REFRACTIVE AND OPHTHALMIC CATECHISM 
 
 FOR THE USE OF 
 
 General Practitioners, Opticians and Students, 
 
 BY 
 
 LAWRENCE J. DAILEY, M. D. 
 
 Formerly assistant in the Eye Department of the Post-Gradoate Medi- 
 cal School and Hospital, New York City, member of the New 
 York County Medical Association, member and ex-presi- 
 dent of the Fulton County Medical Society, Oph- 
 thalmologist and Otologist to the Nathan 
 Littauer Hospital, Gloversville, N. Y. 
 Etc. 
 
 Gloversville, N. Y. 
 
 Collins Publishing Company. 
 
 1898. 
 
Cf7^^(:'^f 
 
 COPYRIGHTED 1898 
 
 BY 
 
 L. J. DAILEY, M. D. 
 
oPro 
 
 PKEFACE. 
 
 In offering this little book to those who are in- 
 terested in refractive work, it is in the hope that 
 the author has succeeded in producing a 
 work that will be, first of all, practical and accur- 
 ate in its methods of determining and correcting 
 the different refractive conditions. 
 
 It makes no pretensions beyond being a con- 
 cise and ready hand-book on the subject of refrac- 
 tive errors, and the instruments used in the work. 
 It has been the aim all through to use the ver}^ sim- 
 plest language and terms consistent with an ac- 
 curate description of the subject matter. From 
 the standpoint of the general practitioner, in 
 which field the author labored for nine years pre- 
 vious to taking up special w(^rk, he hopes he has 
 succeeded in presenting this subject to others in 
 such a manner as to enable them to learn some- 
 thing about refractive errors and glasses without 
 the necessity of reading several tomes — which as a 
 rule they have not the time— and consequently 
 learn very little about the eye, many times to the 
 
 3 
 
4 PREFACE. 
 
 detriment of their patients, as well as to them- 
 selves. In this particular does the author hope 
 that the chapter on the Diseases and Therapeutics 
 of the Eye will prove especiall}^ helpful. 
 
 To those who make a specialty of i^rescribing 
 correcting glasses, and especially to the large 
 number of opticians engaged in this work does 
 the author recommend this book as embodying the 
 most practical and latest methods of determining 
 refractive errors. The catechismal arrangement of 
 the work was adopted principally for the purpose 
 of keeping the subject down to the very foundation 
 of practicability, and allowing nothing of a theo- 
 retical nature to creep in, as there are already 
 plenty of works on theory and practice that can be 
 consulted by those who desire to extend their 
 knowledge on this subject. 
 
 I am under great and lasting obligations to 
 my friend and teacher, Professor Francis Valk, of 
 the Post-Graduate Medical School and Hospital, 
 New York City, for his kindly advice and intelli- 
 gent instruction during the years of 1891 and 1892, 
 when it was my good fortune to be his assistant, 
 and acknowledge the help I have received from 
 his well known work on refraction. 
 
 Also to Prof. D. B. St. John Rossa, for the 
 early instruction I received from him while a stu- 
 
PREFACE 5 
 
 dent in the medical department of the University 
 of the city of New York in the years of 1880, 1881 
 and 1882, where I found it a great pleasure to at- 
 tend his clinics at the college, as well as ten years 
 later at the Manhattan Eye and Ear Hospital. 
 
 I hereby acknowledge my obligation to those 
 who so kindly furnished me some of the cuts, 
 wliile others, mauy of which were selected from 
 various standard works, I acknowledge both here 
 and in the text. The glossary found in the conclu- 
 sion of the book, will, it is hoped, prove a valuable 
 aid in the study of this subject. 
 
 In hoi)es that this little catechism will prove 
 a friend to all interested in this work, either as 
 student, i)ractitioner or optician, the author offers 
 it as a recruit in the missionary field of ophthalmic 
 science. 
 
 Gloversville, N. Y., Sept., 1898. 
 
CONTENTS. 
 
 CHAPTER I. 
 Anatomy of the Eye, ..----.-9 
 
 CHAPTER II, 
 Refraction and Lenses, ...--.- 18 
 
 CHAPTER III. 
 Accommodation of the Eye, 35 
 
 CHAPTER IV. 
 Emmetkopia and Hypermetropia, 39 
 
 CHAPTER V. 
 Myopia, 49 
 
 CHAPTER VI. 
 Astigmatism, .... - 58 
 
 CHAPTER VII. 
 
 Ophthalmoscopy, ... - 78 
 
 CHAPTER VIII. 
 
 Ophthalmometry, 96 
 
 CHAPTER IX. 
 
 Skiascopy, Retinoscopy or Shadow Test, - - - - 106 
 
 6 
 
CONTENTS. 7 
 
 CHAPTER X. 
 
 Presbyopia, 123 
 
 CHAPTER XI. 
 
 Muscular Asthenopia, - - 131 
 
 CHAPTER XII. 
 
 Perimetry, 150 
 
 CHAPTER XIII. 
 Illustrative Cases From Note Book, . . . . 156 
 
 CHAPTER XIV. 
 Diseases and Therapeutics of the Eye, - - . . 182 
 
 Glossary, - 199 
 
 Index, 210 
 
CHAPTER I. 
 
 Anatomy of the Eye. 
 
 Q. What is the anatomical location of the 
 eye? 
 
 A. It is located in the anterior portion of the 
 skull, in the cavity of the orbit, which is a cone- 
 shaped cavity, formed by several of the cranial 
 bones. 
 
 Q. What is the depth of this cavity? 
 
 A. It is about one and three-quarters of an 
 inch deep. 
 
 Q. Which way are the bases of the orbital 
 cavity directed? 
 
 A. Forward and outward. 
 
 Q. What purpose do the orbits serve? 
 
 A. By their strong, bony walls they give pro- 
 tection to the eyeballs, and by the connective tis- 
 sue and fatty matter contained in them, they af- 
 ford a cushion-like bed for the same, thus permit- 
 ting of their free movement in any direction. 
 
10 ■ REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 In front they give attachment to a strong cir- 
 cular muscle, called the orbiculares palpebrarum, 
 and the eye-lids, which afford comparative secur- 
 ity to the eye-ball at its base. 
 
 Q. What is the size and shape of the eye-ball? 
 
 A. It has an antro-posterior diameter of 
 about one inch and a transverse diameter some- 
 what less. It is spheroidal in shape, with a segment 
 of a lesser sphere for its anterior surface, or the 
 cornea, which is transparent and constitutes 
 
 about one-sixth of the globe. 
 Figure 1. 
 
 Vertical section of the eye ball, showing the three coats 
 
 or tissues, the diopric media, ciliary processes and muscle 
 
 as well as capsule of the the lens. (After Gray). 
 
 Q. Of what is the eye-ball composed? 
 
 A. It is composed of three coats, or tunics, 
 
ANATOMY OF THE EYE. 11 
 
 and both fluid and solid refractive media called 
 humors. 
 
 Q. What are the coats or tunics called? 
 
 A. The sclerotic, and its continuation in 
 front, the cornea; the choroid, with its appen- 
 damages, the iris, and ciliary jDrocesses; and the 
 retina, 
 
 Q. What are the names of the refracting 
 media? 
 
 A. From before backwards, the cornea, the 
 aqueous humor, the crystalline lens, and the vi- 
 trious humor. 
 
 Q. What is the character of the sclerotic 
 coat, or tunic? 
 
 A, It is a hard, firm, dense membrane, giv- 
 ing shape to the eye-ball, and attachment to the 
 various muscles of the globe or eye-ball. 
 
 Q. What are the characteristics of the sec- 
 ond coat, or choroid? 
 
 A. It is a thin, highly vascular and pigment- 
 ed membrane, which invests about five-sixths of 
 the globe. It is composed of three layers, the ex- 
 ternal, middle, and internal. The ciliary pro- 
 cesses are formed by the folding of the middle and 
 internal layers of the choroid, and are attached to 
 the crystalline lens by means of the suspensory 
 
12 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 ligament. The iris, which is formed from the 
 choroid coat, receives its name from its various 
 colors, and, in this respect from its resemblance to 
 a rainbow. It is a thin, circular curtain, or dia- 
 phragm, suspended anterior, to the crystalline 
 lens with a circular aperture, called the pupil. Its 
 function is to regulate the amount of light admit- 
 ted into the chamber of the eye. 
 
 Q. What is the ciliary muscle? 
 
 A. A small, circular band about one-eighth 
 of an inch broad, on the anterior surface of the 
 choroid. It is the principal muscle of the accom- 
 modation of the eye. 
 
 Q. What is the retina, or the internal coat 
 of the eye-ball? 
 
 A. It is a very thin, delicate, nervous coat, 
 upon the surface of which the images of external 
 objects are received. It is composed of several 
 layers, but the first layer, or the layer of rods and 
 cones, is mostly concerned in the phenomenon of 
 sight. 
 
 Q. What are the physical characteristics of 
 the dioptric, or refractive media? 
 
 A. Of the cornea, and lens, transparency, 
 density, elasticity; and of the lens, adjustability 
 and their freedom from bloodvessels. Of the aque- 
 
ANATOMY OF THE EYE. 13 
 
 ous and vitrious humors, semi-fluidity and trans- 
 parency, and of all, refractability. 
 
 Q. If they are free from blood-vessels, how 
 do they receive their nutrition? 
 
 A. By imbibition or absorption from the 
 surroundino- tissues, which are freely supplied 
 with blood vessels. 
 
 Q. How is the crystalline lens held in posi- 
 tion? 
 
 A. It is enclosed in a capsule which is thick- 
 er in front than behind, and is retained in position, 
 principally by the suspensory ligaments of the 
 lens, which connects the anterior margin of the 
 retina with the anterior surface of the lens. 
 
 Q. What are the appendages of the eye? 
 
 A. The eye-lid, eye-brows, lachrymal gland 
 and sac, conjunctiva, and nasal duct. 
 
 Q. What are the angles of the eye-lids called ? 
 
 A. They are called the outer and inner can- 
 thus. 
 
 Q. What are the folds of the conjunctiva 
 called? 
 
 A. That fold covering the eyes is called the 
 ocular conjunctiva, and that portion covering the 
 lids, the palpebral conjunctiva. 
 
14 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 Q. What sort of a membrane is the conjunc- 
 tiva? 
 
 A. It is a mucous membrane. 
 
 Q. What are the little glands found on the 
 inner surface of the lids called? 
 
 A. The Meibomian glands. They secrete a 
 mucous to lubricate the lids, and have their open- 
 ings on the edge of the lids. 
 
 Q. What is the function of, and where is the 
 lachrymal gland located? 
 
 A. It is to secrete tears, and is located in a 
 depression at the outer angle of the orbit. 
 
 Q. What is the function and location of the 
 lachmyral sac and duct? 
 
 A. They are to carry off the tears, and are lo- 
 cated, the former at the inner canthus of the eye- 
 lids: the latter is lodged in a groove in the lachry- 
 mal and superior maxillary bone, which opens into 
 the nasal cavity. 
 
 Q. What are the puncta lachrymalia? 
 
 A. Two little openings at the inner part of 
 each lid, which are the mouths of the lachrymal 
 sac. They are slightly elevated above the surface 
 of the lids. 
 
ANATOMY OF THE EYE. 
 
 15 
 
 Q. 
 
 orbit? 
 
 How many muscles are there in each 
 
 FiGUKE 2. 
 
 Muscles of the right orbit, showing those attached to the 
 
 globe of the eye and the one which is not connected with 
 
 the globe, but is inserted into the tarsal border. 
 
 (After Gray.) 
 
 A. There are seven altogether, six of which 
 are attached to the globe of the eye, 
 
 Q. What are their names and action? 
 
 A. Two sui)erior recti to turn the eye-balls 
 up. Two inferior recti to turn the eyes down. 
 Two internal recti to turn the eyes in, and two ex- 
 ternal recti to turn the eyes out. Then there are 
 the superior and inferior oblique muscles which 
 rotate the eye-ball on its antro-posterior axis. 
 
 Q. What are the principal blood-vessels of 
 the eye? 
 
16 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 A. The principal artery is the ophthalmic, 
 which is a branch of the internal carotid artery af- 
 ter that vessel passes through the skull. The oph- 
 thalmic artery gives off two groups of branches, 
 the ones that supply the orbit, called the orbital 
 group, and the branches tliat supply the muscles 
 and globe of the eye, called the ocular group. A 
 small branch of the latter, the arteria centralis 
 retinae, pierces the optic nerve, and passes inward 
 through the center of the nerve to be distributed 
 to the retina, as far forward as the ciliary pro- 
 cesses. 
 
 Q. What are the nerves of the eye? 
 
 A. They are the second, third, fourth and 
 sixth cranial nerves. The second, or optic nerve, 
 is the special nerve of the sense of sight. The 
 third, also, called the motor oculi, supplies all the 
 muscles of the orbit except the external rectus and 
 the superior oblique. The fourth, or trochlear 
 nerve, supplies the superior oblique muscles, 
 while the sixth, or the abducens, supplies the ex- 
 ternal rectus muscle. 
 
 Q. What mechanical instrument is likened 
 unto the eye? 
 
 A. The camera obscura. The retina of the 
 eye corresponding to the sensitive plate of the 
 
ANATOMY OF THE EYE. 17 
 
 camera. Its function is to receive visual impres- 
 sion and to convey them to the optic nerve, which 
 in turn conveys them to the brain. 
 
 Q. What is this phenomenon called? 
 
 A. Tt is called sight, one of the special senses. 
 
 Q. Are all portions of the retina equally sen- 
 sitive to these visual impressions? 
 
 A. They are not. The central part is the 
 most sensitive. 
 
 Q. What is the central part called? 
 
 A., It is called the fovea centralis retinae, 
 the depressed portion of the maculae lutea, or 
 "yellow spot," as it is called frequently. It is lo- 
 cated at the temporal side, and on a level with the 
 lower border of the optic disk, and it can be recog- 
 nized with the ophthalmoscope, principally by the 
 absence of blood-vessels in its vicinity. 
 
CHAPTER 11. 
 
 Refraction and Lenses. 
 
 Q. What is meant by refraction? 
 
 A. That change which takes place in lumi- 
 nous rays as they pass from one medium to anoth- 
 er of greater density. 
 
 Q. What medium is used as a standard of 
 measurement? 
 
 A. Air is used, with an index of refraction of 
 1, as a standard. 
 
 Q. What change takes place in rays of light 
 in passing from the air, say, to one of greater den- 
 sity, and hence greater refractive power? 
 
 A. All the rays striking the denser medium 
 oblique, are bent towards the perpendicular of the 
 refracting medium, while the rays striking the re- 
 fracting body perpendicular to its surface, pass 
 through without undergoing any change. 
 
 Q. What is meant by the term "index of re- 
 fraction" in this connection? 
 
 18 
 
REFRACTION AND LENSES. 19 
 
 A. It means the relative power possessed by 
 different refracting media of bending oblique rays 
 toward the perpendicular when passing from a 
 lighter medium like air, into a denser one like 
 glass, for instance. 
 
 Q, Are there many substances found pos- 
 sessing this power of refracting rays of light? 
 
 A. Yes; they are found to exist in large num- 
 bers in solids, liquids and gases. 
 
 Q. What are the refractive indices of quartz 
 and crown glass used in lenses for the correction of 
 refractive errors found to exist in the eye? 
 
 A. About 1.5, as compared with air as 1. 
 
 Q. What are the refractive indices of the di- 
 optric or refractive media of the eye, that is, the 
 cornea, the aqueous humor, the crystalline lens, 
 and the vitrious humor? 
 
 A. For the cornea, aqueous and vitrious hu- 
 mors, about 1.33; while the crystalline lens has a 
 refractive index of 1.47. 
 
 Q. What are the glasses used in correcting 
 errors of the refractive media of the eye called? 
 
 A. They are called lenses. 
 
 Q. How many kinds of lenses are there as re- 
 gards their action on rays of light? 
 
FiGUBE 3. 
 
 1 8 3 4 5 6 
 
 1. 
 
 2. 
 other . 
 
 3. 
 
 4. 
 
 Double Convex Lens — Convex on both surfaces. 
 Piano-Convex — Plane on one surface and convex en the 
 
 Double Concave — Concave on both surfaces. 
 
 Piano-Concave — Plane on one surface and concave on 
 the other. 
 
 5. Convexo-Concave — Convex on one surface and concave on 
 the other, more convex than concave, making it a plus lens. 
 
 6. Concavo-Convex — Concave on one side and convex on the 
 other, more concave than convex, making in a minus lens. 
 These lenses are also called periscopic meniscus lenses. 
 
 7. Prism Lens. 
 
 8. Convex or Plus Cylindric Lens. 
 
 9. Concave or Minus Cylindric Lens. 
 
REFRACTION AND LENSES. 21 
 
 A. Two kinds, namely: the lenses which 
 converge or bring rays of light to a point, or focus, 
 and the lenses that cause a divergence of the rays 
 after passing through them. 
 
 Q. What other names arethey known by? 
 
 A. Convex lenses and concave lenses. The 
 former are also called magnifying glasses, while 
 the latter are sometimes called minifying lenses. 
 
 Q. What signs are used to denote these dif- 
 ferent kinds of lenses? 
 
 A. The plus sign (-[-) for the convex, and the 
 minus sign ( — ) for the concave. 
 
 Q. How many different forms or shapes 
 have each of these two kinds of lenses? 
 
 A. Three. There is the double-convex, or 
 concave, which is convex or concave on both sur- 
 faces. There is the plano-convex, or concave, 
 which is plane on one surface and convex or con- 
 cave on the other, and there is the convexo-con- 
 cave, or meniscus lens, which is convex on one sur- 
 face and concave on the other, and the concavo- 
 convex which-is concave on one side and convex 
 on the other. These two last kinds are also called 
 periscopic lenses. 
 
 Q. How can you readily tell whether a cer- 
 tain lens is a plus or a minus? 
 
22 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 A. By holding it before your eye and looking 
 through it at some fixed object, moving it slightly 
 from side to side or up and down. If it be a plus 
 lens, the object will move in an opposite direction, 
 while if it be a minus lens, the object will move in 
 the same direction as the lens. This is the simplest 
 test. 
 
 Q. Under what general name are the above 
 variety of lenses known? 
 
 A. They are known as spherical lenses, be- 
 cause they are obtained by sawing a section off a 
 sj)here, and they refract rays of light in all their 
 different meridians. 
 
 Q. And are there lenses which do not refract 
 rays in all their meridians? 
 
 A. Yes; there are the cylindric lenses which 
 are obtained by sawing a section off a cylinder of 
 glass, and which only refract light in one meridi- 
 an, which is at right angles to its axis.. 
 
 Q. How many kinds of cylindrical lenses are 
 there? 
 
 A. There are two kinds; the convex or plus, 
 and the concave or minus. 
 
 Q. How can we readily tell whether a lens 
 be a cylindrical or spherical? 
 
REFRACTION AND LENSES. 33 
 
 A. When holding it before the eye, and look- 
 ing at an object at some distance, the object moves 
 only in one direction when the lens is moved be- 
 fore the eye. Tliat is, it moves against, in one 
 meridian if it is a plus or convex cylinder, and 
 vi'ith, if it be a minus or concave cylinder. 
 
 Q. How can you determine the axis of a cy- 
 linder lens? 
 
 A. Draw two straight lines on some 
 plane surface, a sheet of paper for example, 
 at right angles to each other in the form of a cross, 
 looking at these lines through your cylinder lens, 
 unless they correspond with the axis of the lens, 
 they will appear broken, that is the part of the 
 line passing through the leng will not be continu- 
 ous with the lines beyond the edge of the lens. 
 Now, by turning the lens until the lines become 
 continuous, will give you the two principal meridi- 
 ans of the lens, and the meridian in which there is 
 no displacement of the lines, when the lens is 
 moved, at right angles to this line, will indicate 
 the axis of the cylinder, which is always found at 
 right angles to the refracting meridian of the cy- 
 linder lens. 
 
 Q. Do plus cylinder lenses, like convex spher- 
 icals, bring parallel rays of light to a point at their 
 principal focal distance? 
 
24 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 A. They do not form a point like a spherical, 
 bat a line of light at the focal distance, owing to 
 the refraction taking place in one meridian only, 
 and this line is always at right angles to the axis 
 of the cylinder. 
 
 Q. What is a prismatic lens? 
 
 A. A prismatic lens is a portion of glass, or 
 other transparent substance, included between, 
 two plane surfaces, inclined toward each other. 
 
 Q, What is the action of a prismatic lens in 
 regard to rays of light? 
 
 A. Rays are bent, or refracted, toward the 
 base of the prism. 
 
 Q. What is meant by the focal distance, or 
 point, of a lens? 
 
 A. It means the point at which parallel rays 
 of light are brought together. This is called its 
 principal focal point, which is the inverse of the 
 refractive power of the lens, that is, a lens having 
 a refractive power of 40 inches has only half the 
 refractive power of a lens whose focal point for 
 parallel rays is at 20 inches. 
 
 Q. What is used for a standard of measure- 
 ment in numbering the principal focal point of 
 lens? 
 
 A. A lens whose focal point is at one metre, 
 
REFRACTION AND LENSES. 25 
 
 or about 40 inches, also called a dioptre, which 
 according to the dioptric or French method of 
 enumeration, is taken as a standard. 
 
 Q. Are all lenses- numbered according to the 
 dioptric system? 
 
 A. They are numbered in both the inch and 
 the dioptric systems. 
 
 Q. Are these two systems, that is, the inch 
 and dioptric, readily convertible, one into the 
 other? 
 
 A. Yes, very readily, as it is simply a matter 
 of division and multiplication. For example, if 
 we have a lens whose focal distance is numbered 
 in inches, say 10 inches, and we wish to find how 
 many dioptres there are in it, we simply divide 40 
 inches, one dioptre, by 10 inches, the number of 
 the lens, and as we have seen that the refractive 
 power is the inverse of its focal distance, we find 
 we have a lens of 4 D. 40 inches -f- 10 inches 
 equals 4 D. ; or reversely, if we have a lens number- 
 ed in dioptres, and we wish to find out its focal • 
 length in inches, we have simply to divide 40 inches 
 or one dioptre, by the number of the lens, in diop- 
 tres, and the result will be the focal point in 
 inches; e. g., we have a lens of 4 dioptres, and we 
 wish to find out the number in inches, all we have 
 to do is to divide 40 inches 4- 4D equals 10 inches. 
 
26 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 Although this does not always result, without a 
 small fraction remaining, it is approximately and 
 sufficiently correct for practical purposes. 
 
 Following is a table of the dioptric system 
 
 with their corresponding number in English 
 inches, as well as the approximate or correspond- 
 ing lens of the old system, or Paris inch of 27.07 
 minutes, according to which many of the trial 
 cases are numbered: 
 
 No. of lens 
 
 in 
 dioptres. 
 
 0.12 
 0.25 
 0.50 
 0.62 
 0.75 
 1.00 
 1.25 
 1.50 
 1.75 
 2.00 
 2.25 
 2.50 
 2.75 
 3.00 
 3.25 
 3.50 
 4.00 
 4.50 
 5.00 
 5.50 
 6.50 
 
 Focal distance 
 
 Focal distance 
 
 Corresponding 
 
 in 
 
 in 
 
 lens, 
 
 millimetres. 
 
 English inches. 
 
 old system. 
 
 8,000 
 
 314.96 
 
 288 
 
 4,000 
 
 157.48 
 
 144 
 
 2,000 
 
 87.74 
 
 72 
 
 1,600 
 
 62.99 
 
 60 
 
 1,333 
 
 52.50 
 
 48 
 
 1,000 
 
 39.37 
 
 40 
 
 800 
 
 31.50 
 
 48 
 
 666 
 
 26.22 
 
 24 
 
 571 
 
 22.48 
 
 22 
 
 500 
 
 19.69 
 
 20 
 
 444 
 
 17.48 
 
 18 
 
 400 
 
 15.75 
 
 16 
 
 363 
 
 14.31 
 
 14 
 
 333 
 
 13.12 
 
 13 
 
 308 
 
 12.11 
 
 12 
 
 285 
 
 11.25 
 
 11 
 
 250 
 
 9.84 
 
 10 
 
 222 
 
 8.74 
 
 9 
 
 200 
 
 7.87 
 
 8 
 
 182 
 
 7.16 
 
 7 
 
 154 
 
 6.06 
 
 6 
 
 wn to 20 D. 
 
 or 2". 
 
 
REFRACTION AND LENSES. 27 
 
 Q. How are prismatic lens measured? 
 
 A. Generally by their angle of deviation, 
 instead of their refracting angles. There are two 
 methods used ; the first, and to my mind the easiest 
 is the method proposed by Mr. Charles F. Pren 
 tice of New York City, the well-known optician, 
 which he calls the prism-dioptre, and which he 
 uses for a standard. This is a prism which shall 
 reflect a ray of light one centimetre at a plane one 
 metre (39.37 inches) distance. The second method 
 is by Dr. W. S. Dennett, who takes what he calls 
 the centrad for a standard. It is not so readily un- 
 derstood as the first method. 
 
 Q. What are the special uses of the different 
 lenses in the different refractive conditions of the 
 eye? 
 
 A. The convex sphericals are employed in 
 hypermetropia, where the antro-posterior diameter 
 of the eye is too short. Parallel rays do not come 
 to a focus on the retina, but behind it, as it were. 
 As a convex lens converge rays to a point, we use 
 it in hypermetropia to assist the eye in bringing 
 the rays to a focus more in front, or on the retina. 
 Now, in myopia, the diameter is too long, so the 
 rays are brought to a point before they reach the 
 retina; and as a concave lens causes a divergence 
 
28 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 of the rays of light passing through it, we use it in 
 myopia to assist in bringing the rays to a focus 
 farther back on the retina. The cylindrical lenses 
 are used to correct astigmatism, or where the rays, 
 entering the eye, do not all come to a focus at the 
 same point on the retina, which may occur in ei- 
 ther hypermetropia or myopia. The use of the 
 prism lens is confined exclusively to the correc- 
 tion of muscle difflculties arising from either in- 
 sujBflciency, or other cause, such as paralysis or in- 
 juries. 
 
 Q. What are the requisite qualities for a 
 good lens? 
 
 A. It must be made from clear glass or 
 quartz; it must be carefully and equally ground in 
 all its meridians, and it must be accurately cut as 
 regards its optical axis and center. 
 
 Q. How are lenses generally arranged for 
 convenient use in the correction of the errors of the 
 refractive media of the eye? 
 
 A. A series of the different kinds of lenses 
 are arranged according to their focal power, begin- 
 ning with the weaker numbers and running up in 
 a convenient case, many varieties of which are to 
 be found on the market. A well equipped trial 
 case contains something like the following list of 
 
REFRACTION AND LENSES. 
 
 29 
 
 lenses and accessories found necessary in this 
 work : 
 
 Figure 4. 
 
 Audeinair's Trial Case, made by the Spencer Optical Co. , New York. 
 
 Thirty-five pairs, each of convex and concave 
 spherical lenses; twenty-five pairs, each convex 
 and concave cylindric lenses; prisms from 1 degree 
 to 20 degrees; colored glasses, three kinds, 1 stene- 
 optic disk, 1 blank disk to cover one eye, while the 
 other is being examined; 1 ground glass for the 
 same purpose; 1 disk with small hole; 1 adjustable 
 
30 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 trial frame with double cells; and 1 single cell,trial 
 frame, etc. 
 
 Q. What is the result of combining convex 
 and concave lens? 
 
 A. One will neutralize the other; for exam- 
 ple, if we take a convex lens of 2D. and place it 
 and a concave lens of 2D. together, one will neu- 
 tralize the other, and the result will be a plane 
 glass having no refracting power. We avail our- 
 selves of this neutralizing power when we wish to 
 measure a certain lens and have no instrument for 
 that purpose at hand. In measuring a cylindric 
 lens in this way, the axis of the two must be paral- 
 lel. Of course we use the numbered lenses of the 
 trial case in this procedure. 
 
 Q. What is meant by the "visual angle?" , 
 
 A. It is the angle formed by lines drawn 
 from the two extremities of an object to the nodal- 
 point, or the optical center of the eye. This point 
 is situated about 15 millimetres in front of the reti- 
 na,and about 7 millimetres behind the cornea. Rays 
 of light directed to the nodal-point pass through 
 straight without undergoing any refraction. 
 This "visual angle" determines the size of the reti- 
 nal image of an object, which in order to subtend 
 the same angle on the retina must be larger the 
 
REFRACTION AND LENSES. - 31 
 
 farther it is removed from the eye. The size of the 
 retinal image is to the size of the object as the dis- 
 tance from the nodal-point is to the retina; hence, 
 it follows that the size of the retinal image in hy- 
 permetropia, where the retina is nearer the nodal- 
 point of the eye, is smaller than in emmetropia; 
 and that in myopia, where the retina is farther 
 from the nodal-point than in emmetropia, that the 
 retinal image will be larger. 
 Figure 5. ^ q^ What is the normal acuteness 
 
 Eof vision? 
 A. Snellen determined that the 
 normal acuteness of vision was the 
 power of distinguishing letters 
 formed by strokes whose width 
 vas one-fifth the size of the letter, 
 and subtending an angle of 5 min - 
 utes. This led him to devise a series 
 
 Lof letters known as Snellen's test 
 I type, that are used in connection 
 
 Snellen's Test- with the test case in measuring the 
 
 type. 
 
 (Reduced). vision. They consist of a number of 
 letters of different sizes, which at different dis- 
 tances from the eye are so constructed as to form 
 
 the same visual angle. The letters are numbered 
 from two hundred feet down to ten feet, showing 
 us how far the separate letters should be read with 
 a normal eye. 
 
 T B 
 
 D L N 
 
 P T E R 
 
 r z B s B 
 
 oai^ ZT c 
 
33 REFRACTIVE AND OPHTHALMIC CATECHISM 
 
 Q. How do you test the visual acuteness? 
 
 A. A Snellen test card is hung in a well- 
 lighted room at a distance of twenty feet from 
 where your patient sits, and each eye is tested sep- 
 arately. With a shade or card over the patient's 
 left eye, you ask him to read the test-type from the 
 large letters down as far as he can see. Now, if 
 your patient can see the line that should be read by 
 the normal eye at twenty feet, we use this figure 
 for the denominator of a fraction, and we find that 
 the vision in the right eye is ||, which is equal to 
 1, or normal vision. 
 
