brocks lecture notes on strabismus1

8/3/2019 Brocks Lecture Notes on Strabismus1

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LECTURE NOTES. on

STRABISYUSby

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FREDERIC! W. BROC!


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l . ORGANlSMIC LAWS THAT PERTAIN Ta VISUAL TRAINING

The purpose of visual training is ta bring about a better adjustmentof the individual ta his natural surroundings.

Therefore, training conditions should be made ta s i m ~ l a t e natural surroundings as nearly as possible.

. B. There i s an organismic tendency toward ful l use of existingabi l i t ies .Question:Answer:

Question:Answer:

What, then, causes visual concessions?Concessions occur when there is a lack of demand fora l l existing abil i t ies.I f there is a natural tendency ta make use of aIlexisting abi l i t ies , why do we need visual training?Visual training if i t is properly applied, makes demand for a ll existing abi l i t ies .

c. There is a natural tendency toward cOmpletion of a conternplated actand ta accomplish i t with the least expenditure of energy.We are usually determined ta complete a task once we havestarted. In visual training of the child things go weIl unt i l thegiven task is completed, but once i t has been attained repetition

is not interesting. Renshaw says that i f we get five minutes ofactual training per hour spent, we do weIl.

D. I t is the nature of the posture which d e t e r w ~ n e s the nature of theresponses.The above statement means this : while the eyes are in astrabismic posture, the individual thinks strabismically, but theminute his eyes are in a normal posture he ceases ta thinkstrabismically and thinks th e way we do. 'The shi f t from strabismicta normal posture brings about a complete change in his interpretation.This means that when he looks at a smaIl target with bath eyes

directly, he cannat think strabismically; he must think the way wedo. However, the shif t from strabismic ta norma posture cannatbe accomplishedwithout a change from wanting ta look at a givenfixation abject with one eye only ta wanting ta look at i t withbath eyes simultaneously.Binocular interpretation does no t have ta be taught! Wedonlt have ta break down anomalous retinal correspondence inorder to establish normal re t inal correspondence. Our solepurpose in visual training is to posture an individual adequately,and when that has been accamplished the rest comes easy.

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2We need contraIs. We need ta know when we have normalposture and when we do note No training instrument 1s worthyof i ts nalLe i f i t does permit us te differentiate betiVeen iVhat1s normal and what i5 note And no orthoptist i5 worthy of the

name i f he cannot differentiate between a substitute performanceand a true performance. This i8 not a simple problem. I t i5not easy ta determine when a child trains in a constructiveway and when i t s i ~ l y perforrns ta sati5fy "minimum requirements".Ta differentiate between purposeful and "lackadaiSical" performancestakes adequate controls. Unless we have such contraIs we cannathope ta mainta1n a high level of response.Binocular posture is the abili ty ta ma1ntain Buch relativeeye positions in anticipation of a certain visual task that botheyes directly fixate a single abject of special regard: Binocularposture means, eBsentially, "looking a t a single fixation abject

ri h bath eyes, at th e srune time. 1/Not a ll individuals who ar e adjusted ta their naturalenvironment depend on binocular posture. There are two other:forma of osture around which an individual ma success:fullorganize his seeing: a m ~ n ~ n ~ n g postur.e 'with one eye only,or monocular posture, (b) mallltalmng separate Unes of directgaze for each eye, or strabismic posture.Maintaining monocular'posture, means that only one eyefixates th e abject of special attention. Tge eye that looks atthe abject of regard is the eye that is used fo r the corticalinterpretation of that objecte The other eye is not used for

that purpose. The other eye maybe looking in an entirelydi:f:ferent direction. This eye may have, at the moment, aperceptual purpose or i t may note The question nov{ arises, isi t used for any other purpose? If i t has no other purpose, i3kept in "cold storagef! so to speak, we have monocular posture,for what the other eye is doing at the moment is of no interestto the organismeMaintaining separate lines of di:ect gaze fo r each ere, orstrabismic posture. In the sense deflned here, i t does notinclude aIl strabismics but is lirrted to those who are ambiocularin their visual behavior. The term "aJJbiocular" describes acondition where both eyes are used for separate and distinct

purposes. That is , they attend to different functions at thesallE time. We find this posture in "anomlous projection" ofalterat ing strabismics.My investigations into the nature: of ambiocular vision have definitelyproved that these strabisrrUcs Can look in two directions at once andinterpret the macular images of bath eyes simultaneously.


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I f you play the piano with one hand, i t does not prevent youfrom playing someother chord with the other. I f you cannotcoordinate both hands in this way, you may concentrate your wholeattention on the one task of playing the same tune with bothhands. I t takes more ski l l to play different measures with eachhand than to play the same tune with both hands. The forzrabili ty i l lustra tes the ambiocular strabismic, while the secondexemplifies normal binocular vision, and playing th e piano withone hand corresponds ta uniocular posture.

You may wri te "cat" ri h the right hand "hile writing catmirror-fashion with the le f t hand. This is easier of accomplishrnt than wri ting the word cat wi th both hands in a le f t toright direction. The latter-requires an entirely differentposturing rnechanism for the le f t hand than for the right, whilethe former may be done with a single posturing effort for bathhands. This may serve as a simile ta show why binc>cular posturingis cortically less difficul and requires lS-sEntal effort thanstI'abismic posturing. Monocular posturing is s t i l l l e s s of an .accomplishment, which may be the reason i t ls frequently foundin the mentally deficient. In my own investigations l have, never encountered a strongly integrated ambiocular percept invery young children or in individuals of low intell igence. AlIevidence points to the fact that strabismic posture is muchharder ta learn than binocular posture and ,that i t s acquisitiondenotes a high achievement level, visually speaking. For th esame reason, once this posturing abil i ty has been attained, th eindividual is no t readily willing to give i t up in exchange forbinocular posture, unless the lat ter heightens hisaccuracy ofs p ~ t i a l orientation for exceptionally demanding tasks with whichhe is being confronted and which cannot be solved whilemaintaining strabismic posture.

The term "s trabismic posture", as above defined, represent' sthe sort of visu::!l behavior which l have variously called"anomalous projection" (of the most accomplished order) or"ambiocular vision". I t is often referred to in ophthalmologicall i erature as "anomalous retinal correspondence", IIvicariousfovea ll , - terms wffich are usually promiscuously given toessentially ambiocular and uniocular alternating postures.Tt used ta be IllY rnplicit belief that we had to "breakdown" anomalous projection prior to making any attempt to "building

up" normal projection. This seems no longer justifiablebecause, s t r ic t ly speaking, you cannot "break down" learnedconcepts. Yeu rnay suppress thern by presenting the individualwith new and different demands "hich require new learning. Ifsuch learning is directed toward our eventual goal, theundesirable, (from our point of view) patterns, may graduallybe replaced bv the more desirable patterns and may eventuallydisappear from consciousness because of disuse.When a binocular posturing attempt is made by an individualha r ing strabismc or uniocular posture, the response v,'ill be

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of poor quaIity , but, since i tw i l l be bas ed on .a binocular fieldstructure i t will be capable of interpreting retinal disparityin te r ms depth variables; i . e . , i t will have stereoscopiequalities, provided stereoscopie demands are made.Since stereoscopie demands require binocular posture, suehdemands may serve as a. Ifspecial task" in an attenpt te ellei t

binocular posture with the strabismic.E. Varying perceptual demands may bring abou t varying postural sets.

1. individual, who i3 capable of binoeular posture l mal atcertain times maintain uniocular posture, i f the la t terinvolves less effort and the visuai task can s t i l l beeompleted. 'This is one of the most important tenets in visualtraining. I t raises rather interesting questions. Whyshould an individual maintain accurate binocular posture

when he can complete the task to his entire satisfactionwith a less effortful posture? There is no organismicreason. I t ia therefore essential, in an effort ta improveor establish binocular posturing abili ty, to present theindividual with the kind of task which requires for success-fuI cornpletion exact binocular posture. An individu al ~ h o habitually maintains uniocular posture can see no reasonwhy he should make a greater effort at'obtaining visualdata. whichcan 'be gainel without such addedeffort. Sucheffort l'fould simply be an "added burden", added energyexpenditure, and without organismic purpose.An individual who uses binocular posture can bringtwo pointers tip to tip. This an individual who dependson uniocular or strabismic posture simplycannot do, becausethe task is above his accomplishment level. I t isimportant to kno\'{ that pointers may be used to f oree anindividual to rna.intain binocul ar pos ture.l may point out here that the use of pointers, thewaythey are applied in flpointer training'! in the stereoscope,does not fulf i l l the above requirements. This i5 so be-cause the individual who is capable of rapid a l ternationof fixation can achieve more accuratelz by far, i f hemain tains alternate fixation than if he attempts binocular

fixation while he performs this task.I t is common practice today to use stereoscopiephotographs for binocular fusion training which contain avert ical white line in a certain area of the total fieldfor the one eye, and a horizontal line in ~ ~ e correspondingarea of the total f ield of th e other eye. This may bepermissible with individuals who are known ta possess weIlintegrated binocular f ield structures. However, i t is

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readily dernonstrable that the individual who has astrabismic posture can interpret these photographs tothe entire satisfaction of the technician by alternatefixation and, by doing so, the patient himself will beof th e oninion that he sees both pictures as one,c o n t a i n i ~ g a perfect cross. He arrives at his i n ~ e r pretation via two consecutive impressions by the simpleexpedient of "temporal fusion", even as we achievetemporal fusion of successi


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whether an accurate or an inacurrate posture is being mairttained.A rnuch lI'.ore accurate way of telling is to observe the individual sa.YiIlityto achieve at certain tasks. For instance, i f he iscapa.ble" of the extremely accurate spatial orientation which 1snecessary ta s,uccessfully complete the Pointer test , we areassured that he i s capable of accurate binocular posturing abil i ty.This also means that , while he maintains such accurate posture,he i s capable of interpreting with satisfactory stereosc'opicaccuracy. I f he does no t achieve, i t mean8 simply that we havenot been able ta provide the sort of test conditions which willmake him reach for the highest visu al achievement of which he i3capable.

