the application to the lid an the presence of pus can be detected it should be evacuated by an incision either through the integument of the lid or through the conjunctival cul-de-sac as may seem to be indicated. In chronic inflammation of the gland the local application of mercurial or compound iodin ointment, and the administration of alteratives and tonics, an- indicated. Extirpation of the gland (see page 596) may be necessary should it become so enlarged as to endanger the integrity of the eyeball. Fistula of the lachrymal Gland. — This troublesome variety of lachrymal fistula may be a consequence of dacryoadenitis or may he of trau- matic origin. Cases of congenital fistula of the lachrymal gland have also keen observed. Idie fistulous opening is usually at some point in the upper lid, and the constant flow of tears, which prevents its closure, gives rise to much annoy- ance. It is not easy to bring about a healing of the fistula, and if this is accom- plished, it is at the risk of precipitating a fresh attack of inflammation of the gland. The operative procedure which has proved most effectual is that proposed by Sir William Bowman (see page 596). Dacryops, or cyst of the lachrymal gland, is a rare condition due to occlu- sion of one or more of the efferent ducts of the gland. It has also keen met with as a congenital affection. I pon eversion of the upper lid the cyst may be brought into view as a semi-transparent, elastic swelling, consisting, perhaps, of several nodules. I tilling a spell of crying the cyst may become markedly increased in size. Treatment. — This consists in establishing a permanent opening between the cyst and the conjunctival sac. This may be done by removing a portion ot' the cyst-wall and preventing the closure of the wound by the repeated introduction of a prokc, or, as suggested by von Graefe, a silk thread may be passed through the wall of the cyst, tied in a Loop, and left to cut its way Ollt. 1 Dacryoliths (Lachrymal <' point of juncture with the lachrymal sac. (For description of this operation see page 596.) A- congenital anomalies doubh puncta and double canalieuli have been observed, and in connection with absence of the puncta the canalieuli have been represented by slighl furrow- alone the lid-margin. Malpositions of the Puncta. -In their normal position the puncta lie in contact with the eyeball. Mai posit ions of the upper puncta are not common, bul faulty positions of the lower puncta arc frequently met with. DACRYOCYSTITIS. 265 Emersion of the puncta i- present in nearly all cases of ectropion ; it also occurs in inflammatory thickening of the lid-margin, in senile relaxation of the palpebral tissue, and in facial paralysis. Inversion of the puncta is met with in entropion. Occasionally, owing to the small size or deeply-set position of the eyeball, the puncta are not in apposition with it, and epiphora results, as i1 does when the puncta are everted, through failure of the tears to find their way into the canaliculi. Treatment. — The efficient remedy in all malpositions of the puncta is division of the canaliculus. It not only relieves the epiphora, but usually leads to the rapid disappearance of the conjunctivitis and blepharitis which are its common accompaniments. Atresia of the Canaliculi may occur as a congenital defect in con- nection with absence of the puncta, as has already been mentioned ; it may also be of traumatic origin. ( ircumscribed strictures of the canaliculi, located usually near the juncture of the canaliculi and the lachrymal sac, are of frequent occurrence, especially in association with stenosis of the nasal duet. When the canaliculi are completely obliterated their restoration by opera- tive procedure is impracticable ; but it may be possible to make a passage- way directly into the lachrymal sac, and by repeated probings cause it to remain patulous, as was done in the case to which allusion ha- been made under the head of Atresia of the Puncta. The circumscribed strictures may usually be overcome by the passage of a small lachrymal probe or of the straight probe shown in Fig. 182. Division of the canaliculus may be called for if the stricture is difficult to overcome or is disposed to recur. Dacryoliths occasionally form in the canaliculi. They were formerly sup- posed to be simply concretions of lime, but are now known to be composed in great part of a fungus believed by some investigators to be identical with the leptothrix buccalis. Colin, however, denies this, and suggests the name streptothrix Forsteri. Goldzieher has met with eases in which a cilium occu- pied the center of the dacryolith, and was probably the exciting cause of its development. The presence of dacryoliths in the canaliculus, which may be detected by the circumscribed swelling to which they give rise, causes epiphora and may excite conjunctivitis. Their early removal, which may necessitate division of the canaliculus, is indicated. Polypi have been known to form in the canaliculi, and may project through the puncta. They should be removed, the canaliculus, if necessary, being divided, as soon as their presence is recognized. Foreign bodies, such as eyelashes, bits of the beard of wheat and barley, occasionally find their way into the canaliculi, where they may remain for a long time, causing considerable annoyance. If they project through the puncta, they may be seized with forceps and easily withdrawn ; otherwise division of the canaliculus may be necessary to effect their removal. In one instance (reported by Haflher) an ascaris lumbricoides was removed from the lower canaliculus. Dacryocystitis.— Inflammation of the lachrymal sac, or dacryocystitis, occur- as a chronic and as an acute affection. The former is usually denomi- nated blennorrhea of tfo lachrymal sac, while the latter is often spoken of as abscess of the sac. Etiology and Symptoms.— Primary inflammation of the lachrymal sac i- of rare occurrence. It i- oftenest met with in the new-born, usually in the form of a mild blennorrhea : ii is said to occur in strumous children, and it may be excited by external violence or the entrance into the sac oi an irr 266 DISEASES OF THE LACHRYMAL APPARATUS. fluid. In the large majority of cases dacryocystitis is secondary to, and dependent upon, stricture of the nasal duet. Although inflammation of the lachrymal sac frequently gives rise to con- junctivitis and keratitis, the reverse rarely happens. The truth of this state- ment is strikingly illustrated in gonorrheal conjunctivitis. Although the gonococci doubtless find their way in greal numbers into the lachrymal sac, dacryocystitis as a complication of gonorrheal conjunctivitis is, so far as the writer can learn, practically unknown. On the other hand, there is the closesl pathological sympathy between the lachrymal sac and duet and the nasal passages, and doubtless in a majority of cases dacryocystitis is traceable, directly or indirectly, to nasal disease. Such being the ease, it is not surprising, when one hears in mind how almost universally prevalent catarrhal affections of the nasal mucous membrane are, that inflammation of the lachrymal sac and nasal duct should he of compara- tively frequent occurrence. Watering of the eyes is a usual symptom of acute rhinitis, and probably in most pronounced eases of this affection the mucous membrane lining the lachrymal drainage apparatus participates to a greater or less extent in the general nasal catarrh. With the subsidence of the rhinitis the lachrymal catarrh and the transient occlusion of the nasal duct which has probably accompanied it usually disappear, and the parts return to a healthy con- dition. Exceptionally, however, because of the severity of the inflammation, the occurrence of a second or third attack before the first has been recovered from, a congenita] narrowness of the nasal duct, or a peculiar susceptibility of the lachrymal passages to disease (a susceptibility which is not infrequently inherited), the inflammation of the walls of the duct does not subside with the nasal affection, and presently assumes a more serious character. Under such circumstances the inflammation, which at first was simply a catarrh of the mucous membrane, invades the underlying periosteum, and the temporary occlusion of the duct from engorgement of the submucous plexus of veins give.