m Ufe U.S. NATIONAL LIBRARY OF MEDICINE 4?Cf. ■ return to national library of medicine before last date shown SEP 20 1982 A NEW CLASSIFICATION OF THE MOTOR ANOMALIES OF THE EYE BASED UPON PHYSIOLOGICAL PRINCIPLES. TOGETHER WITH THEIR SYMPTOMS, DIAGNOSIS AND TREATMENT, THE PRIZE ESSAY OF THE ALUMNI ASSOCIATION OF THK COLLEGE OF PHYSICIANS AND SURGEONS, NEW YORK, FOR 181)0. ALEXANDER DUANE, M. D., - H A P ^ * %' ~~— ASSISTANT SURGEON OPHTHALMIC AND AURAL INSTITUTE, NEW YORK. NEW YORK: J. H. VAIL & CO., 18U7, WW PREFACE, The following brochure respresents the result of some ten years' labor and study expended upon the subject of muscular anomalies. Whatever merit it may have is due to the fact that it stands for original investigation in a field still full of difficulties and obscurities. The author's clinicaj experience has convinced him that the classifica- tions propounded furnishes an adequate working basis for the diagnosis of these conditions. And his experience as a teacher at the Ophthalmic and Aural Institue has led him to believe that the principles here laid down, and the means and methods of examination here recommended, have been found by others also to be both intelligible and practicable. Many of these principles and methods have been enunciated in lectures given to successive classes of practitioners, and have been demonstrated in their prac- tical application upon patients before the same gentlemen; the auhor's constant attempt being to present clearly and in a way suited to general comprehension the rules for the diagnosis and management of the muscular anomalies. That this attempt was not unsuccessful he ,has had some reason to believe from the assurances of those that he has taught; and it is, therefore, with th- hope that the result of his work may be useful to others as well that he now offers it to the public. Alexander Duane, M. D. 49 East Thirtieth St.. Neir York. Ajjrit ->!>, IS!)?. EBB A TVM. Page 23, line 11: For "22," read "21/,.11 Reprinted from Annals or Ophthalmologt and Otologt, October, 1896. A NEW CLASSIFICATION OF THE MOTOR ANOMA- LIES OF THE EYE, BASED UPON PHYSIO- LOGICAL PRINCIPLES. THE PRIZE ESSAY OF THE ALUMNI ASSOCIATION OF THE COLLEGE OF PHY- SICIANS AND SURGEONS, NEW YORK, FOR 1896. By Alexander Duane, M. D., new YORK, ILLUSTRATED. Introduction.—Sketch of previous classifications.—Development of the idea of an etiological, as opposed to a simple anatomical classifi- cation. I. Nature of the problems that have to be solved in under- taking a physiological classification. II. The Movements of the Normal Eye.—Actions of the indi- vidual muscles.—Movements of each eye individually and the mus- cles by which they are performed.—Amount of these movements.— Field of fixation.—Author's experiments.—Power of the individual muscles.—Coordinated movements of the two eyes.—Table of asso- ciated parallel movements and the muscles producing them.—Asso- ciated antagonists.—Field of binocular single vision and of binocular fixation.—Author's experiments.—Movements of convergence.— Power of convergence.—Convergence near-point.—Prism-conver- gence.—Movements of divergence.—Nature of divergence action.— Movements of sursumvergence. — Rotation movements. — Ap- pendix.—Diagrammatic representation of the movements of the eye. HI. The Tests Employed and Their Significance.—Object of the tests.—Tests for binocular distant fixation.—Inspection.—Fixation and diplopia tests.—Equilibrium tests —Screen test.—Parallax test.— Tests for associated parallel movements.—Tests for convergence.— Tests for divergence.—Tests for sursumvergence.—Way in which the tests are applied in practice. INTRODUCTION. The nomenclature and classification of the muscular anomalies of the eye have been passing through the same stages that have been noted in the evolution of the nosology of other parts of the body. In the progress of our knowledge in regard to any given 2 NEW CLASSIFICATION OF MOTOR ANOMALIES. set of ailments, the first classification has always been based upon that which first strikes the eye of the observer, namely, the out- ward appearances and symptoms. Thus, many cases of renal dis- ease were first classified as dropsy, and dropsy formerly figured among physicians, as it does still among the laity, as a substantive disease, and to be treated as such. But, as medical science pro- gressed, and the underlying causes of disease were more and more brought to light, it became evident that dropsy is a symp- tom only and to be treated as a symptom, and that the principles of a rational pathology require us to search for the causes of the dropsy and to institute treatment addressed to the removal of these causes rather than to the direct relief of the dropsy itself. In this way a pathological classification is gradually substituted for one that is purely symptomatic, and a scientific, casual treat- ment for one that is empirical, or based solely on the appearances presented. This conception of disease as a symptom of a pathological pro- cess, and the consequent conviction that our therapeusis must be based ultimately upon an etiological foundation, could not have developed, or at all events, could not have become anything more than a plausible theory, barren of practical application, were it not constantly fortified by a steady increase in the number and precision of our means of diagnosis. In this way only can we make those fine discriminations between symptoms that enable us to form accurate inferences as to the diverse origin of phenom- ena which, to a cursory observation, seem identical. For exam- ple, our knowledge of the symptomatic nature of dropsy and of the necessity of treating it from an etiological standpoint, how- ever true it might be, would be a theory only, unprovable and practically inapplicable, were it not for the refined means we now possess for examining the chest and abdomen and for analyzing the urine. These diagnostic means have enabled us to convert theory into fact, and to redeem our treatment from the charge of empiricism. A similar process of evolution has taken place in regard to the motor anomalies of the eye. These were formerly (and to a great extent still are) classified simply according to the appear- ances presented, i. e., as inward, outward, upward, or downward deviations. And, to recur to our former illustration, just as dropsy used to be treated as dropsy, regardless of whether it was due to renal, cardiac, or hepatic disease, so an inward squint was (and often still is) treated simply, as a squint, quite without reference to its origin. The results in both cases have often been disappointing. , NEW CLASSIFICATION OF MOTOR ANOMALIES. 3 The first great step in advance was taken by Donders, when he demonstrated the frequent connection and apparent causal re- lation between strabismus convergens and hypermetropia, and between strabismus divergens and myopia. And, while subse- quent writers have doubtless gone too far in asserting the univer- sal application of his deductions, the service that he himself did to rational therapeutics by indicating one large class of cases in which a strictly causal treatment relieves the symptoms, can scarcely be overestimated. Another exceedingly important advance made was in the dis- covery of the insufficiencies and of the methods of estimating them. These latter, devised by V. Graefe, remain to-day among the chief means of discriminating between the various motor anomalies; and their invention, as in the case of all new methods of precision, opened the way to still further discoveries. The diagnosis and symptomatology of paralytic deviations was also worked out by the same author, and in a manner so admira- bly complete, that little remained for his successors to do ex- cept to gather statistics in regard to the precise etiology of these interesting affections. V. Graefe had pointed out the relation between insufficiency and squint, but since his time this relation has been largely over- looked, the consequence being that the two conditions have of- ten been classed as categorically distinct, and distinct principles of treatment have been applied to them. This arbitrary separa- tion of two things really the same has had a retarding influence upon the development of our knowledge of muscular anomalies. It became, after awhile, apparent that the very term insuffi- ciency was a defective one, implying, as it did, a casual relation, which was by no means always present. Hence, Stevens in this country proposed a system of classification in which the term in- sufficiency was replaced by hctcrofhoria, and the term strabis- mus by heterotopia, the former indicating a tendency to de- viation, which tendency is habitually overcome, and the latter a deviation which is more or less constantly present. The further use of the prefixes Eso-, Exo-, and Hyper-, served to differentiate between deviations or tendencies inward (con- vergent deviation), outward (divergent deviation), and upward (or, more properly, divergence in a vertical plane). This classi- fication is extremely convenient and has been generally accepted, at least in America. Furthermore, the instruments of precision, which the same author devised for measuring the various devia- tions, are doubtless the best extant, and have greatly facilitated the recognition and differentiation of the anomalies in question. 4 NEW CLASSIFICATION OF MOTOR ANOMALIES. Stevens also did service in pointing out that many cases of so- called insufficiency, or heterophoria, were really low degrees of squint—a fact which, as already stated, has been too much over- looked. He further called particular attention to the importance and frequency of the vertical deviations which had received (and, in fact, still receive) too little notice; the fact being that their recog- nition and correction are very necessary features in the manage- ment of many cases of muscular trouble. Stevens' classification, however, is open to the serious objec- tion that it reinstates the idea of grouping deviations according to their anatomical characters and puts the etiological element in the background. That is, it aims to classify motor disorders according to their outward, visible characters, and not according to their cause. In this way, though admirable in other respects, it would seem to be a distinct step backwards. Thus, while the term insufficiency is faulty, because it restricts too narrowly our conception of the possible etiology of a given motor affection, the term heterophoria is objectionable, because it throws away the etiological idea altogether, and once more directs our atten- tion simply to the appearances present, i. e., to the fact that the eye in a certain case deviates up, down, out, or in. To be sure, this has its advantages in that there are many cases in which we cannot say at once, or even after considerable testing, what the true condition underlying these appearances is, and we have, therefore, to content ourselves with a provisional—i. e., an anat- omical—diagnosis. But we should always feel that such a diag- nosis is provisional, and that a really satisfactory diagnosis should express the cause of the deviation as well as its char- acter. That is, the statement that in a given case so many de- grees of esophoria were found should be regarded as only an in- complete presentation of the facts; the final diagnosis not being reached until we have determined the cause of the esophoria, i. e., have made out which one of the many and complex functions of the neuro-muscular apparatus of the eye is deranged. In the meantime, the terms that Stevens has devised are very conven- ient for purposes of record and for indicating the provisional di- agnosis. The next step naturally left to take—the classification, namely, of the motor affections of the eye upon an etiological basis—has been but partially made. Apart from Donder's researches be- fore mentioned, and V. Graefe's demonstrations of the characters NEW CLASSIFICATION OF MOTOR ANOMALIES. 5 displayed by paretic squint, the main contributions to the sub- ject have been A. Graefe's description of convergence-insuffi- ciency, Landolt's observations upon the comparative effect and relative value of advancement and tenotomy in the treatment of various kinds of strabismus, and some of Stevens' recent papers. Nowhere, however, have the observations bearing upon this point been properly co-ordinated, so as to form a complete classi- fication of all the different anomalies, founded upon a strictly eti- ological and physiological basis. To do this, at least in part, is the object of the present essay, which is based almost exclusively upon observations made by the author himself during the past ten years. The subject has seemed to him to be one not only of scientific interest, but also of great practical importance, since, as experience has shown, our plans of treatment are necessarily largely modified by our notions of the real nature and causes of the condition that we are called upon to correct. Moreover, the cases themselves are very numerous; their symptoms, subjective and objective, are multiform and complex; while the results of treatment, which are often brilliant, are often also disappointing, owing, no doubt, frequently, to our ignorance of the exact na- ture of the case before us. It has seemed proper, therefore, to enter into considerable detail in trying to determine what should be the proper classification of such cases, and what precisely are the differential marks by which they can be distinguished one from the other. I. NATURE OF THE PROBLEM. The task that confronts us when we attempt to make any classi- fication of the kind now essayed is that of framing a scheme by reference to which the following problem may, in most instances, at least, be resolved : Given a case with a certain train of symp- toms, to determine the ultimate cause of these symptoms, i. «., the part or function that is primarily deranged, and the manner of its derangement. The solution of this problem obviously pre- supposes, first, an accurate knowledge of the normal state of the various parts and functions that may be involved, and, second, a consideration of the different means we have for determining whether each part or function is actually normal or not. Thus, in the case of deformities about the hip, a proper classification, i. e., one which tells us whether any given deformity is due to a fracture, to a dorsal dislocation, or to hip-disease, is possible only after we have become thoroughly acquainted with the normal re- lations and movements of the hip-joint, and with the means at our 6 NEW CLASSIFICATION OF MOTOR ANOMALIES. command for appreciating the various deviations from the nor- mal and their significance. Applying this principle to the eye, we may say that the solution of our problem is contained in the answers to the following questions: (1). What are the different normal functions of the neuro- muscular apparatus of the eye, and what is their anatomical seat? (2). In what way is it possible for these functions to be de- ranged? (3). What means have we for telling whether any special func- tion is deranged or not, and, if so, what the nature of the derange- ment is? (4). What are the conditions actually met with in practice, and how do they correspond to the scheme that we have framed? The consideration of these questions we will now take up in the order named. II. MOVEMENTS OF THE NORMAL EYE. The functions concerned in the group of .cases under consid- eration comprise (a) the actions of the individual muscles that are inserted into the eyeball; (b) the movements possible to each eye separately through the individual or concerted working of these muscles and (c), the character and extent of the ?nove- ments actually performed by the two eyes when acting together. The actions of the individual muscles are best exhibited in tabular form, as follows : CO 0 i-. n—< i £''~ a 2 qj"£ -^ O'1* OJ .2-- ti S3 >, o rt es eye rally. upper :al me >rnea effect. E-S * > o u Muscle Field of action Lateral an sional effec creasing as &to dim ero, Vertical acl creasing as rt.2 >, limited to Mov late Rotates of vertic an of cc sion Lateral effects ing to z is tr Vertic dimin e External Outer half of Out No ac- No ac- Rectus. field of fixation tion tion Internal Inner half of In No ac- No ac- Rectus. field of fixation tion tion Superior Upper half of In In Adduct- Abduct- Up Abduct - Ad- Rectus. field of fixation ed. ed. ed, ducted Inferior Lower half of In Out Adduct- Abduct- Down Abduct- Ad- Rectus. field of fixation ed. ed. ed. i ducted Superior Lower half of Out In Abduct- Adduct- Down Adduct- Ab- Oblique field of fixation ed. ed. ed. ducted Inferior Upper half of Out Out Abduct- Adduct- Up Adduct- Ab- Oblique field of fixation ed ed. ed. ducted NEW CLASSIFICATION OF MOTOR ANOMALIES. 7 It will be seen from the foregoing table that under ordinary conditions the only two muscles which precisely counteract one another's action, or which are, in the language of physiology, direct antagonists, are the external and internal recti. The superior and inferior recti, for example, are only partially antagonistic, for, while respectively elevating and depressing the eye. so as to be directly opposed to each other in this regard, and while their action in rotating the vertical meridian of the cornea is also precisely opposite, they both adduct the eye. Hence, when acting together they will reinforce the internal rectus, and this action will be most strongly pronounced when the eye is already markedly adducted, i. e., under conditions in which the internal rectus is working at some mechanical disadvantage. The like is true of the combined action of the two obliques, which neutralize each other' as far as rotation of the vertical meridian and as far as elevation and depression are concerned, but work together in pro- ducing abduction and hence assist the external rectus, especially when the eye is already strongly abducted. On the other hand, when the eye is strongly adducted, the lateral action of the two obliques falls away, and these two muscles act simply to elevate and depress the eye respectively. In this position, therefore, they do neutralize each other perfectly, land are direct antagonists. The same is true of the superior and inferior recti when the eye is ab- ducted. For further remarks upon this subject, see the appendix to this chapter. Almost every movement that the eve can make requires the combined action of at least two of the ocular muscles. Thus to lift the eye straight upwards, we must use both the superior rectus and the inferior oblique. The superior rectus, acting by itself, would carry the eye inward as Avell as upward, and would rotate the vertical meridian of the cornea inward. So, too, the inferior oblique, acting by itself, would tend 1o abduct the eye and rotate the vertical meridian outward. Neither, therefore, alone will carry the eye straight upward, but the two acting together, will neutralize each other as far as their lateral working and their effect upon the vertical meridian are con- cerned, and consequently the eye rises vertically, without swerving to the right or left, and without any deflection of its vertical meridian. It is probable that the external and internal recti assist in main- taining the strict verticalitv of this movement, their simultaneous contraction steadying the eye and preventing it from swerving. In this case, therefore, at least two, and probably four muscles, are concerned in the movement. Similarly, depression of the eye is always accomplished by the conjoint action of the inferior rectus and the superior oblique, which neutralize each other to a greater or less extent, as far as their lateral working and their effect upon the vertical meridian are concerned, but which assist each other in carrying the eye downward. Here, too, probably the external and internal recti come into play as steadying and supporting factors. Even in so simple a movement as that of abduction, which might be performed by a single muscle, it is probable that at least two 8 NEW CLASSIFICATION OF MOTOR ANOMALIES. (i. e., both obliques), or even four other muscles (i. e.. all except the internus), take part either in reinforcing the action, or in steady- ing the eye and rendering the movement uniform. See Appendix. The movements of the individual ocular muscles are, as is well known, presided over by more or less discrete nuclei scattered along the walls of the third ventricle, aqueduct of Sylvius, and fourth ventricle; but the precise method in which these are ar- ranged and inter-connected has not yet been sufficiently deter- mined. The Movements Possible to the Eye through the co-ordi- nated action of its six muscles comprise rotations in every con- ceivable plane, the eye being capable of moving from the primary position directly to any secondary position, and from the latter again to any other secondary position, and in so doing may take either a direct or a sinuous course.* The typical direct move- ments from the primary position, together with the muscles con- cerned in the production of these movements, are shown in the following table: *This may be proved by making two fine dots upon a card, so close together that unless very accurately fixed (i. e., if seen ever so slightly in diffusion circles), they will blend into one, and then mov- ing the card slowly in all directions before the eye, the head re- maining fixed. However the card is moved, the two dots will re- main distinct, thus showing that the eye follows them in all their movements. NEW CLASSIFICATION OF MOTOR ANOMALIES. 9 o j< a >■ a I , ■J3 i. o b o Muscles gl^sSi Con- .-vm^'S o cerned, q o a & a Move Eye Laterally* Move Eye Vertically * Rotate Upper End of Verti- cal Meridan of Cornea* Out (Abduc- tion) External Rectus Syner- gists. Superior ;Out Oblique Inferior Oblique Oppo- nents. Superior Rectus. Inferior Rectus. [In] 1 Action I increas I ing the >■ further I the eye I is ab- J ducted, 1 Actions l slight I and de- ! creas- J-ing the [ more the eye I is ab- J ducted. [Up] [Up] Down]) Action equal and op- posite; decreas ing the more the eye is ab- ducted. Actions equal and op- I posite; I increas [ing the I more [Down] | the eye I is ab- J ducted. Resultant Effect Upon Eye. No action, [In] ] Actions I equal and ■ I oppo- site; [Out] I increas I ing the I more I the eye I is ab- J ducted. Actions equal and oppo- site; ■decreas ing the more j the eye I is ab- J ducted. [In] [Out] In Internal 1 Rectus in j No action No action. (Adduc- tion.) Syner-gists. Superior , Rectus In 1 Actions! Action [Upl equal [In] Actions equal increas- 1 and op- and op- 1 ing the1 L posite; more (decreas posite; Inferior L j Rectus ' increas the eye [Down] 1 ing as [Out[ ing as is ad- 1 the eye the eye J ducted. 1 is ad- is ad- J ducted. ducted. Oppo- nents. Action [Down Action Actions Superior : [Out]" equal 1 [In] equal Oblique slight and op- and op- { and di- posite; posite: minish- ►increas - dimin- ing as ing as ishing Inferior f°ut] the eye [Up] the eye [Out] as eye Oblique is ad-ducted, is ad-ducted ' is ad-ducted. Eye carried out mainly by action of ex- ternal rectus ■assisted by the two obliques; the effect of the latter be- ing the greater the more the eye is abduct- ed. The op- posing (ad- ducting) ac- tion of the su- perior and in- ferior recti also dimin- ishes as the eye is abduct- ed. The eye is steadied and its verti cal meridian kept vertical by the traction exerted by the superior and inferior recti and the two obliques. Eye carried in mainly by in- ternal rectus, assisted by the superior and inferior recti: the effect of the latter being greater, the more the eye is adducted. The opposing (abducting)ac- tion of the two obliques dim- inishes as the eye is adduc- ted. The eye is steadied and its vertical me- ridian kept vertical by the counterpois- ing action of the two obli- ques and the superior and inferior recti, * Movements that are completely neutralized by the action of opposing muscles are placed in brackets. 10 NEW CLASSIFICATION OF MOTOR ANOMALIES. 5 Si S O ha 3 o 8 Ph_&< Up"' (Sursum- duction) Muscles Con- cerned. Move Eye Laterally Move Eye Vertically Rotate Upper End of Vertical Meridian of Cornea Resultant Effect Upon the Eye .Superior Rectus Inferior Oblique Up. [In] "I Move- ments r equal [Out] f and op-:Up. j posite. Diagon- ally Up and Out. Syner External [Out] "1 Actions No action Rectus] equal S- and Internal [In] oppo- No action RectusJ __J site. J_________ Superior I [In]; Action Rectus:slight and dim inishing as eye is abducted. Inferior Oblique External Rectus Up, Action marked and in- creasing as eye is abducted. Out; Action Up; Action increasing as slight and de- eye is abduc- creasing as eye ted- is abducted. [In] ") Actions I equal [and op- [Out[ j posite. No action No action [In] ; Action slight and dim- inishing as eye is abducted. Out : Action marked and in- creasing as eye is abducted. Eye carried straight up; vertical meri- dian remains vertical. The counterpois- ing action of the internal and external recti serves to steady eye and keep it in the vertical line- Eye carried up mainly by superior rec- tus, the elevat- ing action of this muscle in- creasing and that of the in- ferior oblique diminishing as the eye is Jib- ducted. Eye carried out mainly by ex- ternal rectus, assisted by in- ferior oblique, especially when abduc- tion is marked. Vertical meri- dian rotated out. Diagon- ally Up and In. Superior Rectus Inferior Oblique Internal Rectus. In: Actionl Up; Action increases as'slight and de- eye is carried creasing as eye inward. lis adducted; finally 0. [Out]; Action, Up; Action slight and de- marked and creasing as eye increasing as is carried in. eye is carried Down Inferior (Deor- Rectus sumduc- Superior tion) Oblique. Syner- In; Action increases as eye is carried [Out] Action slight and de- creasing as eye is carried in. No action. Eye carried up mainly by the in- ferior oblique, the elevating action of this muscle in- creasing and that of the superior rec- tus decreasing as the eye is adduc- ted. Eye carried in by the internal rectus, assisted, especially when adduction is mar- ked, by the super- ior rectus.Vertical meridian rotated [In] 1 Actions I equal [Out] I and op- J posite. External [Out] 1 Actions Rectus.! [ equal Internal [In] f and op- Rectus. J posite. Down. Down. No action. No action. [Out]"! Action 1 equal [In] f and op- J posite. No action. No action. The eye carried straight down, ver- tical meridian re- maining vertical. External and in- ternal recti by their counter- traction serve to steady eye and keep it in the ver- tical line. NEW CLASSIFICATION OF MOTOR ANOMALIES. 11 Muscles Con- cerned. fio=-. Diagon- Inferior ally Rectus. Down and Out Move Eye Laterally. Move Eye Vertically. Rotate Upper End of Verti- cal Meridi- an of Cor- nea. Resultant Effect Upon Eye. Superior. Oblique External Rectus. [In]; Action slight and dim- inishing as eye is abducted. Out; Action increasing as eye is abduc- ted. Down; Ac- tion marked and increasing as eye is ab- ducted. Down: Ac- tion slight and diminishing as eye is abduc- ten. [Out]; Ac- tion slight and diminishing as eye is abduc- ted. In; Action increasing as eye is abduc- ted. Out No action No action. Diagon- ally Down and In. Superior Oblique. Inferior Rectus Internal Rectus. [Out; J Action slight and dim- inishing es eye is adducted. In; Action increasing as eye is adduc- ted. Down; Ac- tion marked and increasing as eye is car- ried inward. Down; Action slight and dim- inishing as eye is adducted. I In; J Action slight and dim inishing as eye is adducted. Out; Action increasing as eye is adduc- ted. The eye carried tloirn mainly by inferior rectus, the depressing ac- tion of this muscle increasing and that of the super- ior oblique de- creasing as the eye is abducted. Eye carried out mainly by external rectus. assisted especially in ex- treme abduction, by the superior oblique. Vertical meridian rotated in. The eye carried 'down mainly by the superior obli- que, the depress- ing action of this muscle increasing and that of the in- ferior rectus dim- inishing as the eye is adducted. Eye carried in mainly by the internal rectus, assisted especially in ex- treme adduction by the inferior rectus; vertical meridian rotated out. The amount that the eye can move in each one of the direc- tions specified may be determined experimentally by placing the subject experimented upon with his eyes in the primary position and directed at an object whose recognition implies accurate fix- ation, (e. g.) a fine double dot on a card, and then moving the object in the given direction, requiring the patient at the same time to follow it with his eyes, but not with his head. The moment when he ceases to follow it will be evidenced objec- tivelv by the perceptible wavering of the eye, which hitherto had steadily followed the object, and subjectively by the fact that the object itself becomes confused and no longer recog- nizable. Then the arc through which the eye has rotated in passing from the primary to the terminal position may be measured either roughly with the eye, or accurately by some form of perimeter.* *This may also be accomplished by Stevens' tropometer or some similar instrument which measures the rotation of the eye by meas- uring the arc traversed by the corneal reflex. 12 NEW CLASSIFICATION OF MOTOR ANOMALIES. By ascertaining the limits of movement in all directions, we de- fine the boundaries of the field of fixation i. e., of the entire space through which the visual line can be carried without moving the head. The measurement of the field of fixation in any given case re- quires that the patient under examination shall, in each excur- sion that he makes with his eyes, put forth the maximum effort of which he is capable. This he will frequently fail to do, thereby making the field appear incomplete. It is only by making sev- eral examinations and taking the maximum of all the measure- ments, that we arrive at a perfectly reliable result, i. e., one which shows the full extent of excursion of which the eye is capable. The discrepancies thus obtained in repeated examinations are well shown in cases 1, 5, and 6, of the following table, which is constructed from observations of my own, made upon normal eyes with the perimeter, and using the fine double dot as a test- object. RIGHT EYES* Case. Up Up & Out Up&In Out In : Down Down & Out Down & In 1 1st exam. 40 35 40 35 40 70 35 25 u 2d exam. 38 45 40 48 48 42 55 50 2 40 50 40 45 60 60 3 50 45 55 55 45 60 65 55 4 Right eye not examined. 