I t i8 legitimate to come to conclusions by inference. I f anindividual is l e f t in an empty room ri h a piece of clean whitepaper and a pencil, and he afterwards shOl'ls a written page and aused pencil, i t is permissible ta infer that the individual wrotewhat i8 on the page. I t is also possible to deduce with whichhand he wro te i t , i f his handedness i8 known and copies of hishand writing are available. If he attempts ta WTite with the non-dominant hand, this will be readily apparent from'the nature ofhis characters, because i t would be almost impossible for him tasimulate wi th his non-dominant hand wri t ing done wi th his otherhand. You could infer these facts only because you had somethingto compare. We know, for instance, that writing ri h the dominanthand is far bet ter integrated, more bal l is t ic , than any writingthat may be attempted with a hand entirely new ta th e task. Wealso know that this ski l l is not easily transperable from onehand ta the other.

How weIl an individual ls postured for a task is indicated bythe ease, the fluidity, with which the task is completed.

Normal binocular vision rlepends on binocular posture. Thetwo terms are actually interchangeable. We cannot separate binocularvision from binocular posture nor can we separate binocular posturefrom binocular vision.

G. Binocular posture makes possible the appreciation of the differentviewpoints of the two eyes looking at objects from different stations.(a) the difference in the proximal stimulations received bythe two eres becauc'"' __of their separated position in the s1.,111-isorganismicall;T . lY'tei =reted as depth variables in stereoscopieperception.(b) Accurate s tereosco ic abili t deoends on (1 ) maintenaTJ.ce01 accurate binocular posture; 2 an organismic desire to achieve;U) the abil i ty of bath eles ta see clearly.

H. The specifie purpose of an visual training is' to bring about anadequate binocular posture rrhich, in turn, guarantees the greatestadeguacy of the 'Visual responses of which the individual is capable.


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THE MEANING OF RETINAL CORRESPONDENCE AND RETINAL RIVALRY IN VISUAL PERCEPTIONFrom a. diagnostic point of vievi i t is important that we know how tointerpret retinal rivalry. Retinal r ivalry is dependent on the existenceof corresponding ret inal areas. Before we can discuss ret inal r ivalryadequately, we must know more about the meaning of ret inal correspondence

. l . RETIN.AL CORRESPONDENCEWe come back to the fundamental concept of ret inal ly correspondingareas in the two eyes. l am prepared to say that in a ll cases the twofoveas are such corresponding ret inal areas. Once this concep t i s ~ clearly established we shall have no further trouble with any of th evisual training concepts which will,be considered here.

A. Corresponding ret inal areas are invariably equidistant and on theSaffie side of the two foveas. No other areas are acceptable asretinally corresponding areas. There ar e no "secondarily"corresponding ret inal areas - which are not geometricallycorresponding - not even in strabismic posture or in the so calledanomalous conditions. The two foveas are always ret inal lycorresponding. Let us be clear on this one thing: there are nopossible exceptions to ret inal correspondence, as above defined.AlI responses which make i t appear as i f there were anomalouslycorresponding ret inal areas are artefacts which have a differentexplanation. I f we def i ne ret inal correspondence as fovea tofovea correspondence, Our thinking :.;; ~ o m e s specifie and w maylay out clear programs for visual training - programs which arenot possible i f we accept the theory of anomalous ret inalcorrespondence. Acceptance of the concept of abnormal retinalcorrespondence, provides a very real reason why strabismus, whichexhibits this supposed forro of seeing, cannot be cured.

Let us assume that an area ten degrees off the fovea of oneeye, has become corresponding with the fovea area of the othereye in a binocular f ield percept. How can we possibly changesuch a relationship? When an individual once has acquired thisrelationship he has no incentive whatever to give i t up ,especially i f he can also have fu l l stereoscopie perception.(Duke-EIder)

True, there are many indiviuals maintaining eye positions,which are within ten degrees of parallellism. Such individualsmay have a very low grade peripheral stereo-awareness but theyinvariably show strong macular suppression. Vmen the suppressionis l i f ted, fovea to fovea corresponrlence is always immediatelyapparent. These conditions will be discussed in greater detailunder th e heading of !!Retinal Slip!!"The concept of fovea ta fovea relationship in a ll binocular


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sensory fields is vi ta l when we seek to determine adequacy of binocularposture. In accepting the presence of a binocular sensory ! le ld wemust assume the existence of fovea to fovea correspondence. Howelse 'could we measure? If we use the phoria tes t of th e Keystone .Visual Survey Series for infini ty, the position of the arrow inrelation ta the numerals which are yisible to the other eye cannotbe interpreted in terms of ret inal positions unless favea to foveacorrespondence exists. When the arrow appears to point at thenumeral 9, we must be able to assume that the two eyes are inexactly paral lel position. I f we could not make this assumption,the phoria t e s t would lose a ll meaning, because we would haveno means of determining the shift in ret inal correspondencewhich would be "normal'! for the particular indiviual' and for noneother. We should have no measuring st ick.

But measurements are possible. Under normal conditions, whenthe arrow points to numbr 8 or number 7, i t is possible to statein mathematical terms how many degrees the eyes are out ofalignment. This we can do because th e centers of both foveas arethe points of referenct:J from which a1l these calculations can bemade. Phoria measurements can be made as accurately as we canmeasure the distance between two cit ies on a map, pravidedweknaw the exact scale of that map and are assured that i t hasbeen drawn correctly. If the map were drawn by approximationinstead of by triangulation, these measurements could no t beinterpreted. In order to determine the distance between twoci t ies , we put the points of the calipers in the center of thetwo city areas and always use these same points ta makecomparisan between different cit ies on this map. Without suchspecifie points of reference there can be no accurate interpretationof the map. We could not, for instance, measure the length ofa table, i f one end if i t were hidden from view. The center ofeach fovea represents, in like manner, the unchanging point ofreference in ocular measurements of al l kinds. If only onefoveal center were available, nomeasurements could be made.This is an important consideration in amblyopia. In amblyopiathe center of one fovea may be necrotic, i . e . , incapable ofconducting nerve i r r ~ u l s e s to the brain. In an amblyopic eyethe blind area is apt ta include and surround the center ofone fovea because of a central scotoma. This means that theindividual cannat fixate along the primary axis. However, i t isthis axis, and this axis alone, that reaches the retinal pointwhich must serve as the locus from which measurements are ta bemade. As long as we have th e fixation point of the other eye,we can draw a circle around the blind area of the amblyopie eye.This circle is visible to the patient while i ts center i8 noteIf i t is possibill ta align the two eyes in su ch a way that thecircle is phenomenally centered around the fixation target of thegood eye, the center of the circle can be used as the secondpoint to which to apply our measuring stick.

Even in an eye ~ n t h a central coloborna, in which case there


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is a large visible destruction of ret inal t issue, we can presentthis eye with a large enough circular target (a ring) to surroundthe entire coloboma. This ring may be centered around a spotsource of l ight , which is visible ta the fixating eye only (thel ight falling into the blind area of the defective eye). Therelative alignment of the two eyes can now be accuratelydetermined. By this method i t is possible ta plot the scotomatousarea of the affected eye, but only because the relationshipbetween re t inal areas of the two eyes is always the same (whileabinocular perceptual field is maintained).

B. Retina1ly corres ondin areas cannot exist where there ls nobinocular perceptual field as above defined. We know that asirnultaneous percept is possible in certain forms of strabismuswhere the two eyes are not in normal alignment. In this casethe two foveas are never in permanent relationship to each other,as Verhoeff has so ably demonstrated. The centers of the respective.foveas can therefore not be used as a measuring-stick for binaryvisual perceptions.

Two films, taken with th e Saille camera, from the sarne point,can be laid on to p of each other sa that l ike images are superimposedand a single clear print can be made thru the two films. On theother hand, even i f th e prints are shawn separately each can beinterpreted accurately and independently of the other.

C. Ambiocular (strabismic) perception seems to be dependent on theretention of two cort ical ly separate sensory f ields, whichobviates th e need for ret inal correspondence.Experiments show that in s trabismic pos ture the corticalimages produced by the right and the l e f t eye are separatelyconsidered and that their closure into a single unitary perceptis obtained by a prQcess of abstraction (a frontal lobe process).The strabismic learn to accept the right and l e f t images of asingle object as belonging to that object, just as we can learnto accept by the sarne process a mirrored abject as being part

and parcel of the ~ e a l object. The. two images are never fused,as l have shown in my investigations relative to strabismicseeing. I t can be demonstrated that in these cases a binocularsensory f ield does not exist , but rather two separate sensoryf ie lds , one for each eye. For this reason an anomaloushoropter is never formed.D. Difference between binocular and ambiocular sensory f ields.