 Now, with the right eye covered, we ask him 
 to read with the left in the same manner, and find 
 that at this distance from the card, thatis, twenty 
 feet, he can only read as far down as the line 
 marked forty feet, or the line that should be read 
 by the normal eye at a distance of forty feet. Tak- 
 ing this number for the denominator of a fraction 
 as before, we find that the vision in the left eye is 
 
 2 
 TO-- 
 
 Now, supposing he could only read at twenty 
 feet, the line that should be read by the normal eye 
 at 200 feet, then we would express his vision by the 
 fraction ^^etc. In many cases you will find 
 that they not only read the normal, or |4 line, but 
 they can do better, that is, they can read at twenty 
 
REFRACTION AND LENSES. 
 
 33 
 
34 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 feet the line that by the normal eye is only sup- 
 posed to be read at fifteen or twenty feet, as the 
 case may be, and in the same way using this 
 number as the denominator, we have the 
 aeuteness of vision expressed by the fraction 20:15, 
 or 20:10, which is better than normal, a condition 
 frequently found to exist. This, then, gives us the 
 aeuteness of vision for distance or the far point 
 (punctum remotum,) as it is called; Avhile we deter- 
 mine the aeuteness of vision for the near point 
 (punctum proximum) by the use of small type 
 called Jager type, numbered 1, 2 and 3, and the 
 ability to read this type without the use of convex 
 glasses gives us the aeuteness of vision for the near 
 point (punctum proximum,) and the difference be- 
 tween the near point and far point is what is 
 known as the "range of accommodation," also call- 
 ed the power, or amplitude of accommodation. 
 
 This we shall consider more fully in a separ- 
 ate chapter. 
 
CHAPTER III. 
 
 Accommodation. 
 
 " Q. What is meant by the accommodation of 
 the eye? 
 
 A. In the chapter on the anatomy of the eye, 
 we likened it to a camera obscura, and like a cam- 
 era, it must be capable of adjusting itself for im- 
 ages at different distances. Now, with a camera, 
 when we wish to get a focus of an image, or pic- 
 ture, at some distant point, we must shorten up 
 the distance from the lens to the focus glass, which 
 corresponds to the sensitive coat of the eye, or 
 retina. This is done, as you all know, by a sliding 
 adjustment of the camera, by which its antro-pos- 
 terior diameter is either increased or diminished, 
 as the case may require. This is very necessary 
 for its adaptation to different distances, as in all 
 lenses the focal point becomes farther away as the 
 object is brought closer. 
 
 Now, the eye-ball being incapable of chang- 
 ing its antro-posterior diameter on account of its 
 
 35 
 
36 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 inextensibility, this adjustment must take place in 
 some other way, and we find that this is accom- 
 plished by the action of the ciliary muscle on the 
 crystalline lens. This lens, as we have seen, is a 
 soft body inclosed in a covering called the capsule 
 of the lens, which is attached to the suspensory 
 ligament, which in turn is attached to the ciliary 
 muscle. By the action of this muscle, the lens is 
 changed so as to make it more convex, thus ena- 
 bling the image coming from a near object to be 
 properly focused at the "yellow spot" of the retina. 
 This change takes place mostly on the anterior sur- 
 face of the lens. This is called the accommodation 
 of the eye. 
 
 Q; Is the accommodation of the eye called 
 into frequent use? 
 
 A. Yes; every time the eye is changed from 
 one object to another situated at different dis- 
 tances. 
 
 Q. Does the accommodative power of the 
 eye differ much in different individuals? 
 
 A. In all persons with emmetropic, or nor- 
 mal eyes, it is nearly the same at the same age. 
 
 Q. What does punctum remotum, or r, mean 
 in connection with the accommodation of the eye? 
 
ACCOMMODATION. 37 
 
 A. It means the farthest point, or the maxi- 
 mum distance of vision at which an eye can see 
 without the aid of glasses. It is determined by the 
 use of the Snellen test-type, and in an emmetropic, 
 or normal eye, it is at twenty feet, or infinity, as 
 rays coming from this distance are practically par- 
 allel. The accommodation is supposed to be en- 
 tirely relaxed and the eye in a condition of mini- 
 mum refraction. 
 
 Q. What does punctum proximum, or p, 
 mean? 
 
 A. It means the nearest point at which fine 
 print, usually Jager No. 1, can be seen without the 
 aid of convex glasses. The ciliary muscles are 
 now fully contracted, the antro-posterior diameter 
 of the crystalline lens is increased, thus increas- 
 ing its refractive power, it bulges forward into 
 the anterior chamber, and the eye is in its maxi- 
 mum condition of refraction. 
 
 Q. What is the difference between the 
 punctum proximum, or p, and the punctum remo- 
 tum, orr, called? 
 
 A. It is called the range power, or amplitude 
 of the accommodation, and is determined as we 
 have seen by the use of the Snellen type. 
 
 Q. Does this "range of accommodation" 
 change much in the same individual? 
 
38 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 A. Yes, very much. It is greatest in young 
 life and gradually diminishes as age advances, un- 
 til the 73d year is reached, when it is entirely lost, 
 and the punctum proximum and the punctum re- 
 motum become the same. 
 
 Q. What is this gradually receding near 
 point called? 
 
 A. It is called presbyopia, or old sight, 
 which generally begins to manifest itself at about 
 the 40th year in emmetropes, sometimes earlier in 
 hypermotropes, and always later in myopes. 
 
 Q. When the near point is closer to the eye 
 at a certain age than is usual, what does it indi- 
 cate? 
 
 A. It indicates myopia. 
 
 Q. When it is farther away than usual, what 
 does it indicate? 
 
 A. It indicates hypermetropia. 
 
 Q. What other action of the eye is intimately 
 associated with the act of accommodation? 
 
 A. The act of converging the eyes, or the 
 change which takes place in the position of the 
 eye, as regards their axis when converging them, 
 so as to look from a distant object to one close to 
 the eves. 
 
CHAPTER IV. 
 
 Emiuetropia = Em. Hypermetropia =- H. 
 
 Q. What name is given to that condition of 
 the eye whose refractive conditions most closely 
 resemble a perfect optical instrument? 
 
 A. Emmetropia, which is defined by Landolt 
 of Paris, to be one, the "retina of which is found at 
 the principal focus of its dioptric system; or one 
 which united parallel rays on its retina, or ex- 
 pressed in another manner, the punctum remotum 
 of which is situated at infinity." ' 
 
 Q. Is this condition of emmetropia very fre- 
 quently found to exist? 
 
 A. The examination of a large number of 
 eyes, by difi'erent investigators, shows it to exist in 
 about twenty per cent, of the eyes examined. 
 
 Q. How are rays of light refiected from the 
 retina in an emmetropic eye? 
 
 A. As the focal point for rays entering the 
 emmetropic eye is at the principal focal point of 
 
 39 
 
40 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 the dioptric media, the emergent rays are parallel 
 on leaving the eye. 
 
 Q. Does an emmetropic eye require the aid 
 of a glass of any kind to see distinctly? 
 
 A. No; as the rays are parallel, the punctum 
 remotum is at infinity, and hence will not require 
 any glass for distant vision. 
 
 Q. Do emmetropic eyes ever undergo any 
 change in their refraction? 
 
 A. Yes; an emmetropic eye may become my- 
 opic from the conditions giving rise to myopia. In 
 fact, some writers contend that emmetropia is only 
 
 Figure 7. 
 
 The Emmetropic Eye. Parallel rays are focused on the retina. 
 (After Valk). 
 
 a stage, or point, reached in the refractive condi- 
 tions of the eye, in its transition from hypermetro- 
 pia to myopia. It is a fact, however, that in em- 
 metropia we have not only the best optical condi- 
 tion to be found in the eye, but we have also, in em- 
 
EMMETROPIA. HYPERMETROPIA. 41 
 
 metropia, the most healthy condition of the media, 
 membranes, etc., and also an eye which is capable 
 of performing the greatest amount of work with- 
 out giving rise to asthenopia, or eye strain, and 
 that any great amount of deviation from this con- 
 dition of refraction is generally accompanied with 
 asthenopia. There are several reasons justifying 
 this claim, denied by many, as to its being a nor- 
 mal eye. It is, however, a good standard to use in 
 estimating refractive errors, and it is likely that 
 for this reason, if for no other, it will continue to 
 be regarded as such. Any deviation from emme- 
 tropia is called ametropia, of which hypermetro- 
 pia, myopia, and astigmatism are varieties. 
 
 Q. What is hypermetropia, and what is its 
 principal cause? 
 
 Figure 8. 
 
 The Hypermetropic Eye. Parallel rays are focused behind the 
 
 retina. (After Valk). 
 
 A. Hypermetropia is that condition or va- 
 riety of ametropia, in which the principal focal 
 
42 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 point of the dioptric media, tliat is, the cornea, 
 aqueous humor, crystalline lens, and vitrious hum- 
 or, lie behind the retina. It is principally caused 
 by the visual axis of the eye being shorter than the 
 focal point of the eye. Some claim it may also be 
 caused by a lack of density, and hence refractive 
 power on the part of the dioptric media. 
 
 Kays of light reflected from the retina of an 
 hypermetropic eye are divergent after leaving it. 
 This condition of hypermetropia is also called far- 
 sightedness. The cause of hypermetropia are 
 nearly always congenital, nearly all eyes being 
 hypermetropic at birth, though it may be caused 
 surgically by the removal of the crystalline lens, 
 as in operation for .cataract. 
 
 Q. What are the symptoms of hypermetro- 
 pia? 
 
 A. On looking at small objects, like fine 
 print, it is hard to maintain distinct vision for any 
 length of time, without blurring, and persons with 
 hypermetropia are generally looking for a strong 
 light to enable them to see more distinctly, and we 
 may have irritation of the eye-lids, or even inflam- 
 mation, or conjunctivitis, following the persistent 
 use of the eyes under these circumstances. The 
 pupil is apt to be contracted in hypermetropia, and 
 looking at the eye closely will generally reveal a 
 
EMMETROPIA. HYPERMETROPIA. 43 
 
 shallow anterior chamber, and if you have a high 
 degree, you can generally notice that the eye is 
 much smaller than normal, giving rise to a short 
 antro-posterior diameter, thus causing axial hy- 
 permetropia. 
 
 The glass used to correct this condition of re- 
 fraction, as we shall see later on, is always a con- 
 vex, or plus, glass; as the action of this glass is to 
 converge rays of light to a point, we place it be- 
 fore the hypermetropic eye, and by assisting the 
 dioptric media of the eye the rays are brought to 
 a focus more in front or on the retina, where it 
 should be, in order to have a clear and distinct 
 image. 
 
 Q. How many kinds of hypermetropia as re- 
 gards its aetiology, or cause, are there, then? 
 
 A. Two kinds; first, where the visual axis of 
 the eye is too short, which is called axial hyperme- 
 tropia, and second, where there is a deficiency in 
 the density or refractive power of the dioptric me- 
 dia, called curvature hypermetropia. To facilitate 
 a description of axial hypermetropia, it is divided 
 into three varieties, that is, manifest, latent, and 
 total hypermetropia. These varieties can best be 
 explained by citing a case for illustration: A 
 young lady twenty-four years old, comes com- 
 plaining of her eyes. She has difficulty in sewing 
 
44 REFRACTIVE AND OPHTHALMIC CATECHISM 
 
 or reading for any length of time without causing 
 strain and headache. Her vision is tested in the 
 usual manner with the Snellen test-type, at twen- 
 ty feet, and we find that she can read down to the 
 line that should be seen by the emmetropic eye at 
 twenty feet, so using this figure as the denomina- 
 tor of a fraction, we have her vision expressed as 
 f^ in both eyes. Now, b}' taking a plus glass of 
 ID. and placing it before her eye, we find that this 
 will not give her increased vision; neither will it 
 cause any blurring of her vision up to f {J Now 
 this ID. convex glass represents her manifest hy- 
 permetropia, but as this does not correct her ame- 
 tropia, or relieve her asthenopia, we conclude to 
 paralyze the accommodation by the use of a solu- 
 tion of atropine, say four grains to the ounce, a 
 few drops instilled three times a day for a period 
 of . three days. We now find that without her 
 glasses her vision is reduced to ^%\ , but with a 
 -|-3 D. lens, her vision is immediately brought up 
 to|o, or normal. Now this 3 D. represents her 
 total hypermetropia, and the difference in the 
 glass accepted before using the mydriatic, and the 
 one accepted after will represent the amount of 
 latent hypermetropia, w^hich in this case is repre- 
 sented by 2D. Now in this case, after recovering 
 from the use of the atropine, she accepts a -^1.75, 
 which gives her |^ vision, the balance of 1.25D. 
 
EMMETROPIA. HYPERMETROPIA. 45 
 
 will be taken care of by the aeeonimodatlon of the 
 eye. 
 
 In some cases, like the foregoing, we may 
 have what is called a spasm of the accommodation, 
 which results from a prolonged effort of the accom- 
 modation in trying to overcome the hypermetro- 
 pia, so as to produce distinct vision before glasses 
 are prescribed, and in these cases we generally 
 find it necessary to use atropine before being able 
 to relieve our patient of their asthenopia. 
 
 We will further illustrate the different varie- 
 ties of hypermetropia by selecting a few represen- 
 tative cases from our note-book : 
 
 First case. Manifest Hypermetropia. Boy 
 eighteen years old, complained of eyes hurting and. 
 vision blurring when he would use his eyes for any 
 length of time. On taking his vision, we find that 
 with the O. D. V. equals || . (Opticum dextrum, 
 or right eye vision); and that of O. S. V. equals || 
 (Opticum sinistrum,or left eye vision). Now with a 
 -r-0.4SD.S. the vision still remains f^}, but the 
 asthenopia, or eye strain, is removed by his wear- 
 ing this glass all the time. 
 
 Second case. Latent Hypermetropia. Young 
 lady, twenty years old, complained in much the 
 same way when using her eyes for study, and we 
 
46 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 find that her vision is 1^, and that with a 
 -|-1.25 D. S. her vision is brought up to I? , but 
 as this does not correct her eye strain, on account 
 of her inability to relax her accommodation, we 
 use a solution of atropine, four grains to the ounce 
 for three days, and we now find her vision has 
 gone back to H, but with a -!-4D. her vision is 
 brought up to U. Now this additional 2.75 D. 
 of hypermetropia brought out by the use of atro- 
 pine, represented concealed or latent hypermetro- 
 pia. While the total is represented by the 4D., 
 which she accepts with a mydriatic. It is very 
 rarely that we can ever correct the total hyperme- 
 tropia by prescribing glasses for full correction 
 without causing strain of the accommodation from 
 the opposite direction, and we must always leave 
 from 1 to 1.50D. uncorrected. This, however, is my 
 custom, and it seems to give the best satisfaction. 
 There are certain cases, for example, where there 
 is interna] strabismus, or squint, accompanying a 
 high degree of hypermetropia, where it may be ne- 
 cessary to prescribe full correction with a view of 
 overcoming the squint. This had better be done in 
 connection with the use of atropine, as in this way 
 you reduce the tendency to convergence by para- 
 lyzing the accommodation. 
 
 It may be best to add, in concluding this sub- 
 ject of hypermetropia, that in order to get perma- 
 
EMMETROPIA. HYPERMETROPIA. 47 
 
 nent relief from the eye strain resulting from it, 
 that it will be necessary to wear the correcting 
 o-l asses all the time, and not alone for close work, 
 as many seem to think all that is necessary. It is 
 very necessary to see that the frames fit properly 
 and that the optical centers of the lens correspond 
 with the pupillary distance of the eyes, as all de- 
 centred lenses act as prisms, and may thus, uncon- 
 sciously, produce the exact condition they are in- 
 tended to correct. This fact it is always best to 
 bear in mind in prescribing glasses, and especially 
 so, if the amount of ametropia be very great. 
 
 Q. Do you ever meet cases of hypermetropia 
 in which the patient will not accept a convex glass, 
 that is, when the vision is already 1,1 and where 
 a convex glass will not only not improve vision, 
 but actually bhir it, yet 3'ou are satisfied from the 
 asthenopia complained of and as the result of 
 your opthalmoscopic and retinosco})ic examina- 
 tion, that your patient has a considerable amount 
 of hypermetropia? 
 
 A. Yes; such cases are frequently met with, 
 and in such cases all the hypermetropia is of the 
 latent, or concealed, variety, and owing to the con- 
 dition of the accommodation, which has become 
 irritable and spasmodic, such cases will not accept 
 a convex glass until you reduce the irritability and 
 
48 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 spasm of the accommodation by the use of a myd- 
 riatic for several days, when you will find you can 
 correct all of the latent hypermetropia. 
 
CHAPTER V. 
 
 Myopia = M. 
 
 Q. What is myopia? 
 
 Figure 9. 
 
 Tiie Myopic Eye . Parallel rays are focused before reaching the 
 retina . (After Valk . ) 
 
 A. It is that variety of ametropia, in which 
 the principal focal point of the dioptric media lies 
 anterior to the retina, and in which only those rays 
 that came from a nearer point than twenty feet, or 
 infinity, can be brought to a point on the "yellow 
 spot" of the retina. This point from which the 
 rays diverge in front of the eye is the punctum re- 
 motiim of the eye, and all rays coming from objects 
 between this punctum remotum and the eye cau 
 
 49 
 
50 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 be seen distinctly, because they are focused on the 
 retina, according to the rule that the nearer the 
 object is to a lens the longer is its focal distance 
 and vice versa. 
 
 Q. How many kinds of myopia have we? 
 
 A. Two kinds. First, the axial myopia in 
 which the axis of the eye is longer than its princi- 
 pal focal distance, and second, curvature myopia, 
 in which the fault lies in the dioptric media, that 
 is, possessing too great refractive power, or too 
 great a curvature, by which the focus for parallel 
 rays are brought to a point too near the nodal- 
 point of the eye. 
 
 Q. Which of those two causes is the princi- 
 pal one in producing myopia? 
 
 A. The first, or the axial myopia, is supposed 
 to be the principal cause. The curvature myopia 
 may be caused by disease of the cornea such as 
 conical cornea, or any other condition that may 
 increase the curvature, and hence the refraction 
 of the cornea or lens. 
 
 Q. What theories are advanced as to the 
 causes which result in conditions which lead up to 
 the development of myopia? 
 
 A. There are three theories as to the cause 
 of myopia. First, the anatomical theory, which 
 
MYOPIA. 51 
 
 holds that the primary cause is to be found in the 
 orbit, which, owing to its peculiar shape, predis- 
 poses to the elongation of the ej^o-ball and thus to 
 Ihe development of axial myopia. Second, or me- 
 chanical theory, ascribes axial myopia to the com- 
 pression of the eye muscles on the eye-ball, thus 
 producing distention of the ball backwards. 
 
 The third, or inflammatory theory, is held by 
 some as the cause, for the reason that myopia is 
 frequently found to exist in connection with in- 
 llammatory conditions, such as chroiditis, sclero- 
 tis, etc., which is caused by obstructing the venous 
 circulation resulting from certain habits of life, 
 such as stooping, or bending over at school or 
 working where the illumination is insufficient to 
 see without extra effort, etc. This, however, is de- 
 nied by some, as only a very small per cent, of 
 those living or working under such conditions, are 
 myopic. It is more frequently seen in some coun- 
 tries than others, thus in Germany it is much more 
 frequently seen than in the United States, 
 
 Q. What are the indications of myopia? 
 
 A. They are both objective and subjective. 
 The objective being a large prominent eye-ball, a 
 dilated pupil, and a deep anterior chamber, while 
 the subjective indications are an inability to see 
 things distinctly, at a distance everything appear- 
 
52 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 ing foggy and indistinct, and in high degrees of 
 myopia, the object must be brought close to the 
 eye to see it clearly. The latter condition of high 
 myopia is also frequently combined with diver- 
 gent strabismus, or a turning out of the eyes, in 
 which case the patient usually uses one eye at a 
 time, as binocular vision is impossible under these 
 circumstances. 
 
 Myopes are usually more given to close work, 
 such as reading and work requiring the object to 
 be brought near the eyes. They are not given, as 
 a rule, to sport of an out-door character, on ac- 
 count, usuafly, of their poor visions. Myopia is 
 very apt to increase, and sometimes it produces 
 such change in the fundus as to very seriously im- 
 pair the eye-sight. There is, in some cases of my- 
 opia, a drawing away of the retina from the chor- 
 oid, about the edge of the optic disk. This is gen- 
 erally semi-lunar in shape, and is called posterior 
 staphyloma. This may extend to the extent of 
 causing a detachment of the retina, and more or 
 less loss of sight. 
 
 There is one other peculiarity about the myo- 
 pic eye, and that is the feeble development of the 
 ciliary muscle. The far point of the myopic eye is 
 "SO near to the eye, that the accommodation is very 
 little employed, and as a result of this non-use, the 
 
MYOPIA. ' 53 
 
 ciliary muscle is never very fully developed, hence 
 it is rarely ever necessary for us to use a mydriatic 
 in myopes, unless we suspect artificial, or spuri- 
 ous, myopia, the result of tonic spasm of the ciliary 
 muscle. 
 
 Q. Is there any compensating feature about 
 myopia at all? 
 
 A. The only possible one that it is known to 
 possess is the well-known fact that it delays pres- 
 byopia, if it does not entirely do away with the ne- 
 cessity of wearing glasses for this condition, 
 which, as we shall see, in emmetropia and hyper- 
 metropia, shows itself at about the 40th year, 
 when it is necessary for us to use a convex glass 
 before the eye to restore the gradually receding 
 near point to a position that enables us to work at 
 close work without straining the eyes. 
 
 Q. How do you proceed to correct myopia 
 with lenses? 
 
 A. Well, we-, have seen, when speaking of 
 concave lenses, that their action causes a di- 
 vergency of the rajB of light passing 
 through them. Now in myopia, we find that the 
 rays coming from the myopic eye are converged to 
 a point in front of the eye, so we wish to change 
 their course so as to produce a parallelism of the 
 
54 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 rays, for we have also seen that as the rays pass 
 from the eye, so also do they pass into the eye. 
 If the rays be made to pass out of the eye in 
 parallel lines by the diverging action of concave 
 glasses, so also will rays coming from infinity pass 
 in in parallel lines, thus producing distinct vision 
 for distance, or infinity, and the weakest concave 
 glass that produces this condition, is the one to 
 prescribe for constant wear, and it should be worn 
 as close to the cornea of the eye as possible, and 
 this glass will usually suffice for all purposes, un- 
 less the myopia be of a high degree, when it will 
 be necessary to give a lens somewhat weaker than 
 this for close work. 
 
 We shall speak of this more fully under the 
 head of presbyopia. We will now bring this chap- 
 ter on myopia to a close by citing a few typical 
 cases as taken from our note-book. Of course, in 
 getting at the acuteness of vision, we resort to the 
 •same method as in hypermetropia. We have a pati- 
 ent sit at a distance of 20 feet from the Snellen 
 test-type, in a well-lighted room, and each eye is 
 measured separately, while a shade or cover is 
 held over the other, and a note is made of the vis- 
 ion of each eye in the proper manner.. You will 
 find that in cases of myopia that if you place a con- 
 vex lens before the eye, the vision is made worse, 
 
MYOPIA. 55 
 
 at once leading you to suspect the existence of my- 
 opia, which you proceed to prove by the use of 
 concave glasses, the ophthalmoscope, and retiuo- 
 scope. 
 
 First case. Simple Myopia. Mrs. S., age 33. 
 O. D. V. equals fH, with a —3 D. S. equals |M- 
 O. S. V. equals f^, with a —3 D. S. equals -{J -|- 
 This case read in the following manner: 
 Right eye vision, without glasses, equals twenty- 
 fiftieths; that is, she could only see at twenty feet 
 the line that should be seen by the emmetropic eye 
 at fifty feet, but by placing a minus glass before 
 her eyes, her vision is brought up to twenty -twen- 
 tieths plus, which means a little better than nor- 
 mal. In the left eye we find the same condition of 
 affairs, and with the same glass she gets the same 
 improvement; hence you see this is a case of sim- 
 ple myopia, or short-sightedness, as it is called. 
 
 The next case is a case in which there is a dif- 
 ference in the amount of ametropia in each eye, a 
 condition called anisometropia. 
 
 Second case. Myopia. Mr. H. G., age 53 years. 
 
 O. D. V. A"o w - 5.50 D. S. = H- 
 O. S. V. ^Vo — w — 6.50 D. S. = U- 
 
 Now, in this case, we find vision very much re- 
 duced without glasses, but with a — 5.50 D. S. over 
 
56 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 the right eye, vision was increased to |^, and with 
 a — 6.50 D. S. over the left eye, vision was made 
 only II -J-. The ophthalmoscope did not show any 
 pathological, or decreased condition of the eye, as 
 we ought reasonably to expect, and his poor vision 
 can only be ascribed to the fact that he did not 
 wear glasses until the last few years, which I think 
 often produces some change in the retinal nerve 
 elements, thus rendering normal vision impossible. 
 
 This man was able to use these glasses for both 
 near and far work, thus partly compensating him 
 for his myopia in not being obliged to use a convex 
 glass for close work only. In the above case, the 
 difference in the correcting glass constitutes, as 
 we have said, anisometropia. 
 
 In the last case just cited, we find that it re- 
 quires a — 5.50 D., or about a 7 inch glass to render 
 the converging rays of this myopic eye parallel. 
 Now, as this distance, that is, 7 inches, is the far 
 point of his eye, everything beyond this point will 
 appear indistinct and hazy. We are thus enabled 
 to get some idea of the amount of myopia in a given 
 case, by having them hold some ordinary type as 
 far from the eye, or at the punctum remotum, as 
 they can see it distinctly. As this point will repre- 
 sent the focal point of the correcting glass, it will 
 give us some idea of the glass required. We must 
 
MYOPIA, 67 
 
 also remember that concave lens have a negative 
 focal point, and instead of estimating the focal 
 point behind, the glass when applied to the eye, 
 you must calculate the focal distance in front, and 
 accordingly in the above case, we find this to be 7 
 inches in the right eye and G inches in the left, be- 
 cause with the negative focal point of the concave 
 correcting lens, at these respective points, the 
 rays are rendered parallel, and distinct vision for 
 distance is rendered possible. 
 
 There are a few cases of myopia, generally in 
 the aged, which is caused by the swelling of the 
 crystalline lens, the result of inflammatory action 
 in the lens substance, as, for example, such as oc- 
 curs in senile cataract. The effect of this swelling 
 is to increase the antro-posterior diameter of the 
 lens, and hence its refractive power, thus produc- 
 ing a myopia by bringing the focal point in front 
 of the retina. In these cases, the patients are 
 sometimes able to read without the use of glasses, 
 where previously glasses were necessary. This is 
 what they call their second sight, and they are apt 
 to speak boastingly of their new possession, little 
 dreaming that it is the initial stage of a condition 
 which when further advanced may rob them of 
 their precious sight entirely. 
 
CHAPTER VI. 
 
 Astigmatisui = As. 
 
 Q. What is astigmatism? 
 
 A. It is that condition of refraction in which 
 rays of light coming from a given point, are not 
 all brought to a focus at the same place on the ret- 
 ina. 
 
 Q. HoTv many kinds of astigmatism are 
 there? 
 
 A. There are two kinds; regular astigma- 
 tism, and irregular astigmatism. 
 
 Q. What is the cause of regular astigma- 
 tism? 
 
 A. A difference in the curvature of the differ- 
 ent meridians, of the cornea, or lens. 
 
 Q. Where is it most frequently found to be 
 located? 
 
 A. In the cornea of the eye. 
 
 Q. What is irregular astigmatism, and what 
 is its principal cause? 
 
 A. It is a difference in the curvature of the 
 
 58 
 
ASTIGMA TISM. 59 
 
 cornea aud leus, the same as regular astigmatism, 
 but generally tlie result of traumatism, disease, 
 or following a surgical operation on the eye. 
 
 Q. How many yarieties of regular astigma- 
 tism haye we? 
 
 A. We haye flye different yarieties. 
 Q. What are their different names? 
 
 A. 1st. Simple Hypermetropic Astigmatism. 
 (All.) In this form one of the meridians of the eye 
 is emmetropic, usually the yertical, while the mer- 
 idian at right angles, usually the horizontal, is 
 hypermetropic. 
 
 2d. Simple Myopic Astigmatism. (Am.) In 
 this form one of the meridians of the eye is emme- 
 tropic, usually the horizontal, while the other mer- 
 idian, usually at right angles, that is, the yertical 
 meridian, is myopic. 
 
 3d. Compound Hypermetropic Astigmatism. 
 (*H. Ah.) In this form of astigmatism, both merid- 
 ians of the eye are hypermetropic, but one more 
 hypermetropic than the other, usually the horizon- 
 tal. 
 
 4th. Compound Myopic Astigmatism. (M. Am.) 
 In this form of astigmatism both the meridians are 
 myopic, but one meridian is more myopic than the 
 orher usually the yertical. 
 
60 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 5th. Mixed Astigmatism. (A. hm. or A. mil.) 
 Tiiis is a condition of refraction in which one mer- 
 idian is hypermetropic and the other meridian my- 
 opic. 
 
 Q. Is astigmatism frequently found to exist? 
 
 A. Yes; it is perhaps the most frequent form 
 of refractive error, as well as the most frequent 
 source of asthenopia, or eye-strain. 
 
 Q. What variety is most frequently met 
 with? 
 
 A. Simple hypermetropic astigmatism, with 
 compound hypermetropic astigmatism a close sec- 
 ond. 
 
 Q. What kind of lens is always used in cor- 
 recting astigmatism? 
 
 A. Cylindric lenses are always uses to correct 
 astigmatism, but, of course, they are used in com- 
 bination with the sphericals in cases of compound 
 astigmatism. 
 
