IMAGE EVALUATION TEST TARGET (MT-3) 1.0 1.1 Hi 1^ 10 18 I . . 1.25 1 1.4 |||.6 '- --'r ■.:'■-.'■ ' ' < 6" ► m VI ^1 7 w Photographic Sciences Corporation 23 WEST MAIN STREET WEBSTER, N.Y. 14580 (716)872-4503 f\ •^ ^"^^^ ^> <^.:^ (moaning "CON- TINUED"), or tha aymbol y (moaning "END"), whichavar appiiaa. Un daa aymbolaa auivanta apparattra aur la damlAra imaga da chaqua microficha, aalon la caa: la aymbola — »• aignifia "A SUiVRE", la aymbola y aignifia "FIN". Mapa, piataa, charta, ate., may ba filmad at diffarant raduction ratioa. Thoaa too iarga to ba antiraiy includad in ona axpoaura ara filmad baginning in tha uppar laft hand comar, laft to right and top to bottom, aa many framaa aa raquirad. Tha following diagrama illuatrata tha mathod: Laa cartaa, pianchaa, tablaaux, ate. pauvant Atra filmte i daa taux da rMuction diff Aranta. Loraqua la documant aat trap grand pour Atra raproiduit an un aau! ciichi, il aat filmA A partir da I'angia aupAriaur gaucha, da gaucha A droita, at da Iwut an baa, an pranant la nombra d'imagaa nAcaaaaira. Laa diagrammaa auivanta illuatrant la mAthoda. 1 2 3 1 2 3 4 5 6 I I ?li '1^ DR. OM£r 4. WOOO. IO*B>A4mmM.. THE FIELD OF MONOCULAR FIXATION AND ITS RELATION TO HETEROPHORIA. 4 R«m1 before (he flection on Ophthalmology et (he forty-seventh Anaaal Meellng of the American Medieal Aisoeiation, at AtlanM. Oa.. May 6-«, 1806. 9 BY CASEY A. WOOD, M.D. ' CHICAGO. RXPRIHTED FROM THB JQUMHAL OF THE AMERICAN MEDICAL A3B0CtATI0JI, NOVEMBER 98, 1896. II CHICAGO: AMSRICAN MKDICAI. ASSOCIATION FRK88. 1806. M r ^7 ^ THK FIELD OF MONOCl'LAR FIXATION AND ITS RELATION TO HETEROPHORIA. BV CASEY A. WOOD, M.D. So little is Htiid in English text-hooks on oplithal- inoloj^y about the tield of tixntion - monocular' or hinocular — and so much space is given to it in that portion of foreign works devoted to physiologic optics that it seemed worth while to bring up the subject ft)r discussion here. Wt^ are so concerned in investi- gating the relations of the extrinsic ocular muscles, as they are engaged in fixing some ])oint (doubtless the most imi)ortant point) immeduitely in front of the eyes, i.e., at the center of the tield of fixation, that we are apt to lose sight of tlu» fact that the fixing of eccentric objects and points at the extreme periphery of the field is also of great importance. It should be rememberetl that while binocular vision may be obtained and maintained with ease, so long as the object fixed is directly in front, this result is often difficult or impossible when looking obliquely to the extreme left, right, up or down. Not only is this true in marked paretic conditions of one or other of the straight or oblitpie muscles, but it is also true in the so-called insufficiencies. In other words the usual tests for heterophoria or heterotropia- the various kinds of photometric measurements especially — give us but one phase of the conditions under which the extrinsic muscles do, or fail to do, their daily work. I wish to confine my observations to one of the means by which we may measure the excursions, in all directions, of eacili eye separately, as indicative of the pari which eccentric excursions play in the pro- duction of muscular asthenopia. bft 2 It is to Laiulolt that we arc chictly iiulebtwl for utilizing tlu» iit»l(l of tixatioii in practical oplithal- inology. The monograph written by Eperon in the Tvut and down. DircH-tly in . . 45^ s^^ In and uu. [TIP I>ir«*ctly down. SAF I ^.^ I>own and in. Directly up . . .430^^^' Up and out These figures vary slightly in individuals, but the 470 ^ «w L field, authorH •t jiK we ran lials, but the 3 tlirectly inferior au^ie is always the larj^est, while the infero- internal is always the smallest. Tlie eyelids, margins of the orbit and bridge of the nose must always atfect the result of these measurements just as they do in determining the extent of the visual field. Stevens, after speaking of the importance of deter- mining tlie absolute as well as the comparative rota- tion of the eyes, not only from side to side but up and down, says: "We have had, until quite recently, no sufficient means f(jr determining these rotations. The judgment which we may form by watching the rotations is not to be relied upon. The perimeter is destitute of any considerable value