Movements Of The Eyeballs And Their Anomalies

Movements Of The Eyeballs And Their Anomalies
By ALEXANDER DUANE, M. D

Physiological Action of the ocular Muscles.' Tbe actions of the external ocular muscles, deduced partly from our knowledge of their origins and insertions, partly from the results produced by their paralysis, are as follows:'

The external rectus (abducens) rotates the eve directly outward (abduction)

The internal rectus rotates the eye directly inward (adduction).

superior rectus carries the eye upward, adducts it, and rotates the upper end of the vertical meridian of the cornea inward (inward torsion, intorsion). Its power of producing adduction and torsion increases as the eye is adducted, and decreases as the eye is abducted; its elevating power, on the contrarv is greatest when the eve is abducted between 20' and 30' and diminishes to zero as the eve is adducted.

The inferior rectus carries the eye downward, adducts it, and causes outward torsion of the vertical meridian of the cornea (extorsion). As in the case of the superior rectus, the power of producing adduction and torsion increases and the vertical action diminishes the more the eye is carried inward ; and, contrariwise, it acts most powerfully as a depressor (and not at all as an adductor) when the eve is abducted 20' or 30'.

The superior oblique (trochlearis) depresses the eye, abducts it, and rotates the vertical meridian inward. The power of producing abduction and torsion increases and the vertical action decreases in proportion as the eye is abducted. In positions of adduction, on the contrary, the superior oblique serves mainly to de ress the eve its action in this regard increasing as that of the inferior rectus diminishes.

inferior oblique elevates the eye, abducts it, and rotates the vertical meridian inward. The power of producing abduction and torsion increases in proportion as the eye is abducted, while the elevating action increases as the eye is adducted, the effect of the muscle in this regard becoming constantly greater as that of the superior rectus grows less.

It will be seen from this that elevation and depression of the eye are effected mainly by the obliques when the eye is adducted and by the superior and inferior recti when the eve is abducted; also that the adducting action of the superior and inferior recti increases (and the opposing action of the obliques diminishes) in proportion as the eye is adducted ; and that the abducting action of the obliques increases (and the opposing action of the recti diminishes) in proportion as the eye is abducted. Hence, while abduction is performed mainly by the external rectus, the latter is reinforced especially toward the end of its course by the obliques; and the internal rectus is similarly reinforced by the superior and inferior recti, which, when the eye is already much adducted, will carry it appreciably farther in.

Lastly, it will be seen that, in directions of the gaze up and in, the torsion-action of the superior rectus will predominate ; in directions up and out, that of the inferior oblique ; in directions down and out, that of the superior oblique; and in directions down and in, that of the inferior rectus. Consequently, when we look up and in or down and out, the vertical meridian of the cornea is tilted toward the nose; when we look up and out or down and in, it is tilted toward the temple. When we look straight up or straight down (and also when we look straight to the right or left), the torsion actions of the oblique muscles and of the recti counteract each other, and hence the vertical meridian remains vertical.

Movements of Each Eye. By the combined action of two or more ocular muscles the eye may be moved in any direction whatever. Thus a movement obliquely upward and inward requires the co operation of three muscles i. e of both elevators and of the internal rectum, the latter (assisted by the superior rectus) carrying the eye inward, while the inferior oblique and, to 'a moderate extent, the superior rectus carry it upward.

In moving the eye obliquely up or down three muscles are always called into play (viz. both elevators or both depressors, combined with either the external or the internal rectus) in moving the eye straight upward, four (i. e. all except the two depressors); in moving the eye straight downward, four (all except the two elevators) in moving the eye directly inward, five (all except the external rectus) ; and in Moving it directly outward, five (all except the internal rectus)

All these movements start from a position of rest, or primary position. When the eve is in this position the muscles are, all balanced i. e. if all six contract simultaneously to an equal extent, they will keep the eye fixed where it is. In all other directions of the gaze (secondary positions) the eye is so placed that some one muscle or pair of muscles works to greater advantage than the antagonistic muscle or pair. In this case, if all six muscles contract simultaneously, the muscle that works to greater advantage will exert a preponderating action, and will hence tend to displace the eyeball away from the position it occupies, and in such a manner always as to carry it back toward the primary position.

For most eyes the primary position is that in which the visual line is directed horizontally or nearly so and straight ahead (i. e. is perpendicular to the line joining the centers of rotation of the two eyes).' The eyes should always be placed in this position when any tests are made for ascertaining whether or not the muscles are in equilibrium.

Field of Fixation. By passing from the primary to all possible secondary positions the eye is enabled to fix a great number of objects i.e. bring the images of these objects successively upon the macula. The portion of space occupied by all such objects that can thus be fixed by movement of the eve alone without moving the head is called the field of fixation.

Its limits represent the limits of excursion of the eve in all possible directions. These limits can be best determined by fixing the patient's head upon the rest of a perimeter in such a way that the eve when in the primary position is directed toward the zero of the perimetric are, and then carrying along the latter a card with two fine (lots set close together upon it. The patient is told to follow the dots with his eye without moving his head. The moment when he fails to do so is evidenced objectively by the wavering of the eve, and subjectively by the fact that the two dots are no longer seen distinctly as two, but run into one. Then the point on the perimetric are to which the card has been carried indicates the amount of excursion of the eye in the given direction.

The limits of the field of fixation have been variousl stated. My own observations (37 measurements of 18 different subjects) gave-

Reduction of the excursion of the eye (contraction of the field of fixation) to less than 30' in any direction must, if substantiated by repeated tests, be regarded as distinctly pathological (see also page 169).

Binocular Vision and Diplopia. We ordinarily use both eyes in seeing (binocular vision), and the eyes are involuntarily so adjusted that the image of the object looked at falls simultaneously upon both macule (binocular fixation). Under these conditions we see singly because the two images are by our consciousness fused into one image, which has somewhat different characters from either of its components (binocular single vision). When one eye fails to fix simultaneously with the other, diplopia generally results. But diplopia will be absent if, as often happens, the image formed in the nonfixing eye is not taken account of by the consciousness (monocular vision from suppression of image); and one image may be thus suppressed even when both eyes are properly directed i. e. there may be binocular fixation, but only monocular vision.