 Q. Should cylindric correcting lenses for as- 
 tigmatism be worn for certain work, or at certain 
 times ? 
 
 A. No; they should be worn for all kinds of 
 work, and at all times. That is, they are for con- 
 stant wear. 
 
ASTIGMATISM. 61 
 
 Q. How do you determine the i)resence of as- 
 tigmatism? 
 
 A. There are several methods that may be 
 named in the following order: Snellen test-type 
 for distance,, the astigmatic chart, the ophthalmos- 
 cope, the shadow test, skioscopy, or retinoscopy, 
 as it is called, Placidos keratoscoi3e, and lastly, by 
 means of the Javal ophthalmometer. 
 
 Q. Describe the method with Snellen test- 
 type? 
 
 A. The patient is seated, as before, at a dis- 
 tance of twenty feet from the letters, and the vis- 
 ion tested in the usual manner. We will find the 
 vision as a rule, below fo though it may be 
 normal, and the patient still have astigmatism. 
 We first try a spherical convex lens, and we find 
 we do not improve the sight any. We next try a 
 spherical concave with the same result. We 
 should remember, to begin with, rather weak 
 sphericals. Now, we will take a convex cylinder 
 and placing it before the eye, we turn it in the cell 
 of the trial frame, until the patient says he can see 
 clearer and better. We keep increasing or 
 decreasing the strength of the cylinder until the 
 very best visional results are obtained, always re- 
 membering to place the axis of the cylinder at the 
 point of clearest vision, and this i)oint will be in- 
 
62 REFRACTIVE AXD OPHTHALMIC CATECHISM. 
 
 dicated in degrees by the figures marked on the 
 trial frame. For example, vre find that our pa- 
 tient has ^ vision in both eyes, and with eith- 
 er a convex or concave spherical, which we would 
 naturally try first, vision is not improved. Then, 
 of course we would try a cylindric lens, taking 
 first a convex of ID. and setting it in the trial 
 frame over the right eye — the left being covered 
 as usual — with its axis at 180°, slowly turning it 
 from left to right until a point is reached when the 
 patient will be able to see better, and we note this 
 point on the trial frame, which in this case we will 
 say, is at 90°. Xow we take a still stronger lens, 
 say a -r-1.25, and vision is made |^-|-, but to be sure 
 we try a still stronger one, say a -f -1.50 D., but this 
 causes a blur, so we go back to our second lens, or 
 ►T-1-25 D. cylinder, and we find this gives us the 
 best result, so we have the vision of this eye cor- 
 rected as follows : 
 
 E. E. V. fl w -I- 1.25 D. Cyl. Ax. 90° = M -|-- 
 
 which reads as follows : Eight eye vision H with a 
 plus one and a quarter dioptric cylinder axis at 
 ninety, vision equals twenty-twentieths plus. For 
 the sake of brevity, we will say that we find the 
 left eye vision the same, and that it is corrected by 
 the same cvlinder lens. 
 
ASTIG3IATISM. 
 
 63 
 
 Q. What is the astigmatic chart,and how is it 
 used to determine the presence of astigmatism? 
 Figure 10. 
 
 Green's Astigmatic Chart. 
 
 A. The astigmatic chart, of which there are 
 many varieties, is a chart numbered like the dial of 
 a clock with the numbers from 1 to 12 in the same 
 relative position. From the center of the chart to 
 the numbers on the periphery radiate lines, gen- 
 erally three in number, thus forming three black 
 lines and two white spaces. The back-ground of 
 the chart is white, so the contrast is well marked. 
 This chart is hung in a well-lighted room, say 10 ft. 
 from our patient, and on about a level with the 
 eyes. When an astigmatic patient looks at 
 the lines he will be able to see the lines in one mer- 
 idian much clearer than those in the meridian at 
 right angles to this; for example, in the case just 
 
64 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 cited, the patient would be able to see tlie lines 
 running in the horizontal meridian much better 
 and clearer than in the vertical, while in the ver- 
 tical meridian he might not be able to distinguish 
 the lines and spaces. 
 
 Xow the cylinder lens with its axis at right 
 angles to the meridian in which the lines are seen 
 most distinctly, that will bring the vertical merid- 
 ian out clear and distinct, will represent your cor- 
 recting cylinder glass, as we find 1.25D. to do in 
 the above case. 
 
 The method of determining astigmatism by 
 the use of the ophthalmoscope, retinoscope,and ob- 
 thalmometer, will be considered under separate 
 chapters. The keratoscope is an instrument in- 
 vented by Placido of Porto, and named for him. It 
 is a disk about 8 or 9 inches in diameter with a hole 
 in the center; on the surface of the disk is a series 
 of concentric circles in black and white. In using 
 it the patient is placed with his back to the light, 
 and by holding this before the eye and looking 
 through the aperture, a reflection of the circles is 
 seen on the cornea. If there be no astigmatism 
 the circles will have a regular shape as seen on the 
 disk, but if there be astigmatism, they will appear 
 oval and irregular with the shortest diameter of 
 the oval corresponding to the meridian v\'hich is 
 the seat of the astigmatism. 
 
ASTIGMATISM. 
 Figure 11. 
 
 65 
 
 Placido's Disk or Keratoscope, 
 
 Q. What is the stenopaeic slit, and for what 
 puri^ose is it used? 
 
 A. It is a metal disk, usually found in a 
 test case, and is made to fit the trial frame. 
 It has a slit about 1 inch long and very 
 
66 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 narrow. It is used to test the vision in the various 
 meridians separately, to confirm the diagnosis of 
 astigmatism. In the above case, which we will 
 take to illustrate the use of the stenopaeic slit also, 
 we would put it before the eye with the slit in the 
 vertical direction, and we find our patient has vis- 
 ion in this meridian of |f. We now turn it so 
 as to bring the slit in the horizontal meridian, and 
 we find that he can only see as far down as the 
 t^ line. Xow, by taking a spherical glass and 
 placing it before the eye, this spherical will act 
 like a cylinder with the stenopaeic disk over the 
 eye. As rays of light are only admitted in the 
 meridian in which the slit is placed, as all the 
 other rays are cut off by the disk, we find that it re- 
 quires a 1.25 D. S. convex to bring the vision up to 
 1^, or normal, and this will represent the num- 
 ber of the cylinder lens, necessary to correct the 
 astigmatism with its axis at right angles, or at 
 90°. 
 
 In using the slit in cases of compound astig- 
 matism, either of the hypermetropic or myopic va- 
 riety, each of the two principal meridians must be 
 tested separately, and the difference in the two 
 will represent the amount of astigmatism. It is 
 unnecessary to add that we do not rely on the find- 
 ing of the stenoaepic slit alone, but it will prove a 
 
ASTIGjIaTISJ^I. 67 
 
 good corroborating test in ^erv many cases of as- 
 tigmatism. 
 
 Q. Tlius far we have only spoken of the first 
 variety of astigmatism, tliat is, simple hyperme- 
 tropic astigmatism. Now how would we proceed to 
 use these various tests in a case of the second va- 
 riety; namely, compound hypermetropic astigma- 
 tism? 
 
 A. Well, in a ease of compound hypermetropic 
 astigmatism, we have a case of simple hypermetro- 
 pia combined with simple hypermetropic astigma- 
 tism. In that case, we would proceed to deal with 
 the hypermetropia alone first, and bring the pa- 
 tient's vision up to the highest point by the use of 
 a convex spherical lens. When we could get no 
 further improvement with sphericals, we take and 
 set this lens in the back cell of the trial frame, and 
 proceed to apply cylinder glasses over it, trying 
 the different numbers, and turning it to different 
 points, until the best possible results are attained, 
 and the very best vision results. This, of course, 
 is the test with the Snellen type, and to make it 
 more clear we will cite another case from our note- 
 book which is a very well marked case of this var- 
 iety of refractive error. 
 
 Miss M. R., age 15 years, was sent to me by her 
 teacher, for me to correct her vision. She could not 
 
68 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 see the blaekbroad even when in a front seat, and 
 the iTse of her eves was accompanied with severe 
 strain and blurring. She also had blepharitis, or 
 inflammation of the edge of the lids, with the for- 
 mation of crusts on them. The Snellen test type 
 gave her vision in each eye without glasses as 
 -f^-^. Now in the usual way, I applied convex 
 spherical lens, but I was only able to bring her vis- 
 ion up to II by the use of spherigals alone, and 
 this proved to be one of 4. SOD. I then placed this 
 in the back cell of the trial frame, and began the 
 use of convex cylinders, and I found that with a 
 convex cylinder of 2D. with its axis 90 deg., her 
 vision became ||. The left eye showed exact- 
 ly the same results, and the other different tests 
 confirmed the result. So, I order for her constant 
 use the following glasses, which she wears with 
 great satisfaction and comfort: 
 
 K. E. Y. = oW w -1- 4.50 D. S. C -I- 2 D. cyl. 
 
 ax. 90° = 1^. 
 
 L. E. V. = 3^V ^ -I- 4.50 D. S. C -I- 2 D. cyl. 
 ax. 90° = f^ 
 
 You are already familiar with the interpreta- 
 tion of these formulae, so we will not trouble you 
 any more with it. This, then, is a typical case of the 
 compound hypermetropic variety of astigmatism, 
 so we shall next proceed to the consideration of 
 
ASTIGMATISM. 69 
 
 the third variety, that of simple myopic astigma- 
 tism. Now with the Snellen type, you find vision 
 generally reduced, though in low degrees, it need 
 not be but very little below normal. You find that 
 spherical glasses do not improve it, so you try the 
 cylinders, of course, and you find that on turning 
 the glass so as to bring the axis of the glass into 
 the 180 deg. meridian, that vision is better, the 
 lines which before were plainer in the vertical 
 meridian of the astigmatic chart are now all equal- 
 ly distinct, and you can if you are not satisfied, try 
 the other tests, but you will soon learn to rely 
 more on the testing case than on any other single 
 test. We make a note of what we have found, 
 and express it in the following formulae: 
 
 R. E. V. = H w — .55 D. cyl. ax. 180° = ||. 
 
 L. E. V. = H w — . 55 D . cyl. ax. 180° = U- 
 
 This shows us then a case of simple 
 mj'opic astigmatism, ''according to the rule,-' that 
 is, the axis of the cylinder is at 180°, which is most 
 generally the case, but if it were at 90° instead, it 
 would be said to be "contrary to the rule,'' but you 
 must remember that in hypermetropic astigma- 
 tism it is ''according to the rule'' at 90°, and ''con- 
 trary to the rule" atl80o. You will observe that in 
 these cases of simple astigmatism, either hyperme- 
 tropic or myopic, one of the meridians of the eye is 
 
70 REFRACTIVE A^D OPHTHALMIC CATECHISM 
 
 eiiiiiietropic, aud the other ametropie, and that it 
 is only necessary to correct but one meridian, aud 
 as light is oulv refracted in one meridian by cylin- 
 dric glasses, you will readily appreciate why cylin- 
 ders are always used in astigmatism. 
 
 The determination of the fourth variety, that 
 is, compound myopic astig-matism, is the same in 
 every respect as that of compound hypermetropic 
 astigmatism, except in the use of concave spheri- 
 cals aud cylinder lens instead of the convex. You 
 will notice that the vision according to the Snellen 
 type is generally lower in myopic than in hyperme- 
 tropic cases, except in cases of very high degree of 
 hypermetropia; but, as a rule, you may suspect 
 myopia first, unless you have good proof to the 
 contrary, when you meet a patient whose vision is 
 very much reduced, say y-Trrr, or even lower. We 
 will likewise select a case of compound myopic as- 
 tigmatism from our case book, to better illustrate 
 the method of correcting this form of refractive 
 error, and in selecting these cases you will observe 
 that I select only those of rather high degree. I 
 do this to make the case more clear to your mind, 
 but you must not conclude from this that all the 
 cases you meet will be so well-marked, for the fact 
 of the matter is, the cases of low degree of trouble 
 are the ones that will require your greatest skill, 
 as well as the ones that will cause your patients, 
 
ASTIGMATISM. 71 
 
 mauT times, the greatest amount of eye strain. 
 In this ease of compound myopic astigmatism, 
 Mr. C, age 23 years, of literary habits, consulted 
 me in regard to his eyes, which were giving him 
 considerable trouble. He had more or less inflam- 
 mation about the lids, with blepharitis, and being 
 of a very nervous temperament, felt that it was 
 largely the result of his eye trouble. He had been 
 wearing a pair of -3D., but did not feel that they 
 were just what he should have. In examining 
 each eye separately by the Snellen test-type, vision 
 was found to be t^ in both eyes. Xow with the 
 — 3D. he could see down to the |^ line, but things 
 did not look distinct, and the lines of the astigma- 
 tic chart were not the same, that is, the lines in the 
 vertical meridian were much darker and clearer, 
 so trying the concave cylinder lenses, I found that 
 with a — 3.25D.S. in the posterior cell of the trial 
 frame, and with a — l,2oD. cyl. with its axis at 
 180°, the lines on the chart were all alike, and not 
 only this, but that the acuteness of vision was 
 brought up to tl? or better than normal. 
 With the left eye, by the same manner, I found that 
 t7 vision was obtained by a — 4D.S, behind, and a 
 — ID. cyl, axis 180° in front, and as any weaker 
 spherical would reduce the acuteness of vision,this 
 combination was ordered for constant wear with 
 perfect result: 
 
72 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 E. E. Y. = i^ w — 3.25 D. S. C — 1.25 cyl. ax. 
 180« = Yh 
 
 L. E. y. = !-« w — 4.00 D. S. C — 1.00 D. cyl. 
 ax. 180° — -f-f . 
 
 You must always remember to give the weak- 
 est concaye spherical lens consistent with good 
 vision, and as there is always some danger of over- 
 correcting the myopia, I make a practice of placing 
 A-f- spherical of .55D. before the correcting combi- 
 nation, and note the result. If they can see just as 
 well at a distance, I then reduce the concave 
 spherical a half dioptre. This I have found to be 
 good practice, but I always correct all the astig- 
 matism I can find, either hypermetropic or myopic. 
 
 Y'our patient may have some trouble in get- 
 ting used to them, especially if there be much as- 
 tigmatism, on account of the distortion of objects, 
 but this will soon pass away, if you can persuade 
 them that it is not going to ruin their eyes, as some 
 of them think. I find it a good practice to tell them 
 beforehand that the glasses will make things look 
 queer and out of shape for a while, but that it will' 
 all pass away in a week or ten days. This little 
 explanation beforehand may save you considera- 
 ble subsequent trouble, as I find few patients that 
 can wear strong minus combination without 
 some trouble of this kind, and some of them are 
 
ASTIGMATISM. 73 
 
 not always ready to accept your explanation, com- 
 ing some time after they have worn the glasses, so 
 it is always better to forestall this by explaining 
 it to them at the time. 
 
 The fifth and last variety of astigmatism is 
 that which is knoAvn as mixed astigmatism. In 
 this form of astigmatism we have one meridian, 
 generally the horizontal hypermetropic, while 
 the meridian at right angles to this, generally the 
 vertical, is myopic. This is a class of cases which 
 fortunately is not very frequently met with, and in 
 something like three thousand cases of refraction, 
 I do not remember to have met it a dozen times. 
 Now as one meridian is myopic, and the other hy- 
 permetropic, your first conclusion would be to cor- 
 rect each meridian with its proper cylinder, that 
 is, the hypermetropic meridian, with a plus cylin- 
 der at 90*^, and a myopic with a minus cylinder at 
 180°. This is what is called a cross cylinder, and 
 you can correct this class of cases very well in this 
 way, but the cross cylinder is an expensive combi- 
 nation, so this must always be a consideration, and 
 instead of it we generally use a concave spherical 
 combined with a convex cylinder, which, as you 
 will see, sives us the same result. 
 
 > t?' 
 
 I shall select a case from my note-book to il- 
 lustrate this also. F. S., age 10 years, is found by 
 
74 REERACTIVE AND OPHTHALMIC CATECHISM. 
 
 the Snellen test to have Y. otf^ in both eyes. I 
 found that with either i3liis or minus spherical, the 
 vision is very little improved, neither could I get 
 any better result by, using cylinders over them, so 
 I suspected mixed astigmatism, more, I may add, 
 as a result of an ophthalmoscopic examination 
 than from any other reason, so I tried cross cylin- 
 ders on her, using a -^.75 in the vertical meridian, 
 and a — 2 in the horizontal meridian, so after sev- 
 eral trials and changes, I find this to be the best, 
 giving her |^ vision in both eyes, and the chart 
 showed the lines distinct in all meridians. 
 
 The retinoscope proved the result, so instead 
 of ordering the cross cylinders, I prescribed the 
 following combination, which with a little study 
 you will understand:— 2 D. S.'C -r-2.75 D. Cyl. Ax. 
 90° both eyes. 
 
 You M'ill ask why I did this, so I must ex- 
 plain. Well, as she is 2D. myopic in only one meri- 
 dian, and 0.75D. hypermetropic in the other, the 
 2D. spherical will not only correct this myopic 
 meridian, but it will remove the hj'permetropic 
 meridian just so much further from emmetropia, 
 or in other words, makes the other meridian 2D. 
 more hypermetropic, which in all will amount to 
 2.75D. hypermetropia. This you will find, if you 
 take the trouble to reduce or measure it, is of the 
 
ASTIGMA TISM. 75 
 
 saDie power as the cross cylinders would be, and 
 at the same time much cheaper and just as good. 
 
 On looking up the statistics on mixed astig- 
 matism, I find some writers claim a greater fre- 
 quency for it, eyen placing it ahead of simple my- 
 opic astigmatism. Howeyer this may be, it does 
 not accord with my experience, and that is all I am 
 aiming at in this little book. 
 
 In concluding this subject of refraction 
 in general, a few obseryations may not be amiss. 
 In the aboye case just cited of mixed astigmatism, 
 you may ask why we did not secure better yision 
 than If. That I cannot tell, but it was probably 
 owing to a defectiye perception on the part of the 
 eye, or it may be owing to some condition that will 
 improye by the use of glasses, and that later on we 
 may be able to do better for her. There are many 
 cases, howeyer, of refractiye errors in which you 
 will not be able to procure yision of tf? ^^^ in 
 these cases you must be satisfied with the best re- 
 sults you can obtain. Now% in cases of anisome- 
 tropia, where there is a great difference in the cor- 
 recting glass for each eye, I do not, as a rule, cor- 
 rect fully the poor eye,for I find that only a few per- 
 sons can tolerate glasses in which there is a differ- 
 ence of seyeral dioptres. In these cases it is best 
 to keep the glasses within one or one and a half 
 
76 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 dioptres of each other, and perhaps later on when 
 the patient shall have become familiar with them, 
 Tou can increase the strength of the lens over the 
 weaker eve, in the hope of being able to develop a 
 greater acuteness of vision in that eye. 
 
 With this, then, we will conclude this chap- 
 ter, and proceed to take np a consideration of the 
 other tests used in the determination of the differ- 
 ent refractive conditions, and the first to engage 
 our attention will be the ophthalmoscope. We 
 have adopted this method of considering the dif- 
 ferent tests under a separate heading, rather than 
 to jumble them by bringing them altogether under 
 one, thus confuse the student and make the subject 
 ai^pear more difficult of comprehension than it 
 really is. We hope this arrangement will com- 
 mend itself to the reader. 
 
DE ZENG^S REFRACTOMETER. 
 
 Figure 12. 
 
 The above represents a new instrument recently introduced to 
 the profession by the Cataract Optical Company, of Buffalo, N. Y., 
 called the Refractometer. By the aid of this instrument they claim 
 that all refractive errors of the eye, and especially latent hyper- 
 metropia, can be readily detected without the use of a mydriatic. 
 
 This claim seems to be pretty well confirmed by those who have 
 used the instrument. 
 
 In presenting it to the consideration of the profession, the manu- 
 facturers have this to say : "In offering the Refractometer to the 
 profession, we do so feeling that it meets the long-felt want of an 
 instrument capable of diagnosing and measuring the refractive 
 errors of the eye, quickly, accurately, and in the majority of in- 
 stances exactly, without the assistance of a mydriatic. The optical 
 and mechanical construction of the instrument are such as to insure 
 precision in all its measurements and a permanency in the adjust- 
 ment of its parts, all of which are formulated on the most scientific 
 principals involved in modern microscopical construction. Believing 
 that in practice it will demonstrate its superiority over other refract- 
 ing instruments, we are, «S5C." 
 
 rr 
 
CHAPTER VII. 
 
 Opbthalnioscopj'. 
 
 Q. What is oplithalmoscopy? 
 
 A. It is a method of examining the interior 
 of the eve by means of an instrument called the 
 ophthalmoscope, in order to determine its condi- 
 tion as to health and refraction. 
 
 Q. When and by whom was the ophthalmo- 
 scope introduced for this purpose? 
 
 A. By Prof. Melmholtz, in the year 1S51. 
 
 O. What was its construction as originally 
 invented and introduced by Professor Helmholtz? 
 
 A. Simply that of a plain mirror, with a hole 
 in the center. 
 
 Q. Has there been an improvement in the 
 make of the ophthalmoscope since its first intro- 
 duction? 
 
 A. Yes; there have been many changes and 
 improvements made in the instrument since then, 
 and many varieties of it can be found on the mar- 
 ket at the present time. 
 
OPHTHALMOSCOPY. 
 
 79 
 
 Q. What particular instrument is most gen- 
 erally used at the j)reseut day? 
 
 A. The Loring ophthalmoscope, or some 
 modification of it. 
 
 Q. What is the mechanical construction of 
 the Loring ophthalmoscope? 
 Figure 13. 
 
 Loring's Complete Ophthalmoscope, with quadrant and 
 tilting mirror. 
 
80 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 A. It consists of a rectangular mirror slight- 
 ly concave, with a hole in the center. This mirror 
 is so attached as to be able to be tilted to the right 
 or left, as the case may require. Behind this mir- 
 ror is a rotating disk containing a series of convex 
 and concave lenses, from 1 to ID. in convex, and 
 from 1 to 8D. concave. The disk can be rotated so 
 as to bring any one of these lenses before the 
 aperture in the mirror when needed. Still behind 
 this circular disk is a quadrant carrying four 
 lenses, a — .Sand a — 16 D. and a -I -.5 and a-^lQ D. 
 This quadrant can be rotated also, so as to 
 bring any of these lenses before the aperture, 
 either alone or in combination with the lens in the 
 disk, so we can get an}' combination we desire 
 from 0.5 to 23D. convex and .5 to 24D. concave. 
 The instrument is arranged with a removable han- 
 dle, thus enabling it to be carried in a small case. 
 
 Q. How many methods are there in using 
 the ophthalmoscope? 
 
 A. There are two methods, the direct and 
 indirect. In the direct method you obtain an 
 erect, or upright image of the retina, while with 
 the indirect method you get an inverted image of 
 the retina. 
 
 Q. How do you proceed to examine the eye 
 with the direct method? 
 
OPHTHALMOSCOPY. 81 
 
 A. You first darken your room, if you have 
 not a special clarlv room for this purpose, and seat 
 your patient with his back to the source of light. 
 An ordinary Argand burner, or any other good 
 light is suitable for this work. The light must be 
 at the side of the head and back far enough so as 
 to leave the face in shadow. The light and exam- 
 iner must be on the same side as the eye under ex- 
 amination, and the examiner must use his right 
 eye in examining the i^atient's right, and left when 
 examining the left, unless there is some good rea- 
 son for not doing so. Now there are several things 
 you must observe before i^roceeding to examine 
 the fundus — that is, you must note the condition of 
 the cornea, the lens, and the vitrious; you must de- 
 termine as to whether they are perfectly transpar- 
 ent, clear and free from spots and specks. You can 
 best observe this by directing the light on the cor- 
 nea at a distance of say two feet or twenty inches, 
 and this is facilitated by the aid of a plus lens, of 
 say, 6 or 7 D. behind the aperture of the ophthal- 
 moscope. 
 
 By moving the mirror of the ophthalmoscope 
 a little from side to side so as to make the light 
 play over the cornea and pupil, you will readily 
 see any spots that may be on the cornea or lens. 
 This may be made still more distinct by the meth- 
 od called oblique illumination, w^hich consists of 
 
82 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 condensing a light on the cornea by means of a 
 convex lens of ISD. Spots that are not clearly 
 seen by means of the ophthalmoscopic mirror can 
 be readily made out by this means. If the cornea 
 and lens are clear, you examine the yitrious for 
 floating bodies by looking from this same distance, 
 and haye the patient roll the eyes in different di- 
 rections — up, down, and sidewise, holding them in 
 each position for a few seconds will cause a gravi- 
 tation of specks or floating bodies (muscae yoli- 
 tantes), and as they pass they can be plainly seen. 
 You can generally find these ''floating bodies'' in 
 high degrees of myopia, and they should always be 
 looked for, as they afford us some idea of how much 
 change of a pathological character has taken place 
 in a given case, and as you will find many patients 
 complaining of seeing them, it is best for you to 
 learn how to detect them with the ophthalmo- 
 scope. 
 
 After having examined the media thor- 
 oughly, you rotate your disk so as to bring the 
 aperture before your eye, and directing a steady 
 light on the pupil of the patient's eye, you slowly 
 approach your patient until you are within an inch 
 or so of his eye, and you will then notice the red 
 fundus with the blood vessels running in different 
 directions, and the soft velvety appearance of the 
 retina called the tapetum. You can now readily 
 
OPHTHALMOSCOPY 
 
 83 
 
 ^ee the entrance of the optic nerve and the disk 
 with the vessels passing over it in various direc- 
 tions, and toward the temporal side of the disk, 
 and on a line with its lower border, at a distance 
 equal to about twice the diameter of the nerve 
 
 Figure 14. 
 
 Showing the direct method of making an ophthalmoscopic exam, 
 ination. (After Noyes.) 
 
 head, or disk, you will notice the macula lutae, or 
 "yellow spot," characterized by its freedom from 
 blood vessels and its darker color. This is the 
 spot where, ordinarily, the focus of the images are 
 formed, and which is most concerned in the physi- 
 ological phenomenon of sight. 
 
 You will also notice the appearance of the re- 
 tina and its uniformity of color, its freedom from 
 abnormal pigmentation and silvery spots, the latter of 
 which has marked significance as resjards disease 
 
84 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 of the kidneys, either Bright's or Diabetis. Ob- 
 serve the nerve head and note if it has a cupped 
 appearance or if the blood vessels cross its bor- 
 der boldly and from the center, or seem to climb up 
 around the edge of the disk; notice the shape of 
 
 FiGDRE 15. 
 
 Showing the indirect method of making an ophthalmoscopic exam- 
 ination. (After Koyes.) 
 
 the disk also, if it be round or oval in shape, the lat- 
 ter indicating astigmatism. Look for posterior 
 staphyloma, or a crescent-shaped drawing away of 
 the retina from the choroid, frequently found in 
 myopia. Every one should learn to observe these 
 things when examining the fundus. This is, of 
 course, onh- for the purpose of determining the 
 condition of the different parts of the eye as to 
 health. The determination of its refraction we 
 
-OPHTHALMOSCOPY. 85 
 
 will describe shortly. This is the direct method 
 ^nd all images are erect. 
 
 FiGUUE 16. 
 
 ^lood vessels of the retiua, showing also the optic disk to side, with 
 the macula lutea in the center. (After Testut.) 
 
 Now, in the indirect method, we get back from 
 the patient, sav 18 inches, and a convex lens of 
 2^ inches focal distance, is held at about its focal 
 distance from the patient's eye. Some practice 
 will be necessary for you to get a distinct image of 
 the retina. You can bring out the image more dis- 
 tinctly by using a convex lens of the ophthalmo- 
 scope before the aperture, say of 4 or 5D. When 
 you do get a distinct picture, you must not forget 
 that everything is upside down, or that you see an 
 inverted image of the retina. I am sure you will 
 And this indirect method more difficult to accom- 
 
86 REFRACTIVE AND OPHTHALMIC CATECHISM 
 
 plish; still bv considerable practice you can mas- 
 ter it all rigbt. You will find it mucb easier to ex- 
 amine bigbly myopic eyes witli tbis metbod tban 
 witb tbe direct metbod, but for determining tbe re- 
 fractive conditions of tbe eye and proving your 
 otber tests by means of opbtbolmoscopy, I would 
 advise you to confine yourself to tbe direct metb- 
 od — wbicb we sball now proceed to describe in 
 detail, taking up an illustrative case of eacb va- 
 riety of refraction to belp us to more fully under- 
 stand it. 
 
 Q. How do we determine tbe presence of 
 emmetropia by examining tbe eye witb tbe opb- 
 tbalmoscope? 
 
 A. In order to correctly measure tbe refrac- 
 tive condition of a patient's eye by means of tbe 
 opbtbalmoscope, two conditions are absolutely 
 essential on tbe part of tbe examiner. First, be 
 must bave an emmetropic eye bimself ; tbat is, if be 
 is not emmetropic by nature, be must make bim- 
 self so by proper correcting lens; or if not, be must 
 take tbis into consideration wben measuring tbe 
 patient's refraction, but if be be astigmatic, tbe 
 only way is to wear correcting cylindric lens dur- 
 ing tbe examination; but if tbe examiner be sim- 
 ply myopic or bypermetropic, be can take tbis into 
 account if be does not wear correcting lens bim- 
 self, remembering tbat wbatever amount of byper- 
 
OPHTHALMOSCOPY. 87 
 
 tropia the examiner may have will neutralize just 
 so much myopia, or if he is myopic, it will neutral- 
 ize the same amount of hypermetropia in the pa- 
 tient's eye; for example, if the examiner be 2D. hy- 
 permetropic, it will neutralize, or overcome, 2D. 
 of myopia in the patient's eye, and if the examiner 
 be 2D. myopic, it will overcome 2D. of hyperme- 
 tropia in the patient. 
 
 The second condition necessary to the accur- 
 ate measurement of refraction with the ophthal- 
 moscope is a complete relaxation of the accommo- 
 dation of the examiner's eye. This you can only 
 accomiDlish by experience and practice. A sense 
 of complete relaxation of the accommodation may 
 be experienced by looking off into infinity without 
 fixing your eye upon any object particularly. Ev- 
 erything under this condition appears hazy. Now, 
 if you hold your finger before your eye, say at 10 
 inches, instead of seeing one, you will see two fin- 
 gers, showing that not only the accommodation is 
 relaxed, but that there is no effort at convergence, 
 thus allowing each eye to see an image of its own. 
 By a little practice you will learn to appreciate 
 this sensation of relaxation, and this must be the 
 condition of your own eye. when using the ophthal- 
 moscope. 
 