for this purpose. By it we can not measure the downward rotation in many casses, for the pupil buries itself behind the lower lid; nor can it measure the rotation inward, for the nose interferes, and even the outward, the only one which can be generally measured, is not well measured.' While I recognize, in general, the advantage of objective over subjective tests, it appears to me that Dr. Stevens' objections to the subjective method of determining the limits of the ocular excursions are weakened by the fact that what we wish chiefly to know is not the extreme limit of rotation of the eye in various directions so much as its l<*nit of observa- tion. What we desire to ascertain in prvjtice is whether the various muscles, alone and in combination, are capable of making all the excursions retiuiretl for the purpose of securing and maintaining single antl binocular vision. Whether an eye would be able to fix an object further to the right or left if the nose were removed, or one higher or lower if a projecting lid or orbital margin were cut away is not of essential importance. We are usually advised, also, to make use of the candle image when the eye is and^lyopic or can not read large type. Now these are just the conditions under wliich we are not usually concerned about the fixation field. It is the e>e that sees and not the \ wgmmm 10 w n, I r hlitid t\ve tliat canwK troiibh' in defective oxcurHions. If an cyi' takcH no part, or only a ftvhU' part, in \\w work of fixation, why troiiblo oufhcInm^h at all al)out its rotation? TlieHo conHidorationH cauHwl \\\v to attem])t to rnnt'dy wluit wtMHH to ho certain (lofectH in tlio tech- ni(|n<' of (Irtorrninin^ thr field of inonooular fixation, as it iw connnonly applied. So far as 1 know, the tno8t t^tfeetive [ilan employed decidedly superior to the old Helt.iholtz-Berthold method -is that exhibited in the modified Landolt apparatus attached to tlie McHardy perimeter. The head of the patient is placed in the primary position and fixed hy biting a ri^id crossbar of hard woikI. Lan^ thus (h'soribes the method of examination: "The balanced test object exhibits a single word of two or three letters printed with the smallest type that can be distinctly seen by the eye under investi- gation. The patient is seattnl at the perimeter, directly facing the fixation point, with his head erect and his chifi supported on that half of the chin-rest which brings the eye that is about to be tested into the middle line, opposite the fixation spot. If the patient can not maintain this position during the whole exam- ination, he is asked to grip the bar of the bite-fixa- tion-apimratus between his teeth, which effectually prevents the least movement of the head. The other eye is covered with a pid and bandage, or its lids are closed and h.eid down by the lashes with the tip of the patient's forefinger. The words in the test object, in the various sized type, are now exhibited, and one, in the finest print that the eye can read, either with- out or with gl' f*8es, is exposed after the test object has been moved to the end of the perimeter arc, which is extended horizontally outward. While the patient, without Tuoving the head, turns his eye to the utmost outward toward the extremity of the arc, the obst^rver slowly moves the test object inward toward the fixation point, but stops directly the patient can read tlu> wtml. and at once records, in degrees, the 1^ B poHiiioii whioh^tlu' U'h! <>l)ji»ct «M'(Mij)ioH in tlic arc. *'Tho arc iH now plartnl horizontally inward, tlu» tcHt object in inovtMl hack a^ain to the extremity «)f the arc, a frenli wonl iH ex|K>Hertain(*d by placing the arc in each iU) degrees of the circle, and recortling the reHultn on a tield of vinion chart. "When the examination of one eye in completed, the luMul in Hhifttnl t(» the opponite Hide of the chin rent and thes^'cond eye in tented in the name manner." On making examinati«»nH with this apparatiiH I long ago noticwl that the continuouH effort to hold ♦he eye at itn extremeHt rotation, in ho many direc- tioiiH, waH excetnlingly fatiguing and often made it difficult to complete the examination. It was alHo HMnarked that the renults varied in the same individ- ual, and I feel certain that thew different meanure- mentH are due to the