The diplopia produced by the fact that one of the eyes deviates from the object that the other eye is looking at is directly proportional to the amount of deviation. It may be corrected by an appropriate movement of the deviating eve or by placing before the eve a prism so directed as to make the rays coming from the object change their course and fall upon the macula.

Per contra, diplopia may be produced without any deviation of the eyes by putting before the latter a prism which will deflect off from the macula the rays that would otherwise be concentrated upon it. In this case the artificial diplopia may be corrected (or the prism may be "overcome") by turning the eye until the macula is so directed as to meet the deflected rays.

When an eye either is deflected to the right or has placed before it a prism with its base directed to the right, an object situated straight ahead will form its image to the right of the macula,, instead of upon the latter. But experience and the sense of touch continually teach us that an object which forms its image on the right of the macula is itself situated to our left; hence, under the conditions noted the object no longer appears straight ahead, but deflected to the left, and by as great an amount as the eye itself is deflected to the right. So also when the eye is deviated up, an object straight ahead appears lower than it is; and in general, however an eye may be deflected, the apparent position of objects seen with it is deflected in the contrary way.

These facts may be expanded for the particular cases as follows

Associated Movements of the Two Byes: Parallel Movements. As has been stated, binocular single vision is attained only when both eyes are directed precisely at the object of fixation, and under normal conditions the two eyes invariably move together in such a way as to effect this end, and that, too, at once and with the utmost precision. In the case of a distant object the movements of the eyes must be such as to keep the two visual lines strictly parallel (associated parallel movements). The typical movements of this class are shown in the following table:

An inspection of the foregoing table will show that the twelve muscles that serve to carry the two eyes in parallel directions may be divided into six pairs, one muscle of each pair being in the right eye and the other in the left, and the two moving their respective eyes in the same direction and to the same extent. The muscles constituting such a pair are called associated antaqonists.

The amount of excursion in every direction made by a pair of eyes in following a more or less distant object which the simultaneously fix determines the field of binocular fixation ; and the amount of excursion that they call make and yet preserve parallelism of their axes, so that no diplopia ensues, determines the field o binocular sin le vision. This latter extends not less than 40' (normally from 40' to 50') in every direction from the primary position; and diplopia, occurring uniformly when the eyes have been carried less than 30' from the primary position, is distinctly pathological.

The tendency ' y to maintain parallelism of the visual lines is so great as to persist even when one eve is excluded by blindness or by being covered with a screen ; so that one eye keeps moving with the other, and binocular fixation is maintained in all directions of the gaze, although only one eye sees the object fixed. Upon this fact depends the test by alternate covering (screen test).

The associated parallel movements are apparently governed by a nervous mechanism distinct from the nuclei that supply the nerves for the ocular muscles; and each of the typical movements (dextroversion, sinistroversion, sursumversion, deorsumversion, and perhaps the oblique movements also) seems to have its separate center. The precise location of these centers, however, has not yet been satisfactorily determined.

Movements of Convergence. By means of the associated parallel movements both eyes can be simultaneously directed at any distant object situated within the limits of the field of fixation. To direct them both at once at some near object requires a greater or less degree of convergence of the visual lines, and this is effected by a simultaneous equal contraction of the two interne. This movement, which tinder normal conditions takes place invariably, immediately, and with the utmost precision, and which, as in the case of the associated parallel movements, takes place even when one eye is excluded from seeing, is apparently governed by a nerve center distinct from the nerve nuclei of the internal recti.

When the object looked at is situated not straight ahead, but to one side or above or below, binocular fixation is effected by a combination of convergence with an associated parallel movement. Thus, in looking at an object situated near the eyes and 45' to the right of the median line, the two eyes first move, each, 45' to the right by a simultaneous equal contraction of the right externus and the left internus (dextroversion) ; then by a simultaneous equal contraction of the right internus and the left internus (convergence) the right eye is turned somewhat to the left again and the left eye somewhat farther on to the right, until both visual lines are properly directed.

Even without being adjusted for near objects, the eyes tend to converge somewhat when directed downward.

The amount of convergence is measured by the distance from the nose of the point (convergence near point, Pc) upon which the eyes can by the utmost effort be made to converge. This should be from I to 1 3/4 inches from the nose. The convergence is also measured by the degree of' prism, placed base out before the eyes, which the latter can overcome by turning inward (prism convergence, improperly called the adduction). The prism convergence, when a distant test object is used, is represented b y prisms of 60' to 90' total refracting angle (= a convergence of the visual lines of 35' to 60').

The maximum amount that each eye turns inward in performing convergence (convergence adduction) is about 30' 35'. It is somewhat less, therefore, than the amount (40' 50') by which each eve can turn inward when moving parallel with its fellow (associated adduction or adduction proper).

Movements of Divergence. In passing from the consideration of near objects to those more remote the eyes diverge from each other. They can even diverge be y yond parallelism (i. e. become absolutely divergent), as, for example, when they look at a distant object through a prism placed, base in, before them, and then overcome the diplopia which the latter produces. The amount of this absolute divergence or diverging power (prism divergence, improperly called the abduction) is from 6' to 8' prism (= an actual separa¬tion of the visual lines of only 3' to 4') The absolute diverging power (divergence abduction) of each eve, therefore, amounts to only 2'. It must not be confounded with the abduction proper (associated abduction), or abso¬lute degree of rotation of each eye outward in performing associated parallel movements which is 40' ,50'.

The movement of divergence consists either in a simultaneous equal relaxation of the two interni, or, more probably, in a simultaneous equal contraction of the two externi. It is often combined with associated parallel movements. Thus, if a prism of 8' is placed, base in, before the left eye, each eye will turn out through an angle of 2' in order to fuse the double images (divergence); then, in order to bring the images on the macula of the two eyes, each eye will turn 2' to the left (sinistroversion), so that the right eve is directed straight ahead, the left eve 4' to the left.

A slight divergence of the visual lines occurs normally when both eyes are directed upward.