A binocular sensory f ield may be compared with two films beinglaid on top of each other for inspection. Wnen variations inphotographs of object .(because of the different locations fromwhich the pictures have been taken) are superlmposed they may' be

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interpreted stereoscopie ally. A_ 'j)iIlocularsensory f ield perceptis neither a r ight nar a l e f t percept bt differs materiallyfrom both. On the other hand, an ambiocular field perceptconstitutes a summation of right and l e f t percepts. In thetota l field of the strabismic a certain area is foveallyperceived by one eye and another area is foveally perceived bythe other eye, resulting in two weIl defined areas of clearvision in the to tal percept. Each clear area is seen exactlyas-the corresponding eye sees i t .

The presence of a binocular sensory field doss not necessarilymean that we have a single spatial percept. A single spatialpercept is possible only when binocular posture is available.Suppose that we make binocular posture t e ~ o r a r i l y impossibleby the elevation of one eye above the other by means of a base

down prisme The fixation object can no longer reach correspondingret inal areas and it is seen double. This means that eventhough the binocular field persists , accurate binocular posturecannot be maintained. I t is evident that vre Imlst differentiatebetween lIusuable" and "non-usuable" binocular fields. Elimination(by suppression) of an unusable binocular field i8 diff il t ,and- sortEtimes impossible with individuals who have ful ly maturedbefore the eyes were thrown out of alignment. The use of prismsis definitely indicated when a non-usable binocular field canthereby be made usable. In a non-us able binocular f ield thespatial concept is distorted because of the very existence of abinocular f ield and accurate spatial orientation becomesdependent on the resurrption of adequate binocular posture. Vlhenthat is not possible, tota l occlusion of one eye will givetemporary rel ief .

Suppose a binocular amblyope with 20/200 vision in botheyes. How can we know whether he has a binocular field perceptor'not? When we put a six degree prism base down over one eye,i t is of diagnostic significance whether or not this prismproduces diplopia. I f diplopia results and the two images canbe vertically aligned by addition of horizontal prism, i tindicates that the amblyope hact a usable binocular field priorto the introduction of the vertical prisme On the other handi f no diplopia is produced, we must assume that a binocularf ield does not existe Establishment of a binocular sensoryfield is desirable because i t will heighten the visualachievement level of the individual.

F. horia measurements throu h h to 6over one eye indicates the existence of asatisfac tory binocular field. When the responses to these testsare uncertain, the existence of strongly established binocularvisual pe'rcept can be doubted. When phoria rneasurements cannot


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made through the above amounts of prisms, it is questionablether a binocular f ield exists at al l . When you cannat make. ia measurernents easily and speedily, watch out! Be sure.. ou are dealing ri h rasurements and not wi th approximations .. ~ e m e m b e r that vertical diplopia may also be produced by basedown prism (over one eye) with an individual who has a strabismicposture. But i t usually takes more than six degrees toproduce diplopia. The s t r a b i s ~ c can bring. the double i ~ a g e s above each other, after a fashlon, but he Wlll usually glveyou a definite clue that his p e r ~ e p t has b:en arrived.at byabstraction rather than from retln posi tJ.on. A patl.ent ofthis type will almost invariably say "1 think that the twoimages are now ab ove each other", or that "one seems to be toone side and the other to the other side." I t usually takesseveral degrees or base-out or base-in prism before he isaware of a la teral sh i r t between these two images. Theresponses are always uncertain and sometirnes qui te unpredictable.The strabismic usually (but not always) refers the right re t inalimage as being to th e r ight of the l e f t retinaI , image, whetherhe i s an esotrope or an exotrope. lVhen double images producedby vertical prisms are reported ta be in close proximity,we know that the patient projects according ta his learnedstrabismic habits. I t i s , then, of no further significancewhether he reports the one ta the r ight or ta the le f t of theother. No effort should be made ta align them by the use ofla te ra l prisms Q The same h o l ~ s true when an exotrope reportsuncrossed diplopia. Such diplopia is evidence of s trabismicposture and time spent on "aligning" the two images will simplybe was ted.

In an effort ta differentiate between strabismic projectionand normal projection i t i8 never advisable ta use mOre than Uta 6 prism diopters of vertical prism. I f the te s t remainsnegati ve with that alllount placed firs t base down and then baseup over the same eye, the existence of a binocular f ieldpercept mustbedoubted under these tes t conditions. Thenature and extent o f a binocular f ie ld structure will have tobe determined by other me ans I t is a red signal! Theques tion nOV{ arises: Are we dealing wi th suppression orstrabismic seeing?

To differentiate between an 8J:1biocular and a monocularf ield percept, it is advisable to us e a stronger vert icalprism (ten p.d.) to determine Ivhetheror not diplopia Ca.ll beexperienced. When a four p.d. vertical prism producesdiplopia, we may conclude that total suppression did no t causethe prior lack of diplonia. Vie are then justif ied in assumingthat a . ~ ambiocular f ield percept, adapted to the strabismus,exists on the a s s u ~ t i o n that an arrbiocular f ie ld perceptpertains a percept adapted to the strabismus.The more vertical prism that is needed to produce a

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sense of dip1opia, in a ~ t r a b i s m i c , the less adapted he may bedeemed to be.2. RETINAL RIVALRYA. When the proximal stimuli, which reach corresponding perceptualareas of the two eyes, emanate from diferent objects in space,they a r ~ unfusable and under certain conditions may r ival witheach other for recognition.

B.

The above holds true on1y under certain conditions.Retinal rivalry is lacking when oneeye is suppressed. But i tis not always possible to suppress totally a ll the stimuli thatreach the cortex via one eye. If suppression does not occur,retinal r ivalry results. This Jans a shif t of dominancy fromone eye to the other, neither eye being able to gain prolongedcomplete control. Washburn laims that a ll binocular visionis based on retinal rivalry and that without i t there cannotbe any binocular vision.

The rules governing re t inal rivalry and suppression havebeen discussed elsewhere.In a binocular field structure two unfusable macular stimulationscreate field stresses which are ?pt to interfere with th eadeguacy of spatial o r i e n t t ~ o n .

The retention of two unfusable macular images is , as a role,unacceptable ta the organism. IVhen a binocular field structurei8 present, retention of fusable macular images is of primaryimportance to the organism. (This does not hold true forperipheral irnagery). If tvro fus able macular images are notmaintained, one of these iWBges must be total ly suppressed.(This condition will be discussed under "Retinal Slip"). Viemust main tain fusable macular images ta be comfortable, providedwe maintain a binocular field structure. .c. I f an individual finds i t i ossible ta maintain e e ositions

that make fusion possible binocular posture , he will make adetermined effort ta suppress a ll proximal stimuli which reachthe less dominant eye, thus eliminating the f ield stresseswhich interfere w2th the adeguacy of spatial organization.That oecurs l'rhen like images carmot be maintained on therespective maculas. Spatial adequacy cannat be maintained unlessone image is eliminated.One wav to solve this problem is ta char1ge 3..11 inadequateposture ta ,,-' adequate one, thus p:,oviding the two macu:ae with


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fusab1e images. I f this is physical1y impossible, a determinedeffort may be made to throw the two eyes into greater disalignme,nt,50 that the non-macular image of the fixation object becomes sopoorly defined (because of i t s peripheral location in the turnedeye) that i t can be easily suppressed.

D. The organismic tendeney ls always toward elimination of ret inalrivalrYt i f i t interfers with the c1earness and quality of thema.cul ar image.Retinal rivar1y (particularly.in the macular areas) 18the most troublesome attribute in a binocular field percept IVhenbinocular posture is lacking. I t is of primary importance thatan individual main tains a clear and unencumbered view of thefixation object. I f the macular stimulations of the turned eyecan be ignored, i . e . , prevented from reaching conscious aware-ness, the clearness and quality of the macular image of thefixating eye are thereby greatly enhanced. Uniocular suppressionis therefore always practiced f i r s t in the mcula.r area of theturned eye. I t may be gradually extended ta the paramacularareas and eventually may invade the peripheral areas as weIl.However, sueh suppression never materially affects the capacUyof the suppressing eye ta see clearly in a uniocular percept,i . e . , when the normally fixating eye isoccluded. ~ u l a r SURpression is a process of adaptation to a new visual rquirementandhas to be learned.

E. The strengthening of retinal r ivalry by visual training iscontraindicated with individuals who ar e incapable of binocularposture.This is a new concept but follows logica1ly from whatwe have considered before. This concept i s , at present,frequently violated in visual training.

When a strabismic patient is incapable of binocularposturing IVe have no right to attempt ta establish retinalr ivalry. I t would interfer with his spatial adequacy. Theproponents of this procedure elaim that by developing retinalrivalry the patient may "s traighten", or i f he does not, hemay then be operated upon with a better chance for a binocularpattern of seeing after operation. This used ta be my ownattitude toward the strabismics. However, l have found thatthe individual who shOl'rs no incentive, under any conditions,to posture binocularly prior ta the acquisition of abinocular field percept, very rarely shows any rr.ore desireto straighten his eyes after a binocular field percept hasbeen forced upon him. I t is these individuals who developthe dread fusion aversion which is knovm as horror fusionalis.

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Today l feel i t much more advisable and certainly macheasier , bath for the patient and for the technician, not tad e Y ~ ~ J . J i n a . L r - i _ y _ ! l I T l 1 n t i l ~ _ h e d o c t _ o r is assured tbat thepatient can (under certain test candi t ian) posture binocularly.Where this assurance is lacking, l find it advisable ta haveth e eyes straightened by operation, prior to any attempt onpart to establish a binocular field percept, and then tadevelop the la t te r by slow degrees.