 In using the ophthalmoscope to measure the 
 refraction of an eye, it is necessary for us to have a 
 
88 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 land-mark, as ir M'ere, to enable ns to accurately 
 determine the refraction in the two principal meri- 
 dians, that is, in the meridians of greatest and 
 least curvature, usually to be found in the 
 vertical and horizontal. For this purpose the 
 minute blood vessels that cross at right 
 angles in the horizontal and vertical meri- 
 dians, are taken as a land-mark. We must be able 
 to see the small vessels clearly without any effort 
 on the part of our own accommodation before we 
 can arrive at any conclusion as to the refraction of 
 the eye under examination. When the greatest 
 and least curvature are at any other meridian than 
 the horizontal and vertical, then the lines in these 
 meridians must be selected for land-marks. 
 
 In a previous chapter you have seen that light 
 reflected from the retina of an emmetropic eye, 
 emerges in parallel lines, so with your ophthalmo- 
 scope before an emmetropic eye, you are able to see 
 the details of the fundus withotit any trouble, but 
 if you should place a convex lens before the oph- 
 thalmoscope, you would produce a convergence of 
 the emergent rays, and your emmetropic eye could 
 not focus them on your retina; hence the rule is 
 that when you see the fundus clearly through the 
 aperture of the ophthalmoscope, btit which blurs 
 or becomes indistinct when a convex lens of ID. is 
 placed before the aperture of the ophthalmoscope, 
 
OPHTHALMOSCOPY. 89 
 
 that the eye under examination is emmetropic, and 
 you will not need a correcting glass. Still as you 
 use the ophthalmoscope more to prove the accur- 
 acy of the test by the trial lens, you have perhaps 
 already found that out. 
 
 Q. How is one to recognize the difference be- 
 tween emmetropia and hypermetropia with the 
 ophthalmoscope ? 
 
 A. We have previously learned that the hy- 
 permetropic eye emits divergent rays. In that 
 case you can readily understand that with your 
 emmetropic eye and your accommodation that you 
 will still be able to see the fundus clearly, as in 
 emmetropia, through the aperture of the ophthal- 
 moscope. But we have just seen that in emme- 
 tropia the placing of a convex lens behind the 
 aperture of the ophthalmoscope would blur the 
 fundus. Now, in hypermetropia this does not oc- 
 cur, but you can still see the small vessels of the 
 fundus after placing a plus lens before the aper- 
 ture, but you keep on increasing the strength of 
 the lens behind the aperture, and pretty soon you 
 will reach one strong enough to blur. Well, this is 
 the measure of the amount of hypermetropia, 
 so we can formulate a rule for the determination 
 and for the approximate estimation of the 
 amount of hypermetropia as follows: In looking 
 through the aperture of the ophthalmoscope into 
 
90 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 a hypermetropic eye, you can see the details of the 
 fundus clearly, and that the Strongest convex lens 
 placed behind the aperture of the ophthalmoscope, 
 that will allow a distinct view of the small vessels 
 of the fundus, will represent the amount of hyper- 
 metropia. For example, a young lady,26 years old, 
 complaining of her eyes, sought aid for her vision. 
 With the Snellen test she accepts a —1.50 D. S., 
 shoAving this to be the amount of her manifest hy- 
 permetropia. Ophthalmoscopic examination 
 through the aperture reveals a distinct fundus,and 
 by rotating a convex lens behind the aperture, we 
 find they remain distinct with a convex lens of 4D. 
 behind the aperture,but any stronger lens causes a 
 blurring, hence this 4D represents her total hyper- 
 metropia. So you see this is a ready way of differ- 
 entiating between emmetropia and hypermetrop- 
 ia; in the former condition, convex lenses cause a 
 blurring, while in the latter case they do not, until 
 -the lens is reached strong enough to measure the 
 total hypermetropia. 
 
 Q. What rule have we then by which we can 
 distinguish between simple hypermetropic astig- 
 matism and simple hypermetropia? 
 
 A. A very simple rule, indeed, if you will 
 only remember that in simple hypermetropic as- 
 tigmatism one of the meridians of the eye is emme- 
 
OPHTHALMOSCOP Y. 91 
 
 tropic and the other is hypermetropic. This 
 emmetropic mericliafl sends out parallel rays, 
 while the hypermetropic meridian emits divergent 
 rays. In the emmetropic meridian joii can 
 see the fundus clearly through the aperture, but a 
 plus lens will blur this meridian when placed be- 
 hind the aj^erture. In the hypermetropic meri- 
 dian you can also see the fundus clearh^, but 
 a plus lens placed behind the aperture of the oph- 
 thalmoscope will not blur, and the strongest con- 
 vex lens through which you can still see the small 
 vessels in the hypermetropic meridian will repre- 
 sent the amount of astigmatism. 
 
 For example, you have a case in which the hor- 
 izontal meridian is clearly seen through the aper- 
 ture, but a convex lens of ID. will cause a blur- 
 ring. Now in the vertical meridian you can also 
 see distinctly through the aperture, and by plac- 
 ing a convex lens of 2D. behind the aperture, yoiL 
 are still able to see distinctly in the vertical, but'*- 
 e^ery thing is blurred and indistinct in the hori- 
 zontal meridian. This lens then, that is 2D., will 
 represent the amount of astigmatism, and the axis 
 of the corresponding cylinder lens must be placed 
 parallel to the meridian seen distinctly with the 
 strongest lens, and, as in this case, we find this to 
 be in the vertical meridian the axis of the correct- 
 ing cylinder lens must be placed in the vertical 
 
92 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 meridian, thus i)roYing that our case is one of sim- 
 ple hypermetropic astigmatism, "according to the 
 rule," or at 90°. 
 
 If this should happen to be a case of com- 
 pound hypermetropic astigmatism, all that is 
 necessary for you to remember is that the emer- 
 gent rays of this eye are divergent in both meridi- 
 ans, but more divergent in one meridian than in 
 the other. It will then require a convex glass of 
 different strength to measure the two separate 
 meridians, and the first glass will represent the 
 amount of the hypermetropia, while the second 
 will not only measure the hypermetropia, but will 
 measure it plus the astigmatism, and the differ- 
 ence in the two convex lenses will represent the 
 amount of astigmatism. For example, if you can 
 see the horizontal meridian distinctly with a plus 
 2D. and the vertical meridian is still distinct with 
 a plus 4D., but the horizontal is blurred and indis- 
 tinct, then the difference between the two lens, 
 that is 2D., will represent the amount of astigma- 
 tism, and as the axis of the correcting cylinder lens 
 must be placed parallel to the meridian seen with 
 the strongest glass, we have for a correcting glass 
 the following formula: 
 
 -I- 2 D. S. C w- -I- 2 D. cyl. Ax. 90°, 
 thus clearly proving to us a case of compound hy- 
 permetroj^ic astigmatism. 
 
OPHTHALMOSCOPY. 93 
 
 Q. How do you determine myopic conditions 
 by the use of the ophthalmoscope? 
 
 A. In speaking of myopia in a former chap- 
 ter, we have seen that as the principal focus of the 
 myopic eye was in front of the retina, reflected 
 rays from the retina, coming from a ijoint further 
 than its principal focus causes a convergence of 
 the emergent rays, and as converging rays 
 cannot enter your emmetropic eye, they 
 must be first rendered parallel, and this is 
 done by the use of the concave lens of the ophthal- 
 moscope. The rule, then, to determine simple my- 
 opia is that the w^eakest concave lens that will ren- 
 der the fundus clear and distinct will measure the 
 amount of myopia. 
 
 For example, supposing you have a case in 
 which everything about the fundus of the eye is 
 blurred when looking through the aperture, and 
 you find that the use of convex lens makes it 
 worse. Now you try a concave lens and you find 
 that things begin to look clearer; you finally con- 
 tinue increasing the strength of the lens behind 
 the aperture until the very weakest lens is 
 reached, that enables you to see the details of the 
 fundus distinctly, and you find this to be a concave 
 lens of 4D. ; then you have a case of simple myopia 
 of 4E). 
 
94 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 If you have a case of simple myopic astig- 
 matism in one meridian the eye is emmetropic, 
 while in in the other it is myopic. In the emme- 
 tropic meridian you can see the fundus distinctly 
 through the aperture, while it requires a concave 
 lens of ID. to see in the myopic meridian distinct- 
 ly, this then will represent the amount of astig- 
 matism, and the axis of the correcting cylinder 
 lens must be placed parallel to the myopic meridi- 
 an; for example, supposing you can see the vertical 
 meridian clearly through the aperture, while it re- 
 quires a concave lens of ID. to see the horizontal 
 meridian distinctly, this then being the very weak- 
 est glass that renders them distinct will represent 
 the amount of astigmatism, and the axis of the 
 correcting cylinder lens must be placed parallel to 
 this meridian, or at 180°, thus showing us a case of 
 simple myopic astigmatism "according to the 
 rule," or at l<SOo. 
 
 In compound myopic astigmatism, the 
 emergent rays in both principal meridians are con- 
 verging, but more converging in one than in the 
 other, so if it requires a minus spherical of 2D. to 
 see the vessels in the vertical meridians and one of 
 5D. to see them distinctly in the horizontal, the 
 five dioptres measure the amount of general my- 
 opia plus the astigmatism, and the difference in 
 the two lenses, namely, 3D.,will give us the amount 
 
OPHTHALMOSCOPY. 95 
 
 of astigmatism; and as in simple myopic astigma- 
 tism, the axis of the correcting cylinder lens must 
 be parallel to the meridian of greatest ametropia, 
 or in this case in the horizontal, or at 180°, we 
 have for a correcting glass for this case of com- 
 pound myopic astigmatism, the following formula: 
 
 —2 D. S. C —3 D. Cyl. Ax. 180°. 
 
 Remember ahvays to use the weakest concave 
 lens that renders the fundus distinct in myopic 
 conditions. 
 
 Yoii will find the diagnosis of mixed astigma- 
 tism with the ojjhthalmoscope perhaps as easy, if 
 not more so, than any other compound conditions, 
 as you have simply to deal with hypermetropia in 
 one of the principal meridians, and with myopia 
 in the meridian at right angles to this one, and you 
 proceed to measure it by using the strongest con- 
 vex in the hypermetropic meridian, and the weak- 
 est concave glass in the myopic, and the correcting 
 glass will be determined by the result you obtain 
 corroborated by the several tests that we have ex- 
 plained or enumerated. 
 
 With this, then, we will conclude this chapter 
 on ophthalmoscopy. Trusting that by the use of 
 simple language we may facilitate the study of 
 this method of diagnosing the pathological and re- 
 fractive conditions of the human eye. 
 
CHAPTER VIII. 
 
 Oplithalinoiuetry. 
 
 Q. What is ophthalmometry? 
 
 A. It is a method of measuring the different 
 diameters of the human eye during life. 
 
 Q. What is its special application in relation 
 to refraction? 
 
 A. Its special application is the determina- 
 tion of corneal astigmatism, by means of measur- 
 ing the radii of the principal meridians of the 
 
 cornea. 
 
 ■ji- 
 
 Q. To whom is tL credit due for first utiliz- 
 ing this method in refractive work? 
 
 A. To Professor Helmholtz, in the year 1854, 
 three years after his introduction of the ophthal- 
 moscope. 
 
 Q. What ophthalmometer is mostly in use at 
 the present time? 
 
 A. The Java! and Schiotz instrument. 
 
 Q. What is the mechanical construction of 
 the Javal ophthalmometer? 
 
 96 
 
OPHTHALMOMETR Y 
 Figure 17. 
 
 97 
 
 JaVAL & SCHIOTZ' OpHTxIALMOMETER . 
 
 This instrument has the perpend'^ular adjustment, by means of 
 a rack and pinion movement attache to the upright cohimn. The 
 mo vablo mire has rack and pinion adjustment and the lens is pro- 
 tested by an extra long tube, which is provided with a brass cap to 
 cover it when not in use. This instrument has a finely enamelled 
 dial, which does not change color with use but retains its whiteness. 
 It is also provided with a small indicating dial at the back, so that 
 the position of the mires can easily be observed by the operator. 
 The improved metal head-piece is provided with Skeels swinging 
 eye shield, and an adjustable chin rest which carries a glass arti- 
 ficiftl cornea. The instrument has the proper fittings for electric 
 light illumination, except the lamps, which are furnished by the 
 company from whom the current is obtained. 
 
 A. Its principal jDarts consist of a reversing 
 telescope, in the center of which, and about mid- 
 
98 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 way between the two convex lens, is a double re- 
 fracting prism, called the Wollaston prism, which 
 "consists of two quartz prisms, so cut that when in 
 position, the apex of each is at the base of the oth- 
 er and the optical angle of each is at right angles 
 to that of the other and to the axis of vision." A 
 large enamelled disk with the degrees numbered 
 from to 180°, in inverted characters, on its per- 
 iphery, while the rest of the disk from the numbers 
 to the center, is a series of concentric circles in 
 white, while the background is black enamel. These 
 circles correspond to a difference of 5° from 5° to 
 45°. The disk is penetrated by the telescope at its 
 center. Attached to the telescope is an arc which 
 rotates when the telescope is turned around the 
 surface of the large disk. On this arc are two 
 sights, or mires, one rectangular in shape, the oth- 
 er cut into a series of steps, each step measuring six 
 millimetres in width. Formerly one of these 
 mires was fastened to the arc, while the other 
 was readily movable along the arc, but by an ar- 
 rangement suggested by Professor Francis Yalk 
 of New York city, both mires are made to move 
 toward or from each other by a milled screw. This 
 he calls the double movable mires. Attached to 
 each mire is a short white pointer, while at the cen- 
 ter of the arc, and at right angles to the short 
 pointers, is a long, white pointer. The mires are 
 
OPHTHALMOMETRY. 99 
 
 white enamelled, mounted on a background of 
 black velvet. These three principal parts, that is, 
 the telescope, the disk, and the arc, rest by means 
 of a tripod on a i)latform. 
 
 By means of an adjustable screw, the tele- 
 scope can be adjusted in the vertical position, 
 while the horizontal adjuvstment is secured by mov- 
 ing it, as a whole, from side to side on the plat- 
 form. The rest of the instrument consists of an 
 upright chin rest, with a drop shade for the pur- 
 pose of covering the eye that is' not being exam- 
 ined. When in use, the instrument is placed on a 
 stand or table of suitable height, so that it can be 
 used without straining or effort on the part of the 
 examiner. 
 
 It may be here remarked that the letters and 
 figures painted upon the disk upside down, appear 
 right side up after being reflected from the cornea 
 and observed through the reversing telescope. 
 
 Q. How do you use the ophthalmometer, and 
 by what method do you determine the presence or 
 absence of astigmatism? 
 
 A. You begin by seating your patient so as 
 to have his chin rest comfortably on the chin rest 
 of the instrument, and the head in such a position 
 as to bring the two eyes on a level, and the eye to 
 be examined before the telescope, while the other 
 
100 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 eye is covered with the shade provided for that 
 purpose. You then rotate the ocular of the tele- 
 scope until you obtain a clear and distinct view of 
 the two spider lines which cross at right angles, 
 and which are for the purpose of focusing the ocu- 
 lar. When the ocular is focused and the telescope 
 properly adjusted, you can, by looking through the 
 telescope, get a clear and distinct picture of the 
 disk and mires as reflected from the cornea. You 
 will now observe the figures to be right side up, by 
 the reversing action of the telescope. You will al- 
 so observe that instead of one picture of the disk 
 and mires, you will see two, one overlaj)ping the 
 other, and you will also notice two more indistinct 
 images at the periphery of the disk. 
 
 To these periiiheral images no attention is to 
 be paid, but the two central ones must engage our 
 full attention, and we must be able to see them 
 clearly and distinctly without any effort on our 
 part, or any straining of our accommodation. 
 
 Each mire is provided with what is called a 
 guide-line, which passes straight through its cen- 
 ter. We turn the arc until these two lines of the 
 mire will come together, as it were, to form one 
 continuous line. When these two lines become 
 continuous, we bring the edges of the mires to- 
 gether, as it were, to form one continuous line. 
 When these two lines become continuous, we 
 
OPHTHALMOMETRY. 101 
 
 bring tlie edges of the mires together by means of 
 the thumb-screw, with the double movable mires, 
 or hj sliding the one along the arc, as the case 
 may be. They must be brought close enough, un- 
 til by the reflected image on the cornea, they ap- 
 pear to touch each other. Now, when the lines 
 are continuous and the edge of the mires appear to 
 touch each other, as just explained, the arc is said 
 to be in the primary position. You must previous- 
 ly have drawn the telescope as far from the pa- 
 tient's eye as is consistent with a clear and dis- 
 tinct view of the central images. By doing this, 
 the i^eripheral images are drawn out of focus, and 
 will appear more blurred. Having thus secured 
 the continuation of the lines and an approxima- 
 tion of the edges of the mires, we note the angle as 
 marked by the long white pointer, previously 
 mentioned as being attached to the center of the 
 arc. This will mark for us the angle of the first, 
 or primary, position. 
 
 AYe now turn the telescope with its arc through 
 90°, -or until the short pointer on the mire occupies 
 the same position as the long pointer on the arc 
 did, before rotating it. This rotating should take 
 place from left to right. If after rotating the arc 
 through 90°, we find the lines on the mires are not 
 exactly continuous, we make them so by rotating 
 the arc a few degrees either way. Now, if the eye 
 
102 REFRACTIVE AND OPHTHALMIC CATECHISM 
 
 be astigmatic, the mires will be found to have over- 
 lapped each other, more or less, according to the 
 amount of astigmatism. This overlapping of the 
 mires is shown by milky whiteness of the overlap- 
 ping parts, and the amount of astigmatism is cal- 
 culated by the amount of overlapping, the overlap- 
 ping of each step on the mire representing one di- 
 optre of astigmatism, and each fraction of a step 
 the fraction of a dioptre. 
 
 The arc, after being rotated through 90° as 
 just stated, is now said to be in the second posi- 
 tion, and when this overlapping takes place, either 
 in or near the vertical meridian, the astigmatism 
 is said to be "according to the rule," which shows 
 that the meridian of greatest curvature is the ver- 
 tical or near the vertical, as the case may be; and 
 the exact point is noted by means of the figures on 
 the edge of the disk, as pointed out to us either by 
 the long pointer now in the primary position, or 
 the short pointer on the mires in the second posi- 
 tion, and the two meridians as indicated by the 
 long and short pointers, will correspond ex.actly 
 with the meridians of greatest and least curvature. 
 
 In some cases, as you turn the arc 
 through 90°, that is, from the primary to the sec- 
 ondary position, you will find that the mires, in- 
 stead of overlapping, are separated as the lines 
 passing through them become continuous. In this 
 
OPHTHALMOMETRY. 103 
 
 case, the astigmatism is said to be "contrary to the 
 rule," and the corneal meridian of greatest curva- 
 ture is horizontal instead of vertical. 
 
 To measure the amount of the astigmatism 
 when "contrary to the rule," the mires had better 
 be brought together while the arc is in the second 
 position, and as it is rotated back to the primary 
 position, through 90°, the amount of overlapping 
 which takes place can be noted, as in the former 
 case, and the degree of astigmatism calculated in 
 the same manner. After completing the-€xamina- 
 tion of one eye, you proceed to examine the other 
 in the same way, making whatever change is ne- 
 cessary in the position of the instrument, so as to 
 get a clear and accurate rellection from the cornea. 
 
 Q. But supposing that the eye under exami- 
 nation be emmetropic, and not the seat of corneal 
 astigmatism, how are we to know it when using 
 the ophthalmometer? 
 
 A. In that case, after placing the edges of 
 the mires together and rotating the arc through 
 90°, or a quarter of a circle, you will observe that 
 there will be no overlapping or separating of the 
 mires as there is in astigmatism, showing that the 
 curvature of the cornea is the same in all meridi- 
 ans, hence not the seat of astigmatism. 
 
 Q. But supposing that the eye is the seat of 
 
104 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 astigmatism, how are Ave to know whether it is of 
 the hypermetropic or myopic variety? 
 
 A. This we cannot tell by means of the oph- 
 thalmometer, as this instrument only points out to 
 us the meridians of greatest and least curvature, 
 and the particular kind of astigmatism resulting 
 from an asymmetrical condition of the cornea, 
 must be determined by some of the auxiliary tests. 
 
 Q. Does the ophthalmometer always give the 
 correct amount of total corneal astigmatism? 
 
 A. It does not, as we may have a certain 
 amount of lenticular astigmatism entering into 
 the total amount of astigmatism, as determined 
 with the ophthalmometer. 
 
 Q. Is there any rule to follow in regard to 
 taking this lenticular astigmatism into considera- 
 tion when prescribing correcting cylinder lens? 
 
 A. There is a rule formulated by Javal, 
 which consists of subtracting .05D. from the read- 
 ing of the ophthalmometer when the astigmatism 
 is "with the rule," and adding .05D. when the as- 
 tigmatism is "contrary to the rule." This rule will 
 be found sufSciently accurate in a large number of 
 cases. 
 
 The utility and applicability of the ophthal- 
 mometer, as you see, is limited to the determina- 
 tion of corneal astigmatism. While we cannot ap- 
 
OPHTHALMOMETRY. 105 
 
 ply it to all the refractive conditions of the eye, it 
 will be found a very serviceable instrument in 
 those cases of astigmatism where any uncertainty 
 exists as to the amount of and also as to the axis 
 of the correcting cylinder lens. Its use will also 
 enable us to forego the use of a mydriatic in many 
 cases, thus saving the patient the inconvenience of 
 undergoing this very unpleasant experience. It 
 will also be found a valuable time-saving test, as 
 many cases otherwise requiring a great deal of 
 time and patience can be readily determined by 
 -the use of the ophthalmometer. 
 
CHAPTER IX. 
 
 Skiascopy, Retinoscopy, or Shadow Test. 
 
 Q. What is skiascopy, Retinoscopy or the 
 Shadow test, as it is called? 
 
 A. It is a method of determining the refrac- 
 tive condition of the eye by means of reflecting 
 light from a given point of illumination, on to the 
 cornea of the eye, by means of a small mirror 
 called the retinoscope, at a distance of forty inches 
 usually, from the patient and watching the 
 movement of the retinal reflex, as it is made to 
 pass over the pupillary space, by causing the reti- 
 noscopic mirror to be slightly moved from side to 
 side, or up and down. 
 
 Q. What kind of a mirror is best to use in 
 this work of retinoscopy? 
 
 A. That is largely a question of individual 
 choice, some preferring a small plain mirror with 
 a central aperture, or one from which the silver 
 has been removed from its central point, while 
 others prefer a slightly concave mirror with a focal 
 
 106 
 
SKIASCOPY 
 
 107 
 
 point of S inches or 10 inches. For my own use, I 
 prefer the plain mirror. 
 
 Q. What are your reasons for preferring the 
 plain retinoscopic mirror? 
 
 Figure 18. 
 
 Plain Mirror Retinoscope. 
 
 A. Because I believe it is much easier to use, 
 and YOU hare only to note the direction of the 
 
108 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 movemeut of the mirror when calculating the re- 
 flction from the retina, while with the concave 
 mirror, all movements of the mirror are reversed 
 before reaching the eye, a fact you must always 
 remember. However, there are some advantages 
 connected with the use of the concave mirror, 
 which will be pointed out later on. 
 
 Q. What position should your patient occu- 
 py in relation to the point of illumination? 
 
 A. With the plain mirror, the light should 
 come through a small hole made in a cover for an 
 ordinary chimney of an Argand burner. The hole 
 in the chimney cover should be opposite the bright- 
 est part of the flame. The hole need not be over 
 three-quarters of an inch in diameter, as it is eas- 
 ier to watch the reflex from a pencil of light than 
 from a diffused one. If you wish to operate at a dis- 
 tance of one metre from your patient, which I think 
 is the best plan, you must have the light close to 
 the mirror, as the distance from the light to the 
 mirror must count in your metre's distance from 
 your patient, the same as if the light came from a 
 point behind the mirror, corresponding in distance 
 from the light to the mirror; for example, if your 
 source of illumination is 12 inches from your mir- 
 ror, you must consider it as coming a distance of 12 
 inches behind the mirror, and this must be reck- 
 oned in your metre's distance from your patient. 
 
SKIASCOPY. 109 
 
 Q. In what direction should your patient 
 look when using the retinoscope? 
 
 A. They should look a little to the right 
 when examining the right eye, and a little to the 
 left when the left is being examined. This is in or- 
 der that the rays entering the eye may pass along 
 the visual axis of the eye, and strike the retina at 
 the maculae lutea, or "yellow spot." 
 
 Q, How are we to determine by the move- 
 ment of the retinal reflex that the eye is ametropic? 
 
 A. By observing the direction in which the 
 reflex moves, when a pencil of light is projected on 
 to the cornea, and by slight movement of the mir- 
 ror made to pass to and fro over the puiDillary 
 sijace. When at a distance of 40 inches with your 
 plain mirror, you will observe that when you are 
 examining an eye that is emmetropic, there will be 
 little or no movement of the reflex across the pu- 
 pillary space when the mirror is slightly rotated. 
 This is because the eye being emmetropic, the rays 
 of reflected light strike the dioptric media of the 
 eye practically parallel, and coming to a focus at a 
 point on the retina, corresi)onding to the principal 
 focal distance of the eye, there is very little, or no 
 movement over the pupil as the mirror is slightly 
 moved, owing to there being little, or no change in 
 the point of illumination on the retina. 
 
110 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 Now in livpermetropia, the reflected rays are 
 brought to an indistinct focus on the retina, in 
 front of the principal focal i)oint of the eve, hence 
 the retinal illumination is greater but less bril- 
 liant, and as the retinoscope is moved on its axis, 
 there will be a greater excursion of the retinal il- 
 lumination, and as it is reflected back by the reti- 
 na through the dioptric media, there will be no- 
 ticed a greater activity of the rays as they move 
 across the pupil, and the movement of the reflex 
 will, 3^ou will observe, be in the same direction as 
 the movement of the light on the face, and also in 
 the same direction as the movement of the mirror, 
 when the plain mirror is used, and contrary to the 
 movement of the light on the face and the direction 
 of the movement of the mirror, when the concave 
 mirror is used. 
 
 In myopia, there will be a movement of the 
 reflex observed also, as in hypermetropia, but with 
 the plain mirror, the movement will be against 
 the movement of the light on the face, while with 
 the concave mirror it will be in the same direction 
 as the light on the face, and likewise in the same 
 direction as the movements of the mirror. For this 
 reason, we think it best not to complicate the mat- 
 ter more than necessary in our descrijDtion, and 
 hence we will imply the use of the plain mirror in 
 this method of determining the different refrac- 
 
SKIASCOPY. Ill 
 
 tive conditions by means of retinoscopy. After 
 finding out the direction of the movements of the 
 retinal reflex in the different forms of ametropia, 
 we shall now proceed to explain more specially the 
 means of measuring the degree of ametropia by 
 this method. 
 
 In hypermetropia, we have previously seen, 
 the rays of light being reflected from the retina of 
 the eye through the dioptric media, diverge. 
 These diverging emergent rays must be rendered 
 parallel before entering the examiner's eye, 
 through the aperture of the retinoscope. This par- 
 allelism of the rays is brought about by the con- 
 verging power of a convex lens placed close to the 
 eye of the patient, in a suitable pair of trial or 
 spectacle frames, and the convex lens that stops 
 the reflex, will measure the amount of total hyper- 
 metropia ; but if you are not fully satisfied, you 
 continue to increase the strength of the convex 
 lens before the patient's eye, until you have a dis- 
 tinct reversal of the movements of the retinal re- 
 flex, as seen at your distance from the patient, 
 namely, 40 inches, and this glass, minus ID., will 
 give you the total amount of hypermetropia. For 
 example, supposing that in looking as to the direc- 
 tion of the retinal reflex, you flnd it to be with the 
 movement of the mirror, and in order to stop the 
 motion entirely, it will require a convex lens 
 
113 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 of 3D., but with any stronger lens, it produces a re- 
 versal of the motion of the retinal reflex. Well, 
 for iDarallel rays, this reversal point at 40 inches 
 distance is produced by a convex lens of ID., so in 
 order to determine the exact amount of hyperme- 
 tropia, this ID. must be subtracted from the 
 strength of the lens that is found to produce a re- 
 versal, which, in this case, is a -!-3D., and as ID. 
 from 3D. leaves a difference of 2D., this represents 
 the amount of total hypermetropia. Now, suppos- 
 ing that the above case, instead of being a case of 
 simple hypermetropia, is a case of compound hy- 
 permetropic astigmatism. Well, in this condition, 
 the emergent rays are divergent in both meridians, 
 but more divergent in one meridian than the oth- 
 er; now, in the meridian of greatest divergence, it 
 will take a stronger convex lens to stop the mo- 
 tion, or to bring about the reversal point, than it 
 will in the other meridian, and the difference in 
 the two lenses will represent the amount of astig- 
 matism. In the case just cited, we will say that a 
 reversal of the motion is produced by a convex 
 lens of 3D. in one meridian, while it requires a con- 
 vex lens of •ID. to produce a reversal in the other 
 meridian at right angles; the difference in these 
 tAvo lenses, namely, ID., will represent the amount 
 of astigmatism. This we will say something more 
 about in treating of the several specific conditions 
 of refraction. 
 
SKIASCOPY. 113 
 
 Q. In looking at the moyement of the reflex 
 at saj 40 inches, you find the action of the reflex 
 very rapid, and the illumination of the pupillary 
 space very great. What is indicated thereby? 
 
 A. A low degree of either hypermetropia or 
 myopia, according to the direction of the light in 
 the pupillary space; that is, if it be with the move- 
 ment of the plain mirror, it is hypermetropia; if 
 against the movement of the plain mirror, myopia. 
 