- place in time to a permanent stenosis from periosteal and osteal thickening. In this way — and, perhaps, still more frequently from the ex- tension of chronic inflammatory affections of the nose to the lachrymal passages -stricture <>/ the nasal duct, which, as has been said, is the usual forerunner of dacryocystitis, commonly arises. The chronic nasal affections of inherited and acquired syphilis, it may be remarked, are especially liable to involve the lachrymal apparatus. Blows upon the bridge of the nose <>r about the inner angle of the eye may not only cause inflammation of the lachrymal sac, as has been indicated, but may lead to the development of stricture of the nasal duct. When once the occlusion of ilir duet is complete, the tears, mucus, and epithelial d6bris which collect in the lachrymal sac are invaded by bacteria and undergo putrefactive change-. This soon leads to inflammation of the lining membrane of the sac, and the condition known aschronic dacryocystitis or blennorrhea of tin- lachrymal sac bee - established. This condition does nol give rise to pain, but the attendant epiphora and regurgitation of mucus and muco-pus through the puncta into the conjunc- tival sac not only cause greal annoyance, but, as ha- been stated, may bring on chronic conjunctivitis and blepharitis, and even corneal inflammation. The accumulation of tear- and mucus frequently Leads to a perceptible distention of the sac (mucoceh (, which disappears under slight pressure with the tip of the finger, the contents of the sac usually regurgitating through the a err/: dacryocystitis. 267 puncta, but exceptionally, when the stenosis of the duct is incomplete, escaping into the nose | Fig. 183). Fig. 183. — Mucocele : fracture of superior maxilla : exostoses of nasal bones. (Case under care of Dr. de Schweinitz in the Philadelphia Hospital.) In some instances this state of chronic catarrhal inflammation lasts indef- initely, without undergoing appreciable change; but in others, through the influence of cold, a slight traumatism, the entrance into the lachrymal sac of pyogenic organisms of unusual viru- lence/ some constitutional disorder or, as seems to happen not infrequently, the sudden occlusion of the canaliculi at their point of junction with the sac, the inflammation undergoes a sudden and acute aggravation. Severe pain, accompanied by great distention of the sac and marked edema of the lids and surrounding parts, comes on, and decided evidences of consti- tutional disturbance, such as fever, loss of ajtpetite, sleeplessness, etc., manifest themselves. These are the symptoms which characterize acute dacryocystitis or abscess of the lachrymal sa& (Fig. I84),and which in many cases of stric- ture of the nasal duct recur from time to time so long as the occlusion of the duct i> permitted to remain. After several days of intense suf- fering the integumenl over the sac assumes a yellowish appearance, becomes thinned, and, if left to itself, usually gives way al a point ju-t below the 1 Besides the commoner pyogenic organisms, the streptococcus pyogenes lias been found in dacryocystitis, especially, it is claimed, in the acute exacerbations. Pig. 184 v.titt- dacryocystitis. 268 DISEASES OF THE LACHRYMAL APPARATUS. internal palpebral ligament, permitting the purulent contents of the sac to escape, and affording the individual immediate and almost complete relief from his sufferings. Exceptionally, the inflammation subsides without perforation of* the sac, and the pus ultimately escapes through the canal iculi and puncta. It is a fact worthy of remark that during an attack of acute dacryocystitis it i- scarcely ever possible to empty the distended sac by external pressure, although alter the subsidence of the acute inflammation pressure will usually cause the contents of the sac t<> regurgitate through the canaliculi and puncta, as, in all probability, was the ease before its onset. From this it would seem probable that when the sac is unduly distended a valve-like closure of the canaliculi at their point of juncture with the sac occurs; and it may he that this i- often a potent factor in the causation of acute dacryocystitis. After the content- of the acutely inflamed lachrymal sac have been evacuated, either spontaneously or by an incision, the inflammation rapidly subsides, and within ten days or two weeks the opening through which the discharge has occurred usually closes, and the sac resumes its previous condition of chronic blennorrhea. Exceptionally, however, the cicatrization of the opening is prevented by the continual discharge through it of tears and muco-pus, and the condition known as lachrymal fistula becomes established — to remain, perhaps, for an indefinite period. Treatment of Dacryocystitis. — There is but one effectual and rational way of curing dacryocystitis, and that is by eradicating the stenosis of the nasal duet upon which, a.- has been stated, it almost invariably depends. During an attack of acute inflammation of the sac, and for some days after its subsidence, operative interference with the strictured duct is out of the question, and we must, for the time being, content ourselves with the administration of anodynes and such other constitutional remedies as the condition of the patient may seem to call for, and the local application of soothing fomentations, to be followed, in all probability, by an early incision through the anterior wall of the sac, below the internal palpebral ligament. Such ;in incision, if made in the direction in which the skin tends to wrinkle — that is, from above and toward the nose downward and outward — does not leave :i perceptible scar, and gives a freer exit to the retained pus than docs an incision into the sac along the canaliculus. A pad of gauze wet with a lotion of opium and boric acid (ext. opii, gr. x-xv, acid, boric, gr. lx, aq. de-til., §iv), and covered with a piece of rubber ••protective" to prevent evaporation, forms a cleanly and convenient substitute for q poultice, and will be found a very useful application in these cases. In chronic blennorrhea of the sac, if for any reason it is not practicable to treat the strictured nasal duet, a considerable measure of relief may he obtained from slitting the lower canaliculus and prescribing a collyrium, either of bichlorid of mercury (1 : 12,000) or of alum (gr. ij) and boric acid (gr. x- xv to s unce), to be dropped into the eye two or three times a day, explicit instructions being given to empty the sac of it- contents b) pressure \\ ith the finger-tip before each instillation of the drops. It i- well to bear in mind that abscesses occasionally occur in the neigh- borhood of the lachrymal sac (prelachrymal abscess), which, from their appearance only, cannot always be distinguished from dacryocystitis. The history of the case, however, ahowing the absence of pre-existing symptoms of lachrymal disease, will usually make the diagnosis plain. Stricture of the Nasal Duct. — A- to the etiology of obstructions of STRICTURE OF THE NASAL DUCT. 269 the nasal duct, little need be added to what has already Keen said upon this subject in treating <>t' Dacryocystitis. How often syphilis, both inherited and acquired, is a factor in their causation, especially when it has invaded the nasal passages, has already been pointed out. 1 Syphilitic gummata have Keen met with in the lachrymal sac, as well as in the duct. Tuberculosis of the nose, through extension to the lachrymal passages, has been known to cause stenosis of the duct, and polypi of the lachrymal sac to produce a like effect. The exanthematous fevers — measles, scarlel fever, and small-pox — also may lead to occlusion of the duct through the inflammation of the nasal mucous membrane which attends them. As to the location of the strictures, there is no part of the duct in which they are not frequently encountered, although their most common situation is at its upper extremity. Multiple stricture, at least in cases of long stand- ing, is the rule. As the strictures are the outcome of periosteal inflammation, they are almost invariably, in part at least, of bony structure. They may be circumscribed and annular in form (a thin bony septum being sometimes encountered), or ill defined and of wide extent, involving a considerable part of the length of the duct. When situated at the lower extremity of the duct their existence is not so easily recognized, and it may happen that a mistake of this kind will render the treatment of no avail. The stenosis of the lachrymal duct which occur- in the new-born is usually of an entirely different character, being due simply to tumefaction of the mem- branous walls of the canal, and in consequence it generally yield- readily to treatment, operative interference being only exceptionally called for. A sim- ilar condition is occasionally met with in adults, and may be suspected if the symptoms of