5 1st exam. 40 48 (50) 60 (50) 62 65 (50) " 2d exam. 40 48 (55) 50 (55) (62) 50 (60) " 3rd exam. (30) 42 (42) 50 (45) 60 65 (60) 6 1st exam. 32 45 32 52 52 65 50 " 2d exam. 38 50 7 32 35 35 55 52 72 65 • (62) 8 44 55 55 60 60 62 70 (65) 9 50 50 60 52- (60) 80 (70) 60 10 40 40 42 50 42 45 50 40 11 1st exam. 47 50 50 40 63 63 67 55 12 Right eye not examined. 13 45 55 (55) 50 60 55 52 (53) 14 1st exam. 52 60 55 52 50 62 60 55 it 2d exam. 40 50 (45) 65 (50) 65 80 (50) 15 (50) 45 52 48 56 62 58 (60) 16 1st exam. 52 50 55 48 56 60 60 (50) 17 1st exam. 40 38 50 40 (45) 68 (65) (50) u 2d exam. 47 52 52 48 (48) 60 (40) 60 18 60 70 62 75 60 65 73 60 *Figures enclosed in parentheses mean that at this point the test object disappear- ed from view behind some projecting part of the face, but at the time of disappear- ance was still within the field of fixation. NEW CLASSIFICATION OF MOTOR ANOMALIES. 13 LEFT EYES. Up Up & Out Up & In Out In Down Down & Out Down & In 1 1st exam. .1 2d exam. 3 4 5 1st exam. c. 2d exam. n 3rd exam 50 42 40 35 40 40 43 40 40 50 40 38 52 50 50 6 Left eye not examined. 7 35 42 8 Left eye not examined. 9 55 60 10 Left eye not examined. 11 1st exam. 12 13 14 1st exam. I. 2d exam. 15 16 Is exam. 17 1st exam. 18 2d exam. 50 50 [40] 46 48 48 40 44 58 45 60 55 60 50 55 42 50 71 45 55 40 45 46 42 [44] 40 35 48 55 48 53 52 48 45 60 50 40 [48] 48 [50] 55 52 70 70 60 65 35 65 [68J 65 70 60 58 60 72 55 47 60 65 50 50 [60] 70 50 50 [50] 60 55 55 45 72 50 56 55 65 52 55 52 60 [50] 40 62 70 50 48 [50] 62 71 72 62 72 60 50 50 38 70 62 60 55 60 62 76 50 60 60 75 32 [50] [48] [50] 60 [40] 60 [40] 60 [60] 52 [52] [40] 68 The average of the observations above tabulated gives rather a larger field of fixation than has been obtained by other experi- menters. Thus, Landolt's figures, while showing a close agreement for excursions in the upper field, are appreciably less for movements downward (about 50° in looking down, 38° in looking down and out, and 47° in looking down and in). On the other hand, the ex- periments of Schuunnann and Donders give the range of downward excursion as 57°, which is somewhat less than those that were found by me, but the upward excursion as only 34°. This latter figure certainly seems too small, in view of the fact that in but one of my cases was the range as low as this, and that in nearly all the others it fluctuated between 40° and 50°.* From the range of excursion of the eye in various directions, we can form a tolerably close estimate of the amount of work that each muscle does in moving the eye. For example, when the eye is abducted 30°-35°, its movement up- wards is effected solely by the superior rectus, and, moreover, the latter is then at its maximum as an elevator. Hence, to determine the maximum elevating power of this muscle, we have only to measure the range of excursion upwards that the eye can make when abducted to this extent. Similarly, the range of excursion downwards, when the eye is abducted 30°, measures the maximum depressing power of the inferior rectus. Making use of the results ♦Certainly the value of 20° found for the range of upward excur- sion bv Hering (cited in Graefe-Saemisch) seems excessively small. It is not unlikely that here there was a pathological condition present, such as an insufficiency of one or both elevators—a phe- nomenon not infrequent. 14 NEW CLASSIFICATION OF MOTOR ANOMALIES. already tabulated,* we find for the maximum elevating power of the superior rectus a value of 30c, and for the maximum depressing power of the inferior recttis, a mean value of 35c>-40o. The maximum elevating power of the inferior oblique and the maximum depressing power of the superior oblique, are not so readily determined, as the eye can hardly be so far abducted as to enable these muscles to work to the greatest advantage, and at the same time do away altogether with the vertical action of the superior and interior recti. It would appear, however, that the maximum vertical effect exerted by the obliques, does not differ materially from that exerted by the straight muscles; only the effect of the latter in the positions ordinarily assumed by the eye is rather more pronounced. The maximum rotating effect of the superior rectus upon the ver- tical meridian (torsion-effect, swivel-movement) will be ascertained by determining the amount of deflection of the vertical meridian when the eye is directed far up and in. In this situation the ver- tical meridian is not acted upon by the other muscles capable of Fig. 1. rotating it, so that the total rotation it undergoes must be ascribed to the action of the superior rectus. So, too, the rotating power of the inferior oblique, the superior oblique, and the inferior rectus is measured by the amount of tilting of the vertical meridian when the eye is directed up and out, down and out, and down and in, respectively. The adducting effect of the superior aud inferior recti and the abducting effect of the obliques are not determinable directly in the normal eye, since these actions always occur as reinforcements of the adducting and abducting actions of the internal and external recti. ♦This can be accomplished by a simple calculation, based upon the principles of spherical trigonometry. Thus if AB represents the path of the visual line in passing from the primary position obliquely up and out, BC (or a) will be the elevation and AC (or b) the outward excursion or abduction of the eye. Then Sin. a= Sin. A. Sin. c and Sin. b = cot A. tan. a. Here c = the range of excursion up and out as given by our table (= about 45°), a = 30, and b = 36v. NEW CLASSIFICATION OF MOTOR ANOMALIES. 15 For the same reason, the total adduction or abduction that the eye is capable of is not a precise measure of the maximum power of the external and internal recti, since the latter are to a certain extent, assisted in their action by the vertical muscles, and partic- ularly so when the eye is already carried pretty far out or in. It is probable, however, from observations in cases of paralysis, that the lateral action of the vertical muscles does not amount to more than 4° or 5° at most, so that the abducting power of the externus may be stated as 40t>-45Q, and the adducting power of the interims as about 50°. Passing now to the third group of functions under considera- tion, namely the character and relations of the movements per- formed by the two eyes when working together we are struck by the fact that, with unimportant exceptions,* these movements are limited to those subserving binocular fixation. Thus, in order to produce the binocular fixation of distant ob- jects, the visual lines must be parallel. In harmony with this fact, we find that there is a whole series of movements—associ- ated parallel movements—in which the visual line of one eve is kept strictly parallel with that of the other; and, moreover, the vertical meridians of the two corme alsoremainparallel.no mat ter how the eye is directed. A second class of movements—movements of convergence— adapt the eyes for the binocular fixation of near objects. A third sort of movement is that of divergence in the horizon- tal plane, causing the eyes to pass from the consideration of a near object to that of one more iemote. In doing this, this movement, like the preceding, subserves binocular fixation; but it may to a certain limited extent, also antagonize the latter by carrying the eyes still further, i. e., from a position of parallelism to one of actual divergence. Another kind of movement, of very limited extent, is that of divergence in a vertical plane, produced by the elevation of one visual line and the depression of the other. This move- ment, called sursumvergence (or deorsumvergence) is denoted as right or left, according as the right or left visual line is higher (or lower). ♦The exceptions are very clearly described by Helmholtz (Phys. Optik, 2d Ed., pp. 031, et seq.) He seems to me, however, to have laid too much stress upon the ability of the eye to make exceptional movements of this sort; the fact being that such movements are extremely limited and, beyond a certain point, cannot be increased by practice. It seems, therefore, that in spite of his statement to the contrary, there is some anatomical basis for the inability of the eye to make unaccustomed movements and that it is not simply a question of training. 16 NEW CLASSIFICATION OF MOTOR ANOMALIES. •t A fifth class of movements comprise those in which the vertical meridians of the two cornece are so rotated as to be no longer parallel. Such a rotation occurs normally in positions of marked convergence, the vertical meridians then diverging at their up- per extremities, and the amount of divergence increasing as the eyes are elevated (Meissner, Le Conte). But, apart from this physiological torsion-movement, a divergent or convergent ro- tation of the Vertical meridians may be produced in the normal eye and demonstrated by suitable apparatus (Helmholtz). The Associated Parallel Movements of the two eyes with the muscles concerned in their production are shown in the follow- ing tables: NEW CLASSIFICATION OF MOTOR ANOMALIES. 17 Both Eyes Moveto R. Eye Muscles con- cerned L- Eye Move eyes laterally* Move eyes vertically* Rotate up- „ ,. . , per end of Resultant ef- vertical feet upon meridians eyes. of cornese. Right (Dex- trover- sion.) External Rectus Internal Rectus To R. No action i No action Synergists Superior Inferior] Oblique Rectus Inferior Superior Oblique Rectus Opponents. Superior Rectus Inferior" Oblique Inferior .Superior Rectus Oblique Left (Sinis-trover-sion.) Internal External Rectus Rectus Synergists. Superior Inferior Rectus Oblique Inferior .Superior Rectus Oblique Opponents. Superior Inferior Oblique Rectus Inferior Superior Oblique Rectus Up Superior Inferior Rectus Oblique [Sur- sum- ver- sion.] Inferior Superior Oblique Rectus. Synergists. External Internal Rectus Rectus Internal External Rectus Rectus To R, ac- [Down actions [To L [ToR tion in- equal creasing and op- the more posite eyes are [Up carried I to R f [To L] ac- [Up] Actions tion sli't equal & dimin- and op- ishing as posite eyes are carried [Down I to R. « 3 [ToL [ToR R eye carried to R by the ex- ternal rectus assisted by the obliques: i L eye carried g g I to R by intern- 3. P.! al rectus assist- ° § | ed by the supe- rior and infer- ior recti, The other muscles act to steady the eyes and keep them in the horizontal plane. Vertical meridiansboth remain verti- cal. To L- ToL action increas es the more eyes are car- ried to L- [To R] .H Ifi V O ■SuSt No action. : No action. [Up| [Down ac- ! I ac- tions [ToL I o § equal [b» and L S3 oppo-LToR ' - site. I m » "1 ac-[Down 1 tions [ToL [equal | and [Up] | oppo-J site. [ToR R. eye carried to L- by the in- ternal rectus, assisted by the superior and inferior recti: L- eye carried to R. by the ex- ternal rectus, assisted by the obliques. The other muscles act to steady the eyes and keep them in the horizontal plane. Vertical meridians re- main vertical [ToL] #£ a up [ToR] TEL I Up [ToR] frff. o o •d b [To LJ S--| [ToL1 3 o O.C. . 0 5 B ► W S « n £•=> [ToR J Both eyes car- ried vertically up by combin- ed action of su- perior rectus and inferior oblique. Exter- nal and inter- j nal recti act to steady eye and No action keeP it in verti- cal plane. Ver- tical meridians " " | remain verti- cal. *Portions enclosed in brackets indicate movements which are completely neutral ized. 18 NEW CLASSIFICATION OF MOTOR ANOMALIES. Both ; Muscles concerned Eyes j Move R Eye Up and to R. Superior Rectus LEye Inferior Oblique Move eyes Move eyes I laterally vertically Rotate up- per ends of vertical meridians of corneas Resultant effects up- on eyes Inferior Superior Oblique Rectus Synergists. External Internal Rectus Rectus TTo L.] ; Up. Action Action marked and slight and increasing as decreasing I eyes are ear- as eyes are|ried to R. carried to R To R. Up. Action Actions slight and de- marked & creasing as increasing | eyes are ear- as eyes are,ried to R. carried to R [To L] Ac- tion slight and de- creasing as eyes are carried toR To R. Action marked & increasing as eyes are carried to R No action. R. eye carried up by superior rectus; L.by in- ferior oblique. R. eye carried to R. by exter- nal rectus as- sisted (espec- iallyin extreme abduction) by inferior o b 1 i- que: L. eye car- ried to R by in- ternal rectus assisted by su- perior rectus. Both vertical meridians tilt- ed to R. Up Inferior Superior [ToR Ac- Up. Action [To R] Ac-] R- eye carried and to Oblique Rectus tion slight marked and in- tion slight up mainly by L. & decreas- creasing as & decreas- inferior ob- ing as eyes eyes are car- ing as eyes lique, L eye by are carried ried to R are carried superior rec- toL- to L. tus; R eye car-ried to L by in-ternal rectus Superior Inferior To L. Up. Action To L Ac- assisted by Rectus Oblique Action slight and de- tion mark- superior rec- marked & creasing as ed and in- tus. L eye car- increasing eyes are car- creasing as ried to L by ex- Synergists. as eyes are ried to L. eyes are ternal rectus carried to L carried to L- assisted by in-ferior oblique. Vertical meri- • Internal External To L. No action. No action, dians both ro- Rectus Rectus tated to L Down Inferior Superior Rectus Oblique [ToL' o ff. Down. [ToR' &% ] Both eyes car-o jr.: ried vertically (Deor- tJ 0 •d 3 !§ £ ! down by com- sum Superior Inferior [ToR '8 n y p ~ bined action of ver- Oblique Rectus Down. [ToL -■a ' inferior rectus sion) rt| and superior J ~ oblique. Ex- ternal and Synergists. internal recti act to steady External Internal [ToR s*S eyes and keep Rectus Rectus !» No action. No action. them in the vertical plane. Internal External [ToL •a « O T Vertical mer- Rectus Rectus en .G " idians remain vertical. NEW CLASSIFICATION OF MOTOR ANOMALIES. 19 Both ] Muscles concerned Eyes | Move R Eye L Eye Move eyes laterally Move eyes vertically Rotate up- per ends of vertical meridians of cornese Resultant effects up- on eyes Down and to R. Inferior Superior Rectus Oblique Superior Inferior Oblique Rectus Synergists. External Internal Rectus Rectus [To L.] Ac tion slight & decreas- ing as eyes are carried to R. To R. Ac- tions marked & increasing as eyes are carried to R ToR Down and to L. Superior Oblique Inferior Rectus Inferior Superior Rectus Oblique Synergists. Internal External Rectus Rectus [To R.] Ac- tion slight and de- creasing as eyes are carried to L- To L- a tion marked and in- Down. Action marked and in- creasing as eyes are car ried to R Down. Actions slight and de- creasing as eyes are car- ried to R. No action. [To R.] Action slight and decreasing as eyes are turned to R. To L. Action marked and in- creasing as eyes are carried to R. No action. R. eye carried down mainly by inferior rectus, R. eye by superior ob- lique, R. eye carried to R by external rec- tus assisted by superior ob- lique, L. by internal rectus assisted by inferior rectus. Both vertical meridians ro- tated to L. Down. Ac- tion marked and increasing as eyes are carried to L. [To L.] Ac- tion slight and de- creasing as eyes are carried to II. Down. Action slight and de- creasing as eyes are car- creasing as ried to L. eyes are carried to L. To L. No action. To R. Ac- tion marked and in- creasing as eyes are carried to L. No action. R. eye carried down mainly by superior oblique, L. by inferior rectus. R. eye carried toL-by internal rectus assisted by inferior rectus;L. eye carried to L- by exter- nal rectus as- sisted by supe- rior oblique. Both vertical meridians ro- tated to R. An inspection of the tables just given will show that in all parallel movements of the eyes each muscle acting upon the right eye is associated with a muscle which acts upon the left eye in a precisely similar manner, and to a precisely equal extent. Such a pair of muscles, one in each eye, are termed associated antagonists (A Graefe). Thus the superior rectus of one eye and the inferior Oblique of the other are associated antagonists, since in all positions that the two eyes may assume, these muscles move their respective eyes to the same extent and in the same direction, so that if they acted alone they would always keep both visual lines and both vertical meri- dians parallel. The associated antagonists and their action may be summarized as follows: 20 NEW CLASSIFICATION OF MOTOR ANOMALIES. ASSOCIATED ANTAGONISTS. MUSCI.E. R. eye. Moves eye laterally to Moves eye Vertically Vertical action in-creasing & Rotates up- latent ac-per end of tiondimin-vertical ishing as meridian eyes are cornea turned to ASSOCIATED ANTAGONIST. L eye External Rectus R Internal Rectus ' L Superior Rectus j L Inferior Rectus L Superior Oblique R Inferior Oblique R No action No action No action No action Up L Down R Down L Up R R R L L Internal Rectus External Rectus Inferior Oblique Superior Oblique Inferior Rectus Superior Rectus The determination of the range of excursion in associated parallel movements comprises the solution of two distinct prob- lems, namely, the determination of the field of binocular single vision and the determination of the field of binocular fixation. We delimit the field of binocular fixation by ascertaining for each direction of the gaze the point at which either one of the eyes fails to follow an object moving before the two. This can be done very conveniently with the double dot used for testing the monocular field of fixation, since the moment when either eye fails to follow the dots or when either eye fails to keep up with the other in following them, is rendered evident by a blurring of the image causing the two dots to run into one. Hering, who used a different method (with after-images), found the binocular field to be of quite small extent, being considerably smaller than the portion common to the two monocular fields. It seems likely, however, that his tests in this case, as in the ease of the monocular field, were made upon a not altogether normal sub- ject. My own researches, although few, to be sure, were made upon quite normal individuals. They gave the following results:* MOVEMENTS OF BOTH EYES. UP- Yfghf UlPenDd Right. Left. Down. D°™htand D°™ "< Casel.......38 52 45 58 fi2 70 80 70 ' Case II......50 52 53 56 59 70 62 70 The delimitation of the field of binocular single vision is ef- fected by noting in any particular direction of the gaze the point at which one eye can no longer keep pace with the other, as evidenced by the development of an insuperable diplopia. The field defined by .ioining all such points is not necessarily coin- cident with the field of binocular fixation, since it is quite conceiv- able that the two eyes following a moving object might fail to fix ♦Examination made for near points. NEW CLASSIFICATION OF MOTOR ANOMALIES. 21 it, but might yet both lag behind to an equal extent, so that the two images, although not formed upon the maculae, would still be formed upon corresponding points. In this ease, binocular single vision would still be present, although binocular fixation would no longer exist. A point upon which some stress has been laid is that this method of delimiting the field of fixation gives uncertain results, since, as is alleged, many people fail to recognize diplopia in eccentric posi- tions of the gaze. It is claimed, in other words, that the normal field of binocular single vision is quite small, and that diplopia occurs normally in looking far up, far to the right, etc., but that its existence is not suspected, because the subject under examination either fails to notice or actually suppresses one image. My own experiments, however, lead me to negative this idea completely. If we employ a candle for our test-object, and place a red glass before one eye of the individual examined, the presence of binocular single vision will be shown by the fact that the candle-flame appears pinkish or, more commonly yellow with a reddish border. Manifest diplopia will be shown by the presence of two flames, one red and the other yellow, and dip- lopia with the suppression of either image by the presence of one flame, either pure red or pure yellow. The differences presented are marked and readily appreciated by an intelligent patient when once they have been pointed out to him. Testing in this way a large number of people with apparently normal eyes, I have uniformly found that the field of binocular single vision extends not less than 400 in any given directio?z and usually extends up to 50° or more. Indeed, most persons still get true binocular single vision, even when the eyes are carried to the extreme limit of their excursion, the field of bin- ocular single vision being larger than either monocular field of fixation taken separately. This is but another instance of the law that the movements of the eyes, however extensive or however limited in themselves, are always under normal con- ditions modified in such a way as to best subserve binocular fixation and binocular single vision. Thus, as the experiments just adduced seem to show, it appears that, no matter what the maximum range of excursion of each eye separately is, the ex- cursion of both together, effected by the co-ordinating action of the association-centres, is such that one eye keeps pace with the other, going neither faster nor slower, and that each stops moving when the other does. Hence, however far the object looked at may be carried in any given direction, no diplopia occurs, or, if it does, it is transient and superable.* ♦These statements presuppose (1) that the visual lines are not far from parallel, i. e., the test-object should not be less than 3 feet from the eyes; and (2) the person examined should endeavor all the time to follow the Object, i. e., must not look beyond it. In the latter ease, of course, the test-object will seem to him double. Such diplopia is, however, usually at once superable by voluntary effort. 22 NEW CLASSIFICATION OF MOTOR ANOMALIES. Each of the main associated parallel movements turning (dextroversion, or the turning of both eyes to the right. sinistroversion, or the turning of both eyes to the left, sur- sumversion, or parallel movement up, and deorsumversion, or parallel movement down) is apparently presided over by a dis- tinct nucleus (association centre). The precise location of these centres has not been satisfactorily determined, but the evidence of their existence from pathology is very strong, lesions in which dextroversion and sinistroversion alone are affected being not in- frequent, and isolated involvement of sursumversion also hav- ing: been recorded. These facts will be referred to later on. Movements of convergence may be regarded as associated parallel movements to which a simultaneous contraction of both interni has been superadded. Thus in looking at a near object situated up and to the right there is a movement of sur- sumversion and dextroversion combined with a contraction of both interni, which neutralizes in part the right-hand move- ment of the right eye, and reinforces the right-hand movement of the left eye. This double contraction of the interni is presided over by a special centre (convergence centre), distinct from the association centres for parallel movements. Convergence, when marked, modifies somewhat the effect of the other muscles that are acting with the interna. Thus when the gaze is directed at a near object in the median line, the superior rectus of one eye and the inferior oblique cf the other no longer act as associated antagonists, the former serving mainly to adduct, and the latter to elevate the eye. In this case, in fact, the superior and inferior obliques in each eye neutralize each other completely, and the two superior and two inferior recti act as synergists to the two interni, all adducting the eye. Again, when the gaze is directed at a very near object, situated upward and to the right, the right superior rectus, since the right eye is not pointed as far to the right as the left one is, will not be working as an elevator at quite the same mechanical advantage as does the left inferior ofblique. Theoretically, therefore, the right eye will lag somewhat below the left. Practically, I have not observed this to occur, although it does seem to me that the field of binocular single vision is smaller for convergent than for parallel movements. The maximum power of convergence is obviously represented either by the angle formed by the two visual lines when both eyes are turned in to their utmost extent, or by the distance from the eyes of the nearest possible point upon which they can be converged. This point is called the fusion near-point, or, better the near-point of convergence (Pc.) Donders in a boy of 15 found the maximum angle of convergence to be 70°, which, NEW CLASSIFICATION OF MOTOR ANOMALIES. 23 with an interocular distance of GO mm., would signifv a near- point of convergence situated 52 mm. from the centre of rotation of either eye and 42 mm. in front of the line joining the centres of both eyes, or about 1^" from the cornea and f" in front of the bridge of the nose. Some can converge to even a greater extent. Prof. Le Conte, for example, who had acquired ex- traordinary facility in the use of his eyes, had a convergence- angle of nearly 1)0°. Schuurmann, on the contrary, found a maximum convergence-angle of only 43°, which would corre- spond to a convergence near-point situated about 2%" from the cornea* aiu.1^22" in front of the bridge of the nose ; and v. Graefe gives to the convergence-angle a value of 60? corresponding to a distance of 2" from the eye, and \\" from the bridge of the nose. My own experience leads me to regard Schuurmann's figures as expressing most nearly the results found in the general average of cases, the convergence near-point in the majority of normal persons that I have examined being situated at about 2" in front of the nose. A distance of H"-2" may, in fact, be regarded as the normal for adults. Children often have a greater power of convergence, and in them the distance may not ex- ceed 1". A distance of less than V denotes excessive, and one of over 'lVr deficient convergence-power. Another method of determining the power of convergence is by ascertaining the strength of frism, which can be overcome by the eyes when placed before the latter with its base out or towards the temple. This method is analogous to that employed by Donders for de- termining the positive portion of the range of accommodation. The strength of prism overcome, in fact, represents the amount of residual convergence* that the subject under examination can ex- ercise when his eyes are adjusted for the distance of the test-ob- ject employed, just as the strength of the concave glass that he can overcome represents the amount of his residual accommodation under the same conditions. The amount of this residual conver- gence naturally varies with the distance of the test-object, decreas- ing as the latter is brought nearer. It also ATaries considerably for the same distance in different individuals, until the latter have by training learned to do what at the outset is quite difficult for them, namely, to look at a distant object and at the same time direct their eyes as if it were much nearer than it really is. When this art has been learned, it will be found that, Normal subjects will for test-objects at a distance of twenty feet overcome prisms of 60°-70° refracting angle (equivalent to a convergence of 40°-50°), so that the maximum convergence produced in this way equals that produced in the natural fashion, i. e., by looking at a very near object. ♦Often improperly called the adduction. 24 NEW CLASSIFICATION OF MOTOR ANOMALIES. Convergence thus produced by prisms is at first associated with an accommodative eff~ort similar to, but less than that ac- companying a natural convergence of the same degree. Thus two cases that I examined showed the following amount of ac- commodation: Actual amount of con-vergence produced by overcoming the prism. 4.3° Accommodation ex-erted. 0.25 Corresponding amount of accommodation for a natural convergence of the same degree. 1.25 6.5° 0.50 2.00 11.00° 1.50 3.25 15.5° 2.50 4.50 19.3° 5.00 5.50 By continual practice, however, the patieut may learn to relax the accommodation while maintaining the convergence, and in this way prisms of 20° or 30°, base out, may be overcome without the accommodation being used at all. I have met with an extreme in- stance of this sort in which the patient could, without making any accommodative effort whatever, overcome prisms representing a convergence-aDgle of nearly 40°. Divergence, or the simultaneous lateral separation of the visual lines, is a process which ordinarily subserves binocular fixation, being used when the eyes fix in succession objects more and more remote. The process may, however, be performed to excess, so that the visual lines diverge from the object of fixa- tion, as when the homonymous diplopia caused by a prism placed base in before the eye is overcome, or, on the other hand, an involuntary or voluntary crossed diplopia is produced by turning the eyes outward. Divergence of the sort last mentioned, i. e., that giving rise to a crossed diplopia, varies greatly in amount, and, although re- garded as normal by those experimenters who have acquired a peculiar facility in producing it, is probably to be classed among the abnormalities. At all events, there are not many in whom the phenomenon is habitual, or who can produce it at will, and when present, it is generally associated with lack of muscular balance, and other evidences of a pathological state. On the other hand, a divergence produced in the act of over- coming a prism placed, base in, before the eyes, is an entirely normal phenomenon of very definite character. Its maximum amount naturally varies with the distance of the object of fixa- tion, increasing as the latter approaches the eye. The strength, in fact, of the prism, base in, that the eyes can overcome when regarding an object at any given distance, represents the amount by which the eyes, when converged upon the object and accom- modated for the latter, can diverge; just as the strength ot the Case 1.. Case 2. NEW CLASSIFICATION OF MOTOR ANOMALIES. 