Movements of Sursumvergence. Divergence of the visual lines in a vertical plane, so that one rises above the other, is called sursumvergence,' and this, again, is denoted as right or left according as the right or left eve is the higher. Right and left sursumvergence are normally equal, but are very limited in amount (= only 2' prism, or 1' of actual separation of the visual lines). The movement is undoubtedly distributed equally between the two eyes, so that a movement of right sursumvergence is the same thing as a movement of left deorsumvergence i. e. in both cases the right visual line moves up and the left visual line moves down, and each moves to an equal extent. Neither the upward movement of one visual line nor the downward movement of the other can be regarded as a measure of' the power of the elevators and depressors of the eye, which is determined rather by the sursumduction (in the proper sense of the term) i. e. the absolute ability of either eye to move upward (= about 40'), and the deorsumduction, or ability of either eye to move downward (~ 50' 60').

Right sursumvergence is measured by the degree of prism placed base down before the right eye (or base up before the left eye), and left sursumvergence by the prism placed base down before the left eye (or base up before the right eye), which the eyes can overcome.

VARIETIES, CLASSIFICATION, ETIOLOGY, AND GENERAL SYMPTOMS or MUSCULAR ANOMALIES.

Varieties of Deviations. All the movements of the eyes, described above, may be deranged pathologically, and the derangement may take the form of over action, under action, or perverted action. The result of these derangements is that binocular fixation and binocular single vision are interfered with, so that one of the eyes deviates or tends to deviate from the object looked at.

Strabismus and Heterophoria. A marked deviation which the patient cannot in general overcome is called a squint or strabismus (heterotropia, manifest deviation); one which, being moderate in amount, is habitually overcome by muscular effort, and hence is elicited only by special tests, is called a: heterophoria or insufficiency (latent squint, latent deviation).

deviation is further classed as constant, if present all the time; intermittent, if sometimes present, sometimes absent; and periodic, if regularly recurring under certain conditions (e. g. if the accommodation is used).

Measurement of Deviations. The magnitude of the deviation may be measured directly by ascertaining either how far the deviating eye stands in or out when the other eye is looking straight ahead, or how far it has to turn in or out in order to perform fixation when the other eye is screened (screen test). The amount of this deflection or of this movement may be got at by taking a linear measurement along the edge of the lower lid,' or it may be determined directly in degrees by means of a perimeter or a tangent scale. Objective measurement performed in this way is termed strabometry.

Indirectly, the amount of a deviation is determined by the amount of diplopia which it produces, this latter, again, being measured either by the actual distance between the double images or by the strength of the prism required in order to unite them (see Table of Diplopia, p. 500). When no diplopia exists spontaneously the artificial diplopia produced by the various forms of phorometer and the, amount of parallactic displacement that the object looked at undergoes when a screen is shifted from one eye to the other, serve as a precise measure of the deviation.

It frequently happens, especially in constant and periodic squint, that the deviation is confined to one eye, the other performing fixation all the time. In this case the non fixing eye is apt to be amblyopic; but whether the poor sight is congenital and gives rise to the deviation, or whether it is itself the result of the latter and springs from the habitual suppression of the visual image (amblyopia from disuse, amblyopia exanopsia) or from the injurious effects of the diplopia upon the squinting eye, is not certain.

In many cases, especially in intermittent squint, and almost always in heterophoria, fixation is performed by each eye alternately (alternating deviation).

The deviating eye B is placed at the center of the graduated arc of the perimeter P P, the are lying on the plane of the deviation. The patient is then required to fix with his two eyes a distant object, A, situated along the central radius R o A. This is the direction which the deviating eye should have in the normal condition. The point n to which the eye in reality is directed should now be determined; the angle 0 R n, formed by the deviating line of sight n with the normal line of sight A o R, is the angle of the strabismus. In order to obtain this angle, it would be necessary only to determine the precise direction of the line of sight of the deviating eye. As this is not an easy matter, it is sufficient in practice to determine the direction of the corneal axis; this differs from the former only by a small angle, which, in comparison with the large angle of the strabismus, may be neglected. The flame of a candle is moved along the arc of the perimeter until its reflection is in the center of the pupil. This will occur when the flame is at n. The corneal axis has now been found, and the size of the angle of strabismus may be read off.

Deviations are also classed according to the direction of the deviating eye, as follows:

The condition in which there is no tendency to deviation in the primary position is called orthophoria.

Etiology of Ocular Deviations; Etiological Classification. Ocular deviations may be grouped according to their etiology, as follows:

CLASSIFICATION.

1. Anomalies of the individual muscles:

(a) Under action, due to faults in (1) structure, (2) insertion, and (3) innervation.

(b) Over action, due to faults in (1) structure, (2) inseition, and (3) innervation.

11. Anomalies of the association centers for parallel movements:

a) Under action, producing an impairment of the movements of both eyes either (1) up, (2) down, (3) to the right, (4) to the left, or (5) obliquely (associated paralysis, conjugate paralytic deviation).

b) Over action, producing an equal excessive movement or equal spastic deviation of both eyes in the same direction (associated. spasm, conjugate spastic deviation).

(c) Perverted action, clonic spasm of associated movements (nystagmus).

III. Anomalies of the center for convergence movements

(a) Under action, convergence in sufficiency, either (1) accommodative or (2) non accommodative.

(b) Over action, convergence excess, either (1) accommodative or (2) non accommodative.

IV, Anomalies of divergence movements:

a) Under action, divergence insufficiency.

(b) Over action, divergence excess.

V. Anomalies of sursumvergence:

a) under action, sursumvergence insufficiency.

b) Over action, sursumvergence excess.

SUMMARY.

1. Associated parallel deviations (conjugate deviations) may be due to

(a) Under action of one of the centers for producing associated parallel movements (conjugate paralysis).

(b) Over action of one of the centers for producing associated parallel movements (conjugate spasm).
11. Convergent deviations (esophoria, convergent strabismus) may be due to

(a) Over action of one or both internal recti or of the other adductors of the eye (superior and inferior recti).

(h) Under action of the external rectus or of the other abductors (the obliques).

(c) Under action of diverge nee movements (divergence in sufficiency).

(d) Over action of the center for 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.

III. Divergent deviations (exophoria, divergent strabismus) 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).

(d)Over action of divergence movements (divergence excess). (e) Two or more of the above causes combined.

IV. Upward and downward deviations (hyperphoria, strabismus sursumvergens and deorsumvergens) may be due to

(a) Over action of an elevator or depressor muscle.

(b) Under action of an elevator or depressor muscle. Under action or over aetion of sursumvergence.