occlusion of the duct are of but short duration. Prognosis and Treatment. — The confessedly poor results which, in the main, have been obtained in the treatment of strictures of the nasal duct are, in the writer's opinion, attributable chiefly to the inadequate size of the probes which are commonly employed to overcome the stenosis. The great merit of the invaluable operation devised by Bowman of slitting the cana- liculus as a preliminary step in the treatment of lachrymal strictures (see page 596) is that it permits the passage of probes sufficiently large to overcome entirely the stenosis and restore completely the normal caliber of the canal. Nevertheless, Bowman himself fell far short of appreciating this fact, as is shown by the small size of the probe- which he employed,-' and, owing to an unreasoning conservatism, which those who have emancipated themselves from its influence can scarcely comprehend, the same may be said, even at the present day, of the greal majority of those who have followed his plan of treatment. The absurdity of attempting with a probe of [.50 mm. diameter to restore to it- normal dimensions an occluded canal which in health has an average diameter (measured in it- shortest axis) of somewhal more than -1 mm., it would seem should be evident to all ; but experience -how- that such is far from being the case. 1 Seventeen em of two hundred and forty cases of stricture of the nasal duel in < •• >ki's clinic were found to be of syphilitic origin. • The largesl of Bowman's probes, No. 6, had a diameter of aboul L.3 mm., or, according to Soelberg Wells, about .'. of an inch. Dr. hsaac Hays of Philadelphia, ii may be remarked, had previously used a slightly larger probe than this 1.50 nun. without dividing the canaliculus. paper by the writer upon "The 1 se of Large Probes in the Treatmi nl ol Stri of the Nasal Duct," Tran . \Ieduxd and Chirurg. Faculty of Maryland, 1877, p. ments of the nasal duel given by Mr. Henry Power in " Lectures upon I 'he Lach- rymal Apparatus," published in the London Lancet, l s - ,; . vol. ii. 270 DISEASES OF THE LACHRYMAL APPARATUS. The accompanying illustration (Fig. 185), which represents graphically the results of measurements of the nasal duct made by the writer, and de- scribed in the paper to which reference has been given, is in this connection instructive : • Bowman's No. 6 probe ; diameter = 1.50 mm. ^k Theobald's No. 1(1 probe; diameter 1 nun. ^fc Average size of 10 adult nasal ducts, cadaver; diameter = ^^ 4.47 — mm. ^^ Largest of Id adult nasal ducts, cadaver ; diameter 5.25 mm. Largest of 70 bony nasal ducts ; diameter = 7 mm. Pig. 185. — Diameters of probes and nasal ducts. Besides the treatment by means of probes, there are other methods of dealing with stenosis of the duct and its accompanying dacryocystitis which have their advocates. Although the gold canula of Wathen and Dupuytren i- probably scarcely ever used at the present day, there are many who still employ styles of different patterns made of lead, silver, or aluminum, and others who practise division of the strictures as recommended by Stilling, to whom the credit of having originated this method of treatment is usually given. The interesting fact, however, has recently come to the writer's knowledge that a- early as 1846 the late Prof. Xathan \l. Smith of lialtimore dealt with lachrymal strictures in this manner, and devised a knife of peculiar pattern for this especial purpose. 1 In intractable cases of dacryocystitis dependent upon occlusion of t he nasal duct, which have failed to yield to less radical measure-:, removal of the lachrymal gland (see page 596), and also excision of the lachrymal sac page 597) or its destruction by means of caustics or the galvano- or thermo-cautery (see page 597), arc practised by some ophthalmic surgeons. and. it is claimed, with excellent results. The writer has had no experience with these last-mentioned procedures, not having encountered cases in which such radical measures seemed to be indicated. As to the employment of styles, lu~ experience with them has not been satisfactory, and leads him to regard them as of limited applicability, being useful only when time will not permit of the proper carrying out of the probing treatment. Briefly described, the writer's method of dealing with strictures of the nasal duct, which he has employed almost without exception in all cases that have come into hi- hands during the past twenty year-, and which has yielded, as a rule, mo-i gratifying results, is as follows j The lower 2 canaliculus, after having been slightly dilated by the passage of a No. 1 or No. 2 probe cocain having been previously instilled into the conjunctiva] sac), is divided well up to its juncture with the lachrymal sac with Weber'- beak-pointed canaliculus knife (Fig. 415), or, preferably, with the writer's article upon "Diseases of the Lachrymal Apparatus," in a System of 1 1 • ■ ■ i (ht /. twelve cells may bo used, the negative pole being connected with a probe which has Keen intro- duced into the duct, while a moist sponge connected with the positive pole is held iu contact with the cheek. NO attempt is made by means of syringes to inject antiseptic or other solution into the lachrymal sac, hut, instead, a collyrium is prescribed, which the patient is instructed to drop into the inner corner of the eye three times a dav, after having pressed out the contents of the sic with the finger-tip. The collyria which have been found most useful are a solution of bichlorid of mercury (1 : L2,000) and one of alum and boric acid, containing 2 per cent. of boric acid and one-half of 1 per cent, of alum. Formaldehyd (1 : 2000) i~ much employed by some surgeons, as are all of the usual antiseptic and astringent collyria. The presence of a lachrymal fistula, even when accompanied by caries of the underlying bone, has not seemed to call for especial treatment. The fis- tula has been found to heal promptly, and the carious bone to become re-cov- ered with periosteum as soon as the stenosis of the duct has been overcome by the passage of the large probes. The frequent dependence of lachrymal disease upon nasal catarrh is kept constantly in mind, and treatment is directed to the nasal passages whenever it seems to he indicated. For tin- purpose a weak solution of bichlorid of mercury (1 : 5000), to which is added a small quantity of chlorid of sodium and glycerin, applied to the nose several times a day by means of a hand- atomizer, has been found especially efficacious. (For full particulars in refer- ence to measures suited to such conditions see seetions devoted to diseases of the rhino-pharynx.) 'Idie length of time during which the probing must be kept up varies con- siderably in different cases : hut it i- a sale rule not to discontinue the use of the probe altogether as long as there is any evidence of dacryocystitis or any roughness of the wall- of the duet noticeable on passing the probe. In obsti- nate cases, however, it is well to lengthen the interval between the probings, as it sometimes happens that the inflammation is kept up by the too frequent introduction of the probe. In several instances, when patients from a distance could not remain under treatment as long as was thoughl desirable, it has been found practicable to teach them to probe their own nasal ducts with the large probes which had been previously introduced, cocain being first instilled to minimize the pain. In this way relapses, which otherwise might have occurred from the too early discontinuance of the treatment, have been I ig 186 Modified form "f lachrymal probe for use by j >; 1 1 1 . ■ 1 1 1 - (actual size). avoided. The probe represented in Fig. 186 was devised by the writer for this purpose, and has been found very useful. In the transient occlusion of the nasal duel which occur- in the new-born operative interference, as has been stated, is seldom called fur: nevertheless, if the collyria of bichlorid of mercury, of alum ami boric acid, and, per- haps, a weak solution (gr. | to §j) of nitrate of silver, have been tried per- Beveringly without effect, it may become necessary to divide the canaliculus and introduce a probe. The outcome of this treatment is usually very Batis- sri:ir the NASAL DUCT. 273 factory, and it is seldom necessary t<» repeal the probing oftener than four or five times. In a ease of this character in ;i child fifteen months old recently under treatment, and in which a complete cure was effected, the duet was probed in all ten times, No. 12, the largest probe used, being introduced upon five successive occasions. The writer's experience with the radical treatment of strictures of the nasal duet by the use of large probes now extends over a period of nearly twenty years, during which time he has employed it in a large number of cases, and has had the opportunity of seeing many of them, from time to time, fur lung periods after the discontinuance of the probing; and his obser- vation is that the eases in which the treatment is systematically carried out in tlu' manner which has been described arc, with comparatively i'vw excep- tions, completely and permanently cured. 