 Q. How do you account for this great illum- 
 ination of the pupil and the rapidity of the reflex 
 action? 
 
 A. The eye being but slightly ametropic, the 
 rays are brought to a focus on a small portion of 
 the retina, near the principal focal point of the eye. 
 This point reflecting back all the light with great 
 magnification, accounts for the bright illumina- 
 tion, while the magnification of the slight motion 
 of the mirror, accounts for the rapidity of the mo- 
 tion seen in the pupillary space. 
 
 Q. When observing the action of the reflex 
 from this same distance, that is 40 inches, and the 
 mo\ ements seem slow, and the illumination of the 
 pupillary space seems dull, what is indicated? 
 
 A. A high degree of ametropia, either hyper- 
 metropia or myopia, according to the movement 
 either with or against the light on the face. 
 
114 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 Q. How do you accouiit for this i^eculiarity? 
 
 A. In high degrees of ametropia, the rays do 
 not focus on the retina at the principal focal point 
 of the eye, hence circles of diffusion are formed 
 with the loss of a large part of the light thrown in- 
 to the eye by the mirror. The reflected light being 
 diminished by the diffusion taking iDlace, less 
 light is reflected back to the pupillary space, thus 
 producing a dull illumination. This dull illumina- 
 tion in turn renders it more difficult to observe the 
 motion of the reflex, hence its apparent slow ac- 
 tion. 
 
 Q. In measuring a hypermetropic eye with 
 the retinoscope and convex lens, what do we aim 
 to do? 
 
 A. To produce a temporary myopia of the 
 patient's eye. 
 
 Q. What is our purpose in doing this? 
 
 A. So as to be able to determine the exact 
 "point of reversal." 
 
 Q. What do you mean by the "point of rever- 
 sal?" 
 
 A. That point at which the motion of the re- 
 tinal reflex is changed from one direction to the 
 opposite. 
 
 Q. Where is the "point of reversal" general- 
 ly fixed in retinoscopic examinations of the eye? 
 
SKIASCOPY. 115 
 
 A. At about 4.0 inches from the examined 
 e}'e, or at about the point at which the examiner 
 sits. 
 
 Q. Where is the "point of reversal" of a myo- 
 pic eye located? 
 
 A. At its punctum remotum, whatever dis- 
 tance this may be from the eye. 
 
 Q. How can we determine between an em- 
 metropic eye and a low degree of hypermetropia 
 by this method? 
 
 A. We have seen that in the emmetropic eye 
 there is no movement of the retinal reflex in the 
 pupil. Now", if we pjace a convex lens of one di- 
 optre before this e^'e, we produce a temj)orary con- 
 dition of myopia of one degree, and the motion of 
 the reflex Avill be seen to move against the move- 
 ment of the light on the face, hence we conclude 
 the eye is emmetropic; but, if we have a hyperme- 
 tropia of low degree, say .05 L)., the movement of 
 the light will be seen to be with the light on the 
 face, or with the movement of the mirror; but if 
 you place a convex lens of 1 D. before the eye, you 
 produce a myopia of .05 D., and by moving further 
 aAvay, the point of reversal will be found to be at 
 about 80 inches from your patient's eye; in other 
 words, shoAving a myopia of half a dioptre, but as 
 you must subtract 1. D. of myopia, caused by the 
 
116 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 use of 3'oiir convex lens of 1 D., from this condi- 
 tion, you will see you have as a result a liyperme- 
 tropia of .05 D. 
 
 Tliis you can iH'ove by putting a convex lens 
 of .05 D. before your patient's eye, wlaen you will 
 observe all the movements of the reflex to cease, 
 this being brought about by this lens bringing the 
 slightly divergent rays of the eye into a condition 
 of parallelism. 
 
 The amount of the hypermetropia is deter- 
 mined, as we have seen, by the convex lens neces- 
 sary to bring about a reversal of the movements of 
 the reflex at a point 10 inches, or 1 D. from our pa- 
 tient. This lens minus 1 I), will give us the total 
 hypermetroi^ia. 
 
 In a case of simple hypermetropic astigma- 
 tism, one meridian emits parallel rays, while the 
 other emits divergent rays. Now in the emmetrop- 
 ic meridian there will be no movement of the re- 
 flex, while in the hypermetropic meridian the 
 movement will be in the direction with the light 
 on the face, and the convex lens necessary to stop 
 this movement will represent the amount of astig- 
 matism. For example, supposing that in the ver- 
 tical meridian there is no movement of the reflex 
 in either direction, but that it requires a convex 
 spherical lens of 2D. to stop the retinal reflex in 
 
SKIASCOPY. 117 
 
 the horizontal meridian, then this lens would re- 
 present the amount of hypermetropic astigmatism, 
 tmd the correcting cylinder glass would be a con- 
 vex cylinder of 2 D. with its axis vertical or par- 
 allel ^'ith the emmetropic meridian. 
 
 In a case of compound hypermetropic astig- 
 matism, the mov€*nient of the reflex will be with 
 the mirror in both meridians, but it will require a 
 stronger convex lens to stop them in one meridian 
 than the other, and the difference in the two lens 
 will measure the amount of astigmatism. For ex- 
 ample, if we have a case in which the movements 
 are stopped in the vertical meridian with a convex 
 glass of 3 D., but in the horizontal meridian it re- 
 quires a convex lens of 4.50 D., then the difference 
 in the two lenses, namely, 1.50 D., will represent 
 the amount of astigmatism, and the axis of the 
 correcting cylinder must be placed parallel with 
 the meridian of least ametropia, or in the vertical, 
 and we would have as a correcting combination 
 the following formula : 
 
 -1-3 D. S. C -1-1:50 D. Cyl. A.x 90«. 
 
 Xow in testing myopic conditions with the re- 
 thioscope, all we have to do is to substitute the 
 concave lens for the convex before the patient's 
 ^ye, and also the remember that with the plain 
 mirror all the movements of the retinal reflex are 
 
118 REFRACTIVE AND OPHTHALMIC CATECHISM 
 
 against the movement of the light on the face, as 
 well as against the movements of the mirror. 
 
 ^^e can in a general way estimate the strength 
 of the redncing lens by finding ont the distance of 
 the punctnm remotum. For example, if this be 20 
 inches from the eye, then we will need a lens of 
 2 D. to lender the converging emerging rays of the 
 myopic eye parallel, and if we find the punctnm 
 remotnin at 10 inches from the patient's eye, then 
 it will require a lens of 10 inches focal, or 4 D con- 
 cave, to render the rays parallel. But you must re- 
 member that ^\e are examining the eye at distance 
 of 40 inches, or 1 D., from the patient, and when 
 we find a glass that will sufficiently diverge the 
 emerging converging rays to bring them to a point 
 at 10 inches, or to cause all the reflex movement to 
 stop at this point, you must remember that you are 
 still ID. from parallelism, so you must add on ID. 
 to the concave glass before the eye, in order to esti- 
 mate accurately the total amount of myoiDia. 
 
 For example, supposing that the punctum re- 
 motum of the myopic eye is at 10 inches, it will re- 
 quire a concave lens of 1 D. to render the rays par- 
 all(^], and to stop all retinal reflex. Xow if you 
 were examining the eye from infinity, or a distance 
 of twenty feet, this would render the rays of light 
 parallel, and at this point of twenty feet all reflex 
 would stop; but as you are situated only 10 inches 
 
SKIASCOPY. 119 
 
 from your patient, all it will require to bring the 
 reflex to a standstill at this point, will be a lens of 
 3D., but in estimating the total amount of myopia, 
 YOU must add on to this 1 D., which will be sufflci- 
 cnt to change the rays coming from the eye and 
 converging at 40 inches to a condition of parallel- 
 ism, or if you are at a point nearer than 40 inches 
 to your patient, say 28 inches, or about 1.50 D., 
 then you must add this on to the concave lens that 
 stops the retinal reflex at this point, in order to de- 
 termine the total myopia. 
 
 This adding to in myo'^iia and subtracting in 
 hyf>ermetropia, have led many to fjrefer to observe 
 the letinal reflex from a distance of 20 feet, or in- 
 finity, and this is a simpler way than any, if your 
 room and light will permit it, in that case you 
 have only to place the convex lens before the eye, 
 that stops all motion at this point, and this lens 
 will represent the total hypermetropia, and the 
 same holds good in myopia. This distance also en- 
 ables you to locate the point of reversal in low de- 
 grees of myopia by simply approaching your i^ati- 
 eut until this point is found; for example, if it is 
 found to be at SO inches from your patient, count- 
 ing the distance from the patient's e^'e to the mir- 
 ror, and from the mirror to the source of illumina- 
 tion, in this estimation, then you have a myopia of 
 .05 D., and you can prove it by placing this lens 
 
120 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 before tlie ere when the rays are parallel, and there 
 will be no point of reversal, but if you increase it 
 you will create a temporary hypermetropia and 
 the motion in the pupillary space will again be 
 seen, but will move with and not against the light 
 on the face. Owing to its simplicity this method 
 of using the mirror at a distance of 20 feet has 
 many advocates. 
 
 Simple, myopic astigmatism is determined by 
 the retinal redex moving against the light on the 
 face, in one meridian only, while in the other me- 
 ridian there is no motion. The amount of astig- 
 matism is measured by the concave glass neces- 
 sary to stop the motion in this meridian. For ex- 
 ample, if the mirror shows the reflex to move only 
 in one meridian and the movement is against the 
 movement of the' light on the face, then you have 
 myopic astigmatism, and if it requires a concave 
 glass of one and a half dioptre to stop this, then the 
 amount of astigmatism is 1.50 D., and the axis of 
 the correcting cylinder must be put at right angles 
 to the myopic meridian. The same is true, also, of 
 compound myopic astigmatism. You must test 
 each meridian separately, and the difference in the 
 two lenses will give you the amount of astigma- 
 tism, and the axis of the correcting cylinder must 
 be at right angles to the meridian of greatest ame- 
 tropia. 
 
SKIASCOPY. 121 
 
 In testing for mixed astigmatism, you must 
 also test each meridian separately. The hyperme- 
 troi)ic meridian ujust be tested with a convex 
 lens, while the myopic meridian must be measured 
 by means of a concave lens. This is not a difficult 
 matter to do, and with a little practice you will find 
 the retinoscope a valuable adjunct in refractive 
 work, especially for young children or illiterate 
 persons. 
 
 The use of the concave retinoscope mirror is 
 the same in every respect, except that you must 
 remember that your point of illumination is really 
 in front of the mirror at its focal distance, and that 
 all the movements of the reflex are exactly the re- 
 verse of what they are with the plain mirror. It is 
 not so necessary to cover your chimney when us- 
 ing the concave mirror. The mirror on the oph- 
 thalmoscope will answer all purposes of a concave 
 mirror for retinoscopic work, and it is often well 
 to observe the condition of the reflex with it, and 
 familiarize yourself with the use of both. The 
 shape of the retinal reflex also throws light on the 
 variety of ametropia we have to deal with; in sim- 
 ple hypermetropia or myopia it is circular in shajie, 
 while in astigmatism of either variety it is more 
 band-like, or ribbon-shaped. 
 
 It is well to observe all these little details, as 
 they will all contribute their own share in assist- 
 ing us in making a diagnosis of the refractive con- 
 ditions of the eye by means of retinoscopy. 
 
CHAPTER X 
 
 Presbyopia, 
 
 Q. What is meaut by presbyopia? 
 
 A. It means that change which takes place 
 in most eyes at a certain period in life, when the 
 accommodation of the eye is not sufficiently strong 
 to adjust the eye for close work, or in other words, 
 when the near point of the eye has receded to such 
 a distance that it is no longer possible to use the 
 eye for close work, with comfort or ease. 
 
 Q. "When does this change in the accommo- 
 dation of the eye generally take place? 
 
 A. It is a very gradual change beginning at 
 about the age of ten years, and gradually increas- 
 ing, until at about the age of seventy-three years, 
 's%]ien it is complete. When presbyopia is fully 
 and comj)]etely developed, there is no longer any 
 punctum proximum, or near point, or in other 
 words, the punctum proximum and the punctum 
 remotum become the same. 
 
 Q. What is the cause of presbyopia? 
 
 133 
 
PRESBYOPIA. 123 
 
 A. It is caused by the crystalline lens of the 
 eye becoming hard, so that the action of the ciliary 
 muscle is no longer sufficient to increase the refrac- 
 tive power of the lens by increasing its curvature, 
 which, as we have seen in a preceding chapter, is 
 necessary to see near objects distinctly. 
 
 This is a slow but gradual change, and we do 
 not, as a rule, suffer any inconvenience from it un- 
 til about the age of 42 years, when the near point 
 has receded from the eye a distance of 40 c, m., or 
 about IG inches, when we find it difficult for us to 
 see distinctly for any length of time when using 
 our eyes for close work, such as reading, writing, 
 etc. This change takes place sometimes earlier 
 than this in hypermetropia, and is always delayed 
 to a much later period in myopes, this depending 
 entirely on the degree of myopia. 
 
 Q. How do you correct presbyopia? 
 
 A. By the use of convex glasses placed before 
 the eye, and w^orn when using the eyes for close 
 work. 
 
 Q. How does a convex lens accomplish this? 
 
 A. By adding refractive power to the dioptric 
 media of the eye, in this way compensating for the 
 'oss of adjustability on the part of the crystalline 
 lens. 
 
124 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 Q. How do we determine the strength of the 
 convex lens necessary for this purpose? 
 
 A. By finding the lens necessary to bring 
 back the punctum proximum of the eve to a point 
 sufficiently close to the eve, to enable the patient to 
 use his eyes for close work without strain or fa- 
 tigue. This is generally at a point 12 inches or 14 
 inches from the eye. 
 
 Q. Is there any rule to go by in prescribing 
 convex lens for presbyopia? 
 
 A. Yes. There is a general rule that assists 
 us in forming some idea as to the strength of the 
 glass necessary, but we must not be satisfied with 
 generalities, so we must test each eye separately 
 for the close point. However, we will give the rule 
 which you must remember is for emmetropia 
 alone, and where you have a refractive condition 
 other than emmetropia, this must be corrected, 
 and the eye made emmetropic before applying the 
 rule. After the eye is rendered emmetropic, either 
 by nature or by a perfect correction of the ame- 
 tropia, we calculate that a patient 45 years old 
 will require a convex lens of ID. to correct his 
 presbyopia; that at 50 years old they will require 
 a convex lens of 2 D.; and at 55 years old, will re- 
 quire one of 2.50 D., while at 60 years old, a 3 D. 
 will be required; but, as previously stated, this 
 
PRESBYOPIA. 125 
 
 rule is only approximately correct, and each case 
 must be carefully tested, but this rule with a given 
 age, will aid us somewhat in our calculation. 
 
 Q. Then in case we have a case of ametropia 
 complicated with presbyopia, how do we proceed 
 to correct the presbyopia? 
 
 A. By first correcting the ametropia in the 
 usual manner, by means of the Snellen test type, 
 and the other methods enumerated; but in order to 
 more clearly understand it, I think it best to take 
 up each case of ametropia separately, and consid- 
 er them in connection with presbyopia, in this way 
 giving us a clearer idea as to how each case is to be 
 treated. In the first place we will take emmetrop- 
 ia, and by following the rule given above, w^e will 
 be able to readily form some idea as to the convex 
 lens necessary to correct a given case of presby- 
 opia, by finding the age of the patient. As this is 
 the very simplest form of presbyopia, there will be 
 found no trouble in correcting it. 
 
 Now, in case our patient is hypermetropic and 
 presbyopic also, we first proceed to correct the hy- 
 permetropia, and after having done this satisfac- 
 torily, we proceed to correct the presbyopia. For 
 example, we have a patient 55 years old, who has 
 a hypermetropia of 1.50 D. as determined in the 
 usual manner. This lens then renders him emme- 
 
126 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 tropic, and at 50 years an emmetrope usually re- 
 quires a convex lens of 2.50 D. to correct his pres- 
 byopia, then in determining the glass necessary, 
 we must add the two together, and we find that 
 -fl.50 D.S. added to a -r-2.50 D.S. equals 4 D.S.; in 
 other words, a 4 D.S. or alOinch glass will be neces- 
 sary to bring his close point near enough to his 
 eye to enable him to use them with any degree of 
 comfort. 
 
 This, then, is a case of simple hypermetropia, 
 with presbyopia. Xow, in case we have a case of 
 compound hypermetropic astigmatism, we proceed 
 in exactly the same way; that is, we correct the dis- 
 tant vision in the usual way and then correct the 
 presbyoj)ia. For example, if v^e have a case of 
 compound hypermetropic astigmatism in a patient 
 50 years old, requiring the following correction for 
 his distant vision, to bring it up to the standard of 
 U, that is, a 4- 2.25 D. S. C — 1.25 cyl. ax. 90^, we 
 must put this glass and the one that at his age 
 would correct his presbyopia if he were emmetrop- 
 ic, together to find out the glass he would need for 
 close work. At 50 years the presbyopia generally 
 amounts to 2 D., so in that case we would have the 
 following formula for reading glasses: -;-2 D. S. 
 added to -r 2.25 D. S. C "h 1-25 cyl. ax. 90°, or add- 
 ed together would equal a -^ 4.25 D. S. 3 w. -^ 1.25 
 cvl. ax. 90° for reading. The cvlinder gl^ass alwavs 
 
PRESBYOPIA. 137 
 
 remaining as you find it, to correct the distant 
 vision. 
 
 Now in case we Iiave simple hypermetropic 
 astigmatism to deal with, then you simply correct 
 the astigmatism by means of a cylinder lens and 
 add to it the convex lens necessary to correct the 
 presbyopia. To cite a case again, supposing our 
 patient requires a -p cyl. of 1.50 D. ax. 90° to cor- 
 rect his hypermetropic astigmatism, and he is 45 
 years old; then we find the glass he would need for 
 his close work would be as follows: -f-1 D. S.^-I- 
 1.50 D. cyl. ax. 90*^, thus giving us a correction for 
 his astigmatism and presbyopia; but this glass 
 could only be used for close work, as it would blur 
 his distant vision, and strain his eye if used for 
 that purpose. 
 
 The cases that will call for some little care in 
 connection with this condition of presbyopia are 
 cases of myopic astigmatism. Now you will re- 
 member that in myopic astigmatism, the eye is 
 emmetropic in one meridian and myopic in the 
 other. Of course, your patient will not get presby- 
 opic in the myopic meridian as soon as he does in 
 the emmetropic. Supposing that he has a myopic 
 astigmatism of, say ID., and that he is 45 years 
 old ; now if he were emmetropic, he would need a 
 convex spherical lens of ID. at 45; t)ut he is astig- 
 
128 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 matic, and. hence he is at 45 presbyopic ID. in the 
 emmetropic meridian, and his myopic meridian has 
 reached a condition of emmetropia on its way to- 
 wards presbyopia. So his punctum proximum is 
 all right for this myopic meridian, while it has 
 receded, in the emmetropic meridian, so we find in 
 order to bring it back to a proper distance in this 
 meridian, will require the aid of a glass that con- 
 verges rays in one meridian only, and, of course, a 
 cylinder, as we have said before, does this, so we 
 would correct his presbyopia by prescribing a con- 
 vex cylinder lens of 1 D. with its axis at 90°, or ver- 
 tical, and we will find that with the aid of this lens 
 he can see distinctly and use his eyes at the close 
 point without trouble. 
 
 In cases of myopic astigmatism, you must put 
 the cylinder glass at right angles to correct the 
 presbyopia; for example, if you have a case of 
 myopic astigmatism at 150° in the right eye, and at 
 30° in the left, then the axis of the convex lens to 
 correct the presbyopia would be at 30° in the right 
 eye, and 150° in the left. 
 
 Let us take the above case of myopic astigma- 
 tism just cited, and say the man is 60 years old, 
 then he will be presbyopic in both meridians of his 
 eye, but more presbyopic in the emmetropic merid- 
 ian than in the myopic. At 60 years, we find that 
 
PRESBYOPIA. 129 
 
 lie will require a convex lens of 3 D. in the emme- 
 tropic meridian, and a convex lens of 2 D. in the 
 myopic meridian, so we would have to give him 
 the following glass: -- 2 D. S. C -r 1 cyl. ax. 90°, 
 for his close work, while for his distant correction 
 he still used his concave cyl. of 1 D., axis at 180°. 
 jS^ow, as we have seen, myoi)ia delays the oc- 
 currence of presbyopia, it will be well to see how 
 we are to deal with cases of myopia of certain de- 
 grees, complicated with presbyopia. We find that, 
 generally speaking, a person having a myopia of 1 
 D., instead of needing a convex lens for close work 
 at the age of from 45 to 48 years of 1 D., as do per- 
 sons with an emmetropic eye, they are generally 
 not obliged to wear glasses for jjresbyopia for 
 about five years later, or not until 50, or there- 
 abouts, and one with a myopia of 2 D., not until 
 about 55 or so, will they need a convex glass for 
 close work, though it is often necessary to reduce 
 the distance glasses 1 or 2 D. for close work, a my- 
 ope of 6 D. say, will require a — 4 D. for reading, 
 and a myope of 10 D. would probably require a — 
 6 or — 8 D., Avhile a myope of from 16 to 20 D. will 
 require a reduction generall}^ of from 4 to 6 D. for 
 close work, as these strong concave glasses cause 
 too great a divergency of the rays, causing difficul- 
 ty in using them for close work. We have told you 
 in a previous part of this work that the accommo- 
 
130 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 elation is very little used in myopia, and it is a 
 fact, that, supposedly from this reason, the ciliary 
 muscle is very poorly fleveloped in this class of 
 persons. 
 
 This will end all we have to say about refrac- 
 tion, or refractive errors, and their correction, but 
 before concluding we must say a few words about 
 asthenopia, or eye-strain, as a result of insufficien- 
 cy of the ocular muscles, and point out the indica- 
 tions for £'orrecting them, a very important part of 
 the work met with in this line. 
 
CHAPTER XI. 
 
 3Iuscular Asthenopia. 
 
 Q. What is meant by muscular asthenopia? 
 • A. It means asthenopia, or eve-strain, caused 
 by some disarrangement in the associated action 
 of the muscles attached to the eve-ball; that is, the 
 ribbon-like muscles, known as the four recti, or 
 straight muscles, and the two oblique, which move 
 the eye-balls in harmony, so that the image from 
 any object in the field of vision is brought to a fo- 
 cus on corresponding parts of the retinae, thus 
 enabling us to see one object and not two. This is 
 called single vision. 
 
 Q. When this condition of single vision is not 
 present, owing to some marked muscular defect or 
 from paralysis of certain muscles, what is it called? 
 
 A. It is called diplopia, or double vision. It 
 is caused by the focus of the image in the field of 
 regard, falling on dissimilar parts of the two eyes, 
 that is, parts of the retina in each eye, not corres- 
 ponding to each other, as is necessary to produce 
 single vision. This produces a separate image for 
 
 131 
 
132 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 each eve, and being api^reciatecl as such, we see 
 two objects instead of one; each image seems to 
 come from different points in the field of vision. 
 
 Q. Is it possible to have a diplopia, or double 
 vision, with one e^^e only? 
 
 A, It is. This condition is called monocular 
 diplopia, and is generally due to irregular astig- 
 matism, caused by surgical operation on the corn- 
 ea, injuries, or some marked difference in the re- 
 fractive condition or power of different parts of 
 the crystalline lens or cornea. 
 
 Q. How can monocular diplopia be induced 
 temporarily? 
 
 A. By holding a prism before the eye so that 
 some of the rays i^assing into the eye will pass 
 through the prism. The ones not passing through 
 the prism will enter the eye and form an image in 
 the proper place, while the rays that pass through 
 the prism are deflected toward the perpendicular 
 of the prism, and striking the retina at a different 
 part will form a separate image, thus giving rise 
 to the formation of two separate images which are 
 seen and appreciated as such. 
 
 Q. Do all cases of muscular insufficiency, as 
 it is called, produce binocular diplopia? 
 
 A. The great ma^rity of the cases of muscle 
 trouble does not. The muscular deficiency does 
 
MUSCULAR ASTHENOPIA. 133 
 
 not allow sufficient disassociation of the move- 
 ments of the eye to cause diplopia, but requires an 
 extra amount of work on the part of the muscles 
 to keep up a condition of affairs b}' which single 
 vision is maintained, hence the asthenof)ia, or e^'e- 
 strain, resulting from this constant effort to main- 
 tain muscular equilibrium. 
 
 Q. But whv is this condition of single vision 
 maintained, when it requires such an effort on the 
 part of the muscles? 
 
 A. Because for some inherent reason, on the 
 part of the eyes, double vision is disagreeable to 
 them, and great effort is made on their part to pre- 
 vent it, consequently when this condition of diplo- 
 pia becomes inevitable, the muscles of the eyes im- 
 mediately exert their entire muscular power to 
 prevent it, by so turning the eye as to bring the 
 rays, striking the two e^es, to a focus at corres- 
 ponding parts of the retinae, thus enabling us to 
 see a single image and not t^o separate images, as 
 would be the result if the focus reached the retinae 
 at any other point or i)art, a very unpleasant and 
 bewildering sensation, as any one ever suffering 
 from it can testify. 
 
 Q. Is this muscular difficulty confined to any 
 particular muscle or set of muscles? 
 
134 REFRACTIVE AND OPHTHALMIC CATECHISM 
 
 A. xso; the trouble may exist in any one, or 
 in any set of them. 
 
 Q. In a ease of asthenopia, hoAv are we to de- 
 termine that the fault lies in the muscles of the 
 eye? 
 
 A. By excluding and differentiating it from 
 other causes of asthenopia, by measuring the 
 strength of the different muscles and comparing 
 the result with that of normal eyes. 
 
 Q. How are these measurements made? 
 
 A. Principally by inducing a temporary con- 
 dition of dii3loj)ia, by the use of prisms. This the 
 eyes will resist to their full power. This strength 
 as measured by the degrees on the prism will re- 
 present the dynamic power of the eye muscles. 
 This is done by i)lacing a prism of a given strength 
 with its apex over the muscle to be measured. For 
 example, if you wish to test the adducting power 
 of the eye or their power to roll inward, you hold a 
 prism with its apex over the insertion of the inter- 
 nal recti, and when the eyes fail to blend the two 
 images, the limit is reached, and the number on 
 the prism will express this in degrees. 
 
 If you wish to measure the abductive power of 
 the eye, you do so by placing the apex of the prism 
 over the insertion of the external recti. The cir- 
 
MUSCULAR ASTHENOPIA. 135 
 
 ciimcl action is determined by holding the prism 
 before the eye with the apex over the insertion of 
 the superior or inferior recti, it does not matter 
 which. 
 
 To be more explicit, we will take a case and 
 test it in the usual manner of conducting one of 
 theses tests in our office. The room is slightly 
 darkened, and a lighted candle is placed on a 
 stand at a distance of twenty feet and on a level 
 with the eyes. The trial frame is placed on the 
 patient, and it is better to place the red glass be- 
 fore one of the eyes, while conducting this exami- 
 nation, as it renders the double images more dis- 
 tinct by the contrast in color. 
 
 We will first proceed to examine the internal 
 recti by placing a prism in the trial frame, or hold- 
 ing it before the eye with its apex in or towards 
 the nose. From 30° to 40° is said to be the normal 
 abductive power of a normal eye, that is, an eye 
 with normal muscular power ought to bring the 
 images together and maintain single vision even 
 with this prism before one eye, or preferably the 
 power of the prism, divided equally between the 
 tAvo eyes. But, if we find that a prism, of say 10°, 
 before the eyes with the apex in or toward the 
 nose, there are two lights, one red and the other 
 white; then we have weak adduction of 10°, in- 
 stead of 30° or 40°, as it should be. 
 
136 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 Xow in the same wa}' we test the external 
 miiscJes and we find that the abductive power is 
 (jo QY 8^, or normal, then we can at least i)resume a 
 lack of equilibrium. The mechanical explanation 
 of this is quite simple. By the refractive action of 
 the prism, the rays of light are bent towards the 
 base and tend to form a separate image for the eye 
 over which it is placed, at a point of the retina not 
 corresponding with the place at which the image 
 is formed on the retina of the other eye. The dou- 
 ble image being disagreeable to the eye, there is a 
 nervous stimulus sent out at once to overcome this 
 by rolling the eye-ball into such a position as will 
 bring the image on corresponding parts of the re- 
 tinae. This the eye succeeds in doing up to a cer- 
 tain point, which by using prisms of increasing 
 strength, is soon discovered. When a point is 
 reached when the eyes can no longer fuse the im- 
 ages, and there is for the time being two images 
 instead of one; the limit of the muscular power of 
 the eye is reached, and this is measured by the 
 prism necessary to bring about this condition in 
 degrees. 
 
 Any great amount of deviation from the fig- 
 ures taken as a standard of normal muscular pow- 
 er is at least presumptive evidence of a lack of 
 muscular equilibrium. The standard for the ver- 
 
MUSCULAR ASTHENOPIA. 137 
 
 tical muscles, or the superior and inferior recti, is 
 about 30. There may also be a general weakness 
 of all the ocular muscles, so that separate tests 
 will show them to be all below the standard; but 
 still there may be no loss of equilibrium; however, 
 this is best determined by other means which we 
 shall proceed to describe. 
 
 The test for muscular equilibrium is best de- 
 termined by producing vertical diplopia by means 
 of a 10° prism, before one eye, base up or down, 
 with the red glass before the other eye, the patient 
 is directed to look at the candle twenty feet away, 
 as before. Instead of one light, he will see two, 
 one above the other, and if the muscles are well 
 balanced, the lights will be in a vertical line; but 
 if not, they will stand out at either side of a verti- 
 cal' line. If the red light is over the right eye, and 
 the red image stands on the same side as the red 
 glass, there is said to be homonymous diplopia, 
 and this is caused by a weakness of the external 
 recti; but if the red light is seen on the other side, 
 or on the side of the vertical line corresponding to 
 the eye, that is, not covered with the red glass,then 
 the diplopia is said to be crossed, and this we find 
 is due to muscular insufficiency of the internal 
 recti. 
 
 Q. What system of nomenclature has been 
 
138 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 adopted to designate the different deviations 
 wliich the eve tends to assume? 
 