The usual approach to strabismus is the establishment ofbinocular seeing, even if this had to be done wi th the eyes instrabisme posture. A binocular f ield structure is forcedupon the individual by means of instruments which ean beadjusted to.the existing angle of strabismus. This normalbinocular.responses are being elicited with the eyes in astrabismic posture in the hope that, once fusion has beenattained, i t can be used to reduce, by gradual steps, theexisting angle of squint.This procedure is no longer acceptable ta me. Instead,l l imit the. training for binocular field percepts ta thepart icular situations where l have found that a patient has')hown a desire f o r ' ~ i n o c u l a r posture. By doing this , l find

~ h a t the patient learns to associate binocular seeing withbinocular posture and, what is more important, ta reservebinocular seeing ta those visual tasks for which he is willingta posture binocularly. When he returns ta strabismeposture, he also returns ta strabismic seeing. This i3 theorthoptic procedure which l am following successfully todayand which l am advocating for adaption by others.

Today, we are very careful, not ta develop binocularfield awareness in situations where i t is not usable. Wefear that projection of binocular field awareness intoconsciousness under such circumstances may result in i t srejection in good and bad situations alike.This new'rr.ethod is applicable in cases of paresis whereconcomitancy of rotations is l a c k i n ~ , a t leas t in the areascontrolled by the paretic muscle (s). I t is possible to

teach an individual to maintain stereoscopie awareness inthose areas of his surroundings where he can posturebinocularly and to le t him rnaintain uniocular or strabismeposture (and unioeular or strabismie thinking) in thoseareas where binocular posture is not possible. The tlYOmodes of visionean eo-exist.It is quite a ll right to assume that if we ma.\.ce astrabismie suffieiently uneowJortable visually, he willstraighten his eyes. Frequcntly that is so , provided onlythat he keep the eyes straight. Unless we have definiteevidenee to that effeet , l'Te have no r ight to follow out the above


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F.

When the patient resents the establishment of binocularf ' e l d proce8ses (usually for good and valid reasons, which

may not be able to recognize), and we nevertheless insis testablishing them, a confl ic t arises. Such conflicts are. ~ ~ u a 1 l Y los t by the doctor. Many patients , whcJ show abil i tyto maintain straight eyes, feel that i t is easier to maintaina slightly esotropic or exotropic position when looking atdistant objects, although they are perfectly willing to maintainbinocul ar vision for close range. l u8ed to spend an immenseamount of time in an effort to change this situation andoccasionally sucocded in getting the patient to maintainadequate binocular posture at far (at least while he was inmv off ice) , only to discover, that after the patient had beendischarged for a year or sa , he usually came back with sl ightlystrabismic posture at fa r , but maintained comfortable visionwith constant binocular fixation at near. Further, suehpatients usually showed abHi ty to maintain binocular postureat far for occasional heightened perceptual needs, wheneversuch needs arase.

We have learned by hard experience that it does not payto establish certain visual patterns contrary to organismicdesires. The organism must be considered f i r s t and foremost.Frequently i t s -needs are not expressed in a desire for straighteyes. I f the pat ien t could have them as easily as he can weara new sui t of clotbes, there would be no problems in strabismus.But even th e best-lcoking sui t will not be worn long, i f i ti8 uncomfortable. No man in his r ight senses would prefer tawear ful l dress clothes th e year around, but he is willing,for th e sake of appearance, to wear them on occasion. Manystrabismics, who find i t more confortable not to maintainbinoaular posture, will maintain i t on special occasions.They are usually ~ o n t e n t e d and happy, unt i l we try taconvince thern that they should no longer continue in thatstate.

I t is , therefore, always inportant to raise the questions;fils i t of suff icient consequence for the patient to undergo thevisual training which l propose for him; to spend th e time andmoney; or aL1 l doing this simply because l.am a perfectionist?"

Binocular lus ter may be considered a forill of retinal r ivalry.Binocular luster , which is an incomplete color mixture,resul ts when two corresponcting functional areas are stimulatedby different, undifferentiated colors. Let us suppose that wekeep one eye closed while we gaze with the other eye at a blank

green wal l . When a pocket flashlight is held against th eclosed l id , so that i t s beam of l ight is direc tel3: t0"t8.-:"d the

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anteriar pole of the cornea, an even reddish glow pervadesthe entire eye. We now have two areas of indifferentiatedcoler = green in the open eye, reddish in the closed eye.In ambiocular (strabismic) vision the patient will statethat he sees a green color with one eye and a red colorwith the other eye. This is so because there apparentlyis no color mixture in ambiocular vision. When a binocularf ield percept is present, the green wall is seen as i f tro:a red glass. The wall may at times appear quite red anq a tother times quite green. I ts color is apt ta vary betWenthose two extremes. Under the most stable conditions theperceived mixture may be an even reddish-green.

The resultant color is not deterrnined by the knownlaws covering calor mixture. I f we could inspect thephenomenal wall by means of a microscope we might find thati t consisted of miscrosopic areas, which would show eithera ll green or a ll red, as would a KodachroI film which hadbeen exposed ta a red and green indifferentiated field. I twould also be possible ta determine that the mosaic of red. and green would be constantly changing, green areas turningred and vice versa. This ls the phenomenon of bino(:Ularluster. I ts presence is an indication of a binocular sensoryf ie ld . I t also means that the other attributes of' binocularvlslon, stereoscopie perception and r e t i n ~ l rivalry, areavailable under suitabJe conditions.

G. Testing the color-mixing abil i ty of an individual in th ebinocular luster test is a useful means of differentiatingbetween binocul::.r, rronocular" d.ud arnbiocular fiel'; structuring.The f i r s t shows an incorrplete celor mixture; the second theerceived color of one e e onl . the third tl'ro ad' acentsometimes sl ightly overlapping areas of unmixed colors,spli t t ing the total stimulated areas in half.This method of d i f ~ ' e r e n t i a t i o n is eminently usable. Theonly reason i t i8 not universally applied is that we know so

l i t t le about i ts meaning. I t is essential that we spend muchmore time and thought on this problem; i t will pay gooddividends. "r believe that ret inal rivalry is destined tobecome one of the most important visual training means of thefuture. We haven't even begun to use i t intelligently. l amhappy to know that retinal rivalry rates are being investigatedin routine optornetric procedures.

Measuring the ret inal r ivalry rate of parallel l inesrunning in opposite directions for alternate eyes - whether bycolor separation (BSM technique) or by polarization (Renshaw'stecbnique) - is of great importance and will result in a betterunderstanding of visual functions, as saon as a sufficientnumber of tests ar e available ta compile stat is t ics . There is


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no reason why r a t ina l r iva l ry should not serve as a means ofdetermining the quali ty of binocular seeing. Further than that ,depending on how the pat ien t reports seeing the l ins s , it i s possibleto state '!{hether the pat ient has binocu13.r, ambiocular or uniocularvision at the tilTe the t e s t is made. I t i s well worth whileta deterrni:18 the r esponses under varying posturing demands. .Bythis method i t is possible to deterrII.ne the most desirableobject ive visual condit ions for binocular posture, l'rhere the l a t te ri5 not a constant fac tor in vision. It i s for this reason thatin ou r own test ing techniques reti:1al r ivalry tests are a MUST

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I I I . TI:1E MEANING OF "REALITY" IN VISUAL PERCEPTIONOne rrust t a k ~ humanJJehavior into consideration when he deals with

people. It is ; :rLilly -inp-rta.'1t to l is ten to people and to t ry tainter!Jret wnt they te l l you. The reason is that what they te l l youxpresses much more accurately what they.perceive than can be determinedby any objective tes t . After al l , what they te l l you is a summation ofwhat they perceive, even though i t may be far from accurately reflectingthe proximal stimulations. AlI proximal stimulations which impingeupon the eye go through a very rigorous sift ing process. Sueh stimulationare gross and disjointed and have to be shaped into soething that i8coherent and, ab ove al l , something that makes sense. The product willnot be acceptable to the organism un t i l i t does make sense. I f Iobserve something that i s not reasonable, l do not want to admit i t ,I am reluctant to admit that l saw something outside of rny commonexperience. If l see a red bear in the park, even through l know thatthere is no such animal, l shall be very hesitant in telling you whatl "thought" l saw, for fear that you might consider r an unreliableovserver. Sa l look twice and attempt to get a different view of thepeculiarly colored animal before l commit myself ta adrnitting seeingthe red bear. This means that only those things which are written w ~ t h i n prior experience make up the real i ty of our visual percepts.

A. 1hings are not real because of their stabi l i ty (or sirrplicity); theyare ~ t a b l e because of their realness.This statement is apt to upset our present ideas regarding visual

functions. The human brain craves knovrledge, yet our thinking capaci tyseems il1adequate to cornprehend corrplicated phenomena unless we breakthem down into smaller 3ub-wholes. Ne cannot, i t appears, understanda complex mechanism or organisrn unless we break i t down in to i tsvarious components and study each one separately. This analyzingprocess has been considered hitherto the only acceptable scientificprocedure.

The breaking-down process seems to be admirably suited to"simplify" our original problems. For instance, in the investigationof matter scientists f i rs t dealt with macroscopic, then microscopiepart icles which eventually were reduced to molecules, atoms and electrons.There is but one difficul ty with this proce33 - i ts i3 not reversible.After we have a ll the pieces in greatest minutiae, we can no longerrelate them to the original problem at hand. This truism starts even nowto pervade all sciences, even medicine. The upswing of psycho-somaticmedicine provides i l lustration.