25 convex glass that can be overcome in looking at the object rep- resents the negative portion'of the range of accommodation for the same distance. For distance, i. e.. when the visual lines are parallel, the divergence* amounts quite regularly to from 3° to 5° (= divergence produced in overcoming a prism of 6° to 10°); and variations above or below these limits must be regarded as distinctly pathological. As to the true nature of divergence^ i. e. ; whether it consists in an active muscular contraction as in the case of convergence, or whether it is simply a relaxation of the interni, allowing the eyes to return to a position of rest, there has been much difference of opinion. Those who adopt the latter view assume that the natural position of the eyes, i. e., that in which all the muscles are fully relaxed, is one of slight divergence, parallelism itself requiring a certain tonic and constant contraction of the interni for its maintenance (Hansen Grut). Some have even thought that the position of complete re- laxation is that in which each visual axis coincides with the axis of the orbit—a state of things implying a divergence of 23°-30° (Le Conte). Those who thus think, however, appear to be misled in regarding as natural a condition which is abnormal, not to say patho- logical. Schweigger has argued strenuously against Hansen Grut's theory and especially to his application of it as explaining the nature of divergent squint, and Schneller also has adduced a variety of arguments, which, however, are not very convincing, to prove that the function of divergence is an active process. For my own part, I believe that in the majority of cases the position of perfect physiological rest is not one of divergence and that, consequently, the lateral separation of the visual lines must be regarded as, in part at least, an active process due to simultaneous contraction of the externi. One argument in favor of this is that many people, when we test their divergence with prisms, experience a marked sense of strain analogous to that felt in overcoming prisms by con- verging the eyes. The latter is certainly an active process, and the former, therefore, in these cases at least, would seem to be one also. Patients, to be sure, who can diverge at will so as to produce crossed diplopia, often assure us that they do so by "relaxing" the eyes; but several observations have convinced me that this relaxa- tion is really a muscular contraction.! Perhaps the strongest argument in favor of the idea that diver- gence is a passive and not an active process as that, in the great majority of cases at least, the diverging poioer, as measured by the ability to overcome prisms, base in, can not be increased at all beyond the initial amount, shown by the subject experimented upon If, for example, in our first trial of a patient, at the maximum prism, base in, that he can overcome is one of 8\ we shall generally find ♦Usually but improperly called the abduction. |A similar instance in which an undoubted muscular contraction was described by the patient as a "relaxation" was one that I met with, in which an homonymous diplopia of 15° (prism) was produced at will. Here, of course, a condition of convergence was present. which could only have been brought about by an active contraction of the interni. 26 NEW CLASSIFICATION OF MOTOR ANOMALIES. that we can not get him beyond this point by any amount of sub- sequent training. If divergence were a process of active muscular contraction it would seem as if it ought to be susceptible of being increased by exercise. But whatever the nature of divergence, whether active or pas- sive, it is certainly a distinct function of the eyes, and probably regulated by a distinct nervous mechanism. The evidence af- forded by pathology, at all events, point very strongly in this direction. Separation of the visual lines in a vertical plane (sursumduc- tion, or, more properly, sursumvergence) is a movement which all normal eyes can perform. It is, however, very limited in amount, not normally exceeding 1° or 1£° (= the divergence produced by a prism of 2° or 3°). It is evidently an active pro- cess associated with a sense of considerable strain, and appears susceptible of being increased by exercise, particularly in those that have a natural or acquired vertical deviation (hyperphoria). The power of producing convergence or divergence of the vertical meridians of the two eyes, the visual lines remaining parallel, is a subject about which very little is known. Even the experiments of Helmholtz, which seem to prove its existence, have been called into question by some, although probably with- out sufficient reason. Appendix. The analysis of the complicated problems involved in the study of the movements of the eyes may be facilitated by re- ference to the diagram (Fig. 2), which represents the field of fixation of a normal eye having a rather extensive power of motion. PROJECTION OF THE FIELD OF FIXATION AND OF THE FIELD OF ACTION OF EACH OF THE OCULAR MUSCLES. C, projection of extremity of line of sight (point of fixation), when eye is in primary position; D, E, O, projection of same when eye is abducted 18°, 30°, and 50°, respectively; B, A, P, projection when eye is adducted 20°, 50°, and 60°, respectively. The distance CO. represents the maximum degree of excursion of the eye outward. Most of this movement is effective by the external rectus, but a certain portion especially towards the outer end of the excursion is accomplished by the united action of the two obliques (see infra). The distance CP. represents the maximum range of excursion of the eye inward. This inward movement is effected mainly by the internal rectus, assisted especially towards the end of the excursion by the superior and inferior recti (see infra). The black lines AAi, BBi, CCi, DDi, EEi, represent the amount and direction of the movement produced by the superior rectus when the eye is respectively adducted 50° (A); adducted 20c (B); in the primary position (C); abducted 18° (D); and abducted 30° (E). The red lines AAe, BB2, CC2. DD2, EE2, represent the amount and di- rection of the movement effected by the inferior oblique, and the dotted lines A As, BB3, CC3, DD3, EE3, the movement effected by the in- NEW CLASSIFICATION OF MOTOR ANOMALIES. 27 ferior oblique and the superior rectus acting together, similarly, the black lines AA4, BB4, CC4, Dl)4, EE4 represent the lines of action of the inferior rectus; AA5. BB.-„ CC5, DD5, EE5, those of the superior oblique; and AA6, BB6, CC6, DD6| EKe, those of the two latter muscles combined. The heavy black lines AjBiCiDiEi and A4B4C4D4E4 represent the limits of the fields of action of the superior and the inferior recti; and the heavy red lines, A2B2C2D2E2 and A^Bj.CsDsEs the limits of the fields of action of the inferior and the superior obliques. The heavy dotted line A6PA3B3 Cs, etc., represents the limit of the field of fixation. It will be seen from the diagram how the vertical (elevating and depressing) action of the superior and inferior recti increases, and how the vertical action of the obliques decreases progressively as the eye is carried from a position of marked adduction (A) to one of moderate abduction (E). It will also be apparent how the lateral action of each of these muscles diminishes as its vertical action in- creases; so that the adductive power of the superior and inferior recti shows a progressive diminution, and the abductive power of the two obliques a progressive increase as the eye passes from A to E. That is, at A (i. e., when the eye is adducted 50°) the superior and inferior recti have no vertical action at all, but simply adduct the eye through a comparatively large extent, while the two obliques have no lateral action at all, but simply elevate and depress the eye. At E, on the other hand (when the eye is abducted 30°), the two recti no longer act as adductors at all, but simply elevate and de- press the eye; and the two obliques no longer exert any vertical effect, but combine to carry the eye outwards, their abductive action, iu fact, being here at its maximum. At A the superior rectus and the inferior oblique acting together to their full extent will carry the eye up and noticeably inwards to A3); since here the adductive action of the rectus is at its max- imum and besides is not balanced by any opposing abductive action on the part of the oblique. Similarly at E the two muscies acting together will carry the eye upwards and noticeably outwards. In in- termediate positions, as at B and D, the lateral action of one muscle will partially counteract that of the other, so that the net lateral effect will be less. E. g., at B the adductive action of the superior rectus is less than it was at A and moreover is now opposed by a moderate abductive action on the part of the inferior oblique, so that the net adductive effect is but slight. The eye. therefore, here is carried up by the inferior oblique, assisted somewhat by the superior rectus, and is also carried slightly inwards (to B3). At D, on the contrary, it is carried upwards mainly by the superior rectus. assisted somewhat by the inferior oblique, and is also carried slightly outwards (to D3), by the preponderating lateral (abductive) action of the latter muscle. At C (the primary position) the adduc- tive action of the superior rectus apparently balances the abductive action of the inferior oblique, and hence the effect of the two ele- vators acting together will be to carry the eye straight upwards. In a similar way the inferior rectus and the superior oblique acting to- r/ether will carry the eye down and in (AA6,BB6), down and out (DD6,EEfi), or straight down (CC6), according as the eye is already adducted, ab- ducted, or in the primary position. The superior or inferior rectus actina together with just sufficient force to neutralize each other's vertical action, will combime to ad- duct the eye, the adducent effect being forcible at A '=AAi+AA4 or AA7), and diminishing gradually to E where it is zero. At E. there- fore, i. e.. when the eye is abducted 30°, the inferior and superior 28 NEW CLASSIFICATION OF MOTOR ANOMALIES. recti acting together will produce no movement and hence in this position are direct antagonists. Similarly the superior and inferior obliques acting together neu- tralizes each others' vertical action, but combine to abduct the eye. The abducent effect is greatest at E (= EE2+EE5=EE8), and dimin- ishes progressively to A, where it is zero. In the latter position, there- fore, i. e., when the eye is abducted 50°, the two obliques, acting simply to elevate and depress the eye respectively, are direct antagonists. The four muscles, superior and inferior recti and superior and in- ferior obliques acting together with the force required to neutralize each other's 'vertical action, will produce a lateral effect varying with the amount by which the eye is already abducted or adducted. Thus if the eye is already adducted 50° (to A), a position in which the obliques exert no lateral action at all, the total effect of the four muscles will be to carry the eye quite a little distance further inward (to A?). If the eye is adducted only 20° (B), the resultant action of the four muscles will be the difference between the adduc- tive action of the two recti (BB7), and the less marked abducent action of the two obliques (BB?); i. e., the eye will be adducted slightly (to B9). At C (the primary portion), the abducent action of the obliques balances the adducent action of the superior and in- ferior recti, so that the contraction of the four muscles will cause the eye to remain stationary. At D, on the contrary, the abductive effect will preponderate somewhat, and the eye, already abducted 18°, will be carried still further moderately outward-* (to D9). At E, i. e., when the eye is abducted 30°, the abducent effect is still more pronounced (= EEs). It is thus apparent that if all four muscles act together they will. if the eye is being adducted or abducted, tend to carry it still further in. the direction in which it is goiny. They will, therefore, reinforce the external rectus in abducting and the internal rectus in adducting the eye, and the amount of the reinforcement will increase in propor- tion as the eye is already abducted or adducted. So that the in- ternal rectus, for example, when it begins to contract (i. e., is just leaving the primary position at C) will receive little or no aid from the contraction of the other four muscles, but, as it continues to act. (e. g. at B), will be more and more assisted by them, and finally when it reaches the limit of its contraction (at A) and is consequently working at a great mechanical disadvantage, will be strongly rein- forced. In like manner the external rectus will, as its own efficiency diminishes with the increasing abduction of the eye, be assisted more and more by the simultaneous contraction of the other mus- cles. And it is altogether probable that it is in this way that the outward and inward excursion movements of the eye are rendered regular and uniform.* *It may be noted that the action of the superior and inferior recti in compensating for an increasing feebleness of the internal rectus is shown in another way also. The internal rectus, as Weiss has pointed out (Arch. f. Augenheilk; Vol. xxix), acts very much more feebly when the divergence of the orbits is great, i. e., when the orbits are shallow and the eyes far apart. But it is under just these condi- tions that the superior and inferior recti act to most advantage as ad- ductors, since, the greater the divergence of the orbits, the greater the angle which the line of action of these two muscles makes with the antero-posterior axis of the eye. and the greater consequently is the lateral effect which they are able to exert. NEW CLASSIFICATION OF MOTOR ANOMALIES. 29 Our diagram may also be used to illustrate the action of the as- sociated antagonists. If alongside of Fig. 3, which represents the held of fixation of the right eye, we place one representing the field of fixation of the left eye (which may be done by turning Fig. 3 end for end, so that O is on the left and P on the right of the figure), we shall see how the field of action (A2B2C2D2E2), of the in- ferior oblique of the right eye agrees in all respects with the field of action of the superior rectus of the left eye. So also of the other associated antagonists (R. superior rectus and L. inferior oblique; R. inferior rectus and L. superior oblique; R. superior oblique and L. inferior rectus). Another point elucidated by the diagram is the amount and kind of torsion movement (rotation of vertical meridian of the cornea) produced by the various muscles. That is the dine BBi represents the fact that when the eye is adducted to B the superior rectus will not only carry the eye itself upwards and inwards (to Bi), but will also rotate the vertical meridian of the cornea so that the latter will have the inclination BBi, i. e., will be inclined inwards. In a similar way, the inferior oblique in the same situation will not only carry the eye upwards and outwards (to B2), but will also rotate the vertical meridian of the cornea outwards, so that it will have the direction BB-2. And the combined action of the two muscles will be to give the vertical meridian the inclination BB3, i. e., one of slight rotation inwards. So also BB6 represents the inclination of the vertical meridian of the cornea (viz., with the upper end rotated inwards), when the eye is carried downwards from a position of adduction (B). Again, the fact that CC3 is strictly vertical shows that when the eye is in the primary position it is not only carried straight upwards by the combined action of the two elevators, but its vertical meridian also remains vertical during the ascent. It will also be observed that the combined action of the superior and inferior recti or of the superior and inferior obliques, or of all four muscles together will 'be not only to keep the eye in the hori- zontal plane (in the line OFi, but also to keep its vertical meridian from rotating either to the right or to the left, as the eye is carried outwards or inwards.* In fact, all the various applications of the laws of Donders and Listing may be deduced from the study of this diagram. Finally the diagram shows the limitation of the field of fixation and the kind and amount of diplopia present in paralysis of any- one of the ocular muscles. Suppose, for example, that the superior rectus is paralyzed. Then the field of fixation while normal below, will, since the inferior oblique is the only elevator left, be repre- sented above not by A3B3C3D3E3, but by A2B2C2D2E9. In other words, when the attempt is made to elevate the eye as far as possible, it will stand at A2, instead of A3, at B2, instead of B3, etc. Since its fellow eye has a normal field of fixation and hence under the same conditions rises to A3, B3, etc., the difference in position of the two eyes and conse- quently also the amount and kind of diplopia produced will be repre- sented by the difference between A2 and A3, B? and B3, etc. The diagram thus gives us a graphic representation of the fact that in paralysis of the *E. g., at C the inward rotation of the vertical meridian produced by the superior rectus will be represented by the angle C3CC2; this inward rotation will be neutralized by the equal outward rotation C6CC4, produced by the inferior rectus: and hence the combined effect of these two muscles will be to keep the vertical meridian from rotating either one way or the other. 30 NEW CLASSIFICATION OF MOTOR ANOMALIES. superior rectus the vertical diplopia increases rapidly when the eye is carried upwards and outwards, while the lateral (crossed) diplopia in- creases as the eyes are carried upwards and inwards. The diagram may also be utilized to map out the field of fixa- tion in cases of combined paralyses. Thus the field of fixation in a case of paralysis of both the superior rectus and the superior oblique would be represented by Y2B2C2D2E2E4D4C4B4A4; and in a combined paralysis of the superior and inferior rectus by A2B2C2D2E2D5C5B5A5. III. THE TESTS EMPLOYED AND THEIR SIGNIFICANCE, The object of the various tests that we make use of is to deter- mine the following data: (1). The precision and steadiness with which binocular fixa- tion is effected (Static Tests). (2). The ability of the eyes to move in various directions while still maintaining binocular fixation (Dynamic Association- tests). (3). The ability of the eyes voluntarily to deviate from the po- sition of binocular fixation (Dynamic Disassociation-tests). These tests 'may be performed both for distance (with the vis- ual lines parallel) and for near (with the visual lines converged). The chief tests for binocular fixation are : (1). Inspection with both eyes uncovered. This gives us an approximate idea as to whether both eyes are directed at the same object, a non-fixing eye appearing to deviate in, out, up, or down, according to circumstances. In making this test we must be careful not to be misled by the presence of a large angle alpha, which may simulate a deviation where none exists. Any error on this score will be prevented by compar- ing the findings with those of the screen test; for a deviation, great enough to be noticeable upon simple inspection, will certainly give evidence of its presence by a distinct movement of the eyes when the cover is shifted from one eye to the other. (2) Fixation and Diplopia Tests. A patient with normal eyes and perfect binocular fixation, will see distinctly with either eye alone, or with both together, and will also see single. If either eye or both fail to fix the object looked at, that object will appear blurred (Fixation-test), and if one eye fixes and the other does not, the patient will in general see double (Diplopia- test), the image of the fixing eye being clear and that of the other more or less shadowy and indistinct. The kind of diplopia present indicates the nature of the deviation. Thus an homony- mous diplopia (i. e., one in which the image formed by the right eye is on the right side, and that formed by the left eye on NEW CLASSIFICATION OF MOTOR ANOMALIES. 31 the left side) signifies abnormal convergence of the visual lines; a crossed or heteronymous diplopia (in which the image of the right eye is on the left side and vice versa) signifies lateral di- vergence ; and vertical diplopia (in which one image is higher than the other) signifies vertical separation of the visual lines, so that one is higher than the other. The last-named variety may be further differentiated into right diplopia, in which the image formed by the right eye is below (indicating the condi- tion in which the right visual line is the higher), and left diplo- pia, in which the contrary conditions prevail. The amount of diplopia is precisely proportional to the amount of deviation. It may be measured either by estimating the linear distance between the two images, the distance of the object looked at being also known,* or by determining the strength of the prism which appropriately placed, will correct the diplopia.f In order to differentiate the double images it is convenient to use a light as a test-object, and have a red glass placed before one of the eyes. By thus giving the two images a different color| we enable the patient the better to distinguish between the two and recognize the fact that diplopia exists; and, moreover, since the red flame must belong to the eye covered with the red glass, we can determine from the patient's statements as to the relative place of the red and white images, whether we are dealing with homonymous or crossed (lateral) or with right or left (vertical) diplopia. (3) Equilibrium Test. This is simply a variety of the diplo- pia test. It consists of two steps. In the first an artificial ho- monymous diplopia is produced by means of a prism of 12° or more, placed base in, before the eyes. If the two images thus produced are on a level, the visual lines themselves are on a level. If, however, the right-hand image should be lower, there is really a natural right diplopia present in addition to the artificial ho- monymous diplopia, i. e., the right visual line is higher, or, to use Stevens' nomenclature, there is right hyperphoria. The amount *A linear distance of 1" between the images is equivalent to a deviation of Vfe* in the visual lines when the test-object is 1 metre distant and to %° when the latter is 20 feet distant. f A prism rarely measures the full amount of the diplopia, as a prism which slightly undereorrects the latter nevertheless brings the double images so close together that the residual correction can be and is effected by the eyes themselves. J A similar difference in character may be imparted to the images by placing a Maddox rod or a Stevens' sphere before one eye; but the red glass is simpler and, in comparison with the Maddox rod at least, is less confusing to the patient and less apt to give am- biguous results. 32 NEW CLASSIFICATION OF MOTOR ANOMALIES. of this latter may be measured by the degree of prism, which, placed base down before the right eye, will rectify the diplopia, • i. e., will bring the images on a levei. In the next step of the test, a strong prism is placed base down before the right eye, produc- ing a marked vertical (left) diplopia. If both eyes are properly adjusted for the object of fixation, the two images will be in a ver- tical line. If, however, the upper image is to the right of the lower, there is really, besides the artificial vertical displacement, a natural homonymous diplopia, or, to use Stevens' expression, there is an esophoria. Similarly, if the upper image is to the left of the lower, there is really a crossed diplopia or exophoria. In either case the amount of the esophoria or exophoria may be measured by the strength of the prism which, placed base out or base in will rectify the diplopia, i. e., wall bring the two images into a vertical line. In Stevens' pborometer, which is the best instrument for this pur- pose, the measurement of the deviation is effected, not by placing additional prisms before the eyes, hut hy revolving the prism that has been used to produce the initial lateral or vertical diplopia until the images are truly horizontal or vertical. The amount of rota- tion is read off on an arc graduated so as to indicate directly the amount of hyperphoria, esophoria, or exophoria present.* One defect of the equilibrium test is that patients often try in- voluntarily to bring the two images into line and thus appear to have no deviation of the visual lines, although one actually exists. On the other hand, the involuntary movements set up in the attempt made to compare two similar images placed at a distance from each other may cause a deviation to be simulated where none is present. I have seen this occur not infrequently—sometimes to a very marked degree. The equilibrium test being thus apt to set up a certain amount of muscular tension and hence disturb the true relation of the visual lii>es, is in actual practice best performed after the tests next to be described in which the eyes are under more normal conditions. (4) Screen Test. This depends upon the fact that the ten- dency to binocular fixation is so strong that it still persists, even when one eye no longer sees the object of fixation. If, therefore, a card be placed before the left eye, and the gaze be directed at a distant object, the left eye will, in case there is no disturbance of innervation causing it to deviate, look straight at the object, just as if the latter were still visible. If now the card is shifted from the left eye to the right, the former being already properly directed, will not have to change position in order to fix the ob- *The same thing may readily be done with the ordinary trial- frame, if we use in it a 12° prism and recollect that with this each rotation of 5° from the horizontal represents 1° of hyperphoria, and each rotation of 5° frwn the vertical 1° of esophoria or ex- ophoria. NEW CLASSIFICATION OF MOTOR ANOMALIES. 33 ject, and will hence remain stationary. If, however, the left eye when screened, deviates in any way, e, g. outward, it will, when the screen is transferred to the right eye, have to turn inward, or to the right, in order to fix the object, and the amount of its ex- cursion inward (movement of redress) will be precisely equal to the amount of its previous deviation. At the same time that the left eye turns inward, or to the right, in order to perform fixation, the right eye, which is now covered by the card and which, ac- cording to the law of associated parallel movements, receives an impulse to move to the right equal to that communicated to the left eye, will move outward. Whether it moves outward to the same extent that the left eye moves in or not, depends upon the relative ability of the muscles of the two eyes to respond to the stimulus imparted to them. If, for instance, the left internus is weak (paretic) a very strong impulse will be required in order to make the muscle contract enough to cause the eye to move in to the proper extent. According to the law of association, an equally powerful impulse will be communi- cated at the same time to the right externus; and, if the latter is normally strong, it will respond much more efficiently to this im- pulse than did the weak internus of the other eye, and will, con- sequently, carry the right eye out much further than the left eye was carried in. It may be stated as a general rule (to which, however, there are not a few exceptions) that in concomitant deviations the deflec- tion behind the screen, and hence also the movement of redress that the eye makes when the screen is removed, are equal for the two eyes, and that in non-concomitant deviations they are unequal, being greater in the eye which has the more powerfully acting muscles. The screen test may also be used to ascertain which oj th two eyes habitually fixes. In doing this the screen instead of being shifted from one eye to the other is simply removed from the eye before which it is placed, leaving both eyes uncovered. Each eye under these circumstances will deviate when the screen is in front of it, and the other eye will fix. If now the eye that is behind the screen is the one that in binocular vision is regularly employed for fixation, it will move into the position of fixation as soon as the screen is taken away, and the other eye will deviate. If, however, the eye that is behind the screen does not ordinarily perform fixation, it will not move when unscreened, and the other eye will continue to fix, i. e., will remain steady in its place. That is, the fact that the eyes perform a movement of redress when the right is unscreened and both are left open indicates that the right eye habitually fixes. If no move- ment takes place, when the right eye is unscreened, the latter can not be the eye that habitually fixes; and if no movement takes place when the right eye and the left alternately are unscreened, there must be an alternating deviation, i. e., one in which either eye in- differently is used to fix with. 3 34 NEW CLASSIFICATION OF MOTOR ANOMALIES. The amount of deviation behind the screen, or of the move- ment of redress made by the eye from which the screen has been removed, may be roughly estimated by marks made upon the lids or may be more accurately determined with the perimeter or by some of the various strabometric methods which have been well described by Maddox {Archives of Ophth., XXL, 1, 1892). An angular deviation of l°-2° is generally sufficient to produce a noticeable deviation behind the screen. Finally, it must be n >ied that the screen test is valueless unless the patient can be got to fix with the uncovered eye. Hence, the test is of no service in those who, owing to a deviation of long- standing, have lost the power of fixation; and it may likewise prove nugatory in children who fail to keep their gaze directed at the object that they are told to look at. (5) Parallax Test. When the screen test is employed, the patient, if his eye deviates behind the screen, will in general no- tice a movement of the object whenever the screen is shifted. This movement is called the parallax, and, if the test-object is so placed as not to be projected upon any surface back of it (e. g., if it is a spot upon a blank wall), furnishes a valuable indication of the amount and character of the deviation. The perception of this movement is really nothing but the perception of a diplopia, which differs from ordinary diplopia in the fact that the two im- ages are seen in succession, instead of at the same time, and, as they occupy different places, give the impression of a single im- age which has moved from one place to another. Thus, if there is convergence (esophoria), the right eye, when unscreened, and before it has had a chance to assume the position of fixation, sees the object a little further to the right than the left eye saw it, i. e.y the object appears to have moved from left to right (homony- mous parallax). If, on the other hand, there is divergence (ex- ophoria), the right eye will when unscreened see the object a little further to the left than the left eye did when it was fixing, i. e., the object appears to have moved from right to left (crossed parallax). So, too, right hyperphoria is indicated by the fact that the object appears to move down when the right eye is un- covered (right parallax), while in left hyperphoria the object seems to move up (left parallax). These various movements are noticeable even when the deviation is very slight; a hyperphoria of 0.1°, for example, being made appreciable by a distinct up and down movement of the object. The amount of the parallax may be measured by the strength of the prism which, placed before the eyes, will neutralize the NEW CLASSIFICATION OF MOTOR ANOMALIES. 