 A. A system formulated by Dr. George A. 
 Stevens of New York city, and which is as follows: 
 
 When the eye tends to turn in from the visual 
 line, it is called esophoria. When the eye tends to 
 turn out from the visual line, it is called exophoria; 
 and when it tends to turn up or down from the vis- 
 ual line, it is called hyperphoria, right or left, as 
 the case may be. We may have a combination of 
 these conditions, such as a turning in and up, 
 when it is called hypo-esophoria, while if it turns 
 out and up, it is called hypo-exophoria, etc. 
 
 The amount of these deviations is measured 
 by the prism necessary to restore them to their 
 normal, or what may be designated as their prim- 
 ary position. For example, if in examining the 
 eyes in this way, with the prism over the left eye 
 and the red glass over the right, we find the red 
 light on the right side of a vertical line, and it re- 
 quires a prism of 3°, with the base over the exter- 
 nal recti, to bring the red light in line with the oth- 
 ers, the case would be one of esoi)horia, or a ten- 
 dency to turn in of 3°, and in correcting it with 
 prism, the base must be placed over the weak mus- 
 cles, or out; or in case cutting the muscles is neces- 
 
MUSCULAR ASTHENOPIA. 139 
 
 sary, or a tenotomy, as it is called, it must be per- 
 formed on the internal recti. 
 
 Now supposing the red light is on the other 
 side of a vertical line; or, that we have crossed di- 
 plopia, and that it requires a prism of 4° with the 
 base in or over the internal recti, then we liave a 
 case of turning out of tlie eye-balls, or exophoria, 
 as it is called, of 4°, and must be corrected, either 
 by a tenotomy of the external recti, or by means of 
 a prism worn with its base in or towards the inser- 
 tion of the weak muscles. Hypo-phoria is deter- 
 mined and measured. in the same way, using, how- 
 ever, an imaginary horizontal, instead of a vertical 
 line. These tests, however, measure only the man- 
 ifest amount of trouble, and a great deal of latent 
 trouble may be discovered after correcting the 
 manifest deficiency. 
 
 It is in these cases in which by the superior, or 
 excessive, power of a muscle or a set of muscles, 
 there is a tendency of the eye to deviate from the 
 visual axis, and in which there is an effort on the 
 part of the weak, or opposing muscles to overcome 
 this tendency, that asthenopia, or eye-strain, re- 
 sults, as well as many other nervous manifestations 
 found associated with it, for the relief of which 
 the physician is put to the greatest tests many 
 times, though we are often able to relieve this 
 
140 REFRACTIVE AND OPHTHALMIC CATECHISM. ■ 
 
 class of cases to a very marked extent, by the cut- 
 ting of a muscle, or the application of a suitable 
 prism. 
 
 I am firmly convinced in the opinion that the 
 greatest amount of good, in the greatest number 
 of cases, is to be obtained by the use of correcting 
 prisms. 
 
 Q. What is the condition called, according to 
 the Stevens' system of nomenclature, when the 
 muscles are properly balanced and no loss of equil- 
 ibrium is found to exist? 
 
 A. Orthophoria, or a condition of equilibri- 
 um, or as he defines it, "the ideal form of adjust- 
 ment.'' 
 
 Q. When the various deviations are taken as 
 a whole, what is it called? 
 
 A. Heterophoria, of which esophoria, exo- 
 phoria, and hyperphoria are varieties. 
 
 Q. Are there any other tests for these condi- 
 tions besides the trial frame test spoken of? 
 
 A. Yes, there are several other tests and in- 
 struments for this purpose, chief among which is 
 the Stevens' phorometer, as well as other forms of 
 the same instrument. Then there is the Maddock 
 rod test, the Maddock double-prism test, and Stev- 
 
MUSCULAR ASTHENOPIA. 
 
 141 
 
 Figure 19. 
 Steven's Phorometer, with Rotatikg Prisms. 
 
 For Directions see other side. 
 
142 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 Directions. 
 
 The phorometer should be so placed that the side of the slide on 
 which the scale of degrees are seen should be from the patient. 
 The side mark R. H. and L. H. will then be before the patient's 
 right eye, and that marked E. S. and E. X. before the left eye. 
 The arm of the instrument is to be brought to a perfect level, as 
 indicated by the spirit level. To determine hyperphoria, the 
 instrument being adjusted to the hight of the patient's eyes and at 
 least four inches in front of them, bring the level of the prism slide 
 to the vertical position. The pointer will then be at O. The 
 patient looking through the two glasses at an object (a lighted can- 
 dle) placed at a distance of twenty feet directly in front, sees double 
 images of the object. Should one ot the images appear higher than 
 the othpr, the prisms are caused to rotate until the images are 
 brought to the same horizontal plane. By making the rotation 
 slowly it will in many instances be carried further than when the 
 correction is quickly made. The pointer then indicates the form 
 and degree of manifest hyperphoria. 
 
 To examine Esophoria and Exophoria, bring the lever to the 
 horizontal position and then make adjustments until the images are 
 in an exact vertical line. 
 
 ens' stenopaeic lens test. They are all based on 
 the same principle of producing contrasting im- 
 ages for the two eyes, and a description of each 
 separately we do not deem necessary in a work of 
 this kind. I am a little partial to the double-prism 
 test of Maddock when testing the horizontal mus- 
 cles, and it is an easy matter to determine with it 
 the manifest esophoria or exophoria. You cannot 
 use it, however, so well with the vertical muscles, 
 and the rod test will answer very nicely for this 
 purpose, as it will also for the horizontal muscles. 
 I am of the opinion that in examining this class of 
 
MUSCULAR ASTHENOPIA. 143 
 
 cases, one should use several of the tests, as you 
 cannot always depend on the result of any single 
 one of them alone. 
 
 Figure 20. 
 
 Maddox's Test for Heterophoria 
 
 Consists of a hard rubber dise mounted in a metal rim of the 
 size of trial lenses, so as to fit easily into the trial frame, which 
 holds in the center a glass rod. 
 
 The effect of this transparent cj'linder is to cause an apparent 
 elongation of a single flame into a thin line of light, quite dissimilar 
 from the flame itself, as seen at the same time Tvith the other eye, so 
 that there remains practically no desire to unite the two images, 
 whose relative position thus easily indicates the condition of equilib- 
 rium of the two eyes. This is always at right angles to the axis of 
 the rod, so that to produce a vertical line, with which to test hori- 
 zontal deviations, the rod is placed horizontally, and to produce a 
 horizontal line, to test vertical deviations, it is placed vertically. 
 The test is made prettier and any desire for single vision still further 
 reduced by placing a red glass before the other eye. 
 
 Q. Why is it that persons suffering from 
 strabismus, or squint, are not usually so unpleas- 
 
144 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 antly affected by the muscular derangement of the 
 eyes? 
 
 A. Because the rotation of the eyes in these 
 cases is, as a general rule, so well-marked, and of 
 such a positive character, that there is little or no 
 effort on the part of the eyes to blend the images, 
 thus producing single vision, and in consequence 
 of this, there is a suppression of the image of one 
 of the eyes, generally the non-flxing eye, or the eye 
 that squints the most. There being no effort on 
 the part of the eye to bring the images at corres- 
 ponding parts of the retinae, there is no strain re- 
 sulting, and consequently no appreciable effect 
 produced. 
 
 This non-use of one of the squinting eyes, in 
 cases of marked strabismus, is generally the cause 
 of the poor sight usually found to exist in one eye, 
 in these cases. 
 
 Eye-strain is to be found in cases where the 
 deviation is but slight, and when, by an extraordi- 
 nary effort on the part of the muscles, double vis- 
 ion, or diplopia, is overcome; but usually produc- 
 ing asthenopia by this extreme effort. Hence it is 
 that these latter cases must be looked after and 
 corrected, when a case of decided deviation, 
 amounting to internal or external strabismus, will 
 give little or no trouble, except in reducing the 
 
MUSCULAR ASTHENOPIA. 145 
 
 vision in one eye, generally to a point of absolute 
 uselessness, a condition called amblyopia ex- 
 anoi^sia, and which is thought by many to be 
 caused by a prolonged continuous suppression of 
 one of the retinal images, while many others think 
 it is caused by a condition of congenital non-devel- 
 opment of the eye, and that there being no instinct 
 on the part of the eye to maintain a certain relation 
 with the visual axis of the other eye, that it grad- 
 ually turns in, as a result of the preponderating 
 influence or power of the internal rectus, a very 
 nice theory, indeed, and x)artly borne out by the 
 fact that we rarely find this condition to exist in 
 cases of external strabismus, or outward deviation 
 of the eyes. 
 
 Another fact that may have some bearing as 
 to the cause of this amblyopia ex-anopsia, is that 
 in most cases where it occurs, the eyes are gener- 
 ally hypermetropic, and the one that turns in,most 
 generally very much so,as this is regarded as a non- 
 developed condition, it is reasonable at least to 
 suppose that there may be some relationship ex- 
 isting between the two conditions. 
 
 Q. Are these cases of heterophoria always 
 confined to one variety of it? 
 
 A. No; there may be two varieties of it com- 
 bined. For example, we may have a case of right 
 
146 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 or left hy])erphoria with esophoria, constituting 
 what is called hyper-esophoria; or we may have a 
 case of right or left hyperphoria combined with 
 exophoria, giving rise to what is designated hyper- 
 exophoria, etc. 
 
 There are also subdivisions of these varieties, 
 with -svhich it is not necessary for us to deal, as I 
 believe them to be more theoretical than practical 
 in their applications. 
 
 Q. Is there always found a lack of converg- 
 ing power for close work where there is found an 
 exophoria, for distance? 
 
 A. Not always. They may or may not be 
 connected. It is, however, always best to test the 
 converging power of the eyes for a close point. 
 This can be done by holding an object, such as a 
 lead pencil, before the eyes, and ask your patient 
 to keep his eyes fixed on it, as you slowly approach 
 the eye. The converging power can in this way be 
 noted, and any deficiency can be readily observed 
 by the slow, sluggish way in which one or both 
 eyes will act as the pencil is slowly brought to a 
 point close to them. The two eyes will follow the 
 pencil until it reaches a certain point, when it is 
 no longer possible for the two eyes to converge 
 to a closer point. When this point is reached, ei- 
 
MUSCULAR ASTHENOPIA. 147 
 
 ther or both eyes will give up, as it were, and rotate 
 outward. 
 
 Many of these cases will require prismatic 
 lenses for close work, while many of them are 
 greatly improved by the systematic exercise of 
 these muscles, either with prism or b}^ trying for a 
 few minutes each day, to converge to a close i)oint. 
 For this purpose, the finger or a lead pencil will 
 answer. 
 
 Q. In case diplopia, or muscular insufiflciency, 
 is caused either by complete or partial paralysis 
 of the muscles, are these same measures available? 
 
 A. The exercise is good for this condition, but 
 we must try and restore the muscles to their 
 proper tone, by the internal administration of 
 medicines, and by the application of electricity, 
 before we can hope to restore harmonious muscu- 
 lar association with a proper restoration of the 
 equilibrium. 
 
 There is a large field for persevering and intel- 
 ligent labor in the domain of muscular insufficien- 
 cy, and many of our most intractable cases will be 
 found to result from this cause. There is, like in 
 all other branches of scientific investigation, an 
 honest difference of opinion as to the relative fre- 
 quency and aeteological significance of this class of 
 
148 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 cases, but speaking alone from the standpoint of 
 personal experience, I am satisfied that the cause 
 of many of the cases of headache and other nervous 
 manifestations that we meet with, is to be found 
 in the muscles of the eye. 
 
MUSCULAR ASTHENOPIA. 
 
 149 
 
 Figure 21. 
 The Dr. Harold Wilson Phorometer. 
 
 THE WILSON PHOROMETER. 
 
 More attention is paid to muscle testing to-day than ever before. 
 Many eyes seeminglj^ impossible to fit, are easily corrected Avlien 
 the condition of the muscles are understood. The most practical 
 instrument for muscle testing (and an instrument is always infinitely 
 superior to a trial frame and prisms) is the Dr, Harold Wilson phor- 
 ometer. 
 
 The large disc (see illustration) contains a Savage double prism, 
 a strong Maddox cylinder, a 15 degree prism and a 10 degree prism 
 — one base in, the other base out. These form practically the only 
 standard muscle tests, and, arranged as they are in this instrument, 
 may be used successively and quickly, one result proving the other, 
 thus insuring an accurate test in the shortest possible time. The 
 disc also contains one blank hole, in front of which may be placed 
 (in a clip provided) any lens desired for a supplementary test. 
 
 A set of revolving prisms, obtaining any value up to 10 degrees 
 to a hairlike nicety by a rotating pinion, are provided for the test- 
 ing. They are almost invaluable for exercising the muscles. 
 
 The Dr. Harold Wilson Phorometer is the only instrument 
 capable of testing the oblique muscles or of performing a complete 
 instrumental muscle test. 
 
 Made by E. Kirstein & Sons Co., Rochester, N. Y. 
 
CHAPTER XII. 
 
 Perimetry. 
 
 Q. What is perimetry, and what is it princi- 
 pally used for? 
 
 A. It is a method used for the purpose of de- 
 termininji; the visual acuity of different parts of 
 tlie retina, to determine its limitation in the differ- 
 ent meridians, or in other words, to measure the 
 "field of vision," which is that part of space which 
 is perceived by an eye, when maintained in a posi- 
 tion of central fixation, simultaneously in differ- 
 ent directions. 
 
 It is principally used for the purpose of draw- 
 ing comparisons between the field of vision found 
 to exist in a normal emmetropic eye, and one the 
 seat of pathological change. Diseased conditions 
 of the brain, of the optic nerve, of the retina, and 
 many other parts directly or indirectly connected 
 with the visual apparatus, may be the means of 
 producing material change in the perceptive pow- 
 er of the eye, and it is for the purpose of diagnosing 
 these changed conditions, that the perimeter is so 
 frequently used. 
 
 150 
 
PERIMETRY. 151 
 
 Q. What standard of visual perception is 
 taken as a basis of calculation in these measure- 
 ments? 
 
 A. The visual perception of a healthy normal 
 emmetropic eye, for different colors, in different 
 meridians. The perception of the eye varies for 
 different colors. It is greatest for white; hence 
 this color is used more than any other in deter- 
 mining its perception. The perception of a normal 
 eye is as follows for white: For the right eye, to 
 the temporal side of the horizontal meridian, 90°, 
 or more; to the nasal side of the horizontal merid- 
 ian, 60°; the upper part of the vertical meridian, 
 about 55°; while for the lower parts of the same 
 meridian, it is about 70°. The intermediate merid- 
 ian will be found to have intermediate perception 
 from the two nearest principal meridians. The 
 perception of the left eye is practically the same. 
 The normal extent of the visual field is largely in- 
 fluenced by the parts surrounding the eye, such as 
 the bony prominences, nose, moustache, etc., so it 
 is necessary when you wish to depend upon your 
 findings, to associate it with other examinations, 
 such as an ophthalmoscopic examination of the 
 fundus, and a test to determine the central visual 
 acuity. 
 
 Q. How many methods are there for deter- 
 mining the visual perception? 
 
152 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 Figure 23. 
 
 Dr. Skeel's Self-Recoeding Perimeter. 
 
 "The instrument here shown is the result of experiments ex- 
 tending over some years, in the endeavor to construct a Perimeter 
 which would be self-recording, and at the same time simple in its 
 construction. In the use of the ordinary instrument, the examiner's 
 attention is divided between watching the eye of the patient, the 
 position of his own hand carrying the test object, in reading the 
 graduations on two arcs, and in marking down the same on the 
 chart. 
 
 In the instrument here described, the reading of the gradua- 
 tions is entirely dispensed with, and the recording of the position of 
 the test object simplified to the pressing of a lever. The appear- 
 ance of the instrument is plainly shown in the cut," 
 
PERIMETRY. 153 
 
 A. There are several, siieli as the bhxckboard 
 test, the finger test, but the principal one and the 
 one now most extensively used, is the test by 
 means of an instrument called the perimeter. 
 Tliere are, like all other instruments, a number of 
 dilferent kinds of perimeters to be found on the 
 market; but an automatic, self -registering perime- 
 iev, made by JMeyrowitz Bros, of New York city, I 
 believe to be the most perfect instrument of its 
 kind. They are all, however, based on the same 
 principle of having an object of definite size and 
 color to a])pear to every point of the retina. This 
 can only be accomplished, and is, by moving the 
 object in different meridians along the inner sur- 
 face of an arc, sufficiently long to describe a quar- 
 ter of a circle at least. This arc is black on its sur- 
 face, and is divided into degrees from 0^ to 90^, on 
 each arm, and when rotated, it describes the figure 
 of a hoUow sphere. 
 
 Charts on which to record the result of peri- 
 metric observations accompany the instruments, 
 and are necessar}^ to preserve a record of your 
 cases. 
 
 In using the perimeter, your patient is seated 
 with his back to a good light, and the chin resting 
 on the chin-rest of the perimeter. The eye to be 
 examined is directed to a fixation point in the cen- 
 
 Vi 
 
154 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 ter of the arc of the perimeter. The other e^^e is 
 eoA^ered by the hand or handkerchief of the pati- 
 ent. The test object is generally a white square, 
 five millimetres each way, and is moved along the 
 perimeter from the periijhery towards the central 
 fixation point. The movement of the object must 
 not be too rapid, and as soon as it comes within 
 the field of vision and can be readily recognized by 
 
 Figure 23. 
 
 ^y 
 
 
 \ 
 
 tMERSON'S fERIMETER CHAH r 
 MEYPOWITZ DROS.N.Y. 
 
 its color, you cease the moving and note the point 
 as marked on the perimeter in degrees. This will 
 indicate the visual perception for this meridian, 
 and you proceed to examine the various other me- 
 ridians in the sajne manner, generally selecting 
 the principal meridians first. After reaching the 
 point where the object first becomes visible, and 
 
PERIMETRY. 155 
 
 after making a note of it on your chart, you pro- 
 ceed to examine for blind spots, or scotoma, as 
 they are called. These are spots on the retina that 
 have lost their perception, either totally or par- 
 tially, from disease or other causes. They are re- 
 cognized by the object becoming invisible as it is 
 moved along the arc of the perimeter at certain 
 points. 
 
 If there are no scotoma present in the exam- 
 ined eye, the test object will remain in view from 
 the moment when it is first observed until it 
 reaches the central point of the arc. There is one 
 point, however, which will be found on the tem- 
 poral side in the horizontal meridian, and at a 
 point on the perimeter marked 10°, where the test 
 object will be invisible for a perceptible space. 
 This is called the blind spot of the eye, which is a 
 normal condition and corresponds to the optic 
 nerve disk, this part of the eye being devoid of vis- 
 ual perception. This spot is also called the blind 
 spot of Mariotte, and must not be confounded with 
 other blind spots, or scotoma, that may be found 
 during a perimetric examination, and are the re- 
 sult of pathological change. You must not forget 
 that when you are examining the temporal merid- 
 ian, it is the nasal side of the eye you are testing, 
 and Avhen examining the upjjer part of the verti- 
 cal meridian, it is the lower part of the retina that 
 
156 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 is under observation. In other words, tliat it is al- 
 waj'S the opposite side of the retina that is beinj>' 
 examined when measuring tlie visual field in any 
 particular meridian. 
 
 Q. Is a generally contracted field necessarily 
 significant? 
 
 A. Yes, it is very significant, as it will be 
 many times the first intimation we may receive as 
 to very serious pathological changes, which may 
 prove very inimical to sight, if it does not in time 
 result in total blindness; hence its importance 
 from a clinical and diagnostic standpoint. Con- 
 tracted fields of vision are to be found in such j)a- 
 thological conditions as glaucoma, or hardening 
 of the eye-ball; papillitis, or choked disk; retinitis, 
 choroiditis, and choroido-retinitis, and many oth- 
 er of the diseased conditions of the eye. For this 
 reason, we have felt justified in saying a few words 
 in regard to the perimeti'ic examinations of the 
 eye. 
 
CHAPTER XIII. 
 
 Illustrative Cases From Note Book. 
 
 In this chapter we shall endeavor to bring to- 
 gether a number of cases of the different forms of 
 refractive error that have been considered in the 
 preceding chapters, for the purpose of placing in a 
 comi^act and convenient form, the different refrac- 
 tive condition recognized at the present time. 
 
 In doing this, we shall make a selection of 
 cases from our case book, with a single object in 
 view, and that is, to select such as will clearly and 
 emphatically demonstrate the particular case un- 
 der consideration. 
 
 Several cases of each variety of refractive 
 error will be cited, beginning with the most fre- 
 quent of them all, that is, simple hypermetropia,or 
 hyperopia, as it is sometimes called. 
 
 Simple Hypermetropia. 
 
 Case I. Mrs. W. H., age 73 years: 
 
 KE.V. = T^<Vw. -I-3D.S. = ff 
 L. E. V. = ^^w. -1,-3 D. S. = f|. 
 
 157 
 
158 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 Ordered the above for distance, to be 
 worn all the time. 
 
 Case II. Mr. T., age 55 years: 
 
 E. E. V. = f^ w. -[- 4.50 D. S. = ||. 
 L. E. V. = ^ w. -I- 4.50 D. S. = H. 
 
 Ordered the above for constant wear, 
 with separate correction for his presby- 
 opia. 
 
 Case III. Miss S., at»e 15 years: 
 
 K. 
 
 E. 
 
 V. 
 
 20 
 
 50 
 
 w. 
 
 -I-2.25D. S. 
 
 20 
 
 2 0- 
 
 L. 
 
 E. 
 
 V. 
 
 20 
 
 40 
 
 w. 
 
 -1- 2.50 D.S. 
 
 . 20 
 
 — 2ir- 
 
 
 Ordered the above for constant wear, 
 
 IMiss L 
 
 ., age 
 
 IS 
 
 years : 
 
 
 E. 
 
 E. 
 
 V. 
 
 20 
 
 40 
 
 w. 
 
 -1 - 75 D. S. = 
 
 _ 20 
 ~ 21)' 
 
 L. 
 
 E. 
 
 V. 
 
 20 
 
 w. 
 
 -1-75 D. S. = 
 
 _ 20 
 - 2-0- 
 
 The ophthalmoscope and retinoscope 
 showed hypermetropia of 4 D. S. 
 
 Ordered solution of atropine for 
 three days, with the following results: 
 
 B. E. V. = A<V w. -I - 3.25 D. S. = H- 
 L. E. V. = A\ w. -I - 3.25 D. S. = H. 
 
 Ordered a -f- 2 D. S. for constant 
 wear with good result and relief of all as- 
 
ILLUSTRATIVE CASES. 159 
 
 thenopia, thoiigli she had previously 
 complained a great deal of her eyes. 
 
 This shows us two varieties of hyper- 
 metropia. The 0.75 D. S. represents the 
 manifest hypermetropia, while the differ- 
 ence in this lens and the 3.25 D. S. repre- 
 sents the latent hypermetropia, that is 
 2.50 D. S. The fact that she did not ac- 
 cept the 4 D. S., as shown by the ophthal- 
 moscope, was probably due to some little 
 spasm of the accommodation, even after 
 using atropine three days, as this is not 
 always long enough to continue it to per- 
 fectly relax the ciliary muscles; but it is 
 not always practical to continue it for a 
 longer period, owing to the resulting in- 
 convenience. 
 
 Case V. Chas. S., age 17 years. 
 
 Internal strabismus, or squint. Both 
 eyes corrected by operation . 
 
 R. E. V. = fA w. -I,- .75 D. S. = U- 
 L. E. Y. = 2I0 w. 2.25 D. S. = tVt- 
 
 This is an interesting case, as it re- 
 presents three separate conditions. First, 
 there is squint, or strabismus; second, 
 there is a condition of anisometropia; 
 
160 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 tliii'd, tlK'io is a (•(niditiou of amblyopia 
 ex-anoi>sia in tlu* left eye, a eoiiditioii, tis 
 we have seen, that is veiT often found in 
 these cases. 
 
 After "getting- the eyes straightened 
 np in good shape by a tenotomy on botli 
 internal recti, and giving liim tlie above 
 correction for constant wear, I could see 
 no improveinent in the perceptive power 
 of the left eye, thougli lie was under my 
 observation for five years. 
 
 Tlu're is, no doubt, a condition of 
 nou-de\elo]tment of the perceptive ele- 
 ments of this eye, and hence no prospect 
 of its imi)roving to any great extent. 
 
 In the next class of cases we shall call 
 your attention to Simple HyiJermetropic 
 Astigmatism. 
 
 Case 1. ]M i ss C. II., age 28 years. Teacher : 
 
 K E. V. = T^^ w. -i- 3.50 D. cyl. cax. 90" = 
 
 20 I 
 T(J 'I"- 
 
 L. E. V. = t'j/'o w. -I - 3.50 D. cyl. ax. 90° = 
 
 20 
 30- 
 
 This correction was ordered, in a well 
 littiug spectacle frame, with the most 
 
ILLUSTRATED CASES. 161 
 
 happy results. Before I saw her she was 
 wearing- a -|- 2 D. cyl. ax. 90°, both eyes, 
 with I" vision. This was the best she had 
 ever seen. 
 
 This beiiig hypermetropic astigma- 
 tism, with axis at 90°, it is "according to 
 the rule." 
 
 The next case is one "contrary to the 
 rule". 
 
 ('ase II. J. M., age 37 years. Farmer: 
 
 R. E. V. = U w. -1-0.75 D. cyl. ax. 180° =- 
 
 20 I 
 
 2 "r • 
 L. E. Y. = 14 w. -1-1.25 D. cyl. ax. 180° = 
 
 2 0* 
 
 Ordered for constant wear, and as he 
 is not jet presbyopic, he can use them for 
 all kinds of work. 
 
 Cnse III. "Between the rules." 
 
 JMiss H. H., age 36 years : 
 
 E. E. V. = f«-w. -1- 1- D. cyl. ax. 15« = 
 
 2,0 I 
 2 "I "• 
 
 L. E. V. = 14 w. -|- .67 D. cyl. ax. 165° = 
 
 20 
 20" 
 
 In this case, you will observe the axis 
 of the astigmatism to be neither "with'^ 
 or "against the rule," but at an intermed- 
 iate point. You will observe, however, 
 
162 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 that the axis in each eye points in the 
 same direction, towards the nose. This 
 is usually the case to which, however, 
 there are many exceptions. 
 
 The next variety of hypermetropia 
 to engage our attention is hypermetropia 
 complicated with astigmatism, or Com- 
 pound Hypermetropic Astigmatism. 
 
 Case I. "With the rule." 
 Mrs. H. : 
 
 R. E. Y. = 20 ^, .|. 1.75 D. S. C -I- 1 D. 
 
 cyl. ax. yOo = 14. 
 L. E. V. = 11 w. -1- 1.75 D. S. C -I- 1 D. 
 
 cyl. ax. 90° = f|. 
 
 Case IT. "Against the rule.'' 
 
 Miss J. C, age 15 years: 
 K E. V. = ^% w. -\r 2.75 D. S. C -|- 2.25 
 
 D. cyl. ax. 180« = f 
 
 L. E. V. = 2V0 w. -I- 2.75 D. S. C -|- 2.25 
 D. cyl. ax. 180« = U. 
 
 Case III. Between the rules. , 
 
 Mr. S., age 57 years: 
 
 K E. V. = ^\ w. -1- 1-25 D. S. C -1- 1-50 
 D. cyl. ax. 95° = |^. 
 
 L. E. V. = 2^w. -1- 2.50 D.S. C -|- 1-50 
 D. cyl. ax. 85°= ^ -\-. 
 
ILLUSTRATED CASES. 163 
 
 Case TV. The same. 
 
 Mrs. I. C, age 47 years: 
 
 R. E. V. = f«- w. -I- 1.50 D. S. 3-1- .55 D. 
 
 cyl. ax. 135° = ||. 
 L. E. V. = 1^ w. -I- 1.50 D. S. r: -I- .55 D. 
 
 To 
 
 ^o 
 
 2 
 
 cyl. ax. 30° — ^Ji 
 
 In this ease you will observe that the 
 axes of the cylinder both point towards 
 the temple. 
 
 The next class of refractive errors to 
 illustrate are the myopic varieties, and 
 we will begin with Simple Myopia. 
 
 Case I. ]\rrs. J. S., age 30 years: 
 
 K E. V. = 20 w. — 3 D. S. = U -I-. 
 L. E. V. = 1^ w. — 3 D. S. = M -I-- 
 
 Ordered the above glass for constant 
 wear. 
 
 Case II. H. G., age 51 years. 
 
 Anisometropia: 
 
 R. E. V. = ^\ w. — 5.50 D. S. = |^. 
 L. E. V. = 2V0 w. — 6.50 D. S. = f^. 
 
 Ordered the above glasses for both 
 distant and close work, with satisfactory 
 
 results. 
 
164 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 In cases where there is not more 
 than one or two dioptres difference in the 
 eyes, you can generally correct both eyes 
 separately, though you are not always 
 able to do so. Each case must be a rule 
 unto itself. 
 
 Myopic Astigmatism "with the rule." 
 Case I. Miss S., age 31 years: 
 
 E. E. V. = U w. — 2.50 D. cyl. ax. ISO^ = 
 
 20 
 30* 
 
 L. E. V. = U w. — 2.50 D. cyl. ax. l&O^ = 
 
 2_0 
 "3 0"' 
 
 This is the best I could do in this 
 case, but this being the first time she ever 
 had her refractive error corrected, may 
 account for it to a certain extent. I have 
 not been able to note whether any im- 
 provement has occurred or not, but like- 
 ly there has been some increase in the 
 visual acuteness. 
 
 Case II. ''Against the rule," 
 
 F. Van W., age 22 years: 
 K. E. V. = |« w. — .55 D. cyl. ax. 90° = 
 
 20 I • 
 
 L. E. V. = |« w. — .55 D. cyl. ax. 90° 
 
 2 I 
 2 "I " 
 
 For constant wear. 
 
ILLUSTRATED CASES. 165 
 
 Case 111. "Between the rules." 
 