The holistic approach accepts as a fundamen tal tenet that thew-hole is greater than the sum of i ts parts. A watch that keeps accuratetime differs greatly from a box filled with aIl the parts of a sirrQlarwatch. The accurate movement is no t con tained in the wheels per sebut i3 the outcome of much p l ~ ~ ~ i n g . For the sarre reason, a l ive humanbeing is an entirely different thing than a cadaver on the dissection


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table. True, i t is a great deal easier to study the histologicalfeatures, th e nerve paths, the individual cel ls , than it is toanalyse the behavior character is t ics and th e thoughts of thel ive person.

Because of our l imitat ions, as far as thinking power isconcerned, we are given ta ~ y e r ~ s i m p l i f i c a t i o n . The simpler a thingi s th e better can we understand i t , but th e less i t conforrn torei1ity . The use of atropin in eye examination i s an example.I m p r ~ e d ' s t a t i c findings are the sole justif ication for i t s use.Madigan, in an excellent paper, has recently shawn that the use ofatropin is of questionable benefit in stat ic retinoscopy. Howeverth e inhibition of accommodation rnakes it a great deal easier forth e physician ta "scope". I t i s this consideration, rather thanany other, which prevents this inadequate technique from becomingextinct.

The rea l i ty of what we see does not depend on the complexityof what we see. This is tremendously important. When we seesomething farniliar, no matter how complex, i t 1s more re l l to usthan a very simple but ambiguous forme We are capable of perceivinga very complex, known, abject more rapidly than a simple nonsensicaloutline. We can reproduce the former ID.1ch more accurately on paperthan we can reproduce the l a t te r "simple" figure of unfamiliar .shape.

B. Stereosco ic erce tion is more fundamental and more real than"fIat" ,two-dimensional erce t ion because th e normal visualsurroundings are plastic or three-dimensional

La\YS pertaining ta sensory perceptions are apt to apply taa ll sense organs. I t i s , therefore , weIl ta study th e la\vspertaining ta sense ~ o d a l i t i e s other than vision and ta try taapply them ta th e visual sense.

Inasmuch as our spat ia l surroundings form the medium whichserves as our milieu from bir th , it is not reasonable that the threedimensional quality of these surrounds should long escape theorganisme Why, then, should "fIat" seeing, or th e seeing in asingle plane, precede the three-dimensional percept? Is i t notpossible that we came to this bel ief because it appears tasimplify our problems in understanding vision? The very factthat we compare the visual organs with th e man-made camera isindicative that we try to reduce th e imnensely complex neuraland cortical processes of seeing to th e s ta t11s of sonething whichi3 within our understanding.

Consider that the one-Gyed individual is capable of orientatinEShimself in a three-dimensional world. Such 2.:1 individu al v:ocl j bever-y much aITIazed i f you should t e l l him that hc''.c' 'lasticseeing. Koehler has shown that variable depth is :;':ll-:rent in

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certain uniocular sensory visual fields which have been exposedto certain specifie figures. Many "fIat 1 figures, such as thereversible staircase, geometric drawings of cubes, octagons,etc . , are pereeivedas three dimensional real objects even thoughthey are actually two dimensional projections. I t seemsunreasonable to assume that perspective seeing ID.lst evolve fromf la t seeing. Certainly, a great deal of experimental evideneeseem3 to contradict such an assumption.

l ~ h o u l d l ike te i l lust ra te la ter (under heading D) theimprob abi l ty of stereoscopie seeing being essentially a learn-edprocess - thru Firs t , (Simultaneous perception) then Second ( f ~ a t ) and f inal ly Third Degree (stereoscopie) fus ion - by quoting the case of a small child who has been under IDlf observation sinceinfancy. The child has been severely cross-eyed sinee birth andnever knew the rneaning of binocular posture prior ta a strabismusoperation.

C. Objective visual training situations should be based on reali tyrather than on siIDElieity of design.Provided the assumption, that stereoscopie V1Slon is morefundalntal than tlflat" VlSl.On, is true, how can we jus t i fY ourpresent visual training methods in regard to .strabismus?Any training instrument that violates the reality ofperception violates a fundamental organismic principle and makes

it harder for the patient ta interpret through i t . I t isimportant ta have instruments that reproduce reali ty as nearly aspOssible in arder to make i t easy for the individual to interpretthe objective si tuat ion. If i t is the intention to make i tdiff icul t for an individual to interpret test conditions, theabove rule may be violated. But the testing and training mustbe limi ted ta those individuals ..mose achievement level ofinterpreting binocular phenomena is high. But if the trainingsetup is to create a situation that is simple and understandable,i t must present s orrething which is real , in other words, somethingwhich is wi thin th e prior experience of the individual. This isespecia11y true when dealing with children. If it is possible,through certain instrumentation, ta re-constitute sorrething whichthe child knows, we are apt to get the response that we are seeking.

I f we are to follow these principles i t vall become necessaryto ' al ter our concept of what constitutes a suitable traininginstrument. l'fe have given primacy ta training principles whichcan no longer be adhered to in the l ight of the above discussion.

D. A new visual experience, when su fnden t l y real , is apt to beadequate at once; but i t may gain added stabilit-r thru repetition.According ta Goldstein, new v i su al experiences are not


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- - - - - - - - ~ - - --- - -.........................

arrived at by th e slow and graduaI extension of prior experiencesjra ther , they appear suddenly as complete ent i t ies Here is the story of a small child which has been under mvobservation ever since she was barn. The child had a severe internalstrabismus from birth and consequently never had a chance ta acquirebinocular vision. One or the other eye was always turned so far inta the corner that you could hardly se e i t . At the age of about foursh e started ta alternate fixation. This, in rny estimation, was acr i t ical period in the child 's visual behavior because it might haverueant the advent of ambiocular seeing, i . e . , th e emergence of theturned eye from the suppression stage. The father was informed that ,should the child learn to interpret macularly from both eyes, i twould seriously interfere with a future binocular pattern of seeing,were the eyes ta be straightened. The father agreed ta l e t the childwear plana lenses with opaque nasal sections. About a third of eachIesn was frosted, (AIsa see Chapter X, half ocluders) so that whenthe child looked s t ra ight ahead wi th the r ight eye, th e frostedsection of the l e f t lens intercepted the direct l ine of gaze of the(turned) l e f t eye. Conversely, i f she wanted ta look straight aheadwith her l e f t eye she could do so with the result that the direct l ineof gaze of the (turned) r ight eye was intercepted by th e shield.

I t may be argued that we did not by tbis means prevent th eformation of an ~ o m a l o u s ret inal correspondence, because the contraocular image of the fixated object was not erased. This objection isvalid only i f i t can be proved that anomalous ret inal correspondencecan forme AlI experimental evidence argues asainst such an assumption.Therefore, we did not worry about the secondaDT re t ina l image,of th efixation abject, foroed on a widely peripheral re t inal area of theturned eye. Vie were concerned that macular images of tl'TO widelyseparated abjects should not form, because th e chiId, in aIl probabili ty,would le '1't"n even tually t 0 interpret them correc t ly in space, 1. e. ,Iearn ta see ambiocularly.

The child wore the occluders unt i l th e parents were ready tohave the child operated on. No visual training was given before theoperation because we could e l ic i t no binocular fixation attempt atany range. The operation was successfully completed when th e childwas seven years old. Two days after th e bandages had been removedthe child came to IllY office. Her visual acuit-v was 2n;20 with eithereye and the eyes were cosmetically s t ra ight . She did not fixatebinocularly when an abject was brought to within arm's reach; rather ,the eyes retained parallelism (Iack of convergence). Because theeyes were straight in distant gaze, an attempt was made at this f i r s tvis i t to e l i c i t a binocular visual response on a distant projectionscreen (a t 16 f t . ) . We reasoned that the attemot at elici t in a a0binocular percept should be made because the ehilcl coulcl not haveIearned a strabisme posture (looking with both eyes in two differentdirections at once) but had alwavs dependecl on a uniocular postureprior to operation.

Tests for retinal r ivalry made on the cl istant screen stowed an

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alternate percept, f i r s t one eye maintaining ful l control of thescreen and then the other. Very soon, however, indications of theformation of a binocular sensory field were apparent and when th eBrock Ring Test (BSM 1, 2, 3) was made there was but a very shortperiod of "sideways motion" before the child exc1aimed that the ringseemed to come toward her and to move back thru the screen.Appropriate size changes were also perceived.Immediate1y after the stereoscopie percept became evident, thescreen was fi l led with a cornplex stereoscopie scene, showing waterbuffalo par t ia l ly immersed in water (BSM 16, 19). This scene wasselected because the child lives near a lake and is qui te familiar

ri h cows. The scene was the nearest approach to her habi tua lsurrounds that was available.She looked at the screen for a l i t t l e while and then al1 of asudden exclaimed - rrsay , daddy, that cow is reaU" This could only

mean that she had reconsti tuted a real cow thru stereoscopie ,cluesand that at f i r s t , she had seen it only as a picture on the screen.If this were not so, the sudden exclamation of surprise and joy couldnot be explained. That she saw the cow stereoscopically wasdefinitely proved by giving her a flash-light projector which threw abaloon-shaped white f i ~ e onto the screen. This baloon, she p1acedselectively on the particular objects in the three-dimensional.fIe!'d'whch happened to be in the sarne plane wi th the screen e Inasmuchas the BSM technique permitted me to move any given object into thesaid plane, there was no possibility of her "guessing". This meant, that she had accurate stereoscopie abil i ty within half an hour aftershe had "learned" binocular seeing.