3» movement. Homonymous parallax will be neutralized by a prism base out, a vertical parallax by a prism with the base up or down, etc. The fact of neutralization or reversal is generally in- dicated by the patient with great precision. Tests for the Associated Parallel Movements. The ability of the eyes to perform associated parallel movements, i. e., the range through which they can move hi any direction and still carry on binocular fixation, is tested in the same way as the abil- ity to maintain binocular fixation while in the primary position. All the tests just described are applicable. Thus inspection en- ables us to say whether the movement of the eyes in, out, up, or down, is too slight or too excessive; also the point where one eye ceases to keep up with the other, this being shown by the fact that the former visibly lags behind or wavers in its course. In this way we may map out the monocular ox binocular field of fix- ation, as may also be done more accurately by the fixation test (with the double dot, as already described). So, too, by the diplopia test we map out the field of binocular single vision, and thus also determine whether the eyes follow each other to a nor- mal extent or not. With the same object in view we apply the screen, parallax, and equilibrium tests to ascertain if there is any visible deflection, parallactic movement, or heterophoria within the limits of the normal field of fixation, and, if so, where they begin, and in what direction they increase. By these various means we determine whether the movements in any given direction are excessive or restricted. In this re- gard, inspection and the diplopia and screen tests are practically the most applicable. The mapping out of the field of fixation is laborious and, for the reasons already given, the results obtained are very uncertain, unless a series of examinations upon the same patient happen to be quite concordant. On the other hand, the diplopia test is readily applicable, and ini my experience gives much more constant and reliable results.. Diplopia may, to be sure, occur normally, as a transient phenom- enon (physiolrgical diplopia) in most people when the gaze is carried far towards the periphery of the field of fixation; but such diplopia, as already stated, is inconstant and superable by voluntary effort. A diplopia occurring under all circumstances as soon as the gaze has been carried from 35° to 40° from the- primary position, in any given direction, indicates an abnormal weakness. This again may be temporary, and a diplopia of this sort occurring about equally far in all directions from the peripherv (concentric contraction of the field of single vision) 36 NEW CLASSIFICATION i-F MO I OR ANOMALIES. indicates a temporary enfeeblement of all the ocular muscles such as may happen in neurasthenia and form one of the evi- dences of a general depression of the muscular forces. On the other hand, a diplopia, insuperable by voluntary effort and con- stantly occurring as soon as the gaze is carried 30° or less in any given direction from the primary position, indicates a true weakness or paresis, of some one of the ocular muscles (paretic diplopia). The differential diagnosis of this condition, based upon the character of the diplopia, will be touched upon later. Tests for Convergence. The tests for binocular fixation in convergence are the same as those for distance, namely, inspec- tion, the fixation and diplopia tests, the screen and parallax tests, and the equilibrium test. All of these, in fact, are habitually ap- plied with the test-object held at the ordinary reading distance, as well as at a distance of 20 feet. The test-object itself for the examination at near points should, as Randall has well said, be something requiring accurate fixation (e. g. a pen-point or fine dot, instead of the finger which is habitually used). In determin- ing the parallax, some device such as a dot on a large card, which does not allow the test-object to be projected upon any surface beyond it, should be employed. It must be borne in mind that, while orthophoria—absence of deviation—is the ideal state for distance, a slight amount of di- vergence is physiological for near. Thus, in testing at 12", we expec1 to find with the phorometer an exophoria of 3° to 0°, and with the screen a crossed parallax of the same, or a somewhat less amount; and orthophoria at this range is actually to be re- garded with suspicion, as probably indicating an undue tendency to convergence. This fact does not militate against the exist- ence in these cases of true binocular fixation for reading, or other occupations requiring precise adjustments. The tests for the associated movements in convergeiice, like- wise are made in the same way as for the associated movements at a distance. In making the diplopia test at near it is best, if using the caudle, to hold the latter not less than 30" from the eyes, so as to reduce as much as possible the effects of projection. If it is desired to determine the field of binocular single vision for clcser ranges, the effects of projection may be obviated by using for a test-object a dot on a large card, the latter being tilted so as always to be perpendicular to the patient's line of sight. A further important fact to determine in testing movements of convergence is the convergence near-point (Pc). This is ascer- tained by carrying a fine object nearer and nearer to the eyes, un- NEW CLASSIFICATION OF MOTOR ANOMALIES. 37 til the latter can no longer be converged upon it, or until it ap- pear, double. The distance of the object from the root of the nrs-e may then be measured. Notice at the same time should be taken as to which eye is the first to deviate when the limit of convergence is reached. The same test should be repeated from either side, the object of fixation being first placed at some point A to the right of the middle line and then carried directly towards the left eye L. The latter obviously will not have to change its position of r.dduction, but the right eye, R, in order to follow the object, must swing inwards through a considerable arc, A C P. If, on repeating the test with the left eye, one of the two is found to sag off from the test-object much sooner than the other eye does, the former must have a relatively weak adducting power. Not only the distance of the convergence near-point, but also the ability of the eyes t> maintain convergence at this distance, should be noted. Lastly the c-uivergence must be tested by determining the maximum strength of prism placed base out before the eyes, which the latter can overcome when looking at a distant object. Usually, if the patient can at the outset overcome a prism of 20° refracting angle, with ease, we assume that he could readily learn to do two or three times as much if sufficiently exercised, and we consider his j rism-convergence as normal. Exceptionally, es- pecially in cases of convergence-insufficiency, we find that the 38 NEW CLASSIFICATION OF MOTOR ANOMALIES. prism-convergence even after repeated trials cannot be got above 10° or 12° (prism), and that even this amount is hard for the patient to do and still harder to maintain. As the exercise of the prism-convergence not infrequently be- gets a condition of convergence-spasm, it is generally best to de- fer testing the convergence in this way until after the divergence has been determined. * It is well in testing the convergence by means of adducting prism to ascertain how much accom?nodation the patient is as- sociating with it. This can be done by using the test-types for the object of fixation and finding what concave glass is required to give the patient full sight. It will generally be found that by re- peated practice with an object of this sort, the strength of the concave glass can be gradually diminished—i. e., the patient gradually acquires the ability, when looking at a distant object, to converge without using his accommodation. A case in which extreme facility in this respect was acquired has already been spoken of. It is often important therapeutically to effect a dis- association of this sort between accommodation and convergence, especially in cases of convergence-insufficiency. Tests for Divergence. The diverging power is determined by the amount of prism placed, base in, before the eyes, which the latter can overcome when looking at a distant object. The strength of prism thus overcome varies in normal cases from 6° to 8° (refracting angle). A divergence of less than 5° (prism) means insufficiency, and one of over 9° an excess of diverging action. Tests for Sursumvergence. The sursumvergence, i. e., the amount by which the eyes can diverge in a vertical plane, is de- termined by the strength of prism placed base up or down before the eyes, which the latter can overcome when looking at a dis- tant object. The right sursumvergence (in which the prisms are so adjusted as to cause the right visual line to be the higher of the two) and the left sursumvergence should both be ascertained. It is usually best to leave some interval of time between the two tests, as after making the effort required to produce right sur- sumvergence (or left deorsumvergence) it is difficult at once to perform the contrary action. A difference of 1° or more between the right and left sursum- vergence or, in any case, a sursumvergence exceeding3° (prism), indicates the probable existence of a hyperphoria. NEW- CLASSIFICATION OF MOTOR ANOMALIES. 39 Way in which the Tests are applied in Practice. In prac- tice I have found it best to apply the tests in the following order: (1) Inspection. I note the apparent relations of the eyes in the primary position and also for associated parallel and con- vergent movements, using for the purpose some rather fine test- object such as a pen-point which the patient is made to follow with the eyes as it is carried in different directions. Any very obvi- ous deflection, e. g., a marked concomitant strabismus or a par- alytic squint, can be made out at once by this means alone. (2) Screen and Parallax Tests. These are made simultan- eously. First, a test-object 20 feet off is taken, and then one at the ordinary reading distance. If inspection has revealed any marked deviation or one which increases notably in any given direction of the gaze, the screen test also is applied in different portions of the field of fixation in order to corroborate these find- ings. (3) Equilibrium Test both for distance and near with the phorometer or with prisms in the trial-frame. (4) Test for Divergence by means of prisms placed base in before the eyes (Abducticn-test of most authors). (5) Determination of the Convergence Near-point both in the median line (test for bilateral convergence) and also, as has been previously explained in the course of this brochure, in lateral positions of the gaze (test of eccentric convergence). (6) Test for Convergence by prisms placed base out before the eyes (Adduction-test of most authors). (7) Diplopia Test with candle at 40"*or more, and some- times also with card and dot at 12". In order to make this test available for diagnosis we must have some ready method of re- cording which shall indicate, not only the character of the diplo- pia, but also its approximate amount, the point at which it be- gins to appear, and the way in which it increases or decreases ir» different directions of the gaze.* These comprise all the tests really necessary, and all these can in most cases be readily performed within ten minutes. If further tests are thought requisite, the Sursumvergence Test (8) *A sample of the scheme which I have adopted for my entries is as follows: Eu 20°, Er 25°—DL; Eu 25°, Er 30Q-DL 2°, DX 2°, which would mean that when the eyes were carried 25°, to the right and 20° up from the primary position vertical diplopia appeared; the image of the left eye being lower (left diplopia); and that when the eyes were carried 30° to the right and 2.")° up the image of the left eye was 2° below and 2° to the right of "that found by the right eye (i. e., there was a left and crossed diplopia of 2° each). 40 NEW CLASSIFICATION OF MOTOR ANOMALIES. and the mapping out of the Field of Fixation (9), may be under- taken. If they are, they should be left to the last, as they gener- ally cause considerable strain of the eyes, and hence, if performed early, are apt to derange the normal relations of the eyes, and thus interfere with any tests that may be made afterwards. If the patient is ametropic or presbyopic, the various tests enu- merated should be made both with and without the correcting glasses, in order to ascertain the effect of the latter upon the mus- cular condition; and other factors that might modify the latter, e. g., the existence of atropine mydriasis, should also be noted. (To be continued.) Reprinted from Annals of Ophthalmology, January, 1807. A NEW CLASSIFICATION OF THE MOTOR ANOMA- LIES OF THE EYE, BASED UPON PHYSIO- LOGICAL PRINCIPLES. THE PRIZE ESSAY OF THE ALUMNI ASSOCIATION OF THE COLLEGE OF PHYSICIANS AND SURGEONS, NEW YORK, FOR 189(3. By Alexander Duane, M. D., NEW YORK. Part 2. Pathology. IV.. Classification of Ocular Deviations. Nature of functions that maybe affected.—Nature of lesions affecting these functions. —Hvpokinesis, Hyperkinesis, Parakinesis.—Variation in degree of the lesions. Superable and insuperable deviations (Hetero- phoria and Squint).—Classification propounded.—Comitant and non-comitant deviations.—(leneral diagnostic laws based upon the presence or absence of comitancy.—Transformation of non- comitant into comitant deviations. V. Anomalies of the Individual Muscles. Muscular under-action and over-action. Three main varieties.—Structural muscular de- viations. Structural (Muscular) squint (Schneller's cases). Structural heterophoria.—Insertional squint and heterophoria.— Innervational deviations. Muscular Paresis. Muscular Spasm; varieties and cases.—Symptoms and Differential Diagnosis of the different Varieties of Muscular Over-action and Under-action. Identity in the symptoms presented by the three varieties. Con- genital deviations. Course of acquired deviations. Diagnosis between under-action and over-action. Slight weakness and over-action (explaining cases of heterophoria and particularly hyperphoria). Diagnosis by the double images. Principles and diagnostic tables. Deductions from the tables. Treatment of muscular over-action and under-action.—Tremor of individual ocular muscles; Unilateral nystagmus. VI. Anomalies of Associated Parallel Movements. Hypokin- sis. Paresis and insufficiency of associated parallel movements. Spasm of associated parallel movements. Peculiar case of spasm observed by the author.—Parakinesis of associated movements (Nystagmus). Theory of nystagmus. VII. Anomalies of Convergence. Hypokinesis. Paralysis of con- vergence.—Convergence-insufficiency. Signs. Nature and etiol- 42 NEW CLASSIFICATION OF MOTOR ANOMALIES. °gy- Varieties of non-accommodative convergence-insufficiency. Accommodative convergence-insufficiency: varieties. Course. Complications. Symptoms. Treatment.—Hyperkinesis. Spasm of convergence. Convergence-excess. Signs. Etiology. Va- rieties of non-accommodative and of accommodative converg- ence-excess. Course. Complications. Symptoms. Treatment. VIII. Anomalies of Divergence. Hvpokinesis.—Divergence-insuf- ficiency. Signs. Etiology. Idiopathic and secondary diverg- ence-insufficiency. Differentiation of the two forms. Course. Symptoms. Treatment. — Hyperkinesis. Divergence-excess. Signs. Etiology. Primary and secondary divergence-excess. Differentiation of the two. Course. Symptoms. Treatment. IX. Anomalies of Sursumvergence. Hypokinesis. Sumsurverg- ence-insufficiency. — Hyperkinesis. _ Sursumvergence-exeess. Sursumvergence-hyperphoria and vertical strabismus. Peculiar cases; anatropia and catatropia. X. Anomalies of Rotation Movements. XI. Recapitulation. Nature of Outward, Inward and Vertical Deviations (Exophoria, Esophoria and Hyperphoria). Varieties of each and their differentiation. IV. THE CLASSIFICATION OF OCULAR DEVIATIONS. We have seen in Section II. of this brochure that as physiologists we have to consider not only the movements of the individual muscles and the relative power of the latter, but also, and more particularly, the associated move- ments of the eyes produced by the coordinated actions of these muscles. It seems obvious that the same principles which we apply to the physiology of the ocular movements should also be applied to their pathology, and that in classi- fying motor disorders of the eye we should concern our- selves not simply irith the disorders and weaknesses of the muscles as snch, but also with the affections of all the various movements of which either eye alone or both eyes together are susceptible. Reasoning in this way, we shall ask if we do not in actual practice meet with pathological conditions which may be classified into the following groups, corre- sponding to the physiological groups which we have al- ready studied? (1) Disorders of individual muscles. (2) Disorders of associated parallel movements. (3) Disorders of convergence. (4) Disorders of divergence. (5) Disorders of sursumvergence. (6) Disorders of the rotation (or swivel) movements. NEW CLASSIFICATION OF MOTOR ANOMALIES. 43 I think that we have a sufficient number of clinical facts to enable us to give an affirmative answer to this query. For example, we meet with quite a number of cases in which the power of convergence is weak—a state that we might attribute (as indeed it often is attributed) to an in- trinsic weakness of the interni, were it not for the fact that the working of the latter in associated parallel movements is quite normal. Here then, evidently, it is the function of convergence that is at fault and not the action of the in- terni per se. Similarly we find excessive divergence action which can not be attributed to weakness of the interni, since the latter act normally both in convergence and in lateral movements, nor yet to excessive strength of the ex- terni as such, since the latter in associated parallel move- ments do not carry the eye too far outward. In this case, therefore, it is the function of divergence, and not the power of the interni, or externi, that is at fault. Both this condition and the preceding one exhibit the common symp- tom of divergence in fixation and would hence ordinarily be classed together as examples of exophoria; but in classi- fying them thus we should be naming not the disease but the symptom. The symptom, moreover, while the most ob- vious, is not necessarily the most important feature of the condition in question; and in our therapeusis we aim not so much to abrogate the exophoria per se, as to remove the state (defective convergence, excessive divergence) caus- ing the exophoria. Similar instances might be given of other varieties of motor disorders in which also the function involved is an ocular movement and not an ocular muscle. The considera- tion of these, however, will be deferred until later when they can be discussed more in detail; those given above being regarded as sufficient for purposes of illustration. If, then, any one of the ocular motor functions may be involved independently of the rest, we must next inquire what may be the nature of the lesion affecting it. In ans- wer to this it may be said that any motor function may be deranged in either one of three ways. (1) It may be performed inadequately or not at all—de- ficiency of movement (Jlyjnd-iuesis). 44 NEW CLASSIFICATION OF MOTOR ANOMALIES. (2) It may be performed excessively—excessive move- ment (Hyperkinesis). (3) It may be performed irregularly or in successive phases of excess and inadequacy—irregular movement (Parakinesis). To the question whether disorders having these various characters are actually encountered in connection with the ocular movements, clinical facts once more enable us to give an affirmative answer. It must, however, be under- stood that these conditions, namely hypokinesis, hyper- kinesis and parakinesis, may be present in very varying degrees. Thus weakness (hypokinesis) may vary all the way from a slight and transient enfeeblement to a complete paralysis; and, similarly, excessive action (hyperkinesis) may range from a moderate degree of over-action to an intense and permanent spasm. It thus happens that there are some deviations so slight as to be habitually corrected by the supplementary effort that the patient is able to ex- ert (Superable deviation,Latent strabismus,Heterophoria); while there are other deviations so great that the patient can overcome them with difficulty if at all, and which are hence more or less constantly present (Insuperable devia- tion, Manifest squint, lleterotropia ). These latter again are divided according to the constancy of their occurrence into Intermittent, when present at intervals, Periodic, when recurring regularly under certain conditions (e. g. in con- vergence), and Constant. It should be borne in mind, however, that these distinctions all represent differences simply of degree and not of kind. The foregoing considerations, confirmed and modified by the results of the examination of quite a large amount of clinical material, have led me to propound the following classification of the motor anomalies of the eye. CLASSIFICATION OF THE MOTOR ANOMALIES OF THE EYE. OCULAR DEVIATIONS IN GENERAL DUE TO 1. Anomalies of Individual Muscles or of their Nerve-nuclei. [a) Under-action. The muscle works inefficiently. 1. Because the muscle itself is ill-developed or atrophied (Struc- tural Squint), or because its attachments are unfavorable for effective action (Insertional Squint). NEW CLASSIFICATION OF MOTOR ANOMALIES. 45 2. Because of impairment of the nerve or nerve-nucleus supply- ing the muscle (Paretic Squint). (b.) Orcr-action. The muscle works excessively. 1. Because the muscle itself is over-developed (Structural Squint), or because its attachments are favorable for effective action (Insertional Squint). 2. Because of over-excitation of the nerve or nerve-nucleus sup- plying the muscle (Spastic Squint). (c.) I'crrcrtcd action. Clonic spasm of individual muscles (some rare forms of Nystagmus). II. Anomalies of the Association Centres for Parallel Movements. {a.) Under-action. Producing an equal impairment in the move- ment of botlv eyes either (1) up, (2) down, (3) to the right, (4) to the left, or (5) obliquely, or (6) an equal impairment of the rotary (swivel) movements of the two eyes. (Associ- ated Paralysis, Conjugate Paralytic Deviation.) (b.) Orcr-action. Producing an equal excessive movement of both eyes in the same direction (Associated Spasm, Conjugate Spastic Deviation). {<•.) Perm-ted action. Clonic Spasm (Ordinary Nystagmus; includ- ing Lateral, Vertical, Rotary and Mixed Nystagmus). III. Anomalies of the Centre for Convergence-Movements. (a.) Under-action. Convergence-Insufficiency (producing one va- riety of Comitant Divergent Squint or Exophoria). 1. Accommodative (due to relaxed accommodation in myopes). 2. Non-accommodative. (b.) Orcr-action. Convergence-Excess (producing one form of Comitant Divergent Strabismus or Esophoria). 1. Accommodative (due to excess of accommodation in hyperme- tropes.) 2. Non-accommodative. IV. Anomalies of the Centre for Divergence Movements. (a.) Under-action. Divergence-Insufficiency (producing one form of Comitant Convergent Squint or Esophoria). (b.) Orcr-action. Divergence excess (producing one form of Com- itant Divergent Squint or Exophoria). V. Anomalies of Sursumvergence. {((.) Under-action. Sursumvergence-Insufficiency. (b.) Orcr-action. Sursumvergeiice-Excess (producing constant or intermittent vertical divergence of the visual lines; includ- ing cases in which one visual line is habitually above (Spas- tic Right or Left Hyperphoria), and cases in which some- times one, sometimes the other, rises higher (Alternating Hyperphoria). VI. Anomalies of Rotation (Swivel or Torsion) Movements. {a.) Habitual or intermittent divergence of the Vertical meridians (Cyclophoria Divergens). (b.) Convergence of the vertical meridians (Cyclophoria Converg- ens). 46 NEW CLASSIFICATION OF MOTOR ANOMALIES. VII. Mixed Forms. Many varieties including particularly— (a.) Convergence-Insufficiency combined with Divergence-Excess. (&.) Convergence-Insufficiency combined with Divergence-Insuffi- ciency. (c.) Convergence-Insufficiency, simple or complicated, combined with under-action or over-action of one or more of the lat- eral or vertical muscles. (cZ.) Convergence-Excess combined with Divergence-Insufficiency. (e.) Convergence-Excess combined with Divergence-Excess. (/.) Convergence-Excess, simple or complicated, combined with under-action or over-action of one or more of the lateral or vertical muscles. (g.) Under-action of one muscle combined with over-action of another. Before taking up the study of the individual anomalies, it is well to consider one or two features common to all of them. Comitant* and Non=comitant Deviations. A wide differ- ence exists both as regards symptoms and physical signs between motor disorders in which the amount of deviation constantly changes according to the direction of the gaze (Non-comitant deviations) and those in which it remains the same (Comitant deviations). The former is apt to be much the more troublesome of the two to the patient, par- ticularly when the deviation keeps changing while the eyes are executing associated parallel movements. This is ap- parently due to the fact that the symptoms occasioned by the deviation, changing as they do with every alteration in the position of the eyes, cannot be allowed for nor be as readily ignored as when they are constant. That is, since the patient sometimes sees single, sometimes double, i. e. is affected with an error of varying amount, he cannot as readily make allowances for his peculiar state of vision as if he saw double all the time and had a constant error to contend with. Moreover, it is less easy for the eye to suppress a false image when the latter, in- stead of occupying always the same spot upon the retina, as it does in comitant deviations, occupies a number of different spots in suc- cession, as it does in the case of a non-comitant deviation. Hence the diplopia tends to persist much longer in non-comitant disorders than in those that are comitant. Besides, the very fact that the de- flection is changeable in amount is the cause of the most trying symp- toms (false projection and vertigo) of a non-comitant deviation; and *The word "comitant1" is here employed in preference to the more usual " con comitant " as being both briefer and etymologically better. NEW CLASSIFICATION OF MOTOR ANOMALIES. 47 when the deflection becomes constant in quantity for all directions of the gaze, these symptoms are apt to disappear. It is obvious that an affection of the individual ocular muscles. whether in the direction of excess or of deficiency, must cause a non-comitant deviation, the angle between the two visual lines be- coming greater and greater the more the eyes are carried in the direction in which the muscles in question normally exert their great- est influence. Thus in a paralysis of the right externus the right eye will lag more and more behind its fellow in proportion as the eyes are carried to the right: and in paralysis of the right superior rectus the right eye will fall more and more below the level of the other, the more the attempt is made to direct the gaze up and to the right. In fact, it is by this very changeableness or non-comitancy of the deviation that we make our diagnosis of the existence of muscular paralysis or spasm. On the other hand, a deviation due simply to an over-action or under-action of either divergence or convergence will not change in the performance of associated lateral or vertical* movements, as long as the object of fixation does not appreciably approach or recede from the eyes. For, for any given distance, the amount of convergent or of divergent action will be constant and the excess or deficiency of this action will also be constant, no matter whether the eyes are look- ing straight ahead, or laterally, or up or down. If, however, the dis- tance of the object of fixation from the eye is altered, the amount of convergent or divergent action changes also, and in general the amount of deflection will change as well. Thus in a pure conver- gence-insufficiency the deviation will become more and more appar- ent as the limit of convergence is approached and will disappear alto- gether when the convergence is relaxed, /. e. when the patient is looking at a distance. In the case of a divergence-insufficiency the reverse will hold good. In anomalies of associated jtarallel movements the motions of the eyes are strictly comitant, and in fact the visual lines remain everywhere parallel, since the ocular movements, while either restricted or in ex- cess in some given direction, are restricted or in excess to the same degree in both eyes. For example, in a case of restricted sursum- version both eyes will fail to move up, but as the failure affects both to an equal degree, the visual lines will in the performance of this movement remain parallel up to the point where they cease to move at all. The foregoing facts may be recapitulated as follows: (1) vl deviation ufrich increases or decreases in the per- formance of associated parallel movements by the eyes signi- fies an anomaly of one or nacre of the ocular muscles — the ♦This statement is not absolutely accurate, for, owing to the fact that the visual lines tend to diverge when the gaze is directed upward and to converge when they are directed downward, an exophoria otherwise comitant will show an increase in the upper and a decrease in the lower portions of the field of fixation. 