 Miss A. E., age 28 years: 
 E. E. V. = fl w. — 1 D. cyl. ax. 105° = 
 
 20 
 2 0- 
 
 L. E. V. = U w. — 1.50 D. cyl. ax. 60° 
 
 20 
 20' 
 
 You will notice that there is a little 
 difference in the axes of the two eyes. 
 
 The next class of cases is myopia, 
 C()m])licated with astigmatism. 
 
 (Ijise 1. INIrs. D., age 29 years: 
 
 E. E. V. =^ ^V w. — 1 D. S. C — 2.75 D. 
 
 cyl. ax. 180° = ||. 
 L. E. V. = ^^% w. — 1 D. S. C — 2.75 D. 
 
 cyl. ax. 180O = f^. 
 
 In the above formula you will ob- 
 serye the astigmatism is "according to 
 the rule." 
 
 Case II. "Against the rule." 
 
 Miss T., age 23 years: 
 
 E. E. V. — ^V^ w. — 1.25 D. S. C — 2.25 
 
 D. cyl. ax. 90° = |^. 
 L. E. V. = 2 0(7 w. — 1.25 D. S. C — 1.25 
 
 D. cyl. ax. 90° = ff . 
 
 u 
 
166 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 You will observe we are not able in 
 this case to bring the vision up to |^, or 
 normal, a result, as we observed by the 
 ophthalmoscope, of pathological change 
 in the fundus of the eye, as we are apt to 
 have in high degrees of ametropia, of the 
 myopic variety. 
 
 Case III. "Between the rule." 
 
 , L. N., age 16 years: 
 
 E. E. V. = |o w. — .75 D. S. C — -55 cyl. 
 
 ax. 120° = f|. 
 L. E. Y. H w. — .75 D. S. C — .27 cyl. 
 
 The last variety of refractive errors 
 to which we wish to call your attention is 
 Mixed Astigmatism. 
 
 Case I. Mr. P., age 36 years: 
 
 E. E. Y. = 1^ w. — 1 D. cyl. ax. 180° C 
 -I- 67 D. cyl. ax. 90° = H. 
 
 L. E. Y. = H w. — 1 D. cyl. ax. 180« C 
 -I - 75 D. cyl. ax. 90° = |^. 
 
 You will observe that the above for- 
 mula calls for a cross cylinder, so for rea- 
 sons already given, I prescribed the fol- 
 lowing: 
 
 E. — 1 D. S. C -I- 1.67 D. cyl. ax. 90°. 
 L. — 1 D. S. C -1- 1.50 D. cyl. ax. 90«. 
 
ILLUSTRATED CASES. 167 
 
 Case II. J. p., age 45 years: 
 
 E. E. V. == f^ w. — .55 D. cyl. ax. 180« C 
 
 75 D. cyl. ax. 90° = 
 
 L. E. V. = H w. — .55 D. cyl. ax. 180° C 
 -1 - 67 D. cyl. ax. 90° = |^. 
 
 I prescribed the following formula: 
 R. — .55 D. S. C -I- 1-25 D. cyl. ax. 90«. 
 L. — .55 D. S. C -I- 111 I>. cyl. ax. 90°. 
 
 This man was exceedingly nervous, 
 and at the present time, four years after 
 fitting his eyes, he tells me he has been 
 very much better since he has been wear- 
 ing glasses. 
 
 In testing this class of cases, you can 
 use the cylinders as above, or you can 
 test them by using the sphericals and cy- 
 linders combined, as in the prescription. 
 The result in either case you will find to 
 be the same. 
 
 With this we shall pass to the consid- 
 eration of specimen cases complicated 
 with presbyopia, and we shall adhere to 
 the same plan we adopted in the begin- 
 ning, of taking up each separate form of 
 refractive error, and consider it in con- 
 nection with this condition: 
 
 Simple Hypermetropia, complicated 
 with presbyopia. 
 
168 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 Case I. Mrs. McD., age 54 years: 
 
 R. E. V. =ft w. -I- 1.T5 D. S. = |«. 
 L. E. V. = U w. -I- 1-75 D. S. = II 
 
 In tliis case tlie near point, even with 
 the above correction, was so far off that 
 she could not use her eyes for close work. 
 In order to bring back the near point to 
 where she coukl read No. 1 Jagar at IG 
 inches, it was necessary to add a 2.00 D., 
 which you see agrees pretty closely to the 
 general rule in these cases, so with a 2.00 
 D. S. — to 1.75 D. S. = 3.75 D. S. for close 
 work or reading, so it was necessary to 
 prescribe two pairs of glasses, one for dis- 
 tance, a — -1.75 D.S., and one for close 
 work, a -|-3.75 D.S. These could be put in 
 separate frames, or they could be put up 
 in a bifocal lens, which for many people 
 is a very convenient form, as it obviates 
 the necessity of carrying about two pairs 
 of glasses, as well as the constant chang- 
 ing; or the distance may be worn in a 
 spectacle frame, and a grab frame con- 
 taining the presbyopic correction placed 
 in front of these for close work. This also 
 I find a convenient method in many 
 cases, the great objection to them being 
 the additional weight and the air space 
 
ILLUSTRATED CASES. 169 
 
 between the pairs of lenses, though I find 
 many who prefer it to the bifocal lens, as 
 many complain of the disagreeable neces- 
 sity of having to look through the strong- 
 er leuvses wlien walking. Many also com- 
 plain of the straight or curved line to be 
 always found in the bifocal lens. How- 
 ever, the manner of wearing double cor- 
 rections is largely a personal matter, and 
 each case must be decided on its individ- 
 ual merits. 
 
 Case II. Simple Hypermetropic Astigmatism, 
 complicated with presbyopia. 
 
 Miss T., age 60 years: 
 
 E. E. V. = tl w. -I- 2.25 D. cyl. ax. 90« =- 
 
 20 
 2 U« 
 
 L. E. y. = f^ w. -1-2.25 D. cyl. ax. 90° = 
 
 2 
 20* 
 
 This correction rendered her eyes 
 emmetropic, and at 60 years of age the 
 presbyopia generally requires a 3 D., so 
 with a -r- 3 D. added, she can read No. 1 
 Jager at about 16 inches, a point I deem 
 sufficiently close for ordinary working- 
 purposes. This lady preferred the two 
 pairs in separate frames, so I prescribed 
 the above formula for distance, and the 
 
170 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 same with a ^- 3 D. S. added for her pres- 
 byopia as follows: 
 
 -I- 3 D. S. C w. -1-2.25 D. cyl. ax. 90° for 
 both eyes. 
 
 Case III. Hypermetropia and Astigmatism, or 
 Compound Hypermetropic Astigmatism, 
 complicated with presbyopia. 
 
 Miss C, age 63 years : 
 
 TffTT 
 
 I- 1.25 D. S. C -1- 111 
 D. cyl. ax, 15° = ||. 
 L. E. V. = ^ w. -I- 1.25 D. S. C -I- ID 
 cyl. ax. 165° = ||. 
 
 The above correction rendered her 
 eye practically emmetropic, so all we 
 have to do is to calculate what glass she 
 will need to correct her presbyopia, and 
 at 63 years, we would expect that she 
 would require something more than 3 D., 
 so by testing for No. 1 Jager at 16 inches, 
 we find it requires a -^ 3.25 D. over the 
 above correction for distance; so we must 
 add this on to the above spherical to get 
 her reading glasses, and we find that 3.25 
 D.S. —1.25 D.S. = 4.50 D.S., so we must 
 have for her reading formula the follow- 
 ing: 
 
ILLUSTRATED CASES. 171 
 
 E. -I- 4.50 D. S. C -I- l.ll'D. cyl. ax. 15«. 
 L. -I-4.50D. S. C-l-l.OOD. cvl. ax. 165«. 
 
 while for her distant correction, we pre- 
 scribed the combination we found neces- 
 sary to restore her eyes to a condition of 
 emmetropia, as given above. 
 
 Case IV. Simple Myopia, with presbyopia. 
 Mr. S. : age 51 years. 
 
 E. E. V. = II w. — 1.00 D. S. = fl 
 
 L. E. V. = Uw. — 1.00 D. S. 
 
 2.0 
 20 
 
 This man being myopic 1 D., it will 
 put off his presbyopia at least five years, 
 and as evidence we do not find him seek- 
 ing aid for his eyes for close work until 51 
 years old, instead of at 43 or 45, as is the 
 case with an emmetrope; ordinarily, at 
 50 an emmetrope will require about 2 D. 
 for presbyopia, but as the myopia com- 
 pensates for 1 D., we find all he will re- 
 quire to correct his presbyopia is a convex 
 lens of 1 D., which we prescribe with sat- 
 isfaction. 
 
172 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 Case V. Simple Myopic Astigmatism, complicat- 
 ed with presbyopia, 
 
 ''a." '^With the rule." 
 
 Mrs. M. S., age 49 years: 
 E. E. V. = fo w. — 1.25 D. cyl. ax. 180° = 
 
 2 
 
 L. E. V. = fo- w. — 1.25 D. cyl. ax. 180° = 
 
 2 
 2 
 
 You will see that this lady is emme- 
 tropic in one meridian and myopic in the 
 other. She will begin to be presbyopic in 
 the emmetropic meridian shortly after 
 forty, and at fifty will need 2 D. to correct 
 the presbyopia in this meridian; but in 
 the myopic meridian she will not begin 
 to get presbyopic for at least five years 
 later, so it will never do to give her the 
 same correction in both meridians, so we 
 must give her 1 D. to corn ct her myopic 
 meridian and 2 D. to correct her emme- 
 tropic meridian. This can only be done 
 by combining sj^herical and cylindrical 
 lenses together, and a little reflection 
 will show what combination you will 
 need for reading glasses, which is as fol- 
 lows: 
 
ILLUSTRATED CASES. 173 
 
 K. -1- 1 D- S. C -I- 1 r>. cyl. ax. 90°. 
 L. -I - 1 D. S. C -I - 1 D. cyl. as. 90°. 
 
 "b." "Against the rule.'' 
 
 Mr. C, age 55 years: 
 
 R. 20 ^. _ 2 D. cyl. ax. 90« = U- 
 L. 20 ^, __ 2 D. cyl. ax. 90° = |^. 
 
 This man is only presbyopic in the 
 vertical meridian, as two dioptres of my- 
 opia Avill postpone his presbyopia for ten 
 years, but we find him slightly presbyopic 
 in this meridian, as he is 55 years old, so 
 we find that we shall have to correct each 
 meridian separately, as in a former case. 
 Xow in the vertical meridian he will re- 
 quire two and a half dioptres, while in 
 the horizontal we find he will not require 
 more than half a dioptre. By testing each 
 eye with No. 1 Jager, we find that this is 
 just what he does require for his close 
 work, so we prescribe the following for- 
 mula for both eyes: 
 -I- .55 D. S. C -I- '-^ D- cyl. ax. 180°. 
 and we find that our patient, who, by the 
 way, is a busy merchant, and uses his 
 eyes a great deal at his books, has little or 
 no trouble with his eyes. I insisted on his 
 wearing his distant correction all the 
 
 15 
 
174 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 time when not usinii" his eyes for close 
 work. 
 
 Case YI. "c." "Between the rule." 
 
 J. E., age 45 years: 
 
 E. II w. — .55 D. cyl. ax. 135o = f|. 
 
 w. — .67 D. cyl. ax. 45o = |o. 
 
 This man is only presbyopic in his 
 emmetropic meridian, so he will require 
 a cylindrical correction alone; and as the 
 presbyopia is always at right angles to 
 the myopic astigmatism, we find that he 
 accepts with perfect correction of his 
 slightly advanced presbyopia, the follow- 
 ing: 
 
 R. -I- 75 D. cyl. ax. 45°. 
 L. -I- 75 D. cyl. ax. 135°. 
 
 Correcting the presbyopia in the 
 more advanced cases of myopia, will only 
 require a reduction in the strength of the 
 concave spherical lens necessary to cor- 
 rect their distant vision. For further in- 
 formation on this point, I refer you to the 
 chapter on myopia and its correction. 
 
ILLUSTRATED CASES. 175 
 
 Muscular Deficiencies : 
 
 Case I. Miss E. 31., age 22 years, saleslady, com- 
 plained of asthenopia and headache, be- 
 sides various other nervous manifesta- 
 tions. 
 
 R. E. V. f^ -|- no improvement with glasses. 
 L. E. Y. f^ -|- no improvement with glasses. 
 
 Ophthalmoscope showed normal, 
 healthy fundus, refraction emmetropic. 
 
 Muscle tests showed the following: 
 
 Adduction, 8°. 
 Abduction, lO^. 
 Exophoria, 4°. 
 
 I advised a tenotomy of the external 
 recti, but it was refused. I then pre- 
 scribed a prismatic lens 1|°, base in, over 
 ■ both eyes, to be worn -all the time. That 
 is nearly three years since, and though I 
 have often met her, she has never com- 
 plained of her eyes, more than to say that 
 she could not go without her glasses for 
 any length of time without a return of the 
 eye-strain. It is always best, when prac- 
 tical, to prej>cribe prisrn in a well adjust- 
 ed, comfortably fitting riding boAv spec- 
 tacle frame. 
 
176 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 Case II. Mrs. S., age 31 years, complained of pain 
 in her eyes and blurring, as well as severe 
 headache and many other nervous symp- 
 toms. 
 
 R. E. V. 1^. No improvement with glasses. 
 L. E. y. |-^. No improvement with glasses. 
 
 Muscle test showed: 
 
 Adduction, 14°. 
 Abduction, 9°. 
 Circumduction, 3°. 
 Exophoria, 5°. 
 
 Advised tenotomy of external recti, 
 but refused. Prescribed 2° prism, base 
 in, to be worn all the time, with almost 
 complete I'elief of the asthenopia while 
 wearing the glasses. I met this lady some 
 time afterwards, Avhen she said she was 
 under eternal obligation to me for having 
 so readily relieved her of her horrible 
 headache, from which she had suffered 
 so long and had spent so much money 
 trying to get rid of, by doctoring and tak- 
 ing all sorts of headache medicines with- 
 out effect. 
 
ILLUSTRATED CASES. 177 
 
 Case III. Hyper-exophoria. 
 
 Mrs. M., age 46 years. 
 
 R. E. V. 1^. No improvement with glasses. 
 L. E. Y. f^. No improvement with glasses. 
 
 This woman was referred to me by 
 her brother, a physician in good standing 
 and large practice. She was an exceed- 
 ingly nervous lady, a confirmed neiires- 
 thenic, w^as prematurely gray and aged, 
 had had severe headaches for years back, 
 had undergone an operation for uterine, 
 or ovarian trouble, in hopes of getting re- 
 lief, without avail. 
 
 Muscle test showed the following 
 condition: 
 
 Adduction, 8°. 
 Abduction, 14°. 
 Exophoria, 5°. 
 Hyperphoria, 2°. 
 
 Advised an operation, which she ac- 
 cepted. Cut both external recti within a 
 few days of each other, as she lived some 
 distance and was anxious to get home. 
 Have only heard from her once, when she 
 reported herself very much better in ev- 
 ery possible way. 
 
178 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 Case III. Mrs. P., age 30 years, complained of eye- 
 strain. 
 
 B. E. V. 1^. No improvement with glasses. 
 L, E. V. f^. No improvement with glasses. 
 
 Ophthalmoscope showed normal 
 fundus and emmetropic refraction. 
 
 Muscle test showed: 
 
 Adduction, 24°. 
 Adbuction, 0°. 
 Circumduction, 3°. 
 
 This woman showed an esophoria of 
 2°, notwithstanding the muscle power ap- 
 peared pretty well distributed. I pre- 
 scribed a -JO prism, base out, with consid- 
 erable benefit; and, as she says, with a re- 
 lief of all her asthenopia. 
 
 Case IV. Mrs. K., age 26 years, complained a great 
 deal of her eyes and headache. 
 
 R. E. V. ff . No improvement with glasses. 
 L. E. V. ff . No improvement with glasses. 
 
 Ophthalmoscope showed a healthy 
 and emmetropic eye. 
 
ILLUSTRATED CASES. 179 
 
 Muscle test showed: 
 
 Adduction, 20°. 
 Abduction, 4°. 
 Esophoria, 3°. 
 
 Prescribed a 1° prism, base out, with 
 marked improvement. 
 
 I think we have given a sufficient number of 
 examples of the different refractive errors and the 
 different muscular insufficiencies, to serve our pur- 
 pose of showing how these cases run in practice, as 
 well as the methods adopted in correcting them. 
 These sami)le cases have been selected from our 
 
 case book, with only one object in view, and that 
 to illustrate the particular form of difficulty under 
 consideration. Of course, we might continue this 
 ad infinitum, but we do not deem it necessary. 
 
 Now, in regard to prescribing what particular 
 kind of frame each case should wear, there is one 
 thing you should always insist on, and that is, for 
 cylindrical and prismatic lens always try to have 
 them wear a well-fitted and perfectly centered 
 spectacle frame. If they will not do this, as is of- 
 ten the case, then the only alternative is the offset 
 nose glass, which will many times do as well. 
 
 In the cases of latent hypermetropia that re- 
 quire the use of a mydriatic, (which are drugs that 
 dilate the pupil and paralyze temporarily the ac- 
 
180 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 tion of the ciliary muscle, thus counteracting any 
 spasm of the accommodation,) the most frequently 
 used is a solution of atropine sulphate, 4 grains to 
 the ounce of distilled water, 1 or 2 droiDS, instilled 
 into the eye every four hours for three days, gener- 
 ally suffice. It takes at least twelve days, and of- 
 ten longer, to recover from the use of this drug, 
 hence it is very objectionable for this purpose, 
 H^'oscyamine is used for this purpose, also, in the 
 strength of two grains to the ounce of water. The 
 effect lasts from seven to ten days. Perhaps the 
 best drug for this purpose, but the most expensive, 
 is a solution of eight grains to the ounce of water> 
 of homatropine. One drop of this solution in each 
 eye every fifteen minutes for an hour and a half be- 
 fore examining, is usually sufficient, and the ef- 
 fects of this drug pass off in about four days' time. 
 
 In these cases of muscular insufficiencies, just 
 cited, you will observe that the vision in each case 
 was normal, or in other words, that the eyes were 
 emmetropic. This is by no means always the case, 
 as in the great majority of cases of muscular insuf- 
 ficiency, some error in refraction is found, and 
 there is one thing to be borne in mind, and that is, 
 always correct your refractive error of whatever 
 variety, fully and completely, before testing for 
 muscle trouble. Many cases where a refractive er- 
 ror is found to exist, together with a deficiency of 
 
ILLUSTRATED CASES. 181 
 
 muscular co-ordination, all that will be found ne- 
 cessary is to correct the error, when the muscular 
 equilibrium will be sufficiently restored, to remove 
 all causes of asthenopia. 
 
CHAPTER XIV 
 
 Diseases aucl Therapeutics of the Eye, 
 
 It was not our original intention to say any- 
 thing in regard to the diseases of the eye and their 
 treatment, but after considering the matter pro 
 and con, we have concluded to add a chapter on 
 this subject, believing that it will not be amiss in 
 a little work of this kind. In doing this, we shall 
 ha^e to abandon the catechismal plan that we 
 have adojDted in the preceding chapters, as it 
 would be difficult to adhere to that method with- 
 out going into the subject too deeply. 
 
 Our aim shall be to simply point out the prin- 
 cipal characteristics of the more common diseases 
 of the different parts of the eye, with a few simple 
 suggestions in regard to their recognition and 
 treatment, as it is a matter of prime importance in 
 connection with refractive work to be able not only 
 to recognize, but diagnose inflammatory condi- 
 tions. 
 
 For the benefit of those of our readers who are 
 not physicians, we will say that the suffix "itis" 
 
 182 
 
DISEASES AND THERAPEUTICS OF THE EYE. 183 
 
 means inflammation, and wherever it is used in 
 connection with the name of any i3articular part of 
 the eye, it means an inflammation of that part; for 
 example, conjunctiyitis means an inflammation of 
 the conjunctiva, either of the eyes or lids or both. 
 Iritis means inflammation of the iris, while retin- 
 itis means inflammation of the retina. 
 
 There are three varieties of inflammation as 
 it occurs in the different parts of the eye as in oth- 
 er localities, namely : acute, sub-acute and chronic. 
 Acute inflammation of almost any part of the eye 
 is accompanied by pain, redness, or congestion, 
 photophobia, or a dread of the light, and lachry- 
 mation, or tearing of the eye. 
 
 Many patients suffering with a chronic in- 
 flammatory condition of the eyes are the victims 
 of refractive errors, and this must be carefully cor- 
 rected before we can expect to cure the inflamma- 
 tory condition, as many of these conditions are not 
 only caused by refractive error, but the asthenopia, 
 or eye-strain, tends to keep it up, and the first step 
 in the treatment of these cases is the removal of 
 the exciting cause by a proper correction of the 
 refractive error. This is especially true of ble- 
 pharitis marginalis, or inflammation of the lids, 
 with the formation of little crusts which mat the 
 cilia, or eye-lashes, together, and provoke a very 
 
184 REFRACTIVE AND 0PHTHAL31IC CATECHISM. 
 
 uncomfortable condition of affairs. This is also 
 true of hordeolum, or stye as it is called, and chal- 
 azion, as well as many recurring corneal inflam- 
 mations. 
 
 Many of these cases can be examined for the 
 purpose of determining their refractive condition 
 while still suffering from a low, or chronic, form of 
 inflammation; but there is one point which I wish 
 to impress upon your minds, and that is never sub- 
 ject an acutely inflamed eye to an examination for 
 the purpose of finding out whether or not it needs 
 a glass. This may seem an unnecessary warning, 
 but I have in mind the case of a lady who consulted 
 me for sore eyes. She told me that her eye had 
 been troubling her for four days, and that the day 
 previous she consulted an optician who told her 
 all she needed was a pair of glasses,after an exam- 
 ination which, she said, extended over an hour. 
 On looking at her eye I found her suffering from a 
 severe attack of acute iritis, and how much she suf- 
 fered during that previous examination can be bet- 
 ter imagined than described. 
 
 The use of the ophthalmoscope or other re- 
 flected light should also be studiously avoided dur- 
 ing an acute attack of inflammation, except when 
 it is absolutely essential, as in acute glaucoma and 
 a few other conditions. 
 
DISEASES AND THERAPEUTICS OF THE EYE. 185 
 
 With these few general observations which 
 are intended for the optician, rather than the phy- 
 sician, we will pass to the consideration of the dif- 
 ferent diseased conditions, only, however, point- 
 ing them out in a general way, without any inten- 
 tion of treating them in a thorough or exhaustive 
 manner. 
 
 The first subject to engage our attention is in- 
 flammatory condition of the eye-lids. As being- 
 appendages of the eye and frequently the seat of 
 inflammation, it is incumbent on us not only to be 
 able to recognize them, but also to diagnose the 
 different forms. 
 
 The eye-lids are frequently the seat of deformi- 
 ties, such as turning out or an eversion of the 
 edges, called ectropion. This, however, is not so 
 frequent a condition as an inversion of the lids, or 
 entropion. The lids are frequently seen to droop 
 either from a redundancy of tissue or paralysis. 
 This is called ptosis. These conditions are only 
 amenable to surgical operations. The lids may be 
 the seat of abscess, or phlegmon which must be 
 treated as in other parts, by hot applications and 
 the knife as soon as it is in a condition to open. 
 Boils, or furuncles, may also occur, which must be 
 treated in like manner. 
 
 Stye, or Hordeolum, is a small boil on the mar- 
 gin of the lid generally, which must be treated by 
 
186 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 hot applications in form of poultices, or hot solu- 
 tions of boracic acid until they are in a condition 
 to open or break of their own accord, which fre- 
 quently they do. 
 
 Chalazion is a cyst of the Meibomian glands. 
 also called tarsal tumors. They are caused by the 
 closing- up of the mouth of these glands from 
 chronic inflammation generally. The treatment 
 generally consists in remoying them with the 
 knife, though the frequent application of a hot bo- 
 racic acid solution sometimes causes them to be 
 absorbed. 
 
 Blepharitis, as we haye seen, is a chronic in- 
 flammation of the edge of the lids. It is frequent- 
 ly caused by a refractiye error Ts4iich should al- 
 ways be corrected, when undertaking the treat- 
 ment of this trouble. A good ointment for this 
 condition is as follows : Yelloy\' oxide of mercury, 
 3 grs., ung. petroleum opt., 1 oz. (yaseline.) Aj)- 
 ply morning and night by rubbing well into the 
 edge of the lids. 
 
 Inflammation of the coujunctiya, or conjunc- 
 tiyitis, as it is called, is a frequent condition. It 
 exists in one of three forms generally. The mild 
 form, or catarrhal conjunctiyitis, or the more se- 
 yere form of a muco-purulent inflammation, or un- 
 der the still more severe form of purulent conjunc- 
 
DISEASES AND THERAPEUTICS OF THE EYE. 187 
 
 tivitis, generally infectious. There is also anoth- 
 er distinct form of conjunctivitis occurring in dif- 
 ferent degrees of severity and called granular con- 
 junctivitis, or granulated lids. The two mildest 
 forms, that is the catarrhal and muco-purulent 
 conjunctivitis, may be confined to the palpebral 
 conjunctiva alone, or may involve the ocular con- 
 junctiva also. It generally calls for some mild as- , 
 tringent application like alum pencil or weak solu- 
 tion of zinc sulphate, 2 grs. to the oz. of distilled 
 water, dropj)ed into the eye three times a day; or a 
 good eye-v>'ater may be made from the following 
 prescription : 
 
 Soda Bi borate, 10 grains. 
 Aqua camphora, 4 drams. 
 Aqua rosa, 4 drams. 
 
 One or two drops in the eye every four hours. 
 
 Purulent conjunctivitis, or ophthalmia, as it 
 is called, calls for the most intelligent and persist- 
 ent treatment. Atropine sulphate solution, 4grs. 
 to the oz., should be instilled into the eye at least 
 three times a day in all cases occurring in young 
 persons. This, how^ever, must be carefully handled 
 in elderly persons if used at all. Cold application 
 from ice must be kept constantly applied in the 
 first stages. Frequent and thorough cleansing 
 w^ith boric acid solution every hour, and nitrate of 
 
188 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 silver solutions, 5 grs. to the oz., must be carefully 
 brushed on the lids at least once a day. This must 
 be carefully done if there is any brasion of the cor- 
 neal tissue. The fellow eye, if not already in- 
 volved, must be carefully protected from infection, 
 as also the eyes of nurses or any one having any- 
 thing to do with it. 
 
 When this form of inflammation occurs in 
 the new-born, as it frequently does, it is called oph- 
 thalmia neonatorum. Granular conjunctivits oc- 
 curs in all degrees of severity, from a few sand-like 
 granulations of the lower lids to the most severe 
 form of lid deformities and blindness. It calls for 
 the most careful and persistent treatment, from 
 the application of weak astringent solution to the 
 scraping of the lids (curetting or grattage, as it is 
 called.) When the scar tissue resulting from se- 
 vere granulation, causes incurvation of the lids, it 
 is called trachoma, and this generally gives rise to 
 a disease of the cornea, as a result of irritation, 
 called pannus, which is caused by the development 
 of blood vessels in the cornal tissue. This is a very 
 unfortunate condition, and very often results in 
 total blindness. This condition generally occurs in 
 persons of a scrofulous nature, and their general 
 constitutional condition must not be overlooked in 
 the treatment. 
 
DISEASES AND THERAPEUTICS OF THE EYE. 189 
 
 The treatment of granulated lids must be 
 carefully and scientifically carried out. In mild 
 forms the alum pencil can be thoroughly applied 
 or the blue pencil (sulphate of copper) may be very 
 lightly applied after applying a solution of co- 
 caine, 4 grs. to the oz. This pencil must be handled 
 with great care if you wish to retain the confidence 
 of your patient. It is a very painful treatment and 
 must be used sparingly. Solutions of nitrate of 
 silver, 3 to 5 grs. to the oz.; sulphate zinc solutions, 
 2 grs. to the oz.; and many others may be used. 
 
 A good collyrium, or eye-water, is made in the 
 following manner: 
 
 Soda biborate, 10 grains. 
 Acid tannici, 10 grains. 
 Glycerine, 2 drams. 
 Aqua dist. q. s. ad. 1 oz. 
 
 One or two drops in the eye three times a day. 
 This, I believe, is , the late Dr. Agnew's formula. 
 For the further treatment of this condition, I must 
 refer you to the more exhaustive works on this sub- 
 ject, as we must be content with a general outline 
 only. 
 
 Catarrhal inflammation of the lids or extend- 
 ing up the nose, frequently results in a blocking up 
 of the lachrymal duct. This may remain in a 
 chronic condition, simply giving rise to obstruc- 
 
190 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 tion, which results in the tears flowing oyer the lids 
 onto the face, constituting a w^eeping, or tearing 
 eye, as it is called. It may result in an attack of 
 acute inflammation with the formation of pus, that 
 ma}' form a large swelling at the inner canthus of 
 the lid, or may discharge itself on the cheek. This 
 is a painful condition, and is called dacryocystitis. 
 This can generally be determined by pressing over 
 the lachrymal sac, ^\ hen the pus is discharged into 
 the eye. This is freqiiently the cause of a chronic 
 conjunctivitis, and must be corrected by incisions 
 into the sac and probing of the duct. The milder 
 forms can generally be corrected by treating the 
 catarrhal condition, and probing the puncta with 
 a small probe. In the severer forms, repeated 
 probing with a probe gradually increased in size, 
 is necessary after first opening it with a canalicu- 
 lus knife used for this purpose. P^equent injec- 
 tion by means of a lachrymal syringe and some- 
 times the introduction of a silver tube or wire is 
 necessary. I prefer the latter myself. 
 
 Inflammatory disease of the cornea, either 
 acute, sub-acute, or clironic, is very frequently met 
 with, and though the different forms of corneal 
 inflammation number a great many, they are all 
 known under the general head of keratitis, and we 
 shall endeavor to give a general description of the 
 varieties most frequently met with. 
 