18 DISEASES OF THE CONJUNCTIVA. By MHl^ E. WEEKS, M. D., OF NEW YORK (I I \ . Congenital Anomalies of the Conjunctiva. — Pigment-patches, like moles, sometimes appear on the conjunctiva, accompanying; moles of the lace Dermoid tumors develop on the ocular conjunctiva (often extending; on to the cornea), at the caruncle, and at the upper outer quadrant of the globe (see page 329). They are at times associated with coloboma oi' the lids. They may be pigmented. Dermoid cysts have also been observed. Telangiectatic patches may appear on the caruncle and also on the palpebral conjunctiva. They are flat, slightly elevated, bright red in color, and often accompany telangiectatic patches on the litis and face. Cavernoma of the conjunctiva also exists as a congenital growth. The color is dark blue, and the conjunctiva is bulged forward at the affected part. When the head is lowered or the child eric- or coughs the tumor increases in si/e. Small subconjunctival lipomata may accompany congenital coloboma of the lids or may exisl alone. Well-developed bone-tissue has been observed situated beneath the ocular conjunctiva, between the margin of the cornea and the outer commissure. The caruncle may present an abnormal development of hair (trichosis caruneulce). Congenital duplication <>/ tin- caruncle has been reported by Stephenson. Hyperemia of the Conjunctiva (Dry Catarrh). — This condition usually affects the palpebral conjunctiva, and is manifested by a persistent redness with no appreciable thickening. The posterior system of conjunctival vessels is involved. Etiology. — The causes of this affection are numerous, and comprise the entrance of minute irritating particles into the conjunctival sac, exposure to strong winds, cold, heat, and glare of light. Conjunctival hyperemia may be produced by use of the eves with poor illumination, eye-strain from errors of refraction or muscular irregularities, by too continuous use of the eyes on line work, by indigestion, alcoholic beverages, rheumatic gout, vaso-motor disturbances, nasal catarrh, lachrymal disease, blepharitis marginalis, acute exanthematous fevers, etc. Pathology. — There i- little change in the tissues ; the blood-vessels are enlarged ami overfull, and there isa scanty -mall cell-in61tration and increase in nuclei. Symptoms. — The lid- feel heavy and hot ; movements of the eye are painful ; there are increased lachrymation and slight photophobia. Attempts to use the eyes by artificial lighl are accompanied by distress. Diagnosis and Prognosis. — Redness of the conjunctiva without discharge L'7I CONJUNCTIVITIS. 275 other than increased lachrymation, and without other appreciable change in the conjunctiva, suffices to establish a diagnosis. The prognosis is favorable, provided the cause can be removed. Treatment. — This should include the prevention of the entrance of for- eign substances into the eye, and the correction of habits and systemic con- ditions that contribute to the continuation of the hyperemia. Errors of refraction and muscular defects should be corrected. Bathing the conjunc- tiva with a solution of boric acid, '2 or •"> per cent., three or four times a day, usually suffices for the local treatment. Strong astringents are not advisable. Conjunctivitis (Ophthalmia). — This term embracesa number of diseases of the conjunctiva characterized by increased altered secretion from the sur- face of the conjunctiva, pronounced distressing symptoms, and transient or permanent pathological changes in the membrane. Simple Conjunctivitis (Catarrhal Ophthalmia). — There is a relatively large number of forms of conjunctivitis which are mild in character and tend to spontaneous recovery, without serious complications, which may be placed in this class. They are characterized by slight swelling of the lids and con- junctiva and the presence of a muco-purulent secretion. The specific disease known as acute contagious conjunctivitis, usually considered under this head, will be described separately. Etiology. — (a) Mechanical <><•. iii. Moras . Fig. IV. Secretion from a case of conjunctivitis, showing \ imococci ; immcrs iii. (Moras). ACUTE CONTAGIOUS CONJUNCTIVITIS. -Ill presence of many small transfusions of blood in the ocular conjunctiva: this is such a common symptom thai Nettleship has given the affection the name of "hemorrhagic catarrhal conjunctivitis." The acute stage, which is often accompanied by slighl rise of temperature and frontal headache, lasts from four to ten days. The discharge gradually diminishes in quantity, becomes thicker, and collect- in little yellow masses at the inner canthi. The swelling of the lids and conjunctiva and the pain- ful symptoms gradually subside, and recovery usually occurs in from two to three weeks, in the subacute stage the conjunctiva at the transition folds presents a swollen, succulent condition, with enlargement of the papillary body and some follicular hypertrophy. Diagnosis and Prognosis. — A history of the presence of the affect inn in all or a number of the members of a family, or of its epidemic character in institutions, will aid much in establishing a diagnosis. The very yellow mass of secretion at the inner canthus is quite characteristic. Acute con- tagious conjunctivitis may be mistaken for purulent conjunctivitis, and, when a pseudo-membrane forms, as it does in about 4 per cent, of the cases, for diphtheritic conjunctivitis. The microscope may be depended on to make the diagnosis clear in doubtful cases. In the greater number of eases recovery ensues without leaving a trace of the disease; relapses and recurrences are frequently observed. Qne attack does not ensure immunity. Phlyctenule may develop in the later stages or trachoma may follow, but these conditions must be regarded as secondary diseases grafted on the primary disease by added infection. The cornea is rarely affected. In adults the attack is more severe than in children. The disease is contagious as long as secretion is present. Treatment. — As the disease is very contagious, isolation should be resorted to if possible. Bathing appliances should be separate. In all cases w r here large numbers of individuals are aggregated quarantine should be rigidlv enforced, and persevered in until all traces of secretion have disap- peared, and even for a few days after that period. For the first three to five days of the acute stage cold application- arc indicated. These may be applied as follows : Thin pads of absorbent cotton, H inches in diameter, or pieces of linen, 1^ inches square and two or three layers in thickness, to the number of ten or twelve, should be placed on a cake of ice over which a thin napkin is spread, and a pad transferred to and from the eye sufficiently often to keep the lids cool — every two minutes. In severe cases the cold applications should be continuous ; in mild cases it will suffice to keep up the applications through the daytime. While this is being done the eye should be cleansed every half hour if the secretion is profuse, less often if the secretion is scanty, with some bland antiseptic solution. Boric acid. 2 or :; per cent., or the bichlorid of mer- cury, 1 :15,000, may be employed. When the acute stage is subsiding the cold applications should lie discontinued, the bathing continued, and in addi- tion a more energetic germicidal astringent may be employed. Nitrate <>t silver, in the solution of 0.5 to 1 per cent., is excellently adapted for t hi- purpose. The application may be made once in twenty-four hours, and may be continued with less frequency until the secretion ceases. Other topical applications an — alum (gr. 1-f.SJ), acetate of lead i'j;w l-f3j), sulphate ol zinc (gr. 1-f.Vp, peroxid of hydrogen, formalin (Schering's solution — 1 : to 1 : 500), Bandaging the eye- and the application of poultices of tea-leaves, oysters, scraped potato.