fatigue incident to the attempt of the eye to fix an object whoHe exact {)oHition at the extremity of rotiition is unknown. The nystagmuH- like movementH of the glolH*. after a numlHT of theH«» trials, in cjuite iKjficeable. liiHtead of using an object attached to the carrier on the iM*rimeter arm I have used an exceedingly simi)le device whereby the rotation of the globe in any direction is rapidly and easily ineasunHl. It may be UHed by all |H»rsonH who can read .bieger xii at fifty .centimeters, and may even Ix' employed for others whow visual acuity at that dintance in C(m8idera!)ly less. Four strips of unglazinl [)archment pajx^r have printed on them words of two letters placed l)etween, as well as Ih'Iow, figures representing the Hition at the he nystagmus- inlh'r of these to the carrier n exceedingly e globe in any It may Int er xii at tifty ed for others ccmsiderably it pajKT have iced l)et\veen, le degrees of strips are, [I ik (i f the peri- primary posi- orate tixation lower line, as faraway from the center as possible. This accomp- lished lu» is reciuestcd to give the tigure placed above the wonl just recognized and to try and read, farther (mt, additional letters on the tigure line. Each word beyond represents about one degn^e on the scale and the nund)er of words so read added to the previous Hgure gives tlu' limit, in degrees, of the Held in that direction. As tach quadrant of the circle is passed over, a slip of paper is removed, revealing the next paper wlu)se lettering, being different, suggests nothii»g to the person under examimition. I have found that instead of making the vertical letters face up and down one can accomplish the purpose of distinct visitm by printing them with type of a bolder face, thus providing for those rare castas in which it is desired to test the muscles (»f an eye that can not read Jaeger xii, or thereabouts. My investigations of the tield of tixation have developed nothing new except that the normal tield, in persons wlujse view is not cut off by the nose, lids or orbital margin«, seems to have wider limits than those set down by Lmidolt, particularly in the downward direction. The causes that detenu ine an unusual shape or abnornud position of the whole tield, as pictured on the perimetric chart are. commonly, actual paresis of one or more of the external muscles of the eye. Apart from an abnonnal contiguration of the face, we also recognize those inHuences that underlie the various forms of heterophoria, /. f., general fatigue, weariness of one or more (jf the extrinsic muscles, age, defective innervation and, possibly, congenital defects in the muscular tiben^ Hut in cases of heterophoria occur- ring during the Hxatiim of objects directly in front of the eye, the state of the refniction exerts a very wide influence, on the size, shape and situation of the whole tield. Its boundaries are enlarged in moderate degrees of hyperopia, but are diminished in the higher grades, owing, as Landolt thinks, to the developed nmscles acting on a not too large globe in the former instance Tf 8 Hiid to the Inck of development, in the hitter cnse, ntfec'ting the muscular elements in common with all other parts of the eye. It is restricted in the ehmgated and enlarged glol)e of the extreme myope, owing mainly to the greater size of the eye and the weakness due U) \hv stretching of the muscles. My former assistant, Dr. T. A. Wocxlruff, and I have carefully measured a large number of tields, nor- mal and abnormal, in jx^rsons of all ages and all states of health and refraction, and I feel justified in think- ing that when carefully done, using the device I have just described, the defective excursions and often the defective muscle or muscles can be readily detected by a glance at the ix»rimeter chart. Take for example a case of simple left hyperphoria of 4 pr. diopters. Here one obtains a jwrimetric picture whose irregular outline covern ))erhaps, as much ground as the nor- mal field but whost^ directly upwanl and downward limits in the left eye are higher than normal. Thus we have not only an indication of the amount nnd kind of the heterophoria but we are enabled, by a comparison with the normal field, to arrive at a con- clusit>n not oidy as to the actual direction of the muscular deftH»t but, als