48 NEW CLASSIFICATION OF MOTOR ANOMALIES. direction in which it increases corresponding to that in which the action of the muscles affected is normally most pronounced. (2) A deviation which remains constant or nearly so while the eyes are performing parallel movements is due, not to an anomaly of individual muscles, but to an anomaly of some one of the associated movements of the eyes. (3) .1 deviation which increases as the eyes are converged denotes a convergence-anomaly, and one which increases as the eyes are passing from convergence to parallelism a diver- gence-anomaly. Transformation of Non=comitant into Comitant Devia= tions. Non-comitancy in parallel movements might be remedied by restricting or increasing the action of the un- affected eye in the same sense as that in which the action of the affected eye is restricted or increased; t. e. by con- verting the anomaly from one of Class I. into one of Class II. This is done in actual practice when, e. g. in a paralysis of the su- perior oblique of the right eye Ave tenotomize its associated antagon- ist, the inferior rectus of the other eye, thereby weakening the lat- ter artificially in precisely the same sense and to the same extent that the right eye is weakened naturally. In nature a, similar, though less perfect, result is commonly attained by the development of a spasm of the direct antagonist or of a pair of antagonistic muscles in the eye affected. Thus in a paralysis of the right externus, which produces a deviation confined to the right half of the field of fixation, is usually followed after a time by a spastic contraction of the right internus, which produces a deviation of the same character in the left half of the field of fixation. Thus the affected eye gets to squint inward, not only when looking to the right, but also when looking to the left, and the deviation, from being markedly non-comitant, be- comes comitant or nearly so. A similar occurrence is regularly ob- served in paralysis of the other muscles. A similar tendency to replace non-comitant by comitant deviations appeal's to prevail, although possibly to a less extent, in divergence and convergence anomalies. Thus a convergence-insufficiency, exist- ing at first without any complication, is very apt later on to become associated with a divergence-excess, so that a sensibly constant devia- tion outward (exophoria) is present both for far and near,where origin- ally it was present for near only. So also a convergence-excess may lead to a divergence-insufficiency, so that the esophoria which at first was marked only for near now becomes equally pronounced for dis- tance. This compensatory process, by which comitancy is evolved NEW CLASSIFICATION OF MOTOR ANOMALIES. 49 out of a non-comitant state, is doubtless the reason for the many mixed forms of divergence and convergence anomalies that we meet with; and the process itself may actually be watched in following the development of many cases of squint. The process in fact seems to take place so generally that it seems safe to enunciate the following law: A non-comitant deviation usually tends to become comi- tant, there being superadded to the morbid condition already existing another by means of which the former is generalized and rendered sensibly equal throughout the whole field of fixation. V. ANOMALIES OF THE INDIVIDUAL MUSCLES.* Hypokineses and Hyperkineses (Paretic and Spastic Squint), Over-action or under-action of the individual ocular muscles, giving rise to a disturbance of the normal balance of the eyes, may be due to (a) Over or under - development of the muscle itself (structural squint, structural heterophoria). (b) Variations in the origin, insertion and direction of the muscles and in the length of their tendons (insertional squint or heterophoria). (c) Over or under-excitation of the muscle due to some affection of its nerve or nerve-nucleus (paretic and spastic, squint and heterophoria). The hypertrophy or the non-development of the muscles; producing what I have called structural deviation is prob- ably in many cases congenital. This is certainly so in those cases of defective elevation of the eye (frequently asso- ciated with ptosis) which have been proved by dissection to be due to absence of the superior rectus (Fuchs). I have seen one marked instance of this congenital anomaly in which ptosis co-existed with almost entire absence of elevation, and I am inclined to think that several other cases of less complete paralysis of elevation, which I have ♦This section, since its first presentation to the Prize Committee, has been largely/ added to and to a certain extent re-modeled. 4 50 NEW CLASSIFICATION OF MOTOR ANOMALIES. observed, were likewise congenital and structural in origin.* Another class of cases of structural deviation, of quite frequent occurrence, are those which Schneller (Arch, fiir Ophth. xxiii. No. 3) describes under the name of muscular strabismus. Such, for example, are those cases of diver- gent strabismus in which, at the time of operation, we find the external rectus thick, broad and fleshy, and provided with a dense, broad tendon, while the internal rectus, on the contrary, is thin and has a narrow tendon, often split up into separate fibrils. Schneller in these cases found that the tendon of the externus, instead of being about equal to that of the internust, was from one-fourth to one-third greater. In convergent strabismus, on the other hand, the ratio was reversed, the tendon of the externus being much thinner than that of the internus and the externus itself being comparatively meager and undeveloped, Schneller reports thirty-four cases of such muscular (structural) strabismus. He regards them (probably with justice) as congenital in origin. Others have supposed that these were cases of acquired atrophy (atrophy of disuse). But the pathological changes are those of sim- ple non-development rather than atrophy, the muscular fibres being merely insufficient in number or size and showing no evidences of fatty or fibrous transformation nor of myositis. The diagnostic features of a muscular squint, according to Schneller, are (1) The deviation is not relieved by atropinization and correction of the refraction (distinction from accommoda- tive convergence-excess and convergence-insufficiency). (2) The field of fixation (/. e. the range of excursion of the eyes) is abnormally large in one direction and abnor- mally limited in the opposite. If the sum of the inward excursions of the two eyes exceeds the sum of the outward excursions by 30°, a convergent strabismus is produced; while a preponderance of outward excursions over inward excursions of 12° is sufficient to cause a divergent squint (Schneller). *See article by the author on "Paralysis of the Superior Rectus and Its Bearing upon the Theory of Muscular Insufficiency" (Archives of Ophthalmology, vol. xxiii No. 1, 1884.) tSchneller found the normal ratio between the breadth of the externus-tendon and the internus-tendon to be 102:100. His measurements were made so as to include more of the scleral attachments than in those made by other observers who have found the ratio to be 88 (Volkmann) and 89 (Fuchs) ■ NEW CLASSIFICATION OF MOTOR ANOMALIES. 51 This latter statement involves a fallacy, strictly speaking, if the range of excursion is, as is usually the case, determined by making the eyes follow a test-object situated within a foot or so'of the eye. For in this case when the eyes are directed to the right, the amount of excursion outward of the right eye = the absolute amount by which the externus can turn it outward (abduction) less the amount by which it is turned inward in order to converge upon the object (con- vergence). The latter (convergence) movement will be excessive either if the right internus acts too forcibly in response to an ordi- nary impulse of convergence (muscular excess) or if, the muscle being normal, the impulse itself is excessive (convergence-excess). In either case the net movement outward will be limited, even when the actual amount of abduction produced by the externus is normal. If, then, the case were one of simple convergence-excess the limita- tion of outward movement would be the same for both eyes. /'. c.. the same whether the gaze is directed to the right or to the left: but if it were one of muscular squint, i. e. of actual insufficiency of the externi (of preponderance of the interni) the limitation might be either unilateral or bilateral. In the latter event the diagnosis of a muscular anomaly, as distinguished from a pure anomaly of convergence, would be substantiated if the limita- tion of abduction were found to be the same for all distances, far as well as near. Degrees of weakness or of over-development, too slight to produce actual squint, probably form an important ele- ment in the causation of many cases of heterophoria (struc- tural heterophoria.) Insertional squint or heterophoria, /. e. that sort of mus- cular under-action or over-action due to variations in the origin and insertion of the tendons, is difficult to distin- guish from the structural deviations due to under or over- development of the muscular fibre itself. The structural deviations, however, are frequently congenital, while inser- tional squint is generally acquired. For example, a very important class of cases coming under the latter category are those in which the insertion of a tendon has been dis- placed by a tenotomy or an advancement. Here by the op- eration an insertional anomaly is produced; and the weak- ness or over-action resulting from this artificial anomaly is precisely similar in symptoms and objective signs to weak- ness or over-action due to natural causes (paresis or spasm, for example).* *Of the exactness of this similarity I have been able to convince myself by re- peated examinations upon cases in which extensive operations had been made either upon the lateral or vertical muscles. 52 NEW CLASSIFICATION OF MOTOR ANOMALIES. Another class of cases in which there is an acquired in- sertional anomaly are those in which a divergent strabis- mus has developed as a result of the gradual divergence of the orbits taking place during the period of growth in child- hood and youth. This divergence, by altering the angle of insertion of the tendons and the amount of tendon in contact with the eye-ball, increases very greatly the power of the externus and diminishes that of the internus, and in itself is quite sufficient to account for the development of the strabismus (see L. Weiss, Arch. f. Augenh. xxix. and Arch, of Oph. xxv. No. 3, 1896). The anomaly in this case is of great importance in that it exaggerates and renders uncertain the effect of a tenotomy of the interni when made upon children. Admitting Weiss's explanation of it, the obvious deduction would be that tenotomy of the interni should be avoided in children with convergent squint who have the orbits and eyes set very close together, since in these divergence of the orbits is likely to take place subse- quently resulting in a preponderance of the externi, which will by itself suffice to correct the convergence. Other kinds of insertional anomalies exist, some so slight as to produce only a moderate degree of Jieteropiioria, in- stead of a squint. They often develop when a non-comi- tant deviation has lasted for some time, and help to trans- form the latter into a deviation of the comitant variety. Muscular paresis and spasms(Innervational Deviations). The subject of the paralyses of the eye muscles has been so thoroughly worked out and so ably presented by the two Graefes and Mauthner, that there is but little to add to their statement. The few points to which it seems necessary to call attention will be touched upon in the remarks on diagnosis. Spasm of the individual ocular muscles may occur (1) As an evidence- of a secondary deviation in a sound eye when the other eye, being paretic, is yet used for fixa- tion. Thus suppose that a patient with a paresis of the right externus nevertheless fixes with the right eye because he sees better with it. NEW CLASSIFICATION OF MOTOR ANOMALIES. 53 Then when he looks at some object situated on his right he has to exert an excessive amount of force to turn his fixing eye out suffi- ciently. The same amount of force is. by the law of association, also transmitted to the left internus, and the latter, not being paretic, will respond with normal vigor to the excessive stimulus, so as to carry the left eye much further to the right than its fellow, and hence quite to the right of the object of fixation. In this case, as the right eye follows the object, and the left eye by an apparently excessive action shoots past it, we might regard the condition as one of veritable spasm of the left internus; whereas the real state of the case is that the latter muscle is normal and contracts excessively only because the stimulation that it receives is excessive. These cases are therefore correctly denominated as cases of false or apparent spasm. (2) In the case of a paralysis of an ocular musle, a spas- tic contraction of one or more of the other muscles in the same eye takes place, by virtue of which, as has been al- ready stated, the deviation becomes more or less concomi- tant and generalized throughout the whole field of fixation. This contraction finally results in a permanent shortening (contracture) of the muscles affected, but before this stage has been reached, a temporary and varying spasm may be set up in the antagonists of the paralyzed muscle, so as to carry the deviation and the diplopia far outside of the field of action of the latter. This was clearly shown in the fol- lowing case which came under my care: Paralysis of Inferior Rectus. Varying Spasm of Superior Rectus of same eye. H., male, aged 2!). Vertigo, blurring of sight, and diplopia for past two years. No history of syphilis. Presents all the evidences (by inspection, screen, and diplopia tests) of a well-marked paresis of the R. inferior rectus. Vertical diplopia (with image of right eye below = DR) increasing to G° to 7° (=14° prism) as the eyes are carried down and to the right; diminishing to zero when the gaze was directed down and to the left. Moderate crossed diplopia everywhere; increasing when eyes are directed down and to left. Vertical diplopia of the same character as that found in the lower field prevailed, although to a less extent in the upper field; most marked in looking up and to the right (Eu & r, DR increasing). This diplopia in the upper field varying much, and partially superable by voluntary effort. Here there was evidently a spasm (variable in amount) of the right elevators, and particularly of the right superior rectus (shown by the fact of the vertical diplopia increasing upward and to the right). The vertical diplopia in the upper part of the field might, it is true, have been due to a paresis of the elevators of the left eye: but the 54 NEW CLASSIFICATION OF MOTOR ANOMALIES. variable character of the diplopia and the fact that it was superable by voluntary effort negative this supposition. (3) Spasm (usually slight) of one or more of the ocular muscles may occur as the result of irritative lesions at the base of the brain, particularly meningitis. (4) Slight transient spasm may occur in chorea. (5) Convulsive tonic spasm may occur in epilepsy and hys- teria, although in these diseases it is not generally the individual muscles that are affected, but the associated movements of the eyes (particularly the parallel move- ments and movements of convergence). Gowers, however (Diseases of the Nervous System), calls attention to a sort of convulsive seizure that maybe styled epileptoid, in which there are suddenly developing tonic and clonic spasms of one or more ocular muscles, associated with more or less obtunding of the consciousness. (6) Finally we may have cases of non-paroxysmal and chronic spasm of some one ocular muscle, which causes the eye to make an excessive movement as soon as it is turned so that the affected muscle can act upon it. Thus cases have been described in which a spasm of the external rec- tus caused the eye to shoot far outward as soon as the eye was turned past the middle line. Mauthner (Augenmus- kellahmungen) casts doubt on all such cases, regarding them as probably instances of secondary deviation of a sound eye due to the fact that the other eye is paretic but still performs fixation, so that an excessive impulse is transmitted to both eyes. That is, he would class all such cases under the category of false or apparent spasm (Group 1 mentioned above). But this statement is certainly too sweeping, since cases of chronic spasm, although doubtless rare, do occur, as witness the following that I observed: Paralysis of L. Externus; Spasm of L. Inferior Oblique. Ber- tha S., aged 8. Deviation of eyes noticed since birth. Used to hold head to right and does so still when looking intently at anything. L. eye cannot move out beyond median line. When eyes are car- ried horizontally to the right, L. eye suddenly fies upward and be- comes buried beneath the upj>er lid. In associated movements in lower field, L. eye moves normally with the R. Behind screen L. eye de- viates high up and somewhat in. Deviation of either eye behind screen about equal. No double images attainable. V. R. 20/40; with +1.00 D. 2o/30. L. *o/70. NEW CLASSIFICATION OF MOTOR ANOMALIES. 55 Here the sudden and excessive upward movement of the left eye when directed inward could only have been effected by a spasmodic contraction of the inferior oblique; the superior rectus acting but slightly as an elevator when the eye is adducted. A similar case in which with paralysis of the R. externus and R. superior rectus there was spasm of the R. superior oblique is the following: Emma D., aged 15. Strabismus since scarlatina eleven years be- fore. Occasional vertigo; no diplopia. Movements of L. eye nor- mal. R. eye cannot move at all to right, nor upward and to right: movement upward almost normal when eyes are carried to left (re- tention of power of inferior oblique): movement downward excess- ive, especially when eyes are directed to left (excessive action of superior oblique); when attempt is made to move eyes straight to left, R. eye; shoots obliquely down and to the left (spasmodic action of superior oblique). In addition to these cases in which spasm was associated with paralysis, I have seen others in which a deviation limited to one portion of the field of fixation was present, which deviation was always marked but yet retried so much in amount from one time of observation to another as to necessitate the assumption of its being spasmodic rather than paralytic in origin. Symptoms and Differential Diagnosis of the Different Varieties of Muscular Over=action and Under-action. No attempt will be made here to go at all fully into the symp- toms produced by insufficiency or over-action of the indi- vidual muscles. This has already been done in various excellent treatises. I will simply give the following facts to which, as I conceive, too little attention has been paid. 1. In the deviations considered in the foregoing para- graphs the abnormality, as has been pointed out, may affect either the muscle itself, its tendon, or the nerve and nerve-nucleus supplying it; /. e. the muscle may act above or under the normal either because it is itself too much or too little developed (Structural Deviation) ; or because the direction and insertion of its tendons are not what they should be (Insertional Deviation); or because the muscle is in a state of paralysis or spasm (Innervational—Paretic or Spastic—Deviation). Now it cannot be too strongly insisted upon that these three varieties, however dissimilar 56 NEW CLASSIFICATION OF MOTOR ANOMALIES. in origin, show in their symptoms and objective signs no real point of difference. Thus weakness of the external rectus, whether arising from feeble and arrested develop- ment of the muscular fibre, or from mal-position of the tendon (natural or produced by a tenotomy), or from lesion of the sixth nerve, gives rise to the same symptoms and offers the same appearances to objective examination. The characters of the paretic and spastic deviations, to be sure, are generally more definite and more striking than are those of the other anomalies mentioned, but this is simply owing to the fact that such cases are usually seen early, before any compensatory changes have taken place and while the diplopia, false projection, vertigo, and other symptoms are therefore still marked. Precisely the same effect will be produced in a patient with binocular single vision if one of the tendons is completely divided. And in cases of long standing—particularly in congenital cases—it is impossible to say with certainty from the symptoms alone without reference to the history whether faulty innervation, faulty insertion, or faulty structure lies at the basis of the anomaly. 2. Congenital deviations present several peculiarities. In the first place they cause little or no trouble for the ob- vious reason that the patient from his infancy has learned to adjust himself to the anomalous condition present. Again, it is remarkable that, even after the condition has existed for years, there is no constant suppression of the diplopia such as occurs in comitant squint, and further- more, there is no tendency, as in the case of other non- comitant deviations, to a transformation into a comitant deviation by the development of a contracture of the an- tagonists. The reason probably is that as the patient has never known any different condition from that which he was born with, and as this condition consequently is the natural one for him, he experiences no inconvenience from its continuance, so that no involuntary tendency is set up toward its rectification. The result is that these congenital deviations, which may be due either to paresis or to a struc- tural defect, afford, as far as objective signs go, the most typical picture of uncomplicated muscular paralysis that we can have. NEW CLASSIFICATION OF MOTOR ANOMALIES. 57 3. Acquired muscular deviations, on the other hand, whether due to anomalies of innervation or insertion, al- ways tend to become comitant; this being affected by a gradually developing contracture of the antagonists when the affected muscle is too weak, and by a weakening of the antagonists when the affected muscle is too strong. It is thus, probably, that many cases of comitant strabis- mus convergens and strabismus divergens are produced; and the few cases of strabismus sursumvergens that I have met with were apparently all developed in this way. Thus paralysis of the R. elevators, when not of congenital origin, is regularly followed by spasm of the R. depressors, causing the right eye to stand lower than the other in all portions of the field of fixation. This process continuing and the spasm developing into a confirmed contracture, the difference in height between the two eyes (L. hypertropia) becomes equal for all directions of the gaze; the limitation of movement of the right eye upward is compensated for by a corresponding increase in its movements downward: and the picture of a typical comitant strabismus deorsumrergens is pro- duced. If but one of the elevators, e. g. the superior rectus, is paretic the spasm is apt to be confined, in the first instance at least, to the cor- responding depressor, /. e. the inferior rectus. In this case the devi- ation will become half-comitant, that is, comitant for movements up and down but not for lateral movements. Thus, if the right supe- rior rectus were the paretic muscle, we should have first a L. hyper- phoria, very marked in the upper right-hand quadrant of the field of fixation and diminishing rapidly, both when the eyes were carried down and when they were carried to the left. Later, when spasm of the right inferior rectus had developed, the L hyperphoria would become pronounced in the lower right-hand quadrant also, and ulti- mately so much so that whether the eyes were carried up or down, the right eye would always stand about the same distance below the left. But in both the upper and lower portions of the field the L. hyperphoria) would still increase as the eyes were carried to the right and diminish to zero as they were carried to the left: so that even under these circumstances the deviation would not be comitant for lateral movements. A case of this sort, in which the inferior rectus was the muscle primarily affected and in which semi-comitaucy was being developed by spasmodic action of the superior rectus has already been men- tioned (under the head of Spasm of the Ocular Muscles). Cases in which a comitant (and even an alternating) lateral squint has developed out of a paresis of the externus, followed by contract- ure of the internus and later by partial restoration of the power of 58 NEW CLASSIFICATION OF MOTOR ANOMALIES. the externus, have been reported by Spicer ("Royal London Ophth. Hosp. Reports," xiv. 1, 1895). I have observed analogous cases, particularly one in which a partial oculomotor paralysis with second- ary contracture of the externus had resulted in a nearly comitant strabismus divergens. In proportion as the deviation becomes transformed from a non-comitant to a comitant one, the symptoms grow less disturbing; for, as already stated, it is always the case that, other things being equal, a comitant deviation will give less trouble than will one that is non-comitant. 4. The diagnosis between over-action and under-action is often difficult. Theoretically, over-action (spasm) is asso- ciated with excessive movement, and under-action (pare- sis) with very deficient movement in some one direction. But, unless the paralysis is nearly total or the spasm is great, it is not always easy to say whether it is the muscle of one eye that is under-acting or whether it is the asso- ciated antagonist of the other eye that is over-acting; and when secondary changes have taken place, transforming the deviation into a comitant one, the diagnosis is often impossible. Before this has occurred the differentiation may be made from the following considerations. OVER-ACTION. | UNDER-ACTION. Points in Common. One eye moves faster and further than the other when both are carried in some one particular direction; and this discrepancy be- tween the position of the eyes and also the diplopia, false projec- tion, and vertigo become more and more pronounced, the further the eyes are carried in that direction. The primary position for both eyes is nearly the same. The absolute excursion of the faster moving eye in the given direction is greater than normal; that of the other eye is normal. The total excursion of the fast- er moving eye in the given direc- tion and m its opposite is greater than normal; i. e., the field of fixation is excessively large in one of its diameters. Fixation is usually performed by the slower moving eye. The amount of deviation may show great and sudden changes from time to time. The absolute excursion of the faster moving eye is normal in all directions; that of the other eye is subnormal. The total excursion of the fast- er moving eye is normal, that of the other eye is subnormal; i. e., the .field of fixation of the latter is contracted in one of its diame- ters. Fixation usually performed by the faster moving eye. The amount of deviation re- mains constant or changes slowly and progressively. NEW CLASSIFICATION OF MOTOR ANOMALIES. 