-, bread and milk, and other domestic concoctions should be 278 DISEASES OF THE CONJUNCTIVA. avoided. These only serve to retard recovery, and in many cases increase the inflammation. Purulent Conjunctivitis (Acute Blennorrhea of the Conjunctiva). — The term purulent conjunctivitis properly applies to all forms of conjunctivitis in which the discharge is more or less copious and comparatively free from mucin. This condition obtains in certain cases of acute contagious conjunc- tivitis in some cases of traumatic conjunctivitis, in the forms induced by the application of a poultice of tea-leaves in simple conjunctivitis (tea-leaf con- junctivitis), and in the later stages of diphtheritic conjunctivitis. As cora- monlv employed, it refers to the conjunctivitis induced by the presence of the gonococcal of Neisser, and is usually considered under the terms gonorrheal conjunctivitis and conjunctivitis neonatorum. Gonorrheal Conjunctivitis. — This disease occurs in men much more frequently than in women. It is characterized by marked swelling of the lids and copious discharge of purulent secretion from the conjunctiva. Etiology. — The gonococcus of Neisser (see Fig. I., Plate 2) in secretion from a diseased mucous membrane is brought in contact with the conjunc- tiva. Probably the nm-i frequent manner of its conveyance is by means of the finger from a urethral or vaginal gonorrhea. The use of a common washing-bowl, towels, etc. may serve to communicate t'iie disease. It is not probable that the contagium can be carried through the air. The discharge in gleet, as well as in pronounced gonorrhea, may serve to set up the affec- tion, but it is supposed to lie less severe when arising from gleet. Pathology and Pathological Anatomy. — Engorgement of the vessels <>t' the palpebral and ocular conjunctiva rapidly develops. An infiltration of leukocytes into the superficial layers of the entire conjunctiva and edema induced by a serous and in some cases a fibrinous exudation occur early. The conjunctival epithelial layer h swollen and uneven. The pathogenic micro- organism grouped in or on the leukocytes in the characteristic manner is seen -Gonococci in the tissu mjunctiva i Bumm). W Pig. 188 Gonoci icci free and mi the cells I liumm). in the superficial layers of the conjunctiva (Fig. 187). The secretion con- tain- the gonococci, which are found free and on the pus-cells (Fig. 188). Symptoms. — The stage of incubation, which la per cent, or bichlorid of mercury (1 : 15,000). For the carrying oul of this treatment two nurse-, a day ami a night nurse, are required. It* the lids become .-ore and erosion of the epithelium is threatened, some borated vaselin may be applied after each bathing. There are many ways of eleansinf; the eye. The lids may be held gently apart and the warm solution be permitted to run into the conjunc- tival sac from a piece of absorbent cotton. A pipette may lie used to force a stream beneath the lid- after they have been gently opened. A speculum with perforated Made- has been devised (Andrews) for cleansing the con- junctival sacs, and a lid-retractor which permits the solution to How through thehandle and into the blade, escaping at openings at the margin of the I. lade, has been made for the same purpose. Except in very skilful hands the instruments devised for cleansing the eyes are dangerous, as they are apt to injure the cornea and induce corneal ulceration. Applications of cold, which are generally made inadequately, may he made too assiduously and the vitality of the cornea threatened. When too much cold is applied the cornea takes on a steamy appearance and breaks down more easily. If corneal luster fails without evidence of loss of sub- stance, the applications of cold should be intermittent. //"/ applications in the acute stage are contraindicated ; they serve to increase exudation and the growth of the gonococcus. In the subacute and atonic stages they may he resorted to with benefit. A- - a- the discharge lake- on a purulent character and the lids are less rigid, local application- to the conjunctiva may he made. For this pur- pose a solution «»f the nitrate of silver, 1 or 2 per cent., is probably the best. The lids are carefully everted, the secretion removed, and. by means of a piece of absorbent cotton wound around the end of a small applicator the solution i- applied to the entire surface of the conjunctiva. This should he followed by application- of cold for one or two hour.-. The treatment out- lined above will suffice to effect a cure in the greater number of eases. Finely pulverized iodoform i- sometimes employed by dusting it into the conjunctival surface two or three time- daily. Peroxid of hydrogen has been advocated by Landolt : it i- of value as a cleansing and germicidal agent. Sublimate solution, 1 : 500, ha- been employed recently by applying it to the conjunctiva sufficiently often to hold the secretion in check. Aqua chlorini, formalin (1 :3000), permanganate of potassium in copious irrigations (1 :500 or 1 : looo). are used to irrigate the eye. \)\\ Wilson of Bridgeport advocates filling the conjunctival sac with a boric-acid ointment (boric acid gr. xlviij, vaselin 3j) every one to two hour- after cleansing, continuing this treatment until the acute stage ha- pa— ed ; he claim- excellent results. In some severe cases Nov,- ha- resorted to scarifying the conjunctiva and brushing in a solu- tion of corrosive sublimate, I : 500, repeating the operation in two or three days if the discharge return-. [f corneal ulcer develops, atropin (gr. ij to sj) should be instilled two or three times daily. Ehrenthaler 1 recommends eserin (gr. ij to Ij) in those cases of corneal ulcer where congestion of the iria is nol present, alternating with atropin in other cases unless perforation is imminent. He avers that the circulation is improved and recovery more certain. 1 Munch, med. Wochemschrift, No 38, 1892. CONJUNCTIVITIS NEONA TOBUM. •J>1 When the lids arc greatly swollen and tense a free canthotomy may be done. This relieves the pressure on the cornea, unloads t h<- blood-vessels, and prevents spasmodic contraction of the orbicularis palpebrarum muscle. In the la-t stage hot-water bathing, the sulphate of copper or alum-crystal, and tannin may be employed. Systemic Treatment. — The bowels should be kept free by use of calomel and a saline Rich food and alcoholic beverages should be forbidden. ( )pium may be administered if there is much pain. Conjunctivitis Neonatorum (Ophthalmia Neonatorum). — This is a purulent affection of the conjunctiva, accompanied by great swelling of the lids and thick purulent secretion, occurring within a few day- after the birth of the child. Etiology. — That form of the affection which develops within three days after the birth of the child is undoubtedly produced by gonorrheal infection from the vaginal secretions of the mother at the time of birth. In cases that have developed ten days to three weeks after birth other causes are found: the small bacillus of acute contagious conjunctivitis, the pneumo-bacillus, and the Klebs-Lofrler bacillus have been observed. The use of -oiled towels or napkins about the infant or the unclean hands of mother or attendant may serve as a means of carrying infectious material to the infant's eve. Ex- ceptionally, inoculation in utero may occur (ante-partum conjunctivitis). Pathology. — The pathology of ophthalmia neonatorum resembles that of purulent conjunctivitis in the adult, so far as the tissue-changes arc concerned. Symptoms. — Slight puffiness of the lids and a tendency to .-tick together will be noticed twenty-four or thirty-six hours after birth, and on inspec- Fig. 189.— Conjunctivitis n< atorum (from a patient in the Philadelphia Hospital under the .'are of I»r. ili j Schweinitz). tion the palpebral conjunctiva will be found to be congested. A- a rule, the change in the lids and the presence of secretion are not sufficient to at- tract attention until the third day. when the secretion ha- become distinctly purulent and the lids somewhat swollen. At the end of the fourth or fifth dav the lids are greatly thickened and of a dusky-red color; the secretion is purulent and quite copious. It either flows out on to the cheek <>r i< retained in greater part by the lid- and bursts forth on attempts t" separate the lid-. 