Was i.t learned? How could she Iearn i t? And how did she knowwhat stereoscopie seeing rneant? Because that was what se'eing a !lreal"cow Iant to her. Why didn't she see rrflat?rr She had never hadbinocular vision before. Since she recognized the stereoscopiepic'ture of the cow as a rrreal rr cow, she IIDst have had an appreciationof this real i ty prior ta the time that her ~ i n o c u l a r percept was born.The only new feature which was added to what she had alreadyexperienced (in uniocular seeing throughout), was the opportunity toreconstitute real i ty solely through stereoscopie clues.I t is about time that we abandoned the concept that one-eyedseeing differs in any major particular from binocular seeing. AlI

that is added in binocular vis ion is apparently a finer depthdiscrimination, and that primarily at close range. I t is t rue that,only through appreciation of retinal disparity can we reconstitute' rea l i ty by means of stereoscopes or stereoscopie projection. Thatis why the BSM equipment is sa valu able as a differentiating agentbetween binocular, uniocular and strabismic seeing.

E. Reality of perception is only possible in adjusted behavior .


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lch

"

Renshaw says t ta t nothing can happen unless the organism isse t to le t i t happen. This is a fundamental concept.A persan who does not know what ta expect, or who is disturbed,15 not in a position to give a clear account of what occurs. Thisholds true in 311 phases of human behavior. Our psychopathie wardsare f i l led today with individuals of this type.

A very important factor in visual t ra in inLis the sett ing up oft raining situations which tend ta create stable visual conditionsaver as much af th e total pereeptual f ield as possible.The peripher31 portions of the visual f ie ld contribute largelyta the maintenance of fusion in binocular vision (Halstead) and i t

seems therefore unreasonable ta exclude sa large a section of theperipheral binocular f ie ld in our training instruments.One of the possible reason5 why narrow fields were designedfor visual training w a s ~ i m p l i f i c a t i o n . We fe l t that we couldsimplify in two directions! (1) tht the sirnplest and least'detailed forms were the easiest to fuse (2) we could reduce thestimulated f ield area (and this was done in certain instances)

unt i l only macular figures remained. Vllien such simplification hasbeen reached the objective visual situation has lost a ll semblance tarel i ty and instead of being easy ta fuse, i t has become diff icul t .The "easy" way for th e binocular processes ta function is in aunified to ta l f ie ld, something which has scarcely been t r jed.

Our tendency in visual training should be to produce trainingsituations where larger and larger portions of the to ta l binocularf ield of an individual take part in the training. This wil l giveus a powerful means of staoilizing the macular functions. I t isthese macular si tuations, which need our particular attention, becausethey are the one which corne most readilyunder the inf1uence of thepatient 's thought processes.I t should be noted that. mental attitudes frequently disrupt,rather than enhance, the fusion processes. Peripheral responsesare much less influenced by undesirable attitudes on the part

of the patient .The ract that uniocular ur alternate macular suppression isthe rnost common visual dysfunction would indicate that i t is theleast diff icul t anomaly to achieve. We can hardly question thatsuppression of this type is a learned process.

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1i!JI 1ill 1h

2h

IV. SINGLE AWARENESS IN BINOCULAR VISIONSuppression is a normal phenomenon in a ll organismic behavior.

A. Suppression is not only a normal, but a necessary, function in binocularvision, because a ll objects in three-dimensional space can not be oncorresponding fusional areas of the two eyes while binocular posture ismain tained.There is no need ta speak of th e significance of physiologicaldiplopia. The subject i8 adequately discussed in available l i terature.We a ll know that i f fixation is held at 30 f t . the horopter will formthere and that an object six feet from the observer will no t be oncorresponding re t inal areas. In order ta obtain fusion of this near

er object fjxation would have to be altered sa that the two eyes wouldconverge at s ix feet . N e Y ~ I ' ' t h e l e s s , i f th e horopter is held at thir tyf'eet and an object is locatedsomewhere in the binocular field but notin direct l ine og gaze, diplopia i8 , as a rule, no t experienced.Diplopia i8 m08t l ikely to occur when the non-fixated object l ies withinthe tr iangle formed by th e two visual axes and the interpupillarydistane. In this position the non-fixated nearer object is broughtbnnon-fovealretinal areas equidistant and on opposite sides of therespective foveas. Both images are then close enough to the foveasto be qui te clearly intrpreted. Because they are not fusable, asense of doubling readily obtains, provided attention is drawn to i t .Placing a pencil ten inches in front of the nose, while looking at adistant abject straight ahead, i8 in fact a preferred method of teaching an individual the awareness of physiological diplopia. If thepencil is shifted a few inches ta the r ight or ta the l e f t , the feelingof "double" becorres le8s and less evident and saon ceases altogether.

x

Let X in the above f i ~ J r e represent the distant fixation abject andPl the location of the pencil where i t is sean double most easily. I ti s apparent that the ret inal points Pl are equidistant an opposite sides


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s

.

of the two maculae (M); When the pancil is intermediate ta the twofixation axes, as when i t occupies position Pl, both retinal imagesare equally distinct and the organism is hard pressed ta decide whichof the two to suppress, i f they both obtrude themselves to consciousness.I f the pencil i8 now rnoved ta a second position P2 ta the right of thefixation axis of the r ight eye, th e ret inal points P2 are no longerequistant from the respective maculas so that the image of the pencilin P2 position is therefore easily suppressed, for the sake of singlevision.

I t is l ikely that in normal occupations and in normal surroundingsanear object i3 more readily seen double when fixation is held at afarther object located in the same general direction, than when thereverse situation pertains, i . e . , when a nearobject is fixated andan object farther away obtrudes i t se l f to consciousness.When an individual has been made conscious of physiologicaldiplopia along the above l ines, how doss this affect his spatialadequacy a t the time when he sees double? Suppose, he lights acigarette, while keeping his gaze at sorne farther distance, and thathe now sees two cigarettes. Will thatpose a question as to where tohold the match? I t seems reasonable that he would make a fusionattempt before proceeding with the l ighting of the cigarette. Thiswould !Dean that to l ight his cigarette, he would have to malee anabstraction, i . e . , he would have to think about how to do i t , wherebefore he did i t without giving i t any thought. Could we say, then,we has improved his spatial awareness? l believe the answer is , No.

; B. Fusion i8 not an essential f1Ctor in "single" awareness of peripheralabjects.In normal binocular vlslon J as we have seen, the abjects whichdo not have their images on retinally corresponding areas are s t i l lperceived singly. Is such an abject seen in the direction where oneeye sees i t and is i t tota l ly suppres3ed in the direction where theother eye sees i t? In other words, is the direction of such an abjectdetermined by a certain projection axis of one eye as i f the othereye had been total ly occluded? The answer is , Na. The effectiveprojection axis i8 apt ta l ie in a somewhat intermediate positionbtween the right and le f t projection axes. This mearrs that the lacali tyof such a'1 object i8 s t i l l binocularly determined even though fusiondoes not occur; Single awareness is then due ta a closure by a processof abstraction.

, The above sort of closure without benefi t of fusion cm only~ X l s t so long as the individual is not aware of diplopia. Diplopia forms anlillperfect closure, even i f the individual accepts the two images asbelonging to a single object in space. Even the consciousness ofd b l ' .ou lng does not necessarily prevent knowledge of th e singleness of~ h e , O b j ~ c t . I t is important to rernember that this type of closure,e l t elther complete or imperfect, is gained by a b 3 t r ~ c t i o n and is ,

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!'l'!i

'i ! '

"; t

26

therefore, a f rontal or pre-frontal lobe process. From the "adequacy"point of view a total closure ls of course preferable to an incompleteclosure, yet we have been inclined to t rain individuals for incompleteclosure where we formerly had a complete closure.

--------- - -..........., - -- '-......-\ -,' - - - ----tJ. BThe above figure will i l lus t ra te the foregoing. I f bath eyesare fixating abject A a t sorne distant point and a pencil P then i saligned with a peripheral object B, i t is placed in position as shownin the figure. The posit ion of th e pencil does not agree with eitherof the secondary fixation axes (broken l ines) and projection occurs

from an intermediate point between the two eyes. When diplopia occurs,the two pencils are sepn in positions indicated by the broken circles.There is an organisrnic tendency to place the two phenomenal pencilaequidistant on either side of the abject with which the pencil is tabe aligned. Only when one eye suppresses, 5 0 that the cortical imageis no longer of any use to the organism, will th e pencil be placed indirec t l ine with the secondary axis of th e other eye which reaches theobjecte In the l a t t e r case the object is less accurately localized;in the former, better . When th e pencil is seen singly, without benefitof fusion, it is assumed that fusion attraction is s t i l l a factor inbringing about the desired effect of thetwo ret inal images forming asingle perceptual uni t . I t can be experimentally shown that , i fdiplopia ls el ic i ted, th e two pencils appear much closer together t h ~ they should be, as deterrnined by their relat ive ret inal posit ions.I t is assumed that fusion attraction furnlshes the necessary binocularcue as to whether diplopiais-crossed or uncrossed 1. e . , whether th eobject is nearer or beyond the fixation plane.