59 5. While the diagnosis .of a marked underaction of one of the ocular muscles usually presents no difficulty, there is quite a large number of cases in which the condition is not so obvious, the weakness of the muscles being comparatively slight* In these cases diplopia does not occur until the eyes are removed some distance (10° to 20°) from the pri- mary position. As soon as it does appear, however, it develops in a perfectly typical fashion, showing marked increase in some one special direction and diminishing elsewhere to zero. Most cases of this sort of anomaly, that I have observed, have been those in which there was a pretty pronounced weakness (perhaps of congenital origin or, rather, due to non-development) of the superior rectus; less frequently the inferior rectus seemed involved. The nature and course of these cases have not been thor- oughly investigated, but it is noticeable that they are frequently associated with a convergence-insufficiency which shows a tendency to go over into a divergence- excess, resulting, in sone instances at least, in a regular divergent squint. The chief symptoms (which, however, are, very likely, attributable to the convergence-insuffi- ciency) are conjunctival irritation, asthenopia (often very marked), headache, and diplopia. In many cases the symptoms are insignificant and this fact coupled with the absence of diplopia in the primary position is probably the reason why these cases have been left uninvestigated. Quite a number of cases of hyperphoria doubtless belong to this category. Another variety of muscular weakness, transitory in its character, is that already referred to as associated with neurasthenia. Here we may find diplopia all round the periphery of the field of fixation, /. e. within 35° of the primary position (Concentric contraction of the field of binocular single vision). This condition would appear to have little significance except as a diagnostic sign of the condition with which it is associated. It is not unlikely that slight degrees of muscular sjtasm are at the bottom of some of the cases of heterophoria that we meet with; e. g. spasm of either one of the elevators *It is to these cases that the old term muscularlinsumciency should be limited. I 60 NEW CLASSIFICATION OF MOTOR ANOMALIES. or of either one of the depressors may occasion a hyper- phoria of more or less varying character (Spastic hetero- phoria). I have notes of five or six cases in which the presence of a varying and even alternating hyperphoria seemed to be due to more or less spasmodic contraction of the vertical muscles. Finally it is quite likely that a large number of cases of slight deviation are due to moderate under-action of one muscle combined with over-action (secondary spasm) of another, so as to produce a more or less comitant deflec- tion. Probably most of the cases of hyperphoria, in which the deviation, although moderate in amount, is present through the whole field of fixation, are attributable to combined anomalies of this sort (concitanf hyperphoria ). Cases of this kind often give rise to asthenopia, headache, neuralgia, and sometimes to gastric disturbance and im- pairment of nutrition. Diplopia is infrequent and when present can usually be readily overcome. 6. The diagnosis of the muscles affected in a case of paralysis or spasm is readily accomplished by means of the double images if the following principles are kept in mind. (a) The diplopia increases progressively as the eyes are carried in that direction in which the action of the muscle affected is normally most pronounced. (b) Paralysis of any given muscle of one eye produces diplopia of the same character and increasing in the same way as does a spasm of the associated antagonist in the other eye. (c) While paresis or spasm of one of the vertical mus- cles does produce lateral diplopia, this diplopia maybe and often is neutralized by the existence of other factors, so that it is of no practical significance in the diagnosis. The latter must rest solely upon the difference in height of the double images and the portion of the field where this difference is most pronounced. This fact", enunciated and explained very clearly by Mauthner, is frequently overlooked, many insisting that paresis of the superior and inferior recti must produce crossed, and paresis of the obliques homonymous diplopia. But, apart from the fact that these pareses are often associated with exophoria or esophoria of sufficient NEW CLASSIFICATION OF MOTOR ANOMALIES. 61 amount to neutralize their lateral diplopia, the natural tendency which the visual axes display to diverge when the eyes are directed up and to converge when they are directed down will work to abro- gate the homonymous diplopia due to a paresis of the inferior oblique and the crossed diplopia due to a paresis of the inferior rectus. As a matter of fact I have found paresis of the superior and inferior recti often associated with homonymous diplopia. The following table, constructed in accordance with the three principles just enunciated, shows succinctly the way in which the diagnosis can be made from the double images. DIAGNOSTIC TABLE of Paralysis and Spasm of the Oenlar Muscles. Note. DII = homonymous diplopia; I)X — crossed diplopia; DR = vertical diplopia with the image formed by the right eye below: DL = vertical diplopia with the image formed by the left eye lie- low. Eu, Ed, Er, El, Eu & r, etc , = associated parallel move- ments in which the eyes are directed respectively up (Eyes up) down, right, left, up and right, etc. P>> = increasing; > in Er, < < in El. DII » in El, « inEr. INDICATES PARESIS OF R. External Rectus L. External Rectus OR SPASM OF L. Internal Rectus R. Internal Rectus II. Variation slight = Paresis of Oblicpie (Spasm of Superior or Infe- rior Pectus) or a comitant esophoria associated with a condition causing varying DX. I Particularly marked in Particularly marked in Ed. [Ed. & r.] {Particularly marked in Eu. [Eu. &1.J Particularly marked in Ed. [Ed. &1.J R. Inferior Oblique R. Superior Rectus R. Superior Oblique R. Inferior Rectus L. Inferior Oblique L. Superior Rectus L- Superior Oblique I L. Inferior Rectus L. Superior Rectus L- Inferior Oblique L. Inferior Rectus L. Superior Oblique R. Superior Rectus R. Inferior Oblique R. Inferior Rectus R. Superior Oblique B. CROSSED DIPLOPIA VARYING IN DIFFERENT DIRECTIONS OF THE GAZE. I. Variation great = Paresis of Internus (Sjiasin of Externus.) CHARACTER OF DIPLOPIA DX > > in Er. D>> in El. < < in El. < ■*** in Er. = PARESIS OF OR SPASM OF L. Internal Rectus R. Internal Rectus R. External Rectus L- External Rectus II. Variation slight = Paresis of a Superior or Inferior Pectus (Spasm of an Oblique) or a comitant exophoria associated with a condition causing varying DII. f Particularly marked in DX>> n Er. ] Eu. [Eu. &r.] -3 "1 in El. | Particularly marked in I Ed. Ed. & r.j f Particularly marked in DX >> in El. J Eu. [Eu. &1.J < < in Er. ] Particularly marked in I Ed. [Ed. &!.] L- .Superior Rectus L. Superior Oblique L. Inferior Rectus L- Superior Oblique R. Inferior Oblique R. Superior Rectusl R. Superior Oblique R. Inferior Rectus f R. Superior Rectus | L- Inferior Oblique I R. Inferior Oblique i L. Superior Rectus f R. Inferior Rectus L. Superior Oblique 1 R- Superior Oblique L- Inferior Rectus NEW CLASSIFICATION OF MOTOR ANOMALIES. 63 ('. VERTICAL DIPLOPIA VARYING IN DIFFERENT DIRECTIONS OF THE UAZE (= PARKSIS OR SPASM OF ELEVATOR OR DEPRESSOR.) 1. Diplopia U^ in Eu. (Paresis or Spasm of Elevator.) CHARACTER OF DIPLOPIA = PARESIS OF OR SPASM OF DR. most marked in Eu. L. Inferior Oblique JR. Superior Rectus & r. [regularly associ- ated with DII >> in DR > > in Eu. - DR most marked in Eu.l L. Superior Rectus !r. Inferior Oblique & 1. [regularly associ-| ated with DX >> in I Eu. & r.] | f DL most marked in Eu.' R. Superior Rectus L, Inferior Oblique 1& r. [regularly associ" ated with DX > > in Eu. &1.] DL most marked in Eu. | & 1. [regularly associ- I ated with DII >> in , l Eu. & r.] R. Inferior Oblique L. Superior Rectus II. Diplopia — — hi Ed. (= Paresis or Spasm of Depressor). DR most marked in Ed.| R. Inferior Rectus L. Superior Oblique & r. [regularly associ-, | ated with DX >> in | , , Ed. &1.] , ! DK ^> in h,a. -j DR most marked in Ed. R. Superior Oblique L. Inferior Rectus & 1. regularly associat- { ed with DII >> in Ed. & r.] \ fDL most marked in Ed.I L- Superior Oblique R. Inferior Rectus | r& r. [regularly associ-1 | ated with DII >> in r.r . ■ • va J Kd- & !-] 1 ' DL most marked in Ed. L. Inferior Rectus R. Superior Oblique I & 1.regular associated I with ith DX>> in Ed. & r. From the foregoing table the following facts are appar- ent: (1) An homonymous diplopia, whether large or small, whicli increases as the eyes are carried to the right indicates under-action o/'some muscle of the right eye or orcr-action r>/"S0ME muscle of the left. (2) A crossed diplopia ivhich increases as the eyes are car- ried to the right indicates under-action of SOME muscle of the left eye or orcr-action o/*Some muscle of the right. Treatment of Anomalies of the Individual Muscles. 1. In every case of over-action or under-action of the muscles our first attempts must be directed to removing the cause of 64 NEW CLASSIFICATION OF MOTOR ANOMALIES. the trouble. This is effected with more or less success in syphilitic paralysis and in the paralysis caused by the pressure of meningitic effusions upon the nerves when we employ the iodides and mercury; in the so-called rheu- matic paralysis, due apparently to exposure to cold,- when we use sodium salicylate and the iodides; and when in hysterical disorders we employ the appropriate moral treatment. 2. When the cause is unknown or cannot be reached, an expectant treatment combined with corroborant measures (especially open-air exercise) must be employed. This is particularly the course to be pursued in spastic deviations, in hysterical and diphtheritic paralysis, and in the limita- tion of the movements of the eye due to neurasthenia. The use of strychnine, advocated by some as being a direct tonic for insufficient muscles, seems to be efficient only so far as it acts to improve the patient's general condition. The same may be said of electricity. 3. When the deflection is slight, confirmed, and espe- cially if it is more or less comitant, prisms often do good service, particularly in the vertical deviations. In the lateral deviations they are of less service, because these are frequently complicated by the presence of divergence or convergence anomalies, in which the prolonged use of prisms is distinctly injur- ious. 4. Operative measures are to be adopted only when we are assured that the condition has reached a stage in which it is no longer likely to undergo change. Even in long- standing cases of paralysis it may be dangerous to oper- ate, since the paralysis may disappear even after lasting for months, and then the operation which previously suf- ficed to correct the deviation will now over-correct or pro- duce a deviation in the opposite sense which may be worse than the original one. On the other hand, the judicious division of a contractured unpar- alyzed muscle may by giving the paralyzed muscle more play assist in restoring the power in the latter. See two cases by Chevallereau (Trans, of VIII. Internat. Ophth. Congress, Edinburgh, 1894) in which the movements of an eye the subject of a partial oculomotor paralysis were restored by tenotomy of the unparalyzed externus. These cases are analogous to those in which the power of the externi, weakened by persistent contracture of interni due to a convergence- NEW CLASSIFICATION OF MOTOR ANOMALIES. 65 spasm, is gradually restored by the very prolonged use of the proper correcting glasses which relieve the spasm and allow the externi to act more freelv. (See Long and Barret's cases, cited in section VII.) In any case care must be taken that the appropriate oj)- cration is performed. The principles of operating, which were admirably enunciated by A. Graefe, may be thus stated: Over-action of a muscle is to be relieved by tenotomy of the over-acting muscle. Under-action is to be relieved by tenotomy of the associated antagonist to the under-acting muscle, or, where this is impracticable, by advancement of the under-acting muscle itself. Sometimes, especially in paralysis of the externus and internus, these operations have to be further reinforced by tenotomy of the direct an- tagonist of the paralyzed muscle. The reason for these i-ules is obvious. When a muscle is too strong we can reduce its action more or less effectively by a tenotomy. If the muscle is too weak, but yet retains some of its power, we can increase this power by performing an advancement. If, however, the muscle has lost all power, an advancement is obviously futile, and if the muscle acts but little an advancement alone is generally insufficient. Then we have only to remember that when a muscle is too weak, the effect upon the movements of the two eyes is the same as if the associated antagonist in the other eye was too strong; and if we tenotomize this antagonist, we shall limit the movement of the sound eye in the same sense and to the same extent as that in which the movement of the affected eye is already limited, /. e. both eyes will again move equally with each other, although the movement of neither will be normal. If no secondary changes have taken place. tenotomy of the associated antagonist alone may suffice, but usually the weakened muscle is opposed by a contractured and hence over- acting muscle in the same eye (direct antagonist), and therefore we may have also to divide the latter in order to secure the proper bal- ance of action. For the particular cases these rules may be expanded as follows: Under-action of the R. externus indicates tenotomy of the L. internus, usually combined with advancement of the R. externus and often with tenotomy of the R. internus. Under-action of the II. internus requires advancement of the R. internus combined with tenotomy of both externi. The advancement in this case is imperatively demanded, because the internus has to be used in convergence as well as in associated 5 66 NEW CLASSIFICATION OF MOTOR ANOMALIES. parallel movements. For the latter it might act sufficientlv well, eevn if intrinsically weak, provided the externus of the other eye was also weakened and to the same extent; but for the proper performance of convergence movements the internus requires to be intrinsically strong, which can be effected only by an advancement. Under-action of the R. superior oblique requires tenotomy of L. inferior rectus. This operation gives very satisfac- tory results. Under-action of the R. inferior oblique requires tenotomy of the L. superior rectus. Under-action of the R. superior rectus is in general best remedied by advancement of the muscle itself. If there is secondary contracture of the inferior rectus, the latter may be divided also, but this operation should be performed with considerable caution owing to the unpleasant effects produced by insufficiency of any one of the depressor muscles. In very slight cases of insufficiency of the superior rectus in which the increase of the diplopia in lateral directions of the gaze would not be very great, and in which the aim is simply to remove the mod- erate hyperphoria in looking straight ahead, cautious tenotomy of the superior rectus of the other eye may replace the operation of ad- vancement. Under-action of the R. inferior rectus requires advance- ment of the muscle itself, which may need to be supple- mented by tenotomy of the R. superior rectus. Over-action of either one of the four recti is remedied by a tenotomy ^f the over-acting muscle. Over-action of the R. superior oblique calls for advance- ment of the L. inferior rectus. In very slight cases this operation may be replaced by a cautious tenotomy of the R. inferior rectus. Over-action of the R. inferior oblique is relieved by ad- vancement of the L. superior rectus or, in very slight cases, tenotomy of the R. superior rectus. It is probably from a failure to conform to these principles that a large part of the disappointment occasioned by the results of tenoto- mies done for heterophoria is due. For example, a L. hyperphoria due to insufficiency of a K. elevator muscle is treated by tenoto- mizing the R. inferior rectus. This operation does not essentially relieve the limitation of movement in the upper field, which really caused the hyperphoria and most likely the symptoms ascribed to the latter; on the contrary, it adds to the condition already existing a NEW CLASSIFICATION OF MOTOR ANOMALIES. 67 new and very troublesome pathological condition, namely, a limita- tion of the movements of the right eye in the lower field also. In other words, to the paresis already present another paresis has been added by operation, and the patient suffers from the combined effects of both. That the effect of both pareses actually co-exist can readily be demonstrated by an examination of the double images. It will be found that the diplopia in the upper field has not been materially re- duced by the operation, while a diplopia which did not exist before has been introduced into the lower field and gives rise to much dis- turbance. In this case advancement of the weak elevator in the af- fected eye or tenotomy of the elevator in the other eye would be the proper operation. Parakineses. Tremor of Individual Ocular Muscles (Uni= lateral or Non=symmetrical Nystagmus). The tremulous movement (alternating spasm) that we denote by the name of nystagmus, although usually affecting equally the asso- ciated muscles in the two eyes, and therefore dependent in all probability upon a lesion of the association-centers, may be confined to the muscles of one eye or be of a different character in one eye from that in the other. Hence, while ordinarily constituting a perversion of the associated parallel movements of the eyes, in these cases it must be regarded as a perversion of the movements of the individual muscles. These cases, are, to be sure, quite rare. Graefe (Graefe-Saemisch) reports four cases of uni- lateral vertical nystagmus (two observed by himself), and adds that, while he has seen cases of slight rotary nystag- mus confined to one eye, he has never met with one of uni- lateral horizontal nystagmus. Frost, however (Trans. Ophth. Soc. of United Kingdom, xiv. 245), reports a case of acquired nystagmus in which the oscillations were hori- zontal in one eye and vertical and rotary in the other. VI. ANOMALIES OF ASSOCIATED PARALLEL MOVEMENTS. liypokineses. Paresis and Insufficiency of Associated Parallel riovements. Paralysis of the lateral associated movements of the eyes is not infrequent in destructive cer- ebral disease, particularly apoplexy, the site of the lesion in paralysis of dextroversion being in the left, and in par- « 68 NEW CLASSIFICATION OF MOTOR ANOMALIES. alysis of sinistroversion in the right half of the brain. In pure cases of this sort the power of convergence is re- tained, showing that the internal reetus, although incapaci- tated as far as consentaneous action with the opposite externus is concerned, is not disabled from performing work in conjunction with its fellow internus. This shows that in these cases we are not dealing with a conjoined paralysis of one externus and one internus, but with an inhibition of one particular movement of the two eyes. Paralysis of sursumversion (without any involvement of the lateral movements) and para lysis of sursumversion and deorsumversion together have been observed (Gowers; Sauvineau, Trans, of VIII. Ophth. Congress, Edinburgh, 1894). Except as diagnostic signs of the condition causing them these associated deviations are of little clinical importance. Whether there are slighter grades of these disorders, not dependent upon severe structural disease and possibly productive of more symptoms on their own account, has not, as far as I know, been positively demonstrated. Certain cases, however, described by Savage (Oph. Record, Jan., 1896) under the name of Asthenic vertical orthophoria in which the combined up-and-down movements of both eyes (sursumversion and deorsumversion) were performed insuffi- ciently and with difficulty would seem to belong in this cate- gory; and possibly the explanation of the conditions called by Stevens Anatropia and Catatropia may be had by assuming a weakness of deorsumversion in the former case and of sursumversion in the latter, so that in either instance both visual lines are off the proper level (see Section IX). Hyperkinesis. Spasm of Associated Parallel riovements. Spasm of the associated lateral movements producing deviation of both eyes to the right (Spastic dextroversion) or to the left (Spastic sinistroversion) is not infrequently observed as the result of irritative lesions of the brain. Deviation to the right is produced by disease of the left side of the brain and vice versa. Spasm of associated movements (particularly, combined vertical and lateral spasm, producing oblique deflections of both visual lines) also occurs as a transient and par- oxysmal manifestation in epilepsy and hysteria. NEW CLASSIFICATION OF MOTOR ANOMALIES. 69 The curious case described by Frost (Trans. Ophth. Soc. United Kingdom), in which there was spastic deviation of both eyes down and to the right, but in which there was no actual impairment of the movements of either eye by itself, was apparently hysterical in character. The following peculiar case of alternating spasm of asso- ciated parallel movements was apparently choreiform in character and would seem to form a sort of connecting link between cases of tonic spasm, such as those just men- tioned, and true nystagmus. Choreiform Spasm of Associated Oblique Movements. Simon N., aged 13 years, came under my care Nov. I'l'. Ittfl'J. Chorea two years ago. Anaemic. Now shows every few minutes, especially when watched, sudden darting movements of both eyes upward and to the right and back again. The return movement takes place in two phases, the eyes shooting down and to the left somewhat beyond the primary position, and then by a sharp jerky motion coming up again to the latter. If the gaze is directed to the left, both eyes dart upward and to the left and then back again. In either case, whether moving up and to the right or up and to the left, the direction of the movement is at an angle of 4.Y with the horizontal, and the eyes are carried up until the pupils are three- quarters buried beneath the upper lids. Slight choreiform twitchings of the face accompany the movements. Orthophoria. No diplopia. Associated movements, although slug- gish, perfectly normal. V. R. ''/,, L. •■••/70. Under homatropine, R. + 1.00 D. l>/i.-,: L. + l..-)0 I). Cyl. Ax. S.7 T. 's/so- Three weeks treatment with arsenic and hydrochloric acid effected no improvement. On Jan. l.">, 1N!):{, R. +0. 7") D. Sph., L. + 1.50 1). Cyl. Ax. S.Y T. given. Patient then passed from observation and has not been seen since. Except for the long interval between the separate spasmodic movements, the appearances presented in this case differ in no re- spect from those observed in nystagmus. Its development, however, in a patient with fair sight and normal muscles, and the past history and present evidences of chorea led me to regard it not as a true nystagmus. If nystagmus at all, it was a very rare form of the affection. Parakineses. Tremor of Associated Parallel Movements (Nystagmus). Nystagmus, as ordinarily met with, con- sists of an equal and parallel movement of the two eyes, both executing a series of rapid oscillations in the same direction and at the same time. These oscillations, which vary in frequency from 30 to 150 a minute, occur in two 70 NEW CLASSIFICATION OF MOTOR ANOMALIES. phases, a rapid darting movement first taking place in a certain direction and this being followed by a movement of return to and beyond the original position of the eyes. The latter or second phase, although slower than the first, is evidently an active movement and not a mere relaxation of the muscles that have just been spasmodically con- tracted. The direction of the movement is usually from side to side (Horizontal nystagmus), sometimes rotary, both vertical meridians revolving in the same direction (Rotary nystagmus), and very rarely vertical (Vertical nystagmus). Not infrequently combinations of two, or even of all three forms are observed (Mixed nystagmus). Movements of this character point to a pathological con- dition of the association-centres, causing the discharge of alternate and excessive stimuli from the latter instead of the simultaneous and equal stimuli of moderate intensity, which enable the normal eye to remain steady in the posi- tion of fixation. The eyes ordinarily, when looking at an object straight ahead of them, are kept in place by simultaneous contraction of the opposing muscles; i. e. they move neither to the right nor to the left, because they receive equal and simultaneous impulses from the cen- tre for right-handed movements (dextroversion) and that for left- handed movements (sinistroversion). If, however, these impulses, instead of being simultaneous, are al- ternate, so that the eyes first receive an impulse from the centre for dextroversion and then one from the centre for sinistroversion, and if these impulses alternate rapidly, we shall have the picture of hori- zontal nystagmus. A similar want of simultaneity in the discharge of impulses from the centres for sursumversion and deorsumversion will produce a ver- tical nystagmus. And a rotary nystagmus will result from the dis- charge of alternate instead of simultaneous stimuli from the centres* which produce rotation of both vertical meridians to the right and to the left respectively. Finally, a combination of some or all of these anomalies accounts for the various forms of mixed nystagmus. This conception of the central origin of nystagmus, and more particularly of its origin from some lesion of the dif- ferent association-centres, seems forced upon us, not only ♦inferred to exist from this very symptom. The right-rotating centre, acting by itself, would produce simultaneous contraction of the right inferior oblique" and in- ferior rectus and of the left superior oblique and superior rectus; and the left-rotat- ing centre would similarly produce contraction of both inferior muscles of the left and both superior muscles of the right eye. NEW CLASSIFICATION OF MOTOR ANOMALIES. 71 by the character of the movements executed, but also by a great variety of pathological data. For further informa- tion as to the latter, reference may be made to the exhaust- ive articles by Graefe (Graefe-Saemisch and Arch, fiir Ophth., xxiv. 3, 1895). VII. ANOMALIES OF CONVERGENCE. Hypokineses. Paralysis and Insufficiency of Convergence. Absolute loss of power of convergence with retention of the power of making associated parallel movements has been occasionally observed. Since either eye can still be turned inward when acting with its fellow to move to the right or to the left, these cases cannot be referred to paralysis of the interni, but indicate some lesion of the convergence- centre, causing a paralysis of convergence (Parallel squint of Schneller). Cases of this sort in which the paralysis was total or practically so (convergence near-point at from 2 to 6 metres), have been described as well as others in which the paralysis was marked but not complete. I myself have seen one case of the sort. The paralysis is frequently associated with paralysis of accommodation and in some of Parinaud's and Sauvineau's cases was accompanied by paralysis of sursumversion and deorsumversion. One peculiar feature is that the prism-convergence (■/. e. the power of overcoming prisms, base out) is retained in some of the cases (Straub). The cases hitherto reported are: Schweigger, Klin. Untersuch, uber das Schielen 1881 (cited by Straub) 2 cases. Parinaud, Arch, de Neurologic, 1883 (cited by Sauvineau). Sales, Trans. Ophth. Soc. United Kingdom, iv. (1884), p. 390 (cited by Cowers). Parinaud, Brain, ix. 330, 1887 (cited by Straub), 5 cases. Stolting and Bruns, Arch, fiir Ophth. xxxiv. 3, 1888 (cited by Straub). Benzler, Deutsch. militar-aerztl. Zeitschr., xviii. (cited by Straub). Peters, Centralbl. f. pract. Augenheilk., xiii. (cited by Straub). 72 NEW CLASSIFICATION OF MOTOR ANOMALIES. Sauvineau, Trans. VTII. Internat. Ophth. Congress, Edinburgh, 1894. Straub, M., Arch, of Ophth., xxv. 3 (1896). Hayne, H. W., ib. Graefe's 10 cases (cited by Straub) come rather under the head of convergence-insufficiency than actual paralysis. Much more frequent and important are those cases in which there is simply a greater or less weakness of conver- gence (Convergence = insufficiency). A. Graefe, who re- garded these cases as quite rare, gives an excellent expo- sition of some ef the physical signs of the condition in a paper read before the Seventh Ophthalmological Congress (1888). In their entirety these signs may be stated as fol- lows: For distance. Lateral orthophoria or slight exophoria (l°-2'°) by all tests (screen, parallax and phorometer). As- sociated lateral movements practically normal. Associated vertical and oblique movements of ten restricted (frequently in an asymmetrical manner) and field of binocular single vision often* markedly limited in some one direction above or below, indicating a weakness of an elevator or depressor (particularly the superior rectus). Diverging power (ab- duction) not over 9°, frequently subnormal (5°-6°). Prism- convergence (so-called adduction) often, although not always, restricted, being acquired with difficulty and per- formed with effort.! For near. Marked exophoria by all tests (/. e. exophoria of 7° or over by both phorometer and parallax, and notice- able deviation out behind the screen). Associated lateral movements normal. Pc (near point of convergence) 3" or over from the root of the nose, and maintenance of eyes in position of extreme convergence for more than a moment difficult or impossible. Convergence near-point about the same whether the object is approximated from a point to the right or from a point to the left of the median line. If, *In about 20 per cent, of the cases that I have observed. In these cases there is often hyperphoria for distance in the primary position. tThat is, the primary adduction (i. e the greatest amount that the patient can be got to do at the first trial) will be'only 8° or 12°, and the addition of even 1° or 2° to this will produce insuperable diplopia. Moreover, the exertion of overcoming a prism of even this amount is associated with a sense of strain, and the patient, if he does succeed in overcoming the prism for a moment, cannot hold the images together. These features constitute a marked difference from those obtaining in normal eyes which, though they may have difficulty in learning to overcome prisms base out, will do so with ease and with rapidly increasing facility after a few trials. NEW CLASSIFICATION OF MOTOR ANOMALIES. 73 when the convergence near-point is reached, one eye be screened and then the object of fixation is carried still closer to the nose, the uncovered eye will, although with difficulty, turn in still further, in order to follow the object, while the eye behind the screen will diverge by an equal amount (preservation of associated adduction, failure of convergence-adduction.