282 DISEASES OF THE (OXJ LXVTIVA. The swelling of the conjunctiva is so intense in some cases that ectropion of the upper lid is produced. Chemosia is not so marked as in purulent con- junctivitis occurring in adults, and involvement of the cornea occurs in a smaller proportion of eases. What has been stated in regard to the symptoms in gonorrhea] conjunctivitis of the adult, excepl as indicated above, applies to conjunctivitis neonatorum. Diagnosis. — The history of the case and the age of the child will suffice to establish a diagnosis. Prognosis. — If not properly treated the prognosis is grave, but not to such a degree as in the adult. Properly treated, the prognosis is good. Careful observation of many eases has taught the writer that if the patient is seen while tin 1 cornea is still dear impairment of vision need not occur, except in the eases in which the affection is very severe and the patient's vitality much impaired. Since the retention of vision depends so much on careful and proper treatment, it is of the greatest importance that the infant should be seen by a competent physician as early as possible. Neglected cases have contributed 20 per cent, to the number of the blind. Prophylaxis. — The great work done by Crede in Leipzig in reducing the number of cases of conjunctivitis neonatorum from 10.8 to 0.2 per cent, in the infants born at the Lying-in Asylum under his charge shows what may be accomplished by prophylaxis, ('rede's method was to drop two drops of ;i "_' per cent, solution of nitrate of silver into the conjunctival sac of the infant'- rye- very shortly after its birth, having first wiped the lids clean. The reaction is quite severe in some cases. It has been found that equally good results may be obtained with a 1 per cent, solution of nitrate of silver, also with a solution of bichlorid of mercury (1 : 4000) dropped into the eye in the same manner. Normal saline solution, used a little more freely, is excellent, but not quite as efficacious a- either the silver or sublimate solution. Aqua chlorini and carbolic acid (1 : 100) have been advocated. Those in charge of a case of conjunctivitis neonatorum should be cau- tioned regarding it- contagious nature, and should be instructed to destroy or to disinfect all appliance-; thai come in contact with the secretion. The in- fant should be removed from the presence of all persons except those in im- mediate attendance. A protective shield for the unaffected eye i> not easily made efficienl ; more reliance may be placed in the ability of the nurse to keep the fellow-eye disinfected. A.lmos1 always, however, the affection i- bilateral. Treatment. — If the lid- arc at all swollen, cold applications, made as described on page '277. and continued until the swelling of the lids partly subsides, are valuable. Three hours of the applications and one hour of intermission i- an excellent way of applying cold. After the -welling has markedly diminished applications of cold for one hour, three times daily, may be kept up until little swelling remains. The pus should be gently removed by lavage with a 2 or ."> percent. solution of boric acid every half hour or every hour, as long as the secretion i- ab lam. After the first two or three days applications of a 1 percent. solution of nitrate of silver may be made by the surgeon to the palpebral conjunctiva, either employing a bit of absorbenl cotton on a -mall applicator or a camel's-hair bru-li.on.-i' in twenty-four hours. As the secretion and swelling diminish the silver solution may be weaker and may be applied less frequently. Should the integumenl of the lid- lose some of it~ epithelium or become roughened, some borated vaselin may be applied after each cleansing if the c\ CROri'OUS (OXJIWCTIVITIS. 283 When ulcer of the cornea occurs, atropin in weak solution (gr. ij to 51) should he instilled twice daily if the ulcer is central ; if marginal, eserin (gr. j to gj) may be alternated with the atropin. The treatment may he varied as indicated w hen considering the treatment of gonorrheal conjunctivitis of adults (page 280). Croupous Conjunctivitis {Membranous Conjunctivitis). — There is a class of cases characterized by a slight swelling of the lids, by a flaky serous discharge, and by the deposit of a fibrinous pseudo-membrane on the surface of the palpebral conjunctiva, extending in some cases on to the ocular con- junctiva, which from a bacteriological or clinical standpoint cannot be included with any other form of conjunctivitis. Graefe ' terms the disease pseudo-membranous or croupous, in contradistinction to the diphtheritic form. The cases are comparatively rare. Etiology. — No exact cause is known. The affection is regarded as a mild diphtheria by some authors. Pathology and Pathological Anatomy. — The conjunctiva is thickened, and shows on section the presence of leukocytes and an increase in nuclei. The epithelial layer is reduced in thickness ; blood-vessels are numerous and are enlarged. The pseudo-membrane consists of fibrin, which includes in its meshwork epithelial cells from the conjunctiva, leukocytes, red blood- corpuscles, and various forms of micro-organisms. The pseudo-membranes found in epidemic conjunctivitis, gonorrheal conjunctivitis, diphtheritic con- junctivitis, and those that cover the surface of the conjunctiva after burns with acids, steam, or after scarifying the conjunctiva, differ from each other microscopically only in their bacterial contents and the products of the bac- terial growth. Thus membranous conjunctivitis has been ascribed to staphylo- cocci, streptococci, Loffler-bacilli, and diplococci. 2 Symptoms. — The symptoms are not severe. The patient complains of ob-euration of vision, slight itching, and some burning pain. There is some photophobia. The lids are slightly swollen and somewhat hyperemic. On everting the lids a grayish pseudo-membrane is found. It can be separated from the conjunctiva with comparative ease, but leaves a slightly bleeding surface. The fibrin filaments do not appear to be so numerous or to pene- trate so far into the conjunctiva as is the case in diphtheritic conjunctivitis. Removal i- followed by rapid regeneration of the membrane, and this tend- ency may continue for from ten days to many months or even longer. Diagnosis. — The diagnosis is arrived at largely by exclusion. The sub- acute nature of the disease, the absence of any known specific micro-organism, and the persistence of the affection serve to establish a diagnosis. Prognosis. — The prognosis is good in perhaps 50 per cent, of the cases. Although the disease persists for a long time, appropriate treatment will often produce a gradual diminution in the tendency to reproduce the membrane ami the patient will recover, d'he cornea remains clear for a long tinn — ten days or perhaps as many week-. It may finally become the -eat of ulcerative pro- cesses and be partly or totally destroyed. Treatment. — Unfortunately, treatment appear- to be of little avail in some cases ; in other- a tardy response is secured. It appears to be almost useless to remove the membrane. Frequent and prolonged bathing with 3ome mild antiseptic solution, as carbolized water, corrosive sublimate (1 : 10,000), chlorin-water, or a I per cent, solution of boric acid, is indicated. 1 Arehivf. Ophtk, 1854, I V.bth., i. 168. For .'in article on " Pathology of < Ihronic Membranous < kmjunctivitis " b i [owe, consult Trans. Ann,. Ophth. Sac., 1 -- '. ♦ "7 . mi. :;. v •vr- Jat-'«V Fig. 190 Bacillus diphtherial, from a culture upon blood-serum; 1000 (Frankel and Pfeifl and extend between them, causing the the time of its formation. Diagnosis. — In some cases it is difficult to discriminate between mem- branous conjunctivitis due to diphtheria and that due to other forms of inflammation. Caustic applications in mild forms of conjunctivitis in in- fant- and children may produce a p-eiido-ineinhrane and an intense plastic infiltration of the lid that may be mi-taken for diphtheria. Severe cases of gonorrheal and of epidemic conjunctivitis may assume a diphtheritic aspect, 1 Arehivf. Ophth., 1854, I Al.ili.. p. 168. DIPHTHERITIC CONJUNCTIVITIS. The history will aid in eliminating error, bul the most conclusive method is that of bacteriological examination. Should the examination of a cover-e specimen fail to afford positive results, cultivation experiments may be tried. Symptoms. — In a typical case the onsel is sudden. Slight discomfort in the lids, increased lachrymation, and congestion of the conjunctiva precede the severer symptoms by a few hours. Swelling of the lid- take- place rapidly: at the end of twenty-four hours the upper lid may have attained four or five times its normal thickness. The folds of the skin of the lid are obliterated; it becomes shiny and assumes a dusky-red hue. The lid is hard to the touch, slightly elastic, closes the eye completely, and cannot be easily raised or exerted. A little flaky serous secretion, sometimes tinged with blood, ooze- from between the lids at this stage. Attempts to open the eye on the part of the patient arc futile, and the surgeon will only partly succeed. A