Two or more of the above causes combined.

V. Mixed forms (hyperphoria combined with exophoria, hyperphoria Combined with esophoria, and esophoria in one part of the field of view combined with exophoria in another) are frequent.

Comitant and Non comitant Deviations. Ocular deviations are divided into comitant' and non comitant. In the former, one eye, even when deviating from the other, always deviates by the same amount, so that the two eyes in all their excursions maintain the same angle with each other. The most typical example of comitant deviations is afforded by the anomalies of the associated parallel movements (associated paralysis, associated spasm, nystagmus).

The ordinary forms of divergent and convergent squint are also generally comitant when they come tinder observation, although probably for the most part non comitant in their origin, the comitancy in this case having developed as a result of the evolutionary tendency, described in the next section, by which new compensatory conditions are gradually superadded to the old Ones.

In non comitant deviations the deflection of the non fixing eye keeps varying as the direction of the gaze is shifted, so that the angle between the two visual lines is continually changing. The most marked examples of non comitance are furnished by disorders (under action and over action) of the individual muscles.

Anomalies of convergence and divergence, when uncom plicated, occupy a middle ground between the comitant and the non comitant deviations. They are comitant in that for any One distance the deflection remains the same whether the eyes are carried tip or down or from side to side, but are non comitant in that the defle ction changes in amount in proportion as the object looked at is brought nearer to the eyes or away from them. They are, however, usually classed as comitant.

The differential diagnosis between comitant and non comitant deviations may be thus stated:

Conversion of Non comitant into Comitant Deviations. In non comitant deviations the deflection is marked for some directions of the gaze, while for other directions the conditions are normal. If, now, some new condition is superadded by which the deflection is made equally marked for all directions of the gaze, the deviation will become comitant. This, in fact, is what tends to take place naturally in all non comitant anomalies.' Thus, a paresis of the right external rectus produce,5 an inward deflection of the right eye, which at the outset is marked only when the eyes are directed to the right. After a time, however, spastic contracture of the right internus develops, which causes an inward deflection of the right eye when the eyes are directed to the left, as well, so that ultimately a condition is produced closely simulating a comitant strabismus convergens.' Again, an exophoria due to a convergence insufficiency is at first present only when the eyes are directed at near points; but after this condition has persisted for a long time the action of divergence for distance, hitherto normal, becomes excessive (divergence overaction), and the exophoria becomes marked for distance also. So, too, a periodic convergent squint, in which the eyes are straight for distance, but, owing to convergence overaction, converge excessively when directed at near objects, is finally converted into a constant squint i. e. becomes marked for distance, too, through the development of an insufficiency of the diverging power or perhaps of an insufficiency Of the external recti. In this way a deviation that was comitant only for one range becomes comitant for all.

Subjective Symptoms of Deviations. The subjective symptoms produced by ocular deviations are (I) diplopia and blurring of sight, (2) false projection and apparent motion of objects, (3) vertigo, (4) asthenopia,, (5) pain in the eyes with conjunctival irritation and blepharitis, (6) headache and neuralgia, and (7) other reflex disturbances, including backache, nausea, impairment of nutrition and energy (sometimes considerable in amount), choreiform spasms, and occasionally graver conditions, such as epilepsy.
1. Diplopia is homonymous, heteronymous, or vertical (right or left) according as the deviation is convergent, divergent, or vertical (right or left hyperphoria) (see ante, Table of Diplopia). Its amount, measured in degrees, is equal to the amount of the deviation present at the time. In ordinary comitant squint (insuperable deviation) it is usually absent, because the image formed by the non fixing eye is either too indistinct to be noticed or is actually suppressed; 1 in non comitant squint it is usually present, at least in the earlier stages of the affection; and in superable deviations (heterophoria) it is present at times, although generally overcome by appropriate forced movements of the eyes (see Table of Diplopia).

In slight deviations the amount of diplopia is just sufficient to cause overlapping of the double images, producing thereby a considerable blurring of the object looked at. This is particularly marked for reading, in which the letters, as they double, become superimposed, and hence appear run together. This confusion of sight is distinguished from that due to an error of refraction by the fact that it disappear , as soon as either eye is covered.

In general the slighter degrees of diplopia, and especially those that can be corrected by voluntary effort, are less readily negligible than is a diplopia of larger amount, and hence give rise to more confusion and trouble.

2. False projection of objects (i. e. the seeing of objects in the wrong place) is particularly noticeable in deviation due to paresis or spasm of an ocular muscle. In this case, when the eve has to use the affected muscle in order to look toward an object, the amount of energy put forth by the muscle is out of proportion to the amount of nerve impulse sent to it, and hence the patient feels as if the eye had moved much farther or much less than it really has. Thus a patient with a paresis of the right externus when looking at an object situated to his right would regard the object as much farther to the right than it really is, because be has to make a very great effort with the paretic muscle to move the eye as far as be needs to do; and this excessive effort corresponds in his experience to an excessive movement of the eye to the right i. e. to the act of looking at an object that is situated very far to the right. The same thing would take place if he bad a paresis of the dextroversion center (the association center for turning both eyes to the right). On the contrary, if he had a spasm of the right externus (or of the dextroversion center), an object situated on his right would appear less far to that side than it really is.

One consequence of this false projection is that objects whose place is thus wrongly conceived of appear to move when the eyes are turned or when the patient approaches them. The reason of this is that the amount of displacement of an object from its true situation, produced by false projection, varies with the different positions of the eyes, so that when we change the position (by turning the eyes or by approaching the object) the object appears to be at one moment in its true place, at the next moment out of it i. e. appears to have moved from one place to another.
This apparent movement of objects, together with the diplopia and the unequal strain put upon the eve muscles, is the cause of the vertigo that so often accompanies ocular deviations.

I Suppression implies that the image produces its proper impression upon the sensorium, but that the patient by some mental process excludes this impression from his consciousness.
If binocular single vision is lost, the power of appreciating depths and distances is necessarily much impaired (loss of stereoscopic vision).