—Graefe). Graefe's test indicates that the convergence is relatively weak— weak, that is, as compared with the absolute power of the eye to move inward (associated adduction). But whether this indicates an absolute weakness of convergence or not depends upon whether we regard the associated adduction (ability of the eye to move inward while its neighbor moves outward) as always normally less than the convergence adduction (ability of the eye to move inward while its neighbor is also moving inward). Graefe proceeds upon the assump- tion that this is the case; but in many persons, whom I examined and who had apparently normal eyes, the associated adduction seemed the greater of the two. In such the fact that they responded to Graefe's test would not necessarily indicate the existence of any- thing abnormal, As to its nature, convergence-insufficiency may be either accommodative or non-accommodative. Non accommoda- tive insufficiency may be due (A) to direct weakness of the interni, e. g. that obtaining after a complete tenotomy of the latter, especially when the operation has been done upon faulty principles, as to relieve a divergence-insuffi- ciency not associated with excess of convergence. This post-operative weakness, which may give rise to a very troublesome asthenopia lasting for several months, is, to be sure, not really an example of convergence-insufficiency, being really a traumatic paresis of the interni, but in its symptoms and course it so much resembles the former as to be most conveniently considered in connection with it. Convergence-insufficiency again occurs (B) secondarily to a divergence-excess—this being an example of that com- pensatory action, already alluded to, by virtue of which a deviation, which is at first marked for one distance only, tends to become generalized so as to become apparent for all distances alike. In these cases there is at first a marked exophoria for distance accompanied by excessive diverging power (10° or over), but with only moderate exophoria for near, good converging power, and no recession of the near 74 NEW CLASSIFICATION OF MOTOR ANOMALIES. point of convergence. Later, the exophoria for near in- creases markedly (without there being necessarily any in- crease in the exophoria for distance), the convergence near-point recedes, and the converging power gets to be performed with more and more difficulty. From some few observations that I have made I think it likely that this sort of extension of exophoria may occur chiefly in young persons as a result of the processes of growth, which, as is well known, favor the development of a divergence of the visual lines and which may abrogate a convergent strabis- mus or convert a case of parallelism of the visual axes into one of divergent squint. If this explanation is correct these cases are instances of a gradually developing bilateral insufficiency of the interni, rather than a real insufficiency of convergence. A similar explanation—viz., the gradual production of an anatomical divergence by developmental processes taking place during the period of growth—may perhaps account for the genesis of some of the cases of convergence- insufficiency not complicated with a divergence-excess. Another variety (C) of non-accommodative convergence- insufficiency appears to be directly dependent upon an insufficiency of an elevator or depreesor muscle, and partic- ularly of the superior rectus. This connection, in view of the assistance that these vertically acting muscles give in effecting adduction, seems not unnatural and, at all events, appears to be quite frequent. Thus in 21 successive cases occurring in my practice 6 exhibited marked insufficiency, or actual paresis of the vertical muscles, and in another series of 27 that I examined 5 at least were thus affected. In three or four other cases there was more or less weak- ness of the superior and inferior recti of both eyes, caus- ing a concentric limitation of the field of single vision. This weakness, from its varying character, could not be regarded as due to paresis, but was (D) simply one of the evidences of the generaJ lack of muscular power and muscu- lar co-ordination that these patients presented. Such cases, therefore, appear to occur especially in neurasthenia. In the latter condition, at any rate, and in allied conditions of general enfeeblement, convergence-insufficiency is of NEW CLASSIFICATION OF MOTOR ANOMALIES. 75 frequent occurrence and often occasions a troublesome and intractable asthenopia which disappears only when the causal affection has been removed. Accommodative convergence=insufficiency consists in the development of a marked divergence for near points due to non-use of the accommodation. Accommo- dation being usually associated with convergence, any condition which prevents the discharge of accommodative impulses will likewise tend to inhibit the convergence. Theoretically this inhibition should occur in all cases, but practically it occurs in a minority only. These cases may be classified as follows: (a) Patients with uncorrected myopia, in whom there is but little necessity for using the accommodation at all. (b) In hypermetropes, who having all along accustomed themselves to using their accommodation without employ- ing a corresponding convergence acquire thereby a rel- ative insufficiency of the latter function, which comes to light as soon as their hypermetropia is corrected. Thus a man with a hypermetropia of 2 I), has been accustomed when looking at an object J3" off to use an accommodation of f) 1).; but when his hypermetropia is corrected by glasses, he suddenly finds that at this distance he has to use only 3 D. of accommodation, an amount with which he has been wont to associate a much smaller degree of convergence. Not being able at first to accustom himself to these new conditions, /. c. not being able at once to converge to a point at 13" without using ."> I)., his visual lines diverge. This di- vergence often gives rise to considerable trouble (persistence of asthenopia, etc.) and constitutes one of the chief reasons why con- vex glasses are not tolerated by many hypermetropes. For a similar reason convergence-insufficiency may de- velop (C) in presbyopes who first put on convex glasses for near. The marked increase in a convergence-insufficiency gen- erally produced by (D) the continuous use of prisms, base in, is also probably in part due to accommodative inaction; the use of such glasses by favoring divergence tending to relax the accommodation still more and hence to superinduce a still further failure of the convergence. The course of a convergence-insufficiency varies greatly. Many cases, particularly those dependent upon general muscular and nervous weakness remain about the same 76 NEW CLASSIFICATION OF MOTOR ANOMALIES. for a long time and then improve as the causal condition improves. Such cases may also show recurrences, when for any reason there is a new deterioration of the vital forces. Cases also of accommodative convergence-insuffi- ciency due to a readjustment of the optical conditions under which the patient has been working (application of convex glasses for hypermetropia and presbyopia) usually get well, the patient accustoming himself after a while to his new refractive state. This is, however, by no means always the case, and, if a tendency to convergence-insufficiency al- ready exists, it may become aggravated and be made per- manent by the use of glasses—indeed, the development of an actual strabismus divergens may be thus superinduced, particularly when the glass chosen for a hypermetropic child has been somewhat in excess of the true hyper- metropia. Convergence-insufficiency due to tenotomy also gener- ally tends to disappear, although this again cannot be taken as the invariable rule. Other cases of convergence-insufficiency, and partic- ularly those occurring in young persons and dependent upon an insufficiency of the elevators and depressors, tend to increase. This seems to take place by the development of a divergence-excess in accordance with the law of compensation already several times referred to, by which a non-comitant deviation tends to become comitant. The course of such cases, if unchecked, is first increase of the exophoria for near, second development of exophoria for distance also, with increased diverging power (Di- vergence excess), next the appearance of an actual diver- gent strabismus for near with sonsiderable exophoria for distance (Periodic squint), and finally divergent strabis- mus for both distance and near (Constant squint). This ten- dency to a constantly increasing divergence may be favored by the injudicious use of convex glasses and particularly by the use of prisms base in, which almost always tend to make the exophoria greater and greater.* *I observed one marked case of this sort, occurring in a girl of nine, who at first had 3n of exophoria for distance and over 6° for near, but who after using prisms for a year had for distance exophoria of 8° with abduction of 10°-12° and spontaneous crossed diplopia, and for near exophoria of 15°. Prism-convergence (adduction) 0°. NEW CLASSIFICATION OF MOTOR ANOMALIES. 77 As has been seen, convergence-insufficiency may be complicated with an insufficiency of one of the vertical muscles, the latter affection, indeed, in these cases prob- ably being the cause of the former. In other cases, a di- vergence-excess is present which is sometimes the cause, but more often the effect, of the convergence-insuf- ficiency. The latter may also, particularly in those whose muscular system generally is weak, be complicated with a divergence-insufficiency.* Slight cases of this sort, in which the insufficiency of divergence is not great enough to produce esophoria for distance constitute the asthenic exophoria of Savage. The symjjfoms of convergence-insufficiency are astheno- pia, either simple, or associated with headache and pain in the eyes, conjunctival irritation, and spontaneous diplopia, producing blurring of vision for near work. Asthenopia is a pretty constant symptom, being met with in all the va- rieties, although in my experience more apt to occur in the non-accommodative than in the accommodative form. It is often very marked and may incapacitate the patient from doing near work. The symptoms are by no means necessarily in direct re- lation with the amount of the deviation, being, in fact, more pronounced in deviation of medium degree than in those which have assumed the proportions of a regular squint. It is for this reason, probably, that the use of concave glasses in myopes affected with convergence-insufficiency sometimes causes distress; since these glasses tend to increase the impulse to converg- ence and thus reduce a large deviation, which is insuperable and gives no trouble, to a smaller one which can lie overcome by effort and hence gives more annoyance. On the other hand, when the de- viation is veiy small to begin with, the symptoms may lie aggravated by the use of convex glasses and of prisms base in, which tend to make it larger and therefore more troublesome. The treatment of convergence-insufficiency must aim first at removing the cause of the trouble. Hence in neu- By exercise of the convergence with prisms the exophoria for distance was reduced to 0°-3°, that for near to 5-6°, the prism-convergence was raised to 40°-50°. and there was no more spontaneous diplopia. This improvement was maintained up to the time that the patient was last seen (7 months after the treatment had been discon- tinued). *I have notes of a case of this sort in a myope of 8-10 D., in whom there was an esophoria of 14-20° (i. e. a real convergent squint) for distance, with diverging power of 2-3°, and exophoria of 8° for near. 78 NEW CLASSIFICATION OF MOTOR ANOMALIES. rasthenia general strengthening measures (out-of-door exercise, tonics) are indicated and are for the most part successful. Accommodative convergence - insufficiency requires the careful correction of the refraction in myopia, while in hypermetropia frequently an under-correction will be indicated. Indeed, it is a safe general rule to fully cor- rect myopia and to under-correct hypermetropia whenever much exophoria exists; and in presbyopia under the same conditions to give a weaker convex glass than would other- wise seem indicated. The immediate causal indication requires training of'the convergence, which can, in general, be effected by system- atic exercise with prisms base out. This often gives strik- ingly good results, but in some cases fails altogether. The wearing of prisms base in should be resorted to only as a temporary expedient, on account of their tendency to produce increase of the trouble; and these prisms should be discontinued at once as soon as signs of such an in- crease begin to manifest themselves. Finally, if an operation is decided upon, advancement of the interni, coupled, in case a divergence-excess is pres- ent, with a tenotomy of the externi, should be made. Te- notomy of the externi alone seldom gives any lasting re- sult. Hyperkineses. Spasm and Excess of Convergence. Marked tonic spasm of convergence, so that both eyes are turned strongly inward, has been observed in hysteria. Minor degrees of over-action of convergence (Converg- ence=excess) are of frequent occurrence. They may be either accommodative or non-accommodative in character. The physical signs of a convergence* excess not compli- cated with a divergence-insufficiency are as follows: For distance. Orthophoria or moderate esophoria (1 -3 ) by all tests (phorometer, screen and parallax). Associ- ated lateral movements normal. Diverging power normal or but slightly subnormal (5°-8°). Prism-convergence (adduction) normal in amount, rapidly acquired, and easy to produce and maintain. Exercise of convergence not infrequently causing the development of temporary homo- NEW CLASSIFICATION OF MOTOR ANOMALIES. 79 nymous diplopia. Homonymous diplopia sometimes also producible by will and apparently without effort. For near. Esophoria by all tests, often exceeding that for distance.* Convergence near-point 1£"-1" or less. Non=accommodative convergence=excess may be 'either (a) idiopathic or may (b) be secondary to a condition of divergence-insufficiency. The former appears to be rare, although I have met with two or three cases. The second- ary variety, on the other hand, appears to be quite com- mon, and develops according to the compensatory law by which deviations in general, tend to become equalized for distance and near. In this case, of course, there will be marked esophoria for distance and the diverging power (abduction) will be much reduced. Non-accommodative convergence-excess probably com- prises most of the cases described by Savage under the name of sthenic esophoria. Accommodative convergence - excess (Accommodative esophoria, Accommodative convergent squint, Ps"eudo-eso- phoria) is very frequent. It occurs under the following conditions: (a) Uncorrected hypermetropia. The effect of this in producing inward deviation of all degrees from a slight eso- phoria to a marked strabismus is too well known to require further comment here. (b) In myopes who for the first time use a concave glass for near points. Such patients will add to the natural amount of convergence for the point they are looking at (which convergence they have hitherto been accustomed to make without using any accommodation) the extra conver- gence imposed in sympathy with the accommodative effort that they now make for the first time. (c) In presbyopes (particularly, hyperopic presbyopes) at the beginning of the presbyopic period. These patients have to exert a very strong effort in order to stimulate their flagging accommodation to the point necessary for distinct *Unless, however, the patient really fixes upon the test object, the esophoria for near may vary greatly and even be replaced temporarily by exophoria. This is par- ticularly apt to be the case in accommodative convergence-excess, where the amount of hypermetropia may ce such as to prevent the patient from seeing the object dis- tinctly. 80 NEW CLASSIFICATION OF MOTOR ANOMALIES. vision, and in sympathy with this excessive call made upon the accommodation an excessive effort of convergence is simultaneously made. (d) As the result of the instillation of a mydriatic. The increase of a convergent squint by the instillation of atro- pine was observed by Long and Barrett (Ophth. Hosp. Re- ports, xii. 1888-1889), who found that it occurred in 11 cases out of 38 in whom this mydriatic was employed. These cases, however, had been under the influence of the atropine for several days. In cases which are but recently under the influence of the mydriatic an increased tendency to convergence due to the latter appears to be even more frequent. Under these circumstances esophoria may de- velop where orthophoria existed before, and a pre-existing esophoria of moderate amount may develop into a well- marked convergent squint. The correct explanation of this phenomenon was first given by Savage, although I myself came independently to the same conclu- sion. The convergence here is evidently due to the excessive effort which the patient makes to see distinctly under the unusual condi- tions presented by mydriasis. Not being aware that he cannot accom- modate, he makes a violent effort to do so, and in making this effort sends out a correspondingly strong impulse for convergence. The cili- ary muscle does not respond, but the interni do; and, as the impulse was excessive, they respond by producing an excessive convergence. The condition, in fact, is quite analogous to the excessive secondary deviation of the sound eye when its fellow attempts to perform fixa- tion by means of a paralyzed muscle. As under the mydriatic the sight is more blurred for near than for distance, this fruitless effort to see distinctly by attempting to put into motion a paralyzed accommodation will be more excessive, and hence too the esophoria will be more pronounced, for near points. For distance, the eso- phoria will generally be greater in proportion to the degree of hypermetropia and the consequent blurring of sight, and will often disappear altogether as soon as the refraction is corrected. These facts are shown in the following cases: Esophoria. Large increase under mydriatic. Miss K., aged 20. Refraction (under homatropine) -f 0.25 sph. O + 0.50 cyl. ax. V, each. When not under mydriatic shows esophoria 3/4° for both distance and near (with and without correction of refraction); di- verging power, 6° Under homatropine, without correction of refrac- tion, esophoria for distance over 8°, for near over 15°, diverging NEW CLASSIFICATION OF MOTOR ANOMALIES. 81 power S . Under homatropine, with correction of refraction, eso- phoria for distance 5°, for near over 15°. 2. J. B., male, aged 15. Hypermetropia (homatropine) 0.50 I). Before homatropine, esophoria 3° for distance, 0° for near. Under homatropine, (with and without correction of refraction), 2'/2° for distance, 7 for near. Diverging power 4C. 3. Kath. S., aged 32. Hypermetropia 2.25D (under homatropine). Before homatropine, esophoria 2°-3° for distance, 1° for near; di- verging power 5°. Under homatropine, without correction of refrac- tion, 12-20° for distance, 12° for near (i. e. has an actual convergent squint). Under homatropine and with correction of refraction, eso- phoria V20 f°r distance; little, if any for near. The course in case of convergence-excess is very vari- able. The accommodative variety, in particular, often decreases or disappears spontaneously either as a result of developmental changes, favoring the genesis of a diver- gence, or in consequence of the decrease of the hyperme- tropia, or because the patient gives up the accommodative effort and with it the effort to converge. Its usually speedy and total disappearance in cases coming under cate- gories B, C, and D above given, is to be ascribed to the last mentioned cause. In other cases, particularly in the very young who are beginning to tax their accommodation more and more with school work, the deviation increases; the regular course being, first, increase of the esophoria for near, then increase of the esophoria for distance with reduction of the diverging power (Development of divergence-insuffici- ency), next the development of an absolute squint for near points where accommodative effort is most required (Periodic squint), and lastly strabismus convergens marked for both distant and near (Constant squint). A squint when thus fully developed usually remains permanently, but may disappear in latter life through the agencies mentioned in the preceding paragraph. As already noted, convergence-excess may be compli- cated with divergence-insufficiency, the latter condition being either the cause or the effect of the former. It is also frequently complicated with some form of vertical de- viation, producing hyperphoria in addition to the esopho- ria. It seems, in fact, not unlikely that these vertical de- 82 NEW CLASSIFICATION OF MOTOR ANOMALIES. viations play an important part in the genesis of the excessive tendency to convergence. The symptoms of convergence-excess are asthenopia, headache, and spontaneous homonymous diplopia, with sometimes more marked reflex disturbances. These symp- toms, however, are much less pronounced and constant than in cases either of convergence-insufficiency or diver- gence-insufficiency, and when present are usually due to the attendant hypermetropia or, at least, disappear when the latter is corrected. The treatment of convergence-excess is largely causal, consisting particularly in the correction of the refraction. In doing this we shall do well to follow the rule that when there is marked esophoria and, particularly, when there is more esophoria for near than for distance, we must fully correct any hypermetropia and, on the other hand, under- correct any myopia, that may be present. The result of treatment, both as regards the removal of the deviation and the relief of the symptoms are very good. Even in well-marked convergent squint a cure is effected much oftener than is generally supposed, the only requisites being that the refractive treatment should be kept up long enough (a year at least)** Long and Barrett (1. c.) analyzing the results in 102 cases, found that a complete cure was effected in 37, while out of 61 cases under 10 years of age 27 (or 44 per cent.) were cured. In addition to correcting the refraction we may try to break up the excessive tendency to convergence by aool- ishing the accommodation altogether for a time. This we effect by keeping the eyes under atropine for a number of days or even several weeks. This may also, if Long and Barrett's figures hold good generally, be used as a means of prognosis, for these authors found that of 5 cases which were improved by atropine all were subsequently improved by glasses, while of 6, in whom the deviation was not affected by the atropine, only 3, and of 4, in whom the atropine made the convergence worse, only 1 received any relief from the correction of their refraction. *This, becomes the continuous relaxation of the interni thus produced allows the weakened externi to act to greater advantage and finally to regain their tone (Long and Barrett). NEW CLASSIFICATION OF MOTOR ANOMALIES. 83 Exercise of the divergence with jirisms is of no service in this condition, and the wearing of prisms base out is to be deprecated as tending to perpetuate and increase the deviation instead of curing it. If these means fail and an operation is thought advisable on account of the deformity or the symptoms, tenotomy of the interni may be done, combined, in case a divergence- insufficiency is present, with an advancement of the ex- terni. VIII. ANOMALIES OF DIVERGENCE. Hypokinesis. Divergence=Insufficiency. Weakness of the diverging power (Divergence-Insufficiency)is charac- terized by the following signs: For Distance.—Esophoria of varying amount (usually 2 -8C), by all tests (phorometer, screen, and parallax). Associated lateral movements normal. Diverging power very much reduced, the reduction being often proportion- ate to the degree of the esophoria ( e. g., with an esophoria of 3° or 4°, the diverging power is about 4 , and with an esophoria of 5 or 6 , the diverging power is only 2 ). In the typical cases of this anomaly, however, the diverging power is disproportionately low, being, for example, only 2 or 3 , when the esophoria is 1° or 2 , and being, perhaps, only 3° or 4 when there is orthophoria or actual exophoria for distance. Exercise of divergence with prisms, base in, is sometimes associated with a sense of decided muscular strain. Prism-convergence (adduction) normal, or often some- what deficient. Exercise of the convergence often gives rise to a temporary homonymous diplopia, and the latter may also in some cases (particularly when the diverging power is much reduced) occur spontaneously, or be evoked by simply placing a red glass before one eye. For iVear.—Signs, unless the condition is associated with a convergence-insufficiency, or with a convergence- excess, fairly normal (i. e., slight esophoria or exophoria, 84 NEW CLASSIFICATION OF MOTOR ANOMALIES. and convergence near-point at about the proper distance). In its origin divergence-insufficiency is either idiopathic or secondary to a convergence-excess. Uncomplicated idiopathic divergence-insufficiency is comparatively rare, and, moreover, some of the cases that would seem to fall in this category are probably either really secondary to some disorder of the vertical muscles (elevators or depressors), or are examples of a spurious divergence-insufficiency, i. e., of a condition in which there is actual weakness of the externi themselves, either natural or produced by operation. In cases of the latter kind the divergence is indeed weak, but the power of mak- ing lateral movements is also lessened, and hence these cases do not fairly come under the head of a simple im- pairment of the diverging function. Complicated idiopathic divergence-insufficiency is more common. In these cases there is either a convergence- insufficiency, which has developed simultaneously with the disorder of divergence, or there is a convergence-excess, which is the result of the latter. Second-itry divergence-insufficiency develops in the man- ner already described (see Section VII.) from a progress- ively increasing convergence-excess. Cases of this sort might be confounded with those of the foregoing category, i. e., those in which a primary divergence-insufficiency is followed by excessive convergence action. The distinc- tive points between the two may be stated as follows: PRIMARY DIVERGENCE - INSUFPI CIENCV, WITH SECONDARY CON- VERGENCE-EXCESS. PRIMARY CONVERGENCE-EXCESS, WITH SECONDARY DIVERGENCE- INSCFFTCIEXCY. Esophoria for distance moder- i Esophoria for distance often ate (not over 8°), and may be less great, and when small usually than the deficiency in the diverg- J disproportionately large in com- ing power (abduction). Esophoria for near small and usually less than that for dis- tance. Condition stationarv. parison with the deficiency of di- verging power. Esophoria for near usually greater than for distance. Condition often progressive. The course pursued by a divergence-insufficiency is in- dicated in what has already been said. The idiopathic variety shows but little tendency to change, the amount of NEW CLASSIFICATION OF MOTOR ANOMALIES. 85 esophoria and of divergence-weakness often remaining the same for years. This variety frequently becomes compli- cated with a condition of convergence-excess, which, how- ever, also remains of moderate degree. On the other hand, a divergence-insufficiency, which is secondary to a con- vergence-excess, is often progressive, the advance contin- uing in many cases until a moderate deviation is converted into a marked and constant strabismus convergens. The symptoms of a divergence-insufficiency are often very troublesome. Asthenopia as a result of near work is not so much complained of, unless there is a simultaneous convergence-insufficiency, but headache and other more remote reflex pains, a sense of constriction in the head, stomach disturbance, general inertness and lassitude, and even interference with the general nutrition are often met with. Spontaneous diplopia may also occur, being, nat- urally, more marked for distance than for near. One peculiarity in the symptoms is that headache and pro- nounced asthenopic sensations (feeling of strain and tiring in the eyes), together with a sense of confusion and dullness in the head, are especially apt to be produced by lookirig long and intently at distant objects, particularly when moving or when brightly illuminated. Such symp- toms are hence often occasioned by watching a theatrical performance, a ball-match, a procession, or a moving throng of people. (Panorama-asthenopia, or panorama- headache of Bennett.)* The treatment of divergence-insufficiency presents many difficulties, the condition being intractable and the result uncertain. Direct exercise of the divergence with prisms, base in, has not, in my experience, been of the least avail. Exer- cise by the performance of systematic lateral movements of the eyes seems unphysiological, inasmuch as it is the externi that are thus practiced, and not the function of di- vergence per se, and, moreover, in these movements the interni are practiced along with the externi. Some, how- ever, seem to have obtained good results by this method. The constant wearing of prisms, base out, is in most ♦Annals of Ophthalmology, January, 1897. 