sensation of weight and tension on the globe is experienced, but aside from this there is little pain. On raising the lid from the globe the palpebral and often the ocular con- junctival surface will be found to be covered with a gray membrane, which, in the average ease, is about one millimeter in thickness. < hi attempts to remove this membrane shortly after it has formed, it will he found to be closely adherent : forcible removal leaves a raw, bleeding surface, which is soon covered again by new-formed membrane. The acute stage, which may last three to seven days, is accompanied by slight rise of bodily temperature, and sometimes by cephalalgia. Gradually the lids become less rigid, the secretion morepuriform ; the pseudo-membrane comes away in lai'ge or small plaques, and finally disappears. Corneal com- plications in the form of ulcers and extensive sloughing frequently develop, not only when the membranous deposit is extensive, but also when it is mod- erate in amount. There is great variation in the degree of severity, rapid destruction of the eye occurring in some cases, while others are so mild that the nature of the disease is not recognized. Prognosis. — Diphtheritic conjunctivitis i- probably the most destructive disease that affects the conjunctiva. The nutrition of the cornea is often interfered with at an early stage, and the membrane slough-. Of 40 cases reported by von Graefe occurring in children, 9 eyes were destroyed, in 3 there were adherent leukomata, in 7 simple leukomata, and in '1\ the cornea remained unaffected. Of 8 cases in adults, 5 sustained perforation of the cornea, and 3 presented marked simple leukomata after t he disease had passed. Symblepharon of varying degree- may result from adhesion of opposing raw- surfaces. Tendinous cicatricial bands may form in the conjunctiva. Great changes in the lid may ensue as a result of the formation of cicatricial tissue. Treatment. — The indication- are to prevent the communication of the disease to the fellow-eye ami to the eyes of other individual.-, to limit the infiltration of the lids, to prevent destruction of the cornea by pressure or by infection, and to check the extension of the diphtheritic process to other mucous membranes. Aseptic or antiseptic solutions may he employed to cleanse the unaffected eye ; n stated intervals, or. better still, Bullets shield may be applied to the sound eye. The patient should !><• isolated, dressings and secretion- from the eye destroyed, and towels, linen, etc. disinfected after use. ('old applications should lie made a- advised on page 277, until the lids are less tense. A free canthotomy will cause desired depletion and relieve the pressure on the eyeball exerted by the tense lid-. The conjuncti- val sac should 1m- carefully cleansed at frequent intervals with a solution oi boric acid, bichlorid of mercury (1 : 5000 or 10,( or chlorin-water (one- 2s. i DISEASES OF THE CONJUNCTIVA. half the U. S. P. strength). To prevent extension to the mucous membrane of the air-passages mercury to saturation has been advised. The usual con- stitutional treatment of diphtheria is indicated. Recently, serv/m-therapy has been resorted to with results which, if uni- formlv as brilliant as in the eases reported, will rob the disease of its terrors. 1 A- soon as the diagnosis is made, 10 cgm. of Behring's diphtheria-antitoxin is injected into the abdominal wall, and the injection is repeated after forty- eighl hours it* there is doI a marked recession of the disease. In many cases improvement is noted before the end of the first twenty-tour hours, and the membrane disappears before the expiration of forty-eight hours. Antitoxin is said to modify favorably the necrotic- process in the cornea. Phlyctenular Conjunctivitis ( Lymphatic < 'onjunctivitis ( Fuchs) ; Scrof- ulous Ophthalmia ; Eczema of the Conjunctival — This disease is characterized by the appearance of one or more small translucent elevations at the limbus or at some point on the ocular conjunctiva, accompanied by an increased local vascularization ( Fig. 191 . [fa single nodule appears, it is situated at the Fig. 191.— Phlyctenular conjunctivitis I De Schweinitz). Pig. 192.— Pus with staphylococci; X 800 (Flugge). apex of a triangular patch of injected vessels, the base of the triangle being directed toward the equator of the globe. The affection is common in chil- dren, never affects the new-born, and is rarely seen in adults. Etiology. — A depraved c lition of the system induced by inherited taints, malnutrition, tilth, and bad hygienic surroundings predisposes to this affection. Although most frequently met with among the children of the poor, the children of the rich are not exempt. Experiments that have been conducted with cultivations made from the content- of the vesicles permit of but little doubt that the immediate cause is the presence of the staphylococcus pyogenes aureus. or aibus beneath the epithelium of the affected portion of the conjunctiva (see Fig. 192). This affection is frequently associated with moist eczema of the lids, face, scalp, ears, or other parts. The nodules of eczema closely resemble those of phlyctenular conjunctivitis, from which the same micro-organism may be cultivated. It is undoubtedly from the eczema- tons process that the infectious principle is derived in many cases. Pustular blepharitis marginalis supplies the necessary bacterium in some cases. Phlyctenular conjunctivitis frequently follows the exanthemata, as measles and scarlel fever. Simple and epidemic catarrh of the conjunctiva encourage to the development of phlyctenular which appear six or seven days after the onset of the acute conjunctivitis due to a secondary infection. Xaso- pharyngeal disease always accompanies the affection. 'Hamilton ami Jones: Brit. Med. Journ., 1895, p. 1419; Morax: Annul, d 1 Oculistique, cxiii. j> 360; Coppez: Bevtu gin. d' Ophthcd., Feb., 1896, p. 51 ; Standish: Trans. Atner. Ophth. iii. 11 50. VERNAL CONJUNCTIVITIS OR CATARRH. 287 Patholog-y. — Apparently as a result of the depreciation of the resisting powers of the tissues of the body, the surface cells do not prevent the entrance and development of the pathogenic micro-organisms. The contents of the nodule in the early stage is a thickened fluid containing many leukocytes and some granules ; later the contents resemble pus. A section of a nodule -hows it to be formed by the elevation of the epithelial layer from the underlying basement-membrane ; the vessels in the vicinity are congested, and there i- an increased number of leukocytes in the adjacent tissue. Symptoms. — The palpebral conjunctiva is congested ; this is also the condition of the ocular conjunctiva in the affected portion. There are -light stinging pain, laehryniation, photophobia, ami annoyance on use of the eye-. 'Idie photophobia in phlyctenular conjunctivitis is slight compared with that accompanying phlyctenular keratitis (see page 305). In almost all cases the preauricular glands are enlarged. Frequently there i- marked coryza, the upper lip becoming thickened by the flow of irritating secretions over it. Diagnosis. — Herpes conjunctivae, vernal catarrh, and trachoma affecting the ocular conjunctiva may be mistaken for phlyctenular conjunctivitis. In herpes the vesicles which spring from the injected conjunctiva are transpa- rent and appear in clusters. They do not select the limbus, and are much more transient. In vernal catarrh the elevations are larger and do not ulcerate. Trachoma of the ocular conjunctiva is associated with trachoma of the palpebral conjunctiva, and seldom affects the limbus conjunctivae. Prognosis. — When the conjunctiva only is affected the prognosis i- favor- able, as recovery occurs without leaving a trace of the disease. The duration is variable, from a few days to a number of month-, successive phlyctenular appearing. Recurrences are frequently observed. Treatment. — This should be local and constitutional. The local treat- ment consists in keeping the eyes clean by the use of some antiseptic lotion. Bathing with a saturated solution of boric acid in water three or four times a day gives good results. An ointment of the yellow oxid of mercury (1—1.5 per cent.), introduced into the conjunctival sac twice daily after the phlyc- tenule has broken down, is of much value. Calomel may be dusted on the conjunctiva once daily if the patient is not taking iodin. A mild altera- tive in the shape of small doses of •calomel may be continued for some weeks with benefit. Nourishing food and general tonic treatment — iron, quinin, cod-liver oil, and perhaps strychnin— may be