3. The remaining symptoms (asthenopia, headache, eye pain, and the various reflex disturbances) are due to the strain imposed upon the muscles when overcoming a deviation. They are hence more pronounced in heterophoria and in squint of low degree an" intermittent squint ( in all of which conditions the patient tries with more or less success to overcome the deviation), than in a marked, constant strabismus, in which, as the deviation is insuperable, the patient makes no attempt to overcome it. Furthermore, the amount of asthenopia and reflex disturbance is roughly proportional to the amount of effort that the patient has to exert in overcoming the deviation. Hence these troubles are more marked in cases of insufficiency than of over action; 1 and in cases requiring exercise of the comparatively weak diverging power (C. Y. cases of divergence insufficiency), and of the still weaker sursumverging power (e. g. cases of hyperphoria) than in cases such as those of divergenceexcess, that demand exercise of the strong converging action for their compensation. In general, asthenopia is a marked feature of convergence insufficiency, and eye pain, with conjunctival irritation and blepharitis, is apt to be associated with the same affection; while headache, neuralgia, nausea, and disturbances of digestion and general nutrition are particularly prone to occur in connection with divergence insufficiency and the vertical deviations.

CHARACTERS AND DIAGNOSIS or THE INDIVIDUAL ANOMALIES.

Affections of Individual Ocular Muscles (Paretic and Spastic Squint). Etiology. Over action or tinder action of an ocular muscle may be due to three causes.

(a) Over development or under development of the muscle itself (structural squint and heterophoria). Thus, congenital non development of the external rectus occurs, producing a convergent deviation ; also congenital non development of the superior rectus, producing a downward deviation of the eye, which may or may not be associated with ptosis. Again, overgrowth of the externus, combined or not with non development of the internus, is at the bottom of a number of cases of divergent squint or of exophoria; and a similar preponderance in muscular development of the internal recti accounts for many cases of convergent squint.

(b) Faulty insertion of the tendon of the muscle, causing undue laxity or tension of the latter, and giving a point of application for the muscular force, which is more advantageous or is less advantageous than normal (insertional squint or heterophoria). Examples of this are (1) the deflection produced by a tenotomv or an advancement ; (2) the over action of the antagonist of a paralyzed muscle after structural changes (true contracture) have taken place in the former; and (3) the exophoria or divergent squint that develops in childhood as a result of increasing divergence of the orbits, a process which gives the externus a more favorable area of application than the internus. This process, which is a normal feature of development in childhood, may, if occurring in children that originally have the orbits set very close together, abrogate a convergent squint, or even cause the latter to pass gradually into a strabismus divergens.

(c) Paresis or spasm of a muscle due to an affection of its nerve or nervenucleus (innervational anomalies, paretic and spastic squint, and heterophoria).

The common causes of paresis are tertiary syphilis and its consequences (especially tabes), meningitis (especially tuberculous), pachymeningitis, tumors of the brain and skull, abscess and hemorrhage of the brain, exposure to cold (so-called rheumatic paralysis), traumatism, and hysteria. Paresis may also, although rarely, be due to diphtheria, diabetes, influenza, Whooping cough, and the action of poisons; and slight impairment of power occurs in neurasthenia and other condition of nervous depression. Spasm, which is much less frequent than paralysis, is due to irritative lesions (meningitis, etc.), chorea, epilepsy, and hysteria; rarely is idiopathic. Spasm also occurs sooner or later in the antagonist of a paralyzed muscle, and ultimately leads to structural changes in the latter (contract tire). A false or apparent spasm is the over action which regularly occurs in the associated antagonist of a paralyzed muscle when an attempt is made to move the latter; the overaction in this case being the result of the excessive stimulus imparted to both muscles. Thus, a patient with a paralysis of the right externus who tries to look to the right makes an excessive effort, which effort causes the right eye to move to the right feebly and the left eye to move to the right very greatly and in an apparently spasmodic way, although, of course, spasm in the true sense of the word is not present here at all, since the eye is simply reacting normally to an excessive stimulus.

One or several muscles may be affected. In insertional and structural deviations isolated affections are frequent, and the muscles most apt to be involved are the external, internal, and superior recti. In innervational deviations, if but one muscle is affected, this is usually the external rectus (abducens paralysis or spasm), although isolated paralysis of the superior oblique (trochlear paralysis) is not uncommon. Isolated paralysis of the other muscles is less often met with, but combined paralysis of some or all of the muscles supplied by the third nerve (oculomotor paralysis) is frequent. Complete oculomotor paralysis causes loss of power in four out of the six exterior muscles of the eyeball, and also in the levator palpebre (causing ptosis), the sphincter iridis (iridoplegia), and the ciliary muscle (eyeloplegia). In some cases, caused generally by syphilis or by the action of poisons such as atropin, the paralysis is confined to the sphincter iridis and the ciliary muscle (ophthalmoplegia interna) ; in others to the sphincter iridis, producing mydriasis without any other symptoms; in others, especially when due to diphtheria, to the ciliary muscle, producing paralysis of accommodation alone; and in still other cases these muscles are exempt, but some or all of the exterior muscles of the eyeball are paralyzed (ophthalmoplegia externa). In rare cases all the muscles of the eyeball, exterior and interior, are paralyzed at the same time (ophthalmoplegia totalis).

Symptoms. The symptoms of muscular under action and over action are (I) limitation or excess of movement of the affected eye in some one direction i. e. as the two eyes move together in that direction one of the two lags more and more behind the other, producing a constantly increasing deviation. This symptom gives rise to all the others namely, (2) diplopia, (3) false projection of objects seen with the affected eye, (4) apparent movement of such objects when the patient approaches them, and (5) vertigo. The explanation of these symptoms has already been given. The characteristic feature about all of them is that they increase as the eyes are carried in some one direction increase, namely, in that position of the eyes in which the affected muscle when normal acts most effectively in moving the eye (see Table, p. 502), and decrease as the eyes are carried in the contrary direction. For example, in an affection of the right superior oblique the diplopia, vertigo, etc. are absent when the patient looks tip, begin to appear when he looks down, increase rapidly when he looks down and to the left, and are much less marked when he looks down and to the right; because, in the first place, the superior oblique, being a depressor, acts normally only when the eyes are directed down, and because, in the second place, it acts much more energetically as a depressor when the eyes are directed down and in.