86 NEW CLASSIFICATION OF MOTOR ANOMALIES. cases a dangerous expedient, as tending to cause disuse and a consequent further enfeeblement of the abducting power. If an operation is resorted to, it should, in the idiopathic cases at all events, be an advancement of the externi rather than a tenotomy of the interni. The latter opera- tion by itself is almost always nugatory, the condition tending, after a temporary period of improvement, to re- turn to its original state. Moreover, the tenotomy, if thorough enough to be efficacious, is liable to substitute for the unpleasant asthenopia for distance an almost equally annoying asthenopia for near. In the secondary cases, however, or wherever a marked convergence-excess is present, tenotomy of the interni may be performed; but even then it is preferably combined with advancement of the externi. Hyperkinesis. Divergence Excess. Over-action of di- vergence (IJivergence-Excess)As marked by the following signs: For distance. Exophoria, usually marked (from 4J up- ward) with noticeable deviation out behind the screen. Associated lateral movements normal. Diverging power excessive (over 9), the excess over the normal amount of 6° or 8° being often roughly proportioned to the degree of the exophoria, but sometimes being disproportionately larger. Prism-convergence (adduction) in uncomplicated cases normal, although possibly performed with difficulty at first. Crossed diplopia for distance often occurring spontaneously, or producible at will. For near. Conditions, unless a convergence-insuf- ficiency also exists, fairly normal (i. e., exophoria less, or, at all events, not much greater, than for distance, and near point of convergence about in its normal situation). A divergence-excess may either be primary in origin or be secondary to a convergence-insufficiency. Primary divergence-excess occurs not infrequently as an uncomplicated affection, but still more often is asso- ciated with a vertical deviation (which may really stand in genetic relation with it), or with a consecutive converg- NEW CLASSIFICATION OF MOTOR ANOMALIES. 87 ence-insufficiency, It may also be associated with a convergence-excess. I have observed several instances of this latter combination, in which,with exophoria for distance and a high diverging power, there was also excessive power of convergence, and either actual esophoria for near, or at least an exophoria slight in amount, and much less than that for distance. The development of a secondary divergence-excess from a convergence-insufficiency has already been traced (see Section VIII). These cases, like the simple ones of con- vergence-insufficiency which represent only a less ad- vanced stage of the same process, often show complicating insufficiency of the vertical muscles. Indeed, as before re- marked, this last-named condition would seem to consti- tute the real cause of the divergence which takes place, first for near and then for distance. The differential points between a primary divergence- excess with a secondary convergence-insufficiency and a primary convergence-insufficiency with consecutive di- vergence-excess are as follows: PRIMARY DIVERGENCE - EXCESS PRIMARY CONVERGEXCE-lNSUFFI- WITH SE )ONDARY CONVERGENCE- CIENCY WITH SECONDARY DI- INSUFEICIENCY. VERGENCE-EXCESS. Exophoria about equal for dis- Exophoria for near much great- tance and near. er than for distance. Converging power and prism- Converging power greatly af- convergence not excessively af- fected. fected. Recession of convergence near- Recession of convergence near- point moderate. point marked. Condition shows little tendency Often markedly progressive. to progress. As above stated, cases of primary divergence-excess show but little tendency to progress. I have had one such case under observation for over nine years, in which the divergence, although large, has shown but moderate fluctuations—indeed, may be said to have remained prac- tically unchanged—during the whole time. Cases, on the other hand, of secondary divergence-excess are often prog- gressive, a moderate degree of exophoria developing gradually into a marked divergent squint. The symptoms presented by a case of divergence-excess are frequently slight. The most troublesome are those due 88 NEW CLASSIFICATION OF MOTOR ANOMALIES. to an associated convergence-insufficiency, and, if this is absent, the patient may complain of nothing except possi- bly of a spontaneously occurring crossed diplopia for dis- tance, or of the deformity occasioned by the noticeable de- viation of the eyes. Headache and asthenopia may, how- ever, also occur. The treatment of a divergence-excess will be addressed mainly to the correction of the refraction and to the relief of an associated convergence-insufficiency. If an opera- tion is performed, tenotomy of the externi may be done; but it will often have to be supplemented by systematic exercise of the convergence and even by advancement of the interni. IX. ANOMALIES OF SURSUMVERGENCE. Hypokinesis. 5ursumvergence=Insufficiency. It is not certain whether sursumvergence, i. e., the separation of the visual lines in a vertical plane, is ever performed by the eyes in the execution of normal movements. It seems, however, likely that some such action may be serviceable incidentally in the act of elevating or depressing the eyes. If so, great impairment of the sursumvergence would con- stitute a serious deficiency. As far as I have seen, how- ever, limitation of sursumvergence appears to have no special injurious effect. Those who regard the amount of sursumvergence as a measure of the strength of the elevators and depressors (which it surely is not) lay more stress than I have done on the limitation of this function, and recommend system- atic exercise of the latter by means of prisms, base up or down, in cases where it is subnormal. I have had some experience with these methods, but not enough to enable me to speak with assurance as to their value. My results, such as they were, have not led me to expect much from training of this sort. Hyperkinesis. 5ursumvergence=Excess. Excessive power of sursumvergence is observed in many patients affected NEW CLASSIFICATION OF MOTOR ANOMALIES. 89 with hyperphoria and particularly in myopes who have an artificial hyperphoria from wearing ill-fitting concave glasses. The latter, as they shift in various positions, produce prismatic effects changing in degree and in direc- tion, and hence requiring a variable effort to overcome the diplopia to which they would naturally give rise. This constant exercise gives rise often to a considerable in- crease in the power of sursumvergence. the latter some- times attaining 10° or more. A true sursumrergence-excess, i. e., a state of habitual divergence of the visual lines in a vertical plane, due to excess of sursumvergence action, constitutes one of the varieties of hyperphoria, and probably accounts for some of the cases of strabismus sursumvergens and strabismus deorsumvergens. These cases must not be confounded with a similar vertical deviation due to paresis or insuf- ficiency of some of the individual muscles. The differen- tial diagnosis between the two will be established by mak- ing the screen and diplopia tests in different portions of the field of fixation, when, if there is an insufficiency of anyindividual muscle, a deviation or a diplopia, showing a characteristic increase in some one direction of the gaze, will be found to exist (see Section VI). In sursumvergence-excess either the right or the left visual line may be habitually higher than the other (rigid and left hyperplioria >, or each alternately may be higher ((dferuating hyj>eiphoria ). If the deviation is considera- ble and not habitually overcome, the condition is known as a vertical squint (iiypertropia), which again is called right or left hypertropia, according as the right or the left visual line is above- Vertical squint is also classified into strabismus su rsu m verge ns when the lower eye is the one that habitually fixes, and strabismus deorsumvergens when the upper is the fixing and the lower the non-fixing eye. Regularly, in such cases, the deflection follows the law of associated movements. That is, if the right eye devi- ates up behind the screen when the left eye is fixing, the latter will, when the screen is shifted so as to cover it, move down in company with the right, which now, being 90 NEW CLASSIFICATION OF MOTOR ANOMALIES. uncovered, is descending in order to get into the position of fixation. In certain remarkable cases, however, the deviation of both eyes is up ( anatropia ), or of both eyes is down (catatropia) behind the screen. That is, if the right eye deviates up behind the screen when the left is fixing, the latter, as soon as the screen is shifted and the right eye moves down to get into the fixing position, will move up. In this case the visual lines, instead of remaining at a con- stant angle, as in the case before cited, will approximate until they become parallel, and will then diverge in the op- posite direction. Stevens (Annates d'oculistique, CXIIL, 3, April, 1895,) was the first to carefully study these cases and call them by the names above given.1 His view of them is that they are due to the fact that initial elevation or initial depres- sion of both visual lines (i. e., an excessive sursumversion or deorsumversion) is, in these anomalous cases, the nat- ural state, to which each eye tends to return when not used for vision. But the condition may also, and perhaps more plausibly, be ascribed to a spasm of sursumvergence, or rather of the action opposed to sursumvergence (that, namely, by which the visual lines, when vertically di- verged, are brought together again). X. ANOMALIES OF ROTATION-MOVEMENTS. Anomalous conditions, in which divergence or converg- ence of the vertical meridians of the two corneae (other than the physiological divergence which occurs when the visual lines are converged) have been described by Savage. His views, however, although urged with much plausibility, are still far from being demonstrated. It seems likely that these conditions, if they exist at all, are rare and of com- paratively little significance. ^chweigger, to be sure (Arch. f. Augenheilk., XXIV., 3-1, 1894), mentions such a case, but without attempting any explanation of the phenomenon. NEW CLASSIFICATION OF MOTOR ANOMALIES. 91 XL RECAPITULATION. The conditions that I have sketched embrace all the dif- ferent deviations, both manifest and latent, that are usu- ally described. As the system of classification here pro- posed differs radically from that generally employed, it may be well, in a brief recapitulation, to show the points of contact between the two. The ordinary classification divides deviations into Out- ward (or divergent), Inward (or convergent), and Vertical (upward or downward). These deviations may be due to the following causes: SUMMARY OF DEVIATIONS. I. Inward Deviations (Esophoria, Convergent Strabis- mus) may be due to: ft. Over-action of one or both internal recti or of the other adductors of the eye (superior and inferior recti). b. Under-action of the external rectus or of the other abductors (the obliques). c. Under-action of the center for producing divergence movements (divergence-insufficiency). d. Over-action of the center fcr producing convergence movements (convergence-excess, which, in turn, may or may not be due to excessive accommodative action). e. Two or more of the above causes combined. II. Outward Deviations (Exophoria, Divergent Strabis- mus) may be due to: a. Under-action of the internal rectus or of the other adductors (superior and inferior recti). b. Over-action of the external rectus or of the obliques. c. Under-action of the center for producing convergence movements (convergence-insufficiency, which, in turn, may or may not be due to insufficiency of accommodative action.) 92 NEW CLASSIFICATION OF MOTOR ANOMALIES. d. Over-action of the center for producing divergence movements (divergence-excess). e. Two or more of the above causes combined. III. Upward and Downward Deviations (Hyperphoria, Strabismus Sursumvergens and Deorsumvergens) maybe due to: a. Over-action of an elevator or depressor muscle. b. Under-action of an elevator or depressor muscle. c. Both of the above causes combined. d. Sursumvergence-spasm, either uncomplicated or com- bined with under-action or over-action of an elevator or depressor. IV. Mixed Forms (Hyperphoria combined with Exopho- ria, Hyperphoria combined with Esophoria, and Esophoria in one part of the field of view combined with Exophoria in another) are frequent. The differentiation of these separate groups included un- der the above general heads is readily made, for all have well-marked signs which are detailed in the foregoing sections (V.-VIIL). The diagnosis, indeed, can in almost every case be made at once by applying the three broad principles laid down in Section IV. (at the end of the re- marks upon comitant and non-comitant deviations). The diagnostic points indicative of the chief conditions met with are recapitulated in the following table. DIAGNOSTIC TABLE—TERMS EMPLOYED. Pc (convergence near-point), the distance of the near- point of convergence from the bridge of the nose, when the object of fixation is carried toward the eyes in the me- dian line. Pc(R), the distance of the near-point of convergence from the bridge of the nose when the object of fixation is carried directly toward the patient's left eye from some point situated to the front and right of him (see Fig. 3 and accompanying explanation). Pc (R) will, in this case, denote the point at which the right eye sags off in con- NEW CLASSIFICATION OF MOTOR ANOMALIES- 93 vergence. Similarly, Pc ( L ) denotes the point at which the left eye ceases to converge when the object is carried from the left side directly toward the right eye. ('onrergeui-e-adduction, the power possessed by either eye of moving inward in response to a convergence-stim- ulus. Its measure is the Pc. Associated adduction, the power possessed by either eye of moving inward in performing associated parallel move- ments, /. e., when the other eye is moving outward. It is regularly greater than the convergence-adduction. Prism-convergence (the adduction of most) is the ability to converge the eyes, when overcoming p'risms, base out. Prism-divergence (the abduction of most authors) is the ability to diverge the eyes as measured by the degree of prism, base in, which the eyes can overcome. This is said to be proportionated the amount of an exophoria or esophoria when it equals 7 -|- the exophoria or 7° — the esophoria (for distance). A. OUTWARD OR DIVERGENT DEVIATIONS.— (EXOPHORIA, DIVERGENT SQUINT.) I. Deviation and its evidences (exophoria, crossed di- plopia) noticeably greater in some directions of the gaze than in others. Pc abnormally remote. Pc (R) greater or less than Pc and still more so than Pc (L). Excursion of one eye and its field of fixation abnormally increased or re- duced in some one direction, both for distance and near. Under=Action of an Adductor or Over=Action of an Abduc= tor riuscle. Note—The diagnosis as to whether it is under-action or over- action that is present may be made from the points detailed under the head of diagnosis (4) in Section V.; and the specific diagnosis of the muscle affected maybe made from the tables of diplopia in same section (0). As there stated, a crossed diplopia (or an exophoria) which increases as the eyes are carried to the right indicates weakness of .whic muscle of the left eye or over-action of some muscle of the right eye; and any exophoria which changes markedly in degree as the eyes are shifted can be due only to under-action of an internus or over-action of an externus. II. Deviation and its evidences (exophoria, crossed di- 94 NEW CLASSIFICATION OF MOTOR ANOMALIES. plopia) sensibly the same in all directions of the gaze. Pc (R) equals Pc (L). Excursion of both eyes and their fields of fixation normal (at least for distance). (a.) Deviation or exophoria slight for distance. Marked for near^ by all tests. Pc abnormally remote. Convergence-adduction less than associated adduction (Craefe's test—see Section VI.). Prism-divergence not specially great (usually 8-10°, or may be subnormal). Prism-convergence subnormal and effected with difficulty. Convergence-Insufficency. Note.—The diagnosis between an accommodative and a non-ac- commodatire convergence-insufficiency will be made by refer- ence to the etiology (see Section VI.) and by observing the effect of glasses. The latter, if suitably adjusted, usually relieve a trouble of purely accommodative origin. (b.) Exophoria marked for distance; less for near (relations for near may be nearly normal). Pc normal, or nearly so. Prism- divergence large (in typical cases disproportionately so; /. e., it is greater than 7° + the exophoria for distance). Prism- convergence often normal and effected with facility. Diverg- ence-Excess. (c.) Exophoria marked for both distance and near. Pc abnor- mally remote. Convergence-adduction less than associated adduction (Graefe's test—see Section VI.). Prism-divergence large, but not disproportionately so, compared with the amount of exophoria. Prism-convergence usually reduced — often greatly. Divergence-Excess with Convergence-Insuffi- ciency. Note.—The determination as to whether the divergence-excess is secondary to the convergence-insufficiency, or is primary, may be made by the differential diagnosis given in Section VII. This condition is not always easy to diagnosticate from a comitant deviation produced by under-action of one or both interni, combined with over-action (due to compensatory contraction) of the externi. Moreover, it is not improbable that a long-continued divergence-excess may give rise not only to an insufficiency of convergence, but to a weakness of the interni per se, due to their protracted inaction and to the unfavorable conditions under which they work. (d.) Exophoria marked for distance. For near, slight exophoria, orthophoria, or esophoria. Pc normal or excessively near. Convergence-adduction greater than associated adduction. Prism-divergence large, sometimes disproportionately so. Prism-convergence normal and readily effected. Divergence- Excess with Convergence-Excess. Note.—These cases are sometimes difficult to diagnosticate from NEW CLASSIFICATION OF MOTOR ANOMALIES. 95 those of anatomical preponderance of both externi (struct- ural deviation), combined with a convergence-excess. The convergence-excess in these cases, being often accommoda- tive, will frequently disappear upon the use of the proper glasses. (e.) Convergence-Insufficency with Divergence-Insufficiency. (See Inward Deviations, B. II., d.) III. Mixed conditions, in which the deviation increases more or less in certain directions of the gaze, but in which the phenomena noted under II. are likewise present (combination of over-action or under-action of muscles with a divergence-excess or a convergence-insufficiency); and conditions in which, by the weakness of some muscles and the over-action of others, a comitant exophoria or divergent squint has been" established, are not readily ana- lyzed into their constituent factors. B. INWARD OR CONVERGENT DEVIATIONS—(ESOPHORIA, CON- VERGENT SQUINT) . I. Deviation and its evidences (esophoria, homonymous diplopia), noticeably greater in some directions of the gaze than in others. Pc abnormally near. Pc(R) greater or less than Pc and still more so than Pc(L). Excursion of one eye and its field of fixation abnormally increased or reduced in some one direction, both for distance and near. Under=Action of an Abductor or Over=Action of an Adduct- or Muscle. Note.—For the specific differentiation see Section V., remarks on diagnosis, (4) and (6). As there stated, a homonymous diplopia (or an esophoria) which increases as the eyes are carried to the right, indicates weakness of some muscle of the right eye or over-action of some muscle of the left eye; and an esophoria which changes markedly in degree as the eyes are shifted can be due only to under-action of an ex- ternus or over-action of an internus. II. Deviation and its evidences (esophoria, homonymous diplopia) sensibly the same in all directions of the gaze. Pc(R) equals Pc(L). Excursions of both eyes and their fields of fixation normal (at least for distance). (a.) Esophoria marked for distance; slight or replaced by ex- ophoria for near. Pc normal. Convergence-adduction equal 96 NEW CLASSIFICATION OF MOTOR ANOMALIES. to or more or less than the associated adduction. Prism-di- vergence low (may be disproportionately so, i. e.. is less than 7°—the esophoria for distance). Prism-convergence normal, or often subnormal. Divergence-Insufficiency. (b.) Esophoria slight for distance; more for near. Pc exces- sively near (less than 1 inch). Convergence-adduction may be greater than associated-adduction. Prism-divergence normal, or but slightly subnormal (never disproportionately low). Prism-convergence normal. Convergence-Excess. Note.—The diagnosis between an accommodative and a non-ac- commodative convergence-excess will be made by reference to the etiology (see Section VI.) and by observing the effect of the long-continued use of glasses (or of atropine), which in most cases will relieve a difficulty of purely accom- modative origin. (c.) Esophoria marked for distance and near. Pc excessively near. Convergence-adduction equals or is greater than asso- ciated adduction. Prism-convergence low in proportion to degree of esophoria for distance, or disproportionately low. Prism-convergence normal. Divergence-Insufficiency and Convergence-Excess. Note.—The determination as to whether the divergence-insuf- ficiency is secondary to the convergence-excess, or is primary, may be made from the differential diagnosis in Section VII. (d.) Esophoria marked for distance; exophoria (of more than 4° or .1°) for near, noticeable by all tests. Pc abnormally remote. Convergence-adduction less than associated adduction. Prism- convergence low. Prism-convergence subnormal and hard to tram. Divergence-Insufficiency with Convergence-Insuf- ficiency. (e.) Converge ucc-Excess ivith Divergence-Excess. (See Outward Deviation, A. II., d). Ill, Mixed conditions, analogous to those given under Outward Deviations III. exist, but are hard to analyze. C. VERTICAL DEVIATIONS—(HYPERPHORIA, STRABISMUS SUR- SUMVERGENS AND DEORSUMVERGENS-) I. Hyperphoria or its evidences (vertical diplopia) in- creasing in some one direction of the gaze. (a.) Hyperphoria increasing as the eyes are carried upward. Over-Action or Under-Action of an Elevator Muscle. (b.) Hyperphoria increasing as the eyes are carried downward. Over-Action or Under-Action of a Depressor Muscle. NEW CLASSIFICATION OF MOTOR ANOMALIES. 97 Note.—For the specific diagnosis of the muscle affected see Section V., remarks on diagnosis (4 and o). II. Hyperphoria the same in all parts of the field (com- itant hyperphoria, comitant vertical strabismus). (a.) Due probably in most case:; to under-action of an elevator or depressor, with over-action of one or more antagonistic muscle. Mixed Cases. (b.) . Sometimes to equal vertical divergence of the visual lines (sec Section VIII). Sursumvergence-Excess. CONCLUSION. One who proposes a new classification must be pre- pared to defend his position by showing that it subserves some useful purpose. That this is the case with the one propounded in the preceding pages seems to me proved by the following reasons: 1. The classification is based upon physiological facts instead of mere external appearances. 2. Its divisions correspond to natural groups, distinct in nature and symptoms, and frequently requiring widely different methods of treatment. 3. The groups so made are readily distinguishable in practice by the signs they afford. 4- We can by means of the scheme here presented ana- lyze the frequently occurring mixed forms, and from our knowledge of the nature and tendency of the component lesions determine to which of the latter our treatment shall be addressed. INDEX. A. Abducting power of the obliques and external rectus, amount of, 14, 15. Abduction (in proper sense of term, denoting the power possessed by each eye of moving outward), 9. Abduction (in its ordinary sense of mut- ual divergence of the visual lines). See Divergence and Prism-Divergence. Accommodation always brought into play when convergence is exercised by prisms, 24: this should be taken into account in making muscular tests, 38. Accommodative convergence-excess, 79. Accommodative convergence-insuffi- ciency, 75. . Adducting power of the superior, infe- rior, and internal recti, amount of, 14, 15. Adduction (in proper sense of term, denoting the power possessed by each eye of moving inward), 9; varieties (convergence - adduction, associated adduction), 93. Adduction (in its usual sense of mutual convergence of the two visual lines). See Convergence and Pvinm-conver- gence. Anatropia, 68, 90. Antagonists, associated, 19,20, 29. Antagonists, direct, 7. Associated adduction, 93. Associated antagonists. 19, 20, 29. Associated convergent movements, tests for, 36. Associated parallel movements, table of, 1719; extent of, 20; centers for, 22; tests for, 35; anomalies of, 67. Association centers, 22. Asthenic exophoria. 77. Asthenic vertical orthophoria, 68. B. Binocular fixation, field of, 20; tests for, 30, 35. Binocular single vision, field of, 2C; tests of, 35. c. Catatropia, 68, 90. Choreiform spasm of associated oblique movements, 69. Classification of ocular deviations, upon what based, 42, 43; author's pro- posed scheme, 44; previous schemes, 1. Comitant and non-comitant deviations, 46 et seq.; laws governing transforma- tion of, 48; character of screen-move- ments in, 33. Comitant hyperphoria, 60, 97. Compensation of deviations, law of, 48, 49. Concomitant. See Comitant. Congenital deviations, characters of 56. Constant squint, 44. Convergence, exercise of by prisms, 23; exercise of, produces spasm of accom- modation, 24, 38; maximum power of, 22; test for, 36. Convergence-adduction, 93. Convergence-anomalies, 71. Convergence-excess. 78; differential di- agnosis of, 96; with secondary diver- gence-insufficiency, diagnosis of, 84, 96. Convergence-insufficiency, 72; charac- ters, 72; non-accommodative, 73; ac- commodative, 75; course, 75; compli- cations, 77, 87, 94; symptoms, 77, diagnosis, 87, 94; treatment, 77. Convergence-movements, 22. Convergence near-point, 22, 92; determi- nation of, 36. Convergence-paralysis, 71. Convergence-spasm, 38, 78. Convergence of the vertical meridians of the corneas, 26; abnormal, 90. Crossed diplopia, 31. Crossed paraliax, 34. D. Deorsumduction (in proper sense of term), 10. Deorsumversion, how effected, 18; par- alysis of, 68. Depressing power of inferior rectus and superior oblique, amount of, 14. Deviations, classification of, 1, 42-46; di- agnostic table of, 92; inward, 91, 95; mixed forms, 92, 95, 96. 97; outward, 91, 63-95: transformation and evolution of law of, 48, 49; vertical, 92, 96. Dextroversion, how effected, 17; par- alysis of, 67; spasm of, 68. Diagnostic table of deviations, 92; of muscular paresis and spasm based on the double images, 61-63. Diplopia, how brought out and differen- tiated. 31; how measured. 31; method of recording, 39; transient, indicating physiological limitation of field of single vision, 35; varieties (crossed, left, homonymous, right, etc.), 30, 31; table of, in muscular paralysis and spasm, 61-63. Diplopia-test, 30, 35, 36, 39. Divergence (or Diverging power), 24; nature of, 25; produced by prisms, 24, 38; of slight amount, physiological for near points, 36; tests for, 38. Divergence-excess, 86,94. Divergence-insufficiency, 83, 96. Divergence of the vertical meridians of the corneae, 27; pathological, 90. Donders' lawdiagramatically illustrated, 29. Downward associated movements. See Deorsumversion. Downward deviations, 92, 96. Dynamic association-tests, 30. Dynamic disassociation-tests, 30. E. Klectricity, 64. Rlevating power of superior rectus and INDEX. 99 inferior oblique, amount of, 14. Equilibrium test, 31, 35, 36, 39. Esophoria, 32; accommodative, 79, sthenic, 79; varieties of, according to the new classification, 91; varieties of, how differentiated, 95. Exophoria, 32; asthenic, 77; varieties of. according to the new classification, 91; varieties of, how differentiated, 93-95. Fxterual rectus, action of, 6, 9-11, 17-19; action of, how modified by the verti- cally acting muscles, 28. F. Field of binocular fixation, 20. Field of binocular single vision, 20; con- centric contraction of, 35, 59; how mapped out, 35, 39; pathological and accidental limitation of, as shown by the varieties of diplopia occurring, 35; physiological limitation of, 35. Field of (monocular) fixation, 12, 40; diagram of, 26, 27; how limited in muscular paralysis, 29, 59; how map- ped out, 35; measurements of, 12, 13. Fixation-test, 30, 35, 36. Fixing eye, how to determine the. 33. Fusion near-point. See Convergence near- point. H. Heteronymous diplopia, 31. Heteronymous parallax, 34. Heterophoria, 3, 43; insertional. 51; spastic, 60; structural, 51. Heterotropia, 3, 44. Homonymous diplopia, 30. Homonymous parallax, 34. Hyperkineses, 14. Hyperphoria, 31, 59; comitant, 60, 97; varieties of, classified according to external character, 89; varieties of, classified according to etiology, 92; varieties of, how differentiated, <)6. Hypertropia. 89. See also Strabismus sursunicergens and Strtibismtis deorsum- vergens. Hypokineses. 43. I. Individual muscles, actions of, 6; an- omalies of, 49; slight cases of anomal- ies of, 59. Inferior oblique, action of, 6, 9-11, 17-19; field of action of, graphically shown, 26; and superior oblique, combined ac- tion of, 28; and superior rectus, com- bined action of, 26, 27. Inferior rectus, action of, 6, 9-11, 17-19; field of action of, graphically shown, 27; and superior oblique, combined action of, 27; and superior rectus, combined action of, 27. Inspection, 30, 35, 36, 39. Insufficiency,discovery of, 3; faulty use of term, 3. See also Heterophoria. Intermittent squint, 44, Internal rectus, action of, 6, 9-11, 17-19; action of, how modified by that of the vertical muscles, 2S. Innervational deviations, 52. Insertional squint or heterophoria, 49, 51. Inward deviations, varieties of, classified according to etiology, 91; varieties, differential diagnosis of, 95. L. Latent squint, 44. Law of comitance, 48,49. Left associated movements. See Sinis- troversion. Left diplopia. 31. Left parallax, 34. Left sursumvergence, 38. Listing's law, diagrammaticallv illus- trated, 29. M. Maddox rod, 31 (note). Manifest squint, 44. Mixed forms of deviation, 92, 95, 96, 97. Mixed nystagmus, 70. Movements, binocular, five classes of, 15, 16; with unimportant exceptions subserve binocular fixation, 15; de- scription of, 17-29. Movements, monocular, 7-14; extent of, 11; can be performed in all directions, 8; tabular view of, 9-11; diagrammatic representation of, 26-29. Movement of redress, 33. Muscles of eye, combined actions of, 27, 2