DISEASES AND THERAPEUTICS OF THE EYE. 191 
 
 They are all eliaracterized by more or less 
 spasm of the eye-lid, dread of light, laehrymation, 
 pain and infiammation, not only of the cornea, but 
 of the ocular and palpebral conjunctiva as well. 
 
 Phlycteuaular keratitis is characterized by 
 the formation of one or more vesicles, or blister- 
 like imstiiles on the cornea, generally at its junc- 
 tion with the sclera, though they may be at any 
 other part of the cornea. It is essentially a disease 
 of childhood, but may occur in the adult. The 
 treiftment consists in washing the eye frequently 
 with a boric acid solution, 1 dram to the pint, and 
 the instillation of a solution of atropine, 2 grs. to 
 the oz., to overcome the blephorospat^m, and ciliary 
 spasiii, usual in these cases. An ointment of yel- 
 low oxide of mercury, not stronger than 4 grs. to 
 the oz., may be used inside the lids, or the follow- 
 ing combination can be us-ed in the form of an oint- 
 ment three times a day: 
 
 Atropine sulphate, 2 grs. 
 
 Yellow oxide of mercury, 3 grs., and 
 
 Vaseline, 1 oz. 
 
 This must be thoroughly mixed or you will get 
 considerable smarting after using it. 
 
 The general health of the patient must be 
 carefully looked after, as they are usually strum- 
 ous, and the syrup of the iodide of iron in doses 
 
193 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 from 5 to 20 drops, according to the age, may be 
 given, well diluted in Avater, after each meal. 
 
 Ulcerative keratitis occurs in several forms in 
 poorly-fed and strumous patients. The local treat- 
 ment is about the same as in phlyctenular kerati- 
 tis, special attention being paid to the general 
 health. These ulcers may, however, occur at auy 
 age, and in elderlj^ persons atropine must be care- 
 fully j)rescribed for fear of any glaucomatous 
 complications. 
 
 Hypopyon keratitis, is keratitis in which pus 
 forms and falls to the most dependent part of the 
 anterior chamber of the eye. This is generally ab-' 
 sorbed, though it may be necessary to evacuate by 
 means of the knife. Hot applications assist in ab- 
 sorbing this pus, but poulticing must be avoided, 
 as it ma}' do much injury, and rarely, in any case, 
 much good. Hot boric acid solution will be found 
 to answer all i)urposes of this kind, or hot bichlor- 
 ide of mercury solutions, 1 to 10,000, may be used 
 instead. 
 
 Interstitial keratitis. This is a circumscribed, 
 or diffused, inflammation of the corneal tissue, not 
 usually accompanied by any ulceration, and the 
 character of the inflammation may be quite acute 
 or very low and chronic. It is, in a great majority 
 of cases, caused by syi^hilis, either inherited or ac- 
 
DISEASES A^^D THERAPEUTICS OF THE EYE. 193 
 
 quired. It may inyolve only a part of the cornea, 
 or continue until the whole cornea is involved. The 
 cornea becomes hazy if not opaque, and total blind- 
 ness may result. It is most frequent in young life. 
 The treatment is princix3ally constitutional; mer- 
 cury and iodide of potash, cod liver oil, iron, etc. 
 Irritating applications must be avoided. They gener- 
 -ally get well under jDroper constitutional treat- 
 ment, but it requires a long time to fully recover. 
 
 As a result of many of these corneal inflam- 
 mations, scars or small opacities, are left on the 
 cornea, and if they be central, or over the pupil, 
 may. interfere ^-^ery materially with vision. When 
 they are not over the puinl, they may be a cause of 
 irregular astigmatism. It is these opacities on the 
 cornea that are frequently called cataracts by the 
 laity, and they will call on you many times to have 
 them removed, as if it were a simple matter. These 
 slight opacities, or scars, can be nicely seen by 
 oblique illumination, which consists in condens- 
 ing with a convex lens the light on the cornea, the 
 source of illumination being to the side of the pa- 
 tient. 
 
 Little spots on the cornea that can hardly be 
 detected by the ordinary method, can be readily 
 seen in this way. 
 
194 REFRACTIVE AXD OPHTHALMIC CATECHISM 
 
 Iritis, or inflammation of the iris, is frequent- 
 ly met with as a result of rheumatism, syphilis, 
 and other causes, and should be recognized in the 
 very beginning. There is inflammation of the cor- 
 junctiva, a tortuous condition of the blood vessels 
 in the ocular conjunctiva, pain over the eye, ex- 
 tending to the side of the head, many times. The 
 pupil is generally small, and there is great dread 
 of the light, as well as lachrymation. By having 
 the j)atient look down and gently pressing with the 
 tips of your index fingers, a very tender spot will 
 always be found at about the upper edge of the 
 cornea. This is almost characteristic of iritis, and 
 should be always looked for when this disease is 
 suspected. 
 
 The local treatment of iritis is atropine first, 
 last, and always, and it should be used in the very 
 beginning before any adhesion takes place be- 
 tween the iris and the anterior capsule of the lens. 
 When this does occur, they should be broken up 
 by the use of atropine, if possible. Generally a so- 
 lution of 4 grs. to the oz. is sufficient, used every 
 two hours, if necessary. Boric acid solutions can 
 also be used, as well as any constitutional treat- 
 ment indicated. These cases should be recognized 
 in the beginning, as in that way you can often save 
 your patient a long siege of suffering. Of course, 
 it is necessary to protect the eyes from strong 
 
DISEASES AND THERAPEUTICS OF THE EYE. 195 
 
 lights, but do not bandage the eye up too much, as 
 it does better when having good ventilation. Nev- 
 er use poultices in iritis. Sometimes it is neces- 
 sary to use eserine from time to time, in these 
 cases, and when occurring in elderly persons, the 
 atropine must be closely watched, for there is al- 
 ways the probability of its being complicated by 
 glaucoma. 
 
 Diseases of the crystalline lens, such as lenti- 
 cular opacities, or cataractous metamorphosis, can 
 be readily detected by means of the ophthalmo- 
 scope, and as very little practice is all that is ne- 
 cessary, we shall not enter into a description of its 
 use, but refer the reader to the chapter on the use 
 of the ophthalmoscope. Opacities of the vitrious 
 humor and disease of the retina and optic nerve 
 are also to be detected with the ophthalmoscope. 
 
 There is one other diseased condition of the 
 eye to which I shall call your attention, and which 
 it is absolutely essential that every person having 
 anything to do with the eye should be able to di- 
 agnose, as an early recognition may be the only 
 means of saving your patient's eye-sight. I refer 
 to glaucoma, or an increased hardness of the eye- 
 ball, caused by a blocking up of its excretory ca- 
 nal. This condition of glaucoma may exist in any 
 one of three forms. It may be acute, sub-acute, or 
 chronic. The intra-ocular tension may be slight, 
 
196 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 SO as to be scarcely recognizable by the tips of 
 your index fingers pressed gently onto the globe of 
 the eye; or it may be very hard. This is an impor- 
 tant symptom. The pnpil is generally dilated and 
 does not respond readily to light. The lens is 
 pressed forward into the anterior chamber of the 
 eye, rendering it shallow. There is generally a 
 partial loss of transparency of the cornea. The 
 pressure behind produces a cupping of the nerve- 
 head, seen with the ophthalmoscope, and the blood 
 vessels climb over the edge of the disk,and are seen 
 to pulsate. The field of vision, as measured by the 
 perimeter, is contracted, though central vision 
 may be good at the time of examination. The 
 cornea is not nearly as sensitive as in health, and 
 one of the characteristic signs is what is called 
 iridescent vision, that consists in a colored halo 
 surrounding artificial lights. This point should 
 always be borne in mind. 
 
 There is always more or less pain, according 
 to the acuteness of the attack, and the invasion of 
 the disease may be so severe as to destroy the sight 
 in twenty-four hours; hence the necessity of re- 
 cognizing it at once. There may be repeated at- 
 tacks of the sub-acute variety, and the chronic 
 form may last for years. It may be confined to one 
 eye or involve both, and is rarely seen before the 
 fortieth year. You must never use atropine or 
 
DISEASES AND THERAPEUTICS OF THE EYE. 197 
 
 other m^'driatic when you have any reason to sus- 
 jject glancoma, as this would only make it worse. 
 Eserine sulphate, 1 gr. to the oz., or muriate of 
 pilocarj^in, 2 gr. to the oz., may be instilled into the 
 eye every four hours, and hot boric acid solution 
 may be applied; but in many cases the only hope in 
 saving the eye rests in the early performance of 
 the operation known as iridectomy. 
 
 The destructive tendency of glaucoma ren- 
 ders it an alarming condition, and it is of the ut- 
 most imiDortance that it be early recognized in or- 
 der to give the patient the very best chance of re- 
 covery; hence the necessity of becoming familiar 
 with its early symptoms. 
 
 The ophthalmoscopic diseases of the eye we 
 shall not consider, as they are interesting, gener- 
 ally, only to the specialist who will not look to a 
 little work of this kind for information to be had 
 in any of the more complete works on diseases of 
 the eye. 
 
 A few words in regard to the removal of for- 
 eign bodies from the eye. It is always best to keep 
 on hand a 4 per cent, solution of cocaine for this 
 purpose. A few drops instilled into the eye will 
 render it anaesthetic, and you can manipulate 
 with the greatest ease and without hurting your 
 patient in the least, a very important matter, as 
 
198 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 far as tbev are concerned. It generally causes a 
 transitory dilatation of the pupil, but this will pass 
 away in a short time. Foreign bodies lodged on 
 the cornea can be remoyed by the means of a si)ud, 
 while those finding lodgment under the lids can 
 be remoyed by first eyerting the lids, and wiping 
 them off by means of a little cotton, wrapped on 
 the end of an ordinary applicator or tooth-i3ick. 
 Care must always be taken in remoying foreign 
 bodies from the cornea, not to injure the corneal 
 tissue but as little as possible, and your instru- 
 ment must always be clean, or you may infect the 
 wound, and produce a seyere corneal ulceration. 
 
GLOSSARY. 
 
 ACHROMATOPSIA— Inability to distinguish 
 colors. 
 
 ABDUCTION— The turning out of the eye-ball. 
 
 ADDUCTION— The turning in of the eye-ball. 
 
 ALBINISM — The absence of pigment in the iris 
 and choroid, as well as other parts of the 
 body. 
 
 AMAUBOSI^^— Loss or dimness of sight. 
 
 AMBLYOPIA — Same as Amaurosis. 
 
 ANAESTHESIA — Loss of sensation, either par 
 tial or complete. 
 
 ANISOMETROPIA— A different refractive con- 
 dition in each eye, either hyperopic or myopic. 
 
 ARCUS SENILIS— A ring formed around the 
 outer edge of the cornea, usually seen in old 
 age. 
 
 ARGYLL— ROBINSON PUPILS — Contracted 
 pupils found in spinal disease; pupils unaf- 
 fected by light, but contracting still more on 
 converging visual axes. 
 
 199 
 
300 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 ASTIGMATISM— A difference in the curvatiire 
 of tlie different meridians of the cornea or 
 lens. 
 
 ASTHENOPIA — Eye strain from any cause. 
 
 BLEPHAEITIS— Inflammation of the edge of the 
 eye-lids. 
 
 BLIXD SPOT, MAERIOTTS— A spot on the reti- 
 na corresponding with the entrance of the op- 
 tic nerve. 
 
 CATAEACT — An opacity of the crystalline lens. 
 
 CENTEAD— Standard used by Dr. Dennett for 
 measuring prisms. 
 
 CHALAZIOX— A little humor on the lids; also 
 called tarsal tumors. 
 
 CHEMOSIS — A swelling of the conjunctiva, gen- 
 erally the result of disease. 
 
 CHOEOID — The middle coat or tunic of the eye- 
 ball. 
 
 CHOEOIDITIS— Inflammation of the choroid. 
 
 CIOATEIX — Scars from any cause. 
 
 CILIAEY BODY— Formed by the union of the cil- 
 iary processes. 
 
 COLOBO^NFA — A displaced pupil, either congeni- 
 tal, or the result of injury or operation on the 
 iris. 
 
 COLOE BLINDNESS— Same as Achromatopsia. 
 
GLOSSARY. 201 
 
 CONJUNCTIVA — [Mucous membrane covering 
 the eye-ball in front and the inside of the eye- 
 lids. 
 
 CONJUNCTIVITIS— Inflammation of the con- 
 junctiva. 
 
 CORNEA — Anterior portion and transparent part 
 of the eve-ball. 
 
 CORNEAL LOUPE — A strong convex lens used 
 to examine the cornea. 
 
 CYCLITIS — Inflammation of the ciliary body. 
 
 DACRYOCYSTITIS— Inflammation of the lach- 
 rymal sac and nasal duct. 
 
 ])AY BLINDNESS— Inability to see clearly on 
 bright days, or in a bright light. 
 
 DIOPTRE — A lens having a focal distance of one 
 metre: 39.36 inches. 
 
 DIOPTRIC SYSTEM— Method of numbering 
 lenses, according to the dioptre. 
 
 DIPLOPIA — Double vision; seeing two objects. 
 
 ECTROPION — A turning out or an eversion of 
 the eye-lids. 
 
 EMMETROPIA— A condition of refraction re- 
 garded as normal, 
 
 ENTROPION — An inversion or turning in of the 
 eve-lids. 
 
20-3 REFRACTIVE AXD OPHTHALMIC CATECHISM. 
 
 EXUCLEATIOX— Removal of the eve-ball. 
 
 EPIPHORIA — An overflow of tears, a "weeping" 
 or "tearing'- eye. 
 
 ESOPHORIA— A tendency of the eyes to turn in 
 from the visual line. 
 
 EXOPHORIA— A tendency of the eyes to turn 
 out from the visual line. 
 
 EX0PHTHAL:MUS— A protrusion of the eyes 
 from their orbits. 
 
 FAR POINT— The greatest distance at which an 
 eye can see clearly without the aid of glasses. 
 
 GLAUCOMA — A disease of the eye that consists 
 in a hardening of the eye-ball from increased 
 intraocular tension. 
 
 GLATTOMATOUS RING— A cupping or depres- 
 sion of the nerve head seen with the ophthal- 
 nifiscope in glaucoma. 
 
 GRAXULAR LIDS— Granular conjunctivitis. 
 
 11 EMI AXOPSI A— Blindness involving one-half 
 the field of vision, either in one or both eyes. 
 
 HEMIOPIA— See Hemianopsia. 
 
 HETEROPHORIA--A lack of muscular equili- 
 brium of the eyes. 
 
 HYPER:METR0PIA— A refractive condition of 
 the eye, in which the principal focal point of 
 the eve is behind the retina. 
 
GLOSSARY. 203 
 
 HYPERPnOEIA— A tendency of the eyes to turn 
 above the visual line. 
 
 HYPOPYON — A collection of pus in the anterior 
 chamber of the eye. 
 
 nORDEOLU3I— See stye. 
 
 lEIS — A diaphram separating the crystalline lens 
 from the anterior chamber of the eye, and 
 regulating the amount of light admitted into 
 the eye. 
 
 IRITIS— Inflammation of the iris. 
 
 KERATITIS— Inflammation of the cornea. 
 
 KERATOSCOPE— An instrument for observing 
 corneal astigmatism or other corneal irregu- 
 larities. 
 
 LENS — A ]Diece of glass or other transparent sub- 
 stance, ground into various shape and used to 
 change the course of rays of light. 
 
 MACCLA LUTE A— The central part of the reti- 
 na where images are ordinarily formed. 
 
 MARRIOTT'S SPOT— See blind spot. 
 
 MEDIA — The refracting parts of the eye: Cornea 
 aqueous humer crystalline lens and vitrious 
 humer, 
 
 MEIBOMIAN GLANDS— Small gland found on 
 the inside of the eye-lids. 
 
204 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 IMUSCAE YOLITA:NTEvS— Floating bodies or 
 black spots before the eyes. 
 
 MYDRIASIS— Dilation of the pupil. 
 
 MYDRIATICS— Drugs that cause a dilatation of 
 
 the pupil. 
 
 MYOPIA — A refractive condition of the eye in 
 which the principal focal point of the eye lies 
 anterior to the retina. 
 
 MYOTICS — Drugs that cause a contraction of the 
 pupil. 
 
 MYOSIS— A contraction of the pupil. 
 
 NEURITIS— Inflammation of a nerve. 
 
 NIGHT BLINDNESS— A functional disease of 
 the retina. 
 
 NYSTAGMUS— An involuntary movement of the 
 ele-balls, oscillatory in character and usually 
 from side to side; usually seen in albinism. 
 
 OPHTHAL]\riA— Inflammation of the conjunc- 
 tiva. Conjunctivitis. 
 
 OPHTHALMITIS— Inflammation of the eye-ball 
 as a whole. 
 
 OPHHTALMOMETRE— An instrument for meas- 
 uring the diameters of the eye. 
 
 OPHTHALMOPLEGIA— Paralysis of the mus- 
 cles of the eye-ball. 
 
GLOSSARY. 205 
 
 OPHTHALMOSCOPE— An instrument for exam- 
 ining the interior of the eye, to determine its 
 condition as to health and refraction. 
 
 is 
 
 OPTIO AXIS — An imaginary line passin 
 through the center of the cornea and lens 
 from an object to the posterior pole of the eye- 
 ball. 
 
 OPTIC DISK— The entrance of the optic nerve. 
 
 OPTOMETER — An instrument for measuring the 
 refraction of an eye. 
 
 ORBIT — The bony cavity in which the eye-ball is 
 located. 
 
 ORTHOPHORIA— A normal equilibrium of the 
 ocular muscles. 
 
 PERIMETRE — An instrument for measuring the 
 field of vision. 
 
 REFRACTION— A bending of rays of light as 
 they pass from one medium to another of dif- 
 ferent density. 
 
 RETINA — The inner coat or tunic of the eye; the 
 sensitive layer. 
 
 RETINITIS— Inflammation of the retina. 
 
 RETINOSCOPE — An instrument for determining 
 the refraction of the eye, by reflecting light 
 from a given point into the eye and observing 
 
206 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 its movement, as the retinoscope is moved 
 slightly on its different axes. 
 
 SCLEKA— The external coat of the eye. 
 
 SCLEBITIS— Inflammation of the sclera. 
 
 SHADOW TEST— See retinoscope. 
 
 SKIASCOPY— See retinoscope. 
 
 SQUINT— Strabismus. 
 
 STKABISMUS— Deviation of the eye from the 
 visual angle, either in (internal strabismus) 
 or out (external strabismus.) 
 
 STAPHYLOMA OF THE CORNEA— A projec- 
 tion of the anterior chamber of the eye, by 
 rupture of some of the corneal tissue, usually 
 the result of disease. 
 
 STAPHYLOMA POSTERIOR — A drawing 
 away of the retina from about the optic nerve 
 disk. Generally crescent shaped and results 
 from disease or high degrees of myopia. 
 
 STYE — A little boil on the eye-lid; also called 
 hordeolum. 
 
 SYNECHIA POSTERIOR— An attachment of 
 the posterior surface of the iris to the anter- 
 ior capsule of the crystalline lens, caused us- 
 ually by iritis. 
 
 TENOTOMY— The operation of cutting the ocu- 
 lar muscles for squint or other purposes. 
 
GLOSSARY. 207 
 
 TEST LETTERS— Series of letters of a certain 
 size and shape, used to test the acuteness of 
 vision. 
 
 TENSION OF THE EYE— Term used to denote 
 the hardness of the eye-ball. 
 
 YELLOW SPOT— The macula lutea, or point 
 where images are formed on the retina. 
 
INDEX. 
 
 A. 
 
 Abscess of lids 185 
 
 Abductive power of eye 180 
 
 Accommodation of eye 35 
 
 Accommodation, range of 34 
 
 Accon'modation, power of 34 
 
 Accommodation, loss of 38 
 
 Accommodation, spasm of 45 
 
 Adductive power of eye 180 
 
 Ametropia 41 
 
 Amblyopia ex.-anopsia 145 
 
 Anatomy of the eye 9 
 
 Anisometropia 56 to 163 
 
 Artery carotid 16 
 
 Arteria centralis retinae 16 
 
 Artery ophthalmJc 16 
 
 Asthenopia 41 
 
 809 
 
210 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 Astigmatism 58 
 
 Astigmatism, causes of 58 
 
 Astigmatism, kind of 58 
 
 Attigraatism, frequency of 60 
 
 Astigmatism, regular 58 
 
 Astigmatism, irregular 58 
 
 Astigmatism, simple hypermetropic 59 
 
 Astigmatism., simple myopic 59 
 
 Astigmatism, compound hypermetropic 59 
 
 Astigmatism, compound myopic 59 
 
 Astigmatism, mixed 59 
 
 Astigmatic chart. Green's 63 
 
 Atropine sulpha^te ISO 
 
 B 
 
 Blepharitis marginalis 186 
 
 Blind spots 155 
 
 Blind spot of Marriotte 155 
 
 Blood vessels of the retina 85 
 
 Blue pencil 189 
 
 Boils 185 
 
 Bright's disease 84 
 
 C 
 
 Canthus 13 
 
 Camera obscura 16 
 
 Centrad 27 
 
 Chalazion ' 186 
 
 Choroid 11 
 
 Choroiditis 51 
 
 Choroido retinitis 156 
 
 Ciliary processes 11 
 
 Ciliary muscle , , 12 
 
 Conjunctiva 13 
 
INDEX. 211 
 
 CoFijunctiva, ocular .< 13 
 
 Conjunctiva, palpebral 13 
 
 Conjunctivitis 186 
 
 Conjunctivitis, catarrhal 186 
 
 Conjunctivitis, muco purulent 186 
 
 Conjunctivitis, purulent 186 
 
 Conjunctivitis, granular 187 
 
 Copper sulphate 189 
 
 Crystaline lens, diseases of 195 
 
 Cupping of the nerve head 196 
 
 Curetting 188 
 
 D 
 
 Dacryocystitis 190 
 
 Diabetis 84 
 
 Dioptric media 12 
 
 Dioptre 25 
 
 Dioptric system 25 
 
 Dioptric table 26 
 
 Diplopia 131 
 
 Diplopia, monocular 132 
 
 Diplopia, vertical 131 
 
 Diseases of the eye 182 
 
 Double vision 131 
 
 B 
 
 Ectropion 185 
 
 Entropion 185 
 
 Emmetropia 39 
 
 Emmetropic eye 40 
 
 Eserine sulphate 197 
 
 Esophoria 138 
 
 Eversion of the lids 185 
 
 Exophoria 138 
 
212 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 Eye strain 41 
 
 Eye water, Agnew's 189 
 
 P 
 
 Far-sightedness 42 
 
 Field of vision 150 
 
 Field of vision, how obtained 153 
 
 Fovae centralis retinae 17 
 
 Foreign bodies in eye 197 
 
 Foreign bodies, removal of 197 
 
 French method of numbering lenses 25 
 
 Furuncles 185 
 
 G 
 
 Glaucoma 156, 188, 195 
 
 Glaucoma, acute 195 
 
 Glaucoma, sub-acute 195 
 
 Glaucoma, chronic 195 
 
 Glaucoma, treatment of 197 
 
 Glossary 199 
 
 Granulated lids 187 
 
 Grattage 188 
 
 H 
 
 Homatropine 180 
 
 Hordeolum 185 
 
 Hyoscyamine 180 
 
 Hypermetropia 39 
 
 Hypermetropic eye 41 
 
 Hypermetropia, cause of 43 
 
 Hypermetropia, kinds of 43 
 
 Hypermetropia, axial „ 43 
 
 Hypermetropia, curvature 43 
 
 Hypermetropia, manifest 43 
 
INDEX. 213 
 
 Hypermetropia, latent 43 
 
 Hypermetropia, total 46 
 
 Hypo-phoria 138 
 
 Hypo-esophoria 138 
 
 Hypo-exophoria 138 
 
 Index of refraction 18 
 
 Index of refractive media 1& 
 
 Index of dioptric media . . . ; 19 
 
 Inversion of the lids 185 
 
 Iris 12 
 
 Iritis 194 
 
 Iritis, treatment of 194 
 
 Iridescent vision 196 
 
 Iridectomy 197 
 
 Jager type 34 
 
 K. 
 
 Keratoscope, Placido's 65 
 
 Keratitis 190 
 
 Keratitis, hypopyon 192 
 
 Keratitis, interstitial » 192 
 
 Keratitis, phlyctenular 191 
 
 Keratitis, ulcerative ■ 191 
 
 Lechrymation 191 
 
 Lachrymal gland 13 
 
 Lachrymal sac 14 
 
 Lenses 20 
 
214 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 Lenses, kinds of 20 
 
 Lenses, signs used for 21 
 
 Lenses, cylindrical 22 
 
 Lenses, cylindrical axes of 23 
 
 Lenses, meniscus 21 
 
 Lenses, periscopic 21 
 
 Lenses, spherical 22 
 
 M. 
 
 Macula lutea 17 
 
 Mad dock's test 143 
 
 Meibomian glands 14 
 
 Mercury oxide 191 
 
 Muscles of the ej^e 15 
 
 Muscular asthenopia 131 
 
 Muscular asthenopia, evidence of 136 
 
 Muscular deficiencies 175 
 
 Myopia 49 
 
 Myopic eye 49 
 
 Myopia, causes of 50 
 
 Myopia, frequency of 51 
 
 Myopia, indications of 51 
 
 Myopia, axial 50 
 
 Myopia, curvature 50 
 
 Myopia, correction of 50 
 
 N. 
 
 Nerves of the eye 16 
 
 Nerves, second or optic 16 
 
 Nerves, third or motor oculi 16 
 
 Nerves, fourth or trochlear 16 
 
 Nerves, sixth or abduceus 16 
 
 Nerves, cupping of optic 196 
 
INDEX. . 215 
 
 O. 
 
 Obpects distortion of 72 
 
 Opacities of the eye 193 
 
 Ophthalmia 187 
 
 Ophthalmoscopy 78 
 
 Ophthalmoscope 78 
 
 Ophthalmoscope, Loriiig's 79' 
 
 Ophthalmoscope, uses of 80 
 
 Ophthalmoscope, direct method of use 83 
 
 Ophthalmoscope, indirect method of use 84 
 
 Ophthalmoscope in emmetropia 89 
 
 Ophthalmoscope in hypermetropia 90 
 
 Ophthalmoscope in hypermetropic astigmatism 91 
 
 Ophthalmoscope in myopia 91 
 
 Ophthalmoscope in myopic astigmatism 94 
 
 Ophthalmometry 96 
 
 Ophthalmometre, Javal & Schiotz 97 
 
 Orbits of the eye 9 
 
 Orbicularis palpebrarum 10 
 
 Opticum dextrum 45 
 
 Opticum senistrum 45 
 
 Optic disk 52 
 
 Orthophoria 140 
 
 P. 
 
 Pannus 188 
 
 Papillitis 156 
 
 Perimetry 150 
 
 Perimeter, Skeel's 152 
 
 Perimeter charts 154 
 
 Phorometer, Wilson's 149 
 
 Phlegmon 185 
 
 Pilocarpine muriate 197 
 
216 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 Placido's keratoscope 65 
 
 Presbyopia 122 
 
 Presbyopia, cause of 123 
 
 Presbyopia, correction of 123 
 
 Presbyopia, when developed 123 
 
 Presbyopia, with ametropia 125 
 
 Presbyopia, with hypermetropia 125 
 
 Presbyopia, with astigmatism 127 
 
 Presbyopia, myopia delays 129 
 
 Prism dioptre 27 
 
 Puncta lachrymalia 14 
 
 Punctum proximum 34 
 
 Piinctum remotum 34 
 
 Pupil 12 
 
 Ptosis 185 
 
 R. 
 
 Refractive media 12 
 
 Refraction and lenses 18 
 
 Ref ractometer, DeZeng's 77 
 
 Retina 11 
 
 Retinoscopy 106 
 
 Retinoscopic mirror plane 107 
 
 Retinoscope in hypermetropia 110 
 
 Retinoscope in astigmatism 120 
 
 Retinoscope in myopia 110 
 
 Retinitis 156 
 
 Reversal point 114. 
 
 Retinal reflex 109 
 
 S. 
 
 Scars 193 
 
 Sclera 11 
 
 Scleritis 51 
 
INDEX. 217 
 
 Scotoma 155 
 
 Section of eye-ball 10 
 
 Second sight 57 
 
 Shadowiest 106 
 
 Silver nitrate : 189 
 
 Skiascopy 106 
 
 Skeel's perimeter 152 
 
 Snellen type 31 
 
 Strabismus 46 
 
 Strabismus, convergens 159 
 
 Strabismus, divergens 52 
 
 Staphyloma posterior 52 
 
 Stenopaeic slit 65 
 
 Stenopaeic slit, uses 66 
 
 Steven's system of nomenclature 138 
 
 Steven's phorometer 141 
 
 Steven's phorometer, directions 141 
 
 Steven's stenopaeic lens test 142 
 
 Stye 185 
 
 Squint 46 
 
 Suspensary ligament 11 
 
 T. 
 
 Tarsal tumors 186 
 
 Tearing eye 190 
 
 Tension of eye-ball 195 
 
 Test type, Snellen 30 
 
 Test type, Jager 34 
 
 Therapeutics of the eye 182 
 
 Trial case 29 
 
 Trial frame 33 
 
 V. 
 
 Visual angle 30 
 
 Visual acuteness 32 
 
218 REFRACTIVE AND OPHTHALMIC CATECHISM. 
 
 Visual acuteness, how obtained 32 
 
 Vision, binocular 52 
 
 Vision, double 52 
 
 Vitrious humor 11 
 
 W. 
 
 Walleston prism 98 
 
 Weeping eye 190 
 
 Wilson's phorometer 149 
 
 Y. 
 
 Yellow spot 17 
 
JUST ISSUED. 
 
 DHIL-EV'S 
 
 REFRACTIVE AND OPHTHALMIC CATECHISM 
 
 I=OR 
 
 01 
 
 Published by 
 
 The Collins Publishing Co., 
 
 Gloversville, N. Y. 
 
 Copies of this book can be obtained at the medical 
 book stores, of medical book agents, of the wholesale 
 optical houses, or will be sent prepaid by the ptib- 
 lishers on receipt of the regular price of two dollars. 
 
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