given. The naso-pharynx should receive appropriate treatment. (Consult also Phlyctenular Kerato- conjunctivitis, page -'107. ) Herpes Conjunctivae. — This occurs ;it time- in connection with herpes febrilis or herpes zoster affecting the lids and face. It is seldom that the complete vesicles are found, as they rupture early, and their site is marked by shreds of epithelium which remain attached to the conjunctiva at the margins of the preceding vesicles. The condition is accompanied by irritation and increased laehryniation. Herpes of the cornea may accompany herpes conjunctivae. The affection is extremely rare. It call- for no treatment other than that given for the affection which it accompanies (see also page 309). Vernal Conjunctivitis or Catarrh (Fruehjahr's Catarrh (Saemisch ; Spring Catarrh; Phlyctama Pallida (Hirschberg)). — This i- a chronic form of conjunctivitis which presents peculiar feature-;. The tarsal conjunctiva is covered by -mall, closely-placed, flattened, papilliform excrescences, which appear to be covered by a delicate grayish film. At the margin of the cornea the conjunctiva is thickened and unequally raised, forming pale, translucent, L>ss DISEASES OF THE CONJUNCTIVA. or waxy nodules, which arc largesl opposite the palpebral fissure, encroach a little on the cornea, hut extend to a greater distance outward into the ocular conjunctiva. Etiology. — Nothing definite is known of the cause of the affection. Some writers believe it to he a form of trachoma, and so classify it. Fuchs is of the opinion that it is a specific disease, and that, although no specific micro- organism has been discovered, it i- produced by such a micro-organism. Both eye- are affected. 'The male sex suffers most, the attacks being expe- rienced between the ages of one and thirty-five years. Pathology. — Little is known regarding the development of the papillae of the tarsal conjunctiva. The elevations about the cornea are preceded by local injection of the vessels ; the thickening develops slowly. The papilla? of the tarsal conjunctiva are composed of a central cylinder or cone, made up of connective tissue and a few small blood-vessels, which is covered by a thickened layer of epithelium. Over the nodules, at the limbus, the epithelial layer is uneven, and is thicker than normal. Symptoms. — The ropy nature of the secretion produces a sensation as of a foreign body in the eye. There are photophobia, burning of the lids, and blurring of vision, principally due to the presence of secretion on the cornea. I %-c of the eyes by artificial light increases the irritation and lachry- mation ; the redness of the ocular conjunctiva about the cornea and the nodules at the limbus are apparent on inspection. On everting the lid the fine fissures of the tarsal conjunctiva due to separation of the papillae are recognized. The disease gives but little annoyance during winter months, but is very trouble- some during the summer months, at which time there is more or less stringy discharge and the eyes are painful. When cold weather comes on the eleva- tions at the margin of the cornea become much smaller, some disappearing entirely ; the tarsal conjunctiva is less thickened, but the papilliform eleva- tions still remain. Burnett -tates that in the colored race the bases of the nodules are pigmented. Diagnosis. — The history of the case is of great value in making a diag- nosis. Xo other form of conjunctivitis recurs and persists to the same extent during the warm weather. The conjunctivitis that accompanies hay fever has none of the anatomical and few of the symptomatic characteristics of this disease. Vernal catarrh may be confounded with trachoma and with phlyctenular conjunctivitis. The elevations on the tarsal conjunctiva do not have the appearance of the follicles of trachoma, nor do they have the same anatomical structure. The pericorneal elevations differ from those of phlyctenular con- junctivitis in that they are not so transient and do not break down and form ulcers. Prognosis. — The disease recurs for a number of years, and may then dis- appear entirely. In the greater number of cases no injury is done to the central area of the cornea : however, the nodule- may advance for a consider- able distance, and in rare cases may cover the cornea, abolishing useful vision. Treatment. — -A complete cure by means of treatment must not be expected, but much can be done to relieve distressing symptoms, and the advance of i he uodules on to the cornea maybe checked. Bathing the eye- with ;i warm solution of boric acid three time- daily will serve to keep them fairly clear of secretion. This, with the application of a smooth ointment of the yellow oxid of mercury i I .', percent.) in the conjunctival sac twice daily, will pro due.' very favorable results. Calomel and solutions of bichlorid of mercury GRANl LAB < 'ONJUNl "JTVITIS. arc useful. It' the nodules arc large, they may be reduced and their advance checked by destroying them with the cautery ; electrolysis has been recom- mended. Randolph advises salicylic acid applied to the conjunctiva in the form «>t' an ointment (gr. iij— 3iv) and as a collyrium (gr. v-f.^j). Follicular Conjunctivitis (Conjunctivitis FolUculains Simplex). — This inflammation of the conjunctiva is characterized by the occurrence of -mall, oval, pale or light-red elevations in the transition folds of the conjunctiva. A tew follicles the size of a pinhead are often observed in the tarsal con- junctiva. Etiology. — Follicular conjunctivitis occurs among persons inhabiting crowded quarters and among those whose habits and surroundings are not cleanly. Soelberg Well- states that he thinks that there can be no doubt that the disease i- contagious. It is often met with in the young, ami i- of fre- quent occurrence in inmates of residential schools. Pathology. — The follicles are due, according- to Krause and Schmidt, to an abnormal enlargement of the lymphatic follicles of Krause, which are not visible to the unaided eye in the normal state, but which are situated imme- diately beneath the epithelium of the conjunctiva. They are supposed to be neoplastic growths. The follicles are composed of a ma— of lymphoid cells contained in a delicate network of connective tissue having an incomplete capsule in which a few small vessels ramify. Symptoms. — These are few and not pronounced; indeed, follicular con- junctivitis may exist for months without the knowledge of the individual affected. On inspection the lower lid appears to be slightly thickened ; there may be increased Iachrymation, some mucoid secretion, and the ocular con- junctiva may be injected. On everting the lower lid the transition fold is found to be reddened, and may be swollen to such an extent that the follicles will not be visible ; however, in the greater number of cases the follicles appear as small, oval, translucent nodules, arranged in row-, lying in the transition fold. They may be few or numerous. Although ordinarily con- fined to the lower, they may be found in large numbers in the upper, transition fold. Diagnosis and Prognosis. — If the conjunctiva is not greatly swollen, the diagnosis is easy. Follicular conjunctivitis differ- from typical trachoma in that it is more transient, is more amenable to treatment, ami is not followed by cicatricial changes. The -prognosis i- favorable for a return to the nor- mal condition of health in a number of month- if medicinal measures are adopted, and in two or three week- if surgical measures arc employed. There is no tendency to involvement of the cornea. Treatment. — The patient should not be allowed to use the same bathing appliances with other-, and should be isolated when practicable. The hygienic condition- should be made a- good a- possible 3 and cleanliness should be insisted upon. ( lonstitutional treatment in the form of tonic-, iron, strychnin, or (jui niii should lie employed. Locally, a mild astringent collyrium of zinc sulphate (gr. j to ^j), alum (gr.j to §j), tannic acid, and glycerin (gr. 30—60 to §j) may lie employed. The sulphate of cupper or alum-crystal may be lightly applied to the follicle- every forty-eighl hour-. For the surgical tri atm< nt of this affection see Surgical Treatment for Trachoma, page 563. Expression of the follicle- with suitable forceps is the nio-t efficienl measure to destroy them. Granular Conjunctivitis i Trachoma ; Granular Ophthalmia ; Mill Ophthalmia). — This disease of the conjunctiva presents as it.*- dist active feature iii its early or first stage numerous discrete, oval bodies in the tarsal 19 290 DISEASES OF THE CONJUNCTIVA, conjunctiva :m