This characteristic feature of these conditions gives rise to another symptom (6) namely, altered position of the head, the patient in each instance holding it in such a way as to prevent the development of diplopia, etc. Thus, if the deviation is such that diplopia occurs when the eyes are turned to the right, he gets over the difficulty by turning his head to the right, so that the eyes themselves are directed to the left.

The symptoms vary in intensity from a slight, transient diplopia, elicited only by the different tests for heterophoria, to the complete immobility produced by total paralysis.

In ophthalmoplegia interna (7) mydriasis and (8) paralysis of accommodation will occur; and in complete oculomotor paralysis both these symptoms together with (9) ptosis.

Course and Prognosis. Structural deviations, particularly if congenital, show little tendency to increase or decrease. Insertional deviations are apt to increase, except when the result of a tenotomy or advancement, in which case they usually decrease because of the contraction that takes place in the process of healing.

Paretic or spastic deviations may recover spontaneously or as the result of treatment. This is always the ease in hysterical affections, and is the rule in the cycloplegia due to diphtheria. On the other hand, in diphtheritic paralyses of the external muscles and in paralyses due to exposure to cold the condition often persists for a long time or even permanently; and ophthalmoplegia interna, except when due to the action of drugs, is usually incurable.

In chronic paralyses the prognosis is uncertain, the condition being sometimes recovered from, often remaining stationary, and in yet other cases advancing progressively. The tendency to advance is particularly marked in the slowly developing paralyses of nuclear origin affecting isolated muscles, and especially in the variety of paralysis known as ophthalmoplegia externa (see page 511). In these cases one muscle after another is, in the course of months or years, successively involved (progressive ophthalmoplegia), the process often extending to other centers besides the nuclei of the eye muscles, and causing death through involvement of the respiration or other vital action.
Paralyses of sudden development, on the other hand, do not usually show this tendency to advance, and often indeed disappear completely. It is, however, to be remarked that those cases that get well rapidly and spontaneously are particularly apt to be the precursors of tabes, disseminated sclerosis, and general paresis.

two classes of acutely developing ophthalmoplegia, however, this grave prognosis does not apply. In one (recurrent ophthalmic migraine) a total oculomotor paralysis, preceded usually by violent migraine, recurs at more or less periodical intervals and, after lasting for a day or two in some cases and two or three months in others, disappears almost or quite completely. In the other (transient bilateral ophthalmoplegia) a paralysis, usually, but not always, affecting all the ocular muscles and always bilateral, develops rapidly, and disappears completely after lasting one or two months.
Under action of an ocular muscle, whether due to paralysis or not, after lasting for a time leads to over action, and finally to permanent contracture of the opposing muscle in the same eye. In lik~ manner, continuous overaction of a muscle leads to enfeeblement of its antagonist. The deviation in both instances is thus gradually converted into a comitant one (see page 508). Contracture of the opponent does not, however, usually take place in congenital paralysis.

The symptoms, especially the false projection and vertigo gradually grow less pronounced as the patient accommodates himself to his Dew experiences. The diplopia often remains for a very long time, and may even persist after the deviation has become comitant.
Diagnosis. The diagnosis of the muscle affected may in the case of (1) under action or over action of a single muscle be made from the double images by means of the table on page 514. (See also Figs. 320 322.)

2. A diplopia increasing in more than one direction indicates an affection Of more than one muscle, the diagnosis of the specific muscles being made from the table. E. g. a right diplopia increasing both in looking up and to the left and up and to the right indicates weakness of the left superior rectus and the left inferior oblique ; and a left diplopia increasing in looking up and to the right, combined with a right diplopia increasing in looking up and to the left, indicates a paralysis of both superior recti or a paralysis of one superior rectus, combined with spasm of the inferior oblique in the same eye.

3. Crossed diplopia (with the image of the affected eye somewhat below), combined with inability of the eve to move upward, inward, or to any great extent downward, although it can still move out well, indicates oculomotor paralysis. The latter is complete if there are also ptosis, mydriasis, and paralysis of accommodation.

Convergent Deviations; Esophoria and Convergent Squint.A convergent deviation may exist in all degrees, from an esophoria of 2' or 3', elicited only by careful tests with the phorometer, to a constant convergent squint. In any case it may be due to

1. Weakness of one or both externi or over action of one or both interni, or to both these causes combined (muscular deviation). The weakness or over action, which may be structural, insertional, paretic, or spastic in origin, produces a more or less non comitant deviation having the characters already given of a purely muscular anomaly (see pages 510 and 511). Briefly stated, these characters are as follows :

Outward movements of one or both eyes diminished, or inward movements of one or both increased, the increase in the latter case being equally marked whether the eve turns inward in obedience to a convergence impulse, or in performing an associated parallel movement with the other eye. In performing associated parallel movements the restriction of outward movement and the increase of inward movement are marked for distance as well as for near. The amount of restriction or increase usually differs for the two eyes, and the sum of the inward and outward movements, or total range of excursion, is greater in one eve than in the other, and in one eve, at least, is absolutely greater or less than normal (enlargement or contraction of the field of fixation). Degree of convergence or esophoria (as measured by the diplopia, deviation behind the screen, parallax, and phorometer) is not materially different for distance and near, but changes noticeably as the eyes are moved to the right or to the left. Near point of convergence usually closer to the eyes than normal, but often nearer when the object looked at is carried from one side obliquely inward toward the nose than when it is carried inward from the other side.

The determination of the specific muscle affected can by means of the table on page 514 be deduced from the direction of the gaze in which the diplopia or deviation increases the most.

2. Convergence excess. The signs of this are

For distance, convergence or esophoria less than for near, and usually slight. Prism divergence (so called abduction) normal or at least not disproportionately low (i. e. with an esophoria of 3' 4', not below 4'). Prism convergence (adduction) readily performed. Associated parallel movements normal and equal in the two eyes. Total range of excursion normal in both eyes.

For near points, convergence or esophoria marked (by all tests). Convergence near point excessively close to the nose, and equally so whether the object looked at is carried toward the nose from the right or from the left. Eye moves farther inward in response to a convergence impulse than when executing parallel movement in conjunction with the other eye. Excess of inward movement same for each eye.