A a..ridi t ional experiment can be set up wi th the BSM slides No. land No. 2 (the red and the green ring) and th e rabbit sl ide (BSM 20).While fixation is held at the rabbit, the rings can be graduallydisplaced sa that eventually fusion of rabbit and phenomenal ring canno longer be maintained simultaneously. If fusion of th e rabbit isrnaintained, fusion of the rings i5 eventually broken. This is evidentwhen the color of the perceived ring changes from a mixed reddish-green


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"ee

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color to green or red, or when two interlocking rings are seen, onebeing green and the other red. I t ispossible , to interpret partia1lyinterlocking rings, both perceived in crossed disparity, as beingdoser, ta the observer than the rabbit on the screen. H o ~ v e r , the. two ringsr l i lappear mJre closely inte.rlocked when the color f i l ters are worn tharJ.'. when they ar e taken off. This indicates that a fusion attraction occuredwFdch , even though incoDlJlete, was interpreted as depth variant betweenrabbit and the two rings. On the other hand, if the phenomenallyperceived displacelIlnt bet'l'leen the twa rings equals that of the actuaJ.d i s P f a c ~ m e n t on the screen, bath rings are seen to l ie in theplane with the rabbit. I t may be said, then, that fusion attraction)even thou h i t does not suffice for co lete closure (seeing an objectsingly must be interpreted as depth variable. I t is important thatwe keep this in mind because it permits us to e l i c i ~ y gross stereopercepts.when the two eyes are not adequately postured for stereo-aceuracy. Manystrabismics, when we f i r s t see them, are capable of posturing accuratelyenough for gross stereopsis. This becomes of importance in training.Fusion attraction can only occur within certain limits of rat inaIdisparity.

I t may be asked, "If closure i8 possible, where there can be nofusion inthe s t r ic t sense of the term, why does this principle not holdtr'Ue a ll the way ta strabismie dispari y?1IAs previously reported, i t has became apparent from aetualobservations that during incomplete fusion the depth variation betweenthe objects in question is measurably less than i f fusion efforts were

lacking. These same experiments have shown, however, that i f the ringdispari ty becomes too grea t , both rings (as perceived) suddenly "dropback" to the plane of the screen and are then interpreted as a pair ofinterlocking rings in a "fIat" percept.Dr. Verhoeff told me sorne yearS ago that he learned throughpractice to prevent fusion of stereograms ta such an extent that a l lfigures which are not exaetly alike ( i .e . , having stereoscopie qualities)are seen double and fIa t rather than single and three-dimensional. I thas been nv experience that many individu aIs are capable (and willing)to inhibi t stereoscopie fusion (prevent fusion attraction) and sorne, infact, will keep their eyes sufficiently off alignment ta prevent fusionat a ll cost.The above phenomenon is frequently eneountered with adul ts whoare subjected ta the Broek Ring test on a dis tant screer" Sa::... of i:-hemWill not, at f i rs t , l e t the phenomenal ring come off the screen. Theyprefer to see two rings in interloeked position. H:;wever, once this

r r . e n ~ a l inhibition is broken they rarely are capable of preventing stereofUSlon in subsequent t r ia ls , unless they are psychopathie.bb' In the Brock ring experirnents binocular f i ' at:' or .; "': h ~ J ' ; "t L1era lt, in other wards, the rabbi t is maintai ned as a , i r .g l e fuse object

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in the center of the total binocular field. Within certain smalllimits of disparity the rings may then be appreciated as fused andbeing nearer or beyond the central target (the rabbit). I f the ,disparity i5 widened, there may be awareness of double-rings capableof stimulatlng the fusi,on sense to such an exten t that they also areseen either nearer or beyond the rabbit. This means that thedisparl ty is then beyond fusi on abi l t but within fusion-attraction.Finally, the rings may be brought te such widely disparate positionsthat they are seen as interlocking rinEs in the plane of the rabbit .Fusion attraction has then been b r o k ~ n . In a ll three cases there isone Comnlon factor: The central target is being maintained withinfusable limits. Anothp-r possibili ty may be encountered: Anindividual may elect to r8tain the ring (s) ~ ~ t h i n fusable limits ofretinal dispari ty and le t the rabbi t "double" when the dispari tybetween the two perceptual objects (ring and rabbit) becones toogreat. In all instances, however, one of the two perceptual objectsi8 rnaintained on sufficiently .corresponcling ret inal areas to rnakefusion possible. This is not the case in strabisrnus where fixationis maintained by one cye onlv. Here one end of the measuring stick15 lacking indetermining dispari ty in terms of depth variable.

D. I t 15 the ~ n a b i l i t y to sUEpress diplopia in normal surroundings thatleads ta the most serious visual diff iculties.

E.

That is something which needs to be remembered in strabismustraining. l am glad to have found a means of helping the strabismicobtain binacular posture without having to teach him to see doublethe,process. l reminded of this time anc again by patients whomtauRht ta see double befarethey knew the true meaning of fusion.

~ n e ~ e patients found i t very dif f ieul t ta lose the sense of seeing_ ~ ~ eVen though their e y ~ s remained straight. l know of a few who, ~ r , , ~ e v e n or eight years of binocular seein::r s t i l l complain of

a n ~ ~ ~ ~ ~ on small fixation abjects, although they show good peripheralh o ~ r ~ o l-central fusion. These cases were c l ~ s e d as instances of.. , r ru 'was th) Slonalis. I t has been my belief fo r a long time that i tToa ."':t candi tian which preven tedsuccessful completion of the cure.l k n ~ w n inclined to believe that i t could have been prevented, hadstrabistQ hen What l know now. The fact is that since l have trainedfusion ~ v ~ s ~ i t h o u t attemptin; ta establish diplopia at the outset,belie'le th r ~ l o n has not been a serious problem. For this reason lseein;;:" in\h ~ s u a ~ training m e t ~ a d s which tend. to produce "double.unso-.:6ct. ~ } l a l surroundlngs of the patlent are to be conslderedt'"\ ...... a' ~ ' I ~ ' " " -., - - . ~ ~ t ' ' ' ' nos t . ' ~ , e . !})'sSions are almost due to lack of adeouate binoculara; "='1 ' - . : . . . : . : . . : ~ . . . : . . . . c - - : ~ ___ -: -__ : -___ :- :_ _ _ _ _ _ ~ . . . . . : . . . : - - = - _ ~ : - - ~ " r ~ ; ; - < 1 ~ : 1 Qsually disappear nhen adequate binocular posture haso : ~ J ~ ~ a r ~ V i s u a l train in must be directed toward strengtheninc'.(;.s 3 '" re."tl l)

IJ t-trJal visual acui ty may be caused by lack of direct


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fixation abili ty of the affected eye, the establishment of binocularposture must bring about a better ability to fixate directly withthe subnormal eye and, p ~ r f o r c e , bring about a heightening of visualacuity. When a central scotoma is no t the cause of low visual acuity,such training always produces increased acuity of that eye.

F. Macular suppression does no t create amblyopia-ex-anopsia.I t has frequently been assumed that i f an eye is suppressed i tloses i ts abili ty to see clearly. This assumption appears no longerto be true. Such an eye simply takes on other functlons which areadaptations to the particular visual set. The ret inal fibres neverceaae being stimulated by the l ight impulses that reach i t ; proximalstimuli will invariably reach the brain. In otherwords, the afferentnerve paths remain open and active. How, then ean the perceptualfaculties of the amblyopie eye deteriorate? This question has to beanswered before we can intell igently eonsider the nature of amblyopiaexanopsia. The only possible answer is that these undesirable impulsesare bloeked in the"brain in sueh a way that they eannot reach the levelof conscious awareness, and that this blocking may eventually resultin permanent inabil i ty to see clearly with the affected eye.In uniocular amblyopia, where the amblyopie eye is not notieablyout of alignment, almost norial peripheral awareness can freqently bedemonstrated to exist, but maeular awareness seems to be defini telylacking. In sorne of the eyes where visual aeuity is below 6/200,

foveal stimulation of the affected eye, by a strong point source ofl ight, only produces the sensation of a "glow", the patient not beingaware of the l ight i t se l f unless i t i s thrown on off-foveal re t inalareas of the eye. I t can also be shown that when the lip,ht is notseen directly, the pupillary reflex constriction to l ight stimulationis also lacking, showing that the foveal re t inal stimulation i5 beingblocked prior to the geniculate body, i . e . , before i t reaches thecerebral cortex. In these instances the blocking is no t on a corticallevel but i8 due to a lack of transrnissibility of these stimulationsfrom the fovea to the geniculate body. I f the blocking occured in thecortex, the pupillary reflex arc would be intact . This information hasbeen obtained through experimental evidence and should be indicativethat the anblyopia is due to destruction of foveal fibres rather thanto non-use.

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v. RETINAL SLIP - A VISUAL CONCESSIONA. Art i n ~ l e q u a t e binocular posture results in ret inal sl ip.

When binocular visual functions can be shown to exist while oneeye fixates a small f ixat ion object ,direct ly but the other eye issl ightly off corresponding position, then that eye has "slipped" awayfrom accurate binocular posture. This phenomenon is best described bythe term "retinal sl ip" . I t is a descriptive term, which may not beany longer-in generaI use.

Peckham, many years ago, established experimentally that binocularvision is not lost when the eyes are not accurately aligned on a singleobject of regard. These findings gave th e psychologists th e basis fortheir theory that re t ina l correspondence is not innately determined andthat i t may vary considerably with different individuals and fordifferent visual demands. They have long since abandoned th e concept ofpoint ta point relationship between the two eyes.