Convergence excess is often due to excessive accommodative action exerted to overcome hyperopia or astigmatism, the association between accommodation and convergence being so intimate that one function can hardly be brought into play without bringing in the other with it. In this accommodative convergence excess the signs above enumerated will tend to disappear upon the instillation of atropin and the continuous wearing of the proper correcting glasses. But cases of non accommodative convergence excess also occur, and in these glasses afford no relief.

3. Divergence-insufficiency.-The sign of this are-

For distance, convergence or esophoria marked. Prism divergence (abduction) disproportionately low absent or even negative (i. e. there is homonymous diplopia that the patient cannot overcome, except when prisms, base out, are placed before the eye). Prism convergence (adduction) normal or often subnormal. Associated parallel movements and range of excursion equal in both eye, and normal or nearly so.

For near points, convergence or esophoria slight or absent or even replaced by exophoria. Convergence near point not abnormally close to the nose, and about equally far from the latter when the object looked at is carried inward from the right to left.

In rare cases the insufficiency may be so great as to constitute an actual diverqence paralysis (Parinaud, Uhthoff, Straub). These cases are characterized by homonymous diplopia for distance, with marked convergent squint when the eyes are directed straight ahead; both the diplopia and the convergence diminishing progressively as the eyes are carried to the right or to the left. Such cases may be secondary to an abducens paralysis.

4. A convergence excess which has lasted a long time is regularly followed by a divergence insufficiency, and a divergence insufficiency of long standing is followed by a convergence excess. The mixed form thus produced is characterized by marked esophoria (and often by homonymous diplopia) for both distance and near, excessive approximation of the convergence near point, and limited, absent, or negative prism divergence (abduction). The constant over action of the convergence seems to lead to actual over development of the interni, and the under action of the divergence to actual insufficiency of the externi, thus causing still further increase of the deviation. When the deviation becomes too great for the patient to overcome, so that binocular vision can no longer be maintained, a squint develops, which, at first intermitten, afterward becomes constant.

This conversion of an esophoria into a convergent squint is favored by the presence of any condition amblyopia of one eye anisometropia) which renders binocular vision of little value.

A convergent squint thus developed is prone to increase. But in children such a squint often diminishes and sometimes disappears, owing to the tendency that the eyes have to become divergent during the age of growth (see page 510).

The symptoms of convergent deviations are homonymous diplopia (espe¬cially in cases that are passing from the state of a heterophoria to that of a squint); unilateral amblyopia and loss of stereoscopic vision (in true squint); and asthenopia, headache, neuralgia, and nutritive disturbances in esophoria _proper (especially in divergence insufficiency).

Divergent Deviations; Exophoria and Divergent Squint.- A divergent deviation, whether a slight exophoria or a marked divergent squint, may be due to-

1. Weakness of one or both interni or over action of one or both externi, or to both these causes combined (muscular deviation). The weakness or over action may be structural, insertional, or innervational, and produces, particularly when unilateral, a more or less non comitant deviation having the following characters, indicative of a purely muscular anomaly (see pages 510 and 511).

Outward movements of one or both eyes increased or inward movements of one or both diminished, the diminution in the latter case being equally marked whether the eye turns inward in obedience to a convergence impulse or in performing an associated parallel movement with the other eye. In performing associated parallel movements the restriction of inward movement and the increase of outward movement are marked for distance as well as for near. The amount of restriction or increase usually differs for the two eyes; and the sum of the inward and outward movements, or total range of excursion, is greater in one eye than in the other, and in one eye, at least, is absolutely greater or absolutely less than normal. Degree of divergence or exophoria (as estimated from the diplopia, deviation behind the screen, parallax, and phoromieter) not materiallv different for distance and near, but changes noticeably as the eyes are carried to the right or to the left. Nearpoint of convergence often more remote from the eye than normal, but may be much farther when the object looked at is carried from one side obliquely inward toward the nose than when it is carried obliquely inward from the other side.

The determination of the specific muscle affected may be deduced (by means of the table on page 514) from the direction of the gaze in which the crossed diplopia or the exophoria increases the most.

2. Convergence insufficiency. The signs of this are-

For distance, but slight divergence or perhaps orthophoria. Prism-divergence (abduction, so called) not usually above 10’ and often subnormal (6'). Prism convergence (adduction) often performed with difficulty even after a number of trials. Associated parallel movements and total range of excursion normal or nearly so, and equal in both eyes.

For near points, exophoria of 6' and upward and divergence marked (by all tests). Convergence near point over 3" (often from 6" to 10") from the nose, and equally distant from the latter whether the object looked at is carried toward the nose from the right or from the left. Maintenance of convergence for more than a moment difficult. Eyes turn farther inward in performing associated parallel movements than in performing convergence movements (i. e. when the convergence Dear point is reached either eye can turn still farther inward, but the other eye will then diverge). Limitation of movement inward same for each eye.

In some cases the insufficiency is so great as to constitute an actual convergence paralysis (Parinaud, A. Graefe). The characteristic sign of this is that, while either eve can move inward to a normal degree, provided the other eve moves outward, it cannot move inward at all in response to an impulse of convergence. Hence, the convergence near point, instead of receding to only 6" or 7” is situated a yard or more from the eyes, and when the object looked at is brought nearer than this, insuperable crossed diplopia develops.

Owing to the intimate relation existing between accommodation and convergence, those who use their accommodation but little in looking at near points will tend to converge less than they should. Hence, convergence insufficiency occurs in myopes who wear no glasses for near, and also in hyperopes and preshyopes who wear too strong convex glasses for near. This accommodative insufficience will disappear if the myope is made to wear concave glasses for near, and if, in the other conditions, the strength of the convex glass is lessened. But a non accommodative convergence insufficiency, not corrigible in any such way, also exists.

3. Divergence excess. The signs of this are distance, exophoria or divergence marked. Often spontaneous crossed diplopia. Prism divergence (abduction) high (in pure cases disproportionately so i. e. with an exophoria of 4' or 5' there may be a prismdivergence of 130 or 15'). Prism convergence (adduction) usually normal. Associated parallel movements and range of excursion equal in both eyes and normal or nearly so.

For near points, exophoria or divergence slight. Convergence Dear point and power of maintaining convergence normal. Convergence near point same whether the object looked at is carried from the right or from the left obliquely toward the nose.