Du!ing retinal slip we may assume either that a new horopter,which no longr maintains correspondence between th e centers of the twoTovae, has formed, or that th e normal horopter is s t i l l present. Inthe la t ter case it has been moved away from the plane of th e fixationabject, to a farther point in a sl ip toward convergence. The l a t t e rassumption i s more l ikely to be correct.Personally, l have a variable condition of exophoria and ret inal

slip toward exo. l often rnaintain a binocular pattern that is justadequate ta maintain a peripheral binocular f ield structure but is nolonger capable of accurate stereo-perception, due ta a lack of macularfusion. l have noticed when driving a car that suddenly l am aware oftwo t raff ic l ights (quite close t o g e t h e r ~ i f there is not any part icularneed for keen visual discrimination. I t is a simple matter to fusethem, but this results in appreciable difference in the general appearanceof th e landscape. I t seems to me that l have this sensation of doublingduring "retinal slip" only because l have taught myself to be aware ofdiplopia and because rqy eyes are aloost equally dominant. Mostindividuals, who demonstrably have an exophoric s l ip , report that theynever see double. The fact that doubling occurs in my orrn case showsthat during phases of r e t ~ n a l slip my,horopter l ies considerably beyondmy gaze, (or normally behind th e eyesJ , the eyes being in a somewhatdivergent position. The significant fact remains that l have neverseen the doubling of a cowl l ight of al1 oncoming car or of the t a i ll ight of a car. T . ~ i s must meal1 that accuracy of binocular postureis maintaincod ;vI-: ;, . '.,r ~ \ ' e ne,::d for ;oncentrated attention arises. I tis also sigrnfic..nt ." ' ; a :


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cannot be obtained. I t is fortunate for my safety and for that of, : ~ , - , - - - _ . _ , - ~ - - - - -other m o t o r s t s ~ o n the road that l do not maintain a ret inal sl ipwhenever visual demands require good binocular posture. As saon asthe eyes become alerted the re t inal slip i s irnmediately and in -st inct ively taken up.

Let us define ret:i,nal sl ip as a tropia position of very moderate 3 . l 1 l Q ~ ! 1 : t - = - - - ( T h l s IIDSt not be collSused with conditions of excessive phoriaswhich may not be in evidence while binoeular posture i s maintained.)

The essential difference between ret inal sl ip and a t ropia. position is that in the former case the binocular pattern of seeing i3pripherally maintaine


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determination of depth variables the retinal sl ip has to be takenup. The nature of the task, therefore, deterlllnes whether or notaccurate posture will be maintained.

The lack of understanding of these underlying principles hasbeen a source of a great deal of perplexity to many examiningpracti t ioners. Frequently WB observe a high exotrope who, nevertheless,shows adequate stereo-accuracy behind a stereoscope. Because, we maynot be able to observe the individual's eye positions, we fa i l to seethat for the special task which he cannat successfully perform withthe eyes in a tropia position, - he posture binocularly long enough toperform i t . By the time he looks out from behind th e instrument beagain shows bis exotropia. I t follows that , unless a desire can bedeveloped in this individual for maintenance of binocular postureunder less demanding conditions, his strabisll1Us cannot be "cured".

D. Periodic strabismus is an extension of retinal sl ip.The only effective way to solve this problem, that l can see,i f to strengthen binocular posture in visual situations which correspondwithhis normal visual surrounds. I t is for this reason that aprojection screen placed across the room is becoming so important inVisual training. Pictures that recreate thru color separation orpolarization) visual situations similar ta the patient 's normalsurrounds can be projected onto the screen. can then be taught toposture binocularly instead of uniocularly in situations which aretransferrable to his normal surrounds. Until we train in normalsUIToundings, we S,hall find that the periodic squinter may walk inwith one eye in a tropia position and then proceed to maintainbinocular posture in a l l our training instruments. This will be trueregardless of his abi l i ty ta maintain fusion through la tera l prismwhich forces him ta over-converge. Duction exercises are, definitely,not the answer in such cases.The periodic strabismic chooses to have binocular'visionwhenever he wants i t , but frequently, for bis own reasons, choosesnot to have i t . That is why you dare not leave i t up to anindividual 's judgment whether or not he wants to keep bis eyes straight .The only way to overcome these habits is ta strengthen binoeular

posture so that he no longer needs to make this choice. Until you dothat , the occasional squinter will invariably be seen with his eyesturned at a time when he is no t particularly interested in what is goingon. The minute he s i ts behind a training instrument he follows throughin great style. He gets an hourIs or half hour's workout and this canbe kept up for years without his ever getting heyonrl that stage.

E. In more extensive suppressions the suppressin2 eye rnay be turned toa noticeable degree and stereoscopie abili ty will, then, no longer beevidence.


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As with a periodic squinter the fusion processes become lessand less important to the individual, the central suppression extendsfarther and farther into the peripheral f ield. This may bring aboutan eventual shif t from a habituaI binocular pas ture ta an habi tualstrabismic posture. He may eventually abanoon binocular visionaltogether, except for special occasions.Nearly a l l strabismies have occasional moments when theymaintain binocular vision. The only reason this is no t generallyknown is that most 01 us have never taken the trouble to discover thefacto My whole training procedure no\'{ centers around the search forthe part icular visual tasks ta which the strabisme l'espnds by aneffort ta find out under what conditions he will respond binocularly.To visi t ing doctors i t appears as i f we spend an unreasonable amountof time to obtain binocular posture (maclar stereopsis). But tirnethus spent invariably pays good dividends.We find a point of attack, once binocular posture has beenobtained - under whatever conditions and at whatever range-thateliminates the "breaking down ll process, which used to be a longpreliminary period of training before any attempt to elici t binocularpercepts was made. We are no longer concerned with breaking downanomalous (strabismic) projection, provided we find a means of getting

} , h ~ p a t i e n t to posture binocularly for even fractional periods. Wetackle the problern at the most logical position. This means that wedo not attempt ta get an in i t ia l binocular posture at infini ty position.Parallelisrn is expeted only at the end of training.

Marked ret inal slips or actual intermittent tropias accur mostcommonly in distant g a z ~ or during- mOr.1ents of inattention requiringonly lo\'{ postural demands.Because vre found the above to be true, Strabismus training inour office follows this general routine:l ) We find the position and visual task which will bring aboutan attempt at binocular posture. Almost without exception this position

is found to be ,n thin easy arml s reach of the patient, at distancesvarying from four to twenty inches.2) In order ta succeed in that attempt we see ta i t that

the patient is confronted with a visual problern that requires b i n o c ~ l a r posture for adequate solution. We assume that the patient will makean effort ta posture binocularly i f he is presented with a problemthat cannat be solved while maintaining strabisrnic posture or byalternate fixation.J) Because fIat fusion targets do not require binocular posturefor their solutton we no longer consider the attainment of Firs t orSecond degree fusion as an adequate criterion of a binocular fieldstructure. For this reason "flc. t" tarr;ets are seldom used in our

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office for strabismus training, nor fo r correction.of marked ret inalslips. From hard experience we have learned to rember that a11strabismics who have fai r visual acuity with either eye can lookalternately s t targets presented to them in stereoscopes or othertraining instruments and are capable of interpret ing the to talsituation in terms of bath, the r ight T1uS the 1ef t , percepts. Areport of three dots in a row (BF Unit or a cross (0 series) is there-fore not proof of binoeular posture. Additional evidence is necessary.4) Individuals, on whom ne duction firidir.Lgs Ca.. be made J arenot admitted ta stereoscopes for further tes ts . This is one of ourinviolable rules. .5) We do not consider the Keystone Visual Survey Test to bea diagnostic tes t in Strabisnrus. This does not rnean that a KeystoneVisual Survey t es t would fai1 to disqualify a strabismic in a.

general survey.' The individual might conceivably report "the dog abovethe pig"; "the arrowunder n i n e " ~ the "three balls in verticalalignment ll if he were a. clever alternator, but he could not rnaster th estereometrie t es t and would be disqualified on that accaunt. On theother hand, i f we have no other information we cannot conclude frqrnthe Keystone Visual Survey above that the patient has any certaintype of strabisrnus. When the stereoscopie t es t is fai led, weimrnediately question a ll other tests of the visual survey as to theirvalidity .6) We accept as a fac t that a strabismic may gain informationfrom one eye and then th e other, in temporal sequence, relative toa given single area in Space (straight ahead) and that these impressionsmay undergo a cor t ica l closure. We have seen that sueh closure occursoften ri hout th e pat ient ' s wishes. M:lst of these individuals seernto be incapable of maintaining permanent fixation with one eye intraining instrument. Alternation of fixation seems for them to bean entirely involuntary act.

G. T6 overcome retinaI s l i p s , i t is necessary to maKe perceptualdemands which require adegpate binocular postures for theircompletion.Skilled manipulations that require adequate binocular posture,

provide the requisite demands. Stereoscopie abili ty also furnishedthis control.Let us remember tha t cortical closure of temporally successiveevents i8 a common oecurenee. We see in i t moving pictures, insuccessive fixations while reading. In other l'TOrds, i t is not a

p r e r ~ a t i v e of strabismies only. 'The abil i ty to differentiate betweenfusion a.r1d closure at a higher cortical level is one of

brocks lecture notes on strabismus1

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