4. A convergence insufficiency which has lasted a long time is regularly followed by a divergence excess, and a divergence excess which has lasted a long time by a convergence insufficiency. The mixed form thus produced is characterized by marked exophoria (or divergent squint) and often by crossed diplopia for both distance and near, excessive prism divergence (abduction), and marked recession of the convergence near point. Here, as in esophoria, the constant over action of the divergence produces apparently an actual over development of the externi, and the under action of the convergence an actual insufficiency of the interni, thus causing still further increase of the deviation. Here also, when the deviation becomes too great for the patient to overcome, so that binocular vision can no longer be maintained, a squint develops, at first intermittent, afterward constant. As in the case of the convergent deviations, the presence of anisometropia or unilateral amblyopia favors this conversion of an exophoria into a divergent squint.

A divergent squint thus developed usually increases.

The symptoms of divergent deviations are crossed diplopia (especially in cases that are passing from the state of a heterophoria to that of a squint) ; unilateral amblyopia and loss of stereoscopic vision in cases of confirmed squint; and asthenopia and conjunctival irritation with pain in the eyes in exophoria (particularly in convergence insufficiency). Headache is less frequent and other symptoms are rather rare.

Vertical Deviations; Hyperphoria and Vertical Squint. Vertical deviations, whether superable (hyperphoria) or productive of an actual squint, are either comitant or non comitant.

1. Non comitant hyperphoria is occasioned by under action or overaction of one or more of the elevators or depressors. As in this case the deviation (determined by the vertical diplopia, deflection behind the screen, parallax, and photometer) varies noticeably in different directions of the gaze, the diagnosis of the specific muscle affected can readily be made from the table on page 514. In a number of these cases the hyperphoria is apparently due to spasmodic action of the muscles, since it changes in amount from one examination to another, and after a time disappears altogether.

2. In a comitant hyperphoria the deviation (determined by the diplopia, deflection behind the screen, parallax, and photometer) remains sensibly the same in all directions of the gaze. Some of these cases may be due to a vertical separation of the visual axes, due to excessive sursumvergence, but most are probably examples of a non comitant hyperphoria which has become comitant through the agencies already described (see pages 508, 513). In this case the diagnosis of the muscle affected is usually no longer possible.

The deviation is often slight (only I' or 20). When slight it can be overcome by the action of sursumvergence. In well marked cases it will genet ally be found that there is a difference of I' or more between the right and left sursumvergence, the former predominating in right hyperphoria and the latter in left hyperphoria.

Hyperphoria does not, in general, show any great tendency to increase, and cases of actual vertical squint i. e. of a vertical deviation so great that binocular fixation can no longer be performed, and but one eye fixes are rare. Such a squint is called a strabismus sursumvergens if the deviating eye stands higher, and strabismas deorsumvergens if it stands lower, than the one which regularly performs fixation.

The symptoms of vertical deviations are vertical diplopia, blurring of binocular vision, asthenopia, headache, neuralgia, nausea, vertigo, disturbance of nutrition, choreiform twitchings, and other evidences of reflex trouble. The symptoms in general are more frequently present, more varied in character, and more severe in' this form of ocular deviation than in any other.

Associated Parallel Deviations. Associated parallel deviations comprise

1. Associated Paralysis and Spasm. Paralysis of the movements of both eyes to the right or of both eyes to the left frequently occurs in destructive lesions of the brain, and especially in apoplexy. This condition is not due to paralysis of the externals of one eye and the interring of the other, since the internus may still act in movements of convergence, but it is due to the involvement of the higher (association) center governing the movement of both eyes to the right or to the left (dextroversion and sinistroversion). Paralysis of the movements of both eyes up and of both eyes down has also been observed, but is rare.

Spasm of the associated parallel movements occurs in irritative lesions of the brain involving the association centers or tracts, and also in hysteria. It produces a spastic deviation of both eyes in the same direction (right, left, up, down, or obliquely).

2. Nystagmus. Nystagmus consists in a very rapid oscillating movement of the eye in some one direction. Almost invariably both eyes take part in the movement, the oscillations of the two being equal and in the same sense. According to the direction of the movement nystagmus is called horizontal, vertical, rotary (when both eyes roll like wheels in the same direction), or mixed (when oscillations of two different kinds are combined). Horizontal nystagmus, is much the most frequent form.

Nystagmus is due to alternate discharges from the association centers for parallel movements. For example, in horizontal nystagmus there is first a discharge from the center for turning both eyes to the right (dextroversion center), followed at once by a discharge from the center for turning the eyes to the left (sinistroversion center). In those who are subject to it is often set up by the attempt to fix the eyes on an object or to turn them in some special direction. It occurs
(a) As a result of visual defects (such as cataract, opacities of the cornea, diseases of the retina and choroid, and albinism), which, being either congenital or acquired SOOD after birth, have prevented the patient from ever seeing well or from learning to direct his eyes properly.
(b) As a late acquired affection in disseminated sclerosis, in hereditary ataxia, and in hemorrhage, degeneration, inflammation, and tumors of the meninges, cord, and brain (especially the cerebellum). A special acquired form occurs in miners (miner's nystagmus), who work by a bad light and with their eyes in a strained position. Nystagmus may also be produced by a rapid rotation of the body or any other cause affecting the functions of the semicircular canals (auditory disease).'

In some of the forms acquired late in life, particularly miner's nystagmus, the oscillation of the eyes produces an apparent movement of objects looked at, with consequent vertigo. Otherwise the disease causes no symptoms.

Nystagmus occasionally disappears spontaneously or as a result of the removal of the optical defect that caused it; and miner's nystagmus may disappear on removal of the patient from the hurtful conditions under which he lives. Otherwise the condition is not susceptible of amelioration.

Treatment of Ocular Deviations. The first indication to be fulfilled where possible is 1, to remove the cause of the deviation. Hence in paralysis or spasm due to syphilis, meningitis, periostitis, and exudative processes in general we use iodids and mercurials; in rheumatic paralyses we employ the iodids, salicylates, and diaphoresis; in diabetic paralyses, the appropriate diet; and in miner's nystagmus we remove the patient from his hurtful surroundings.

2. The next indication to be fulfilled in all cases causing symptoms is to correct the refraction. Such correction will in many cases (e. g. those of accommodative convergence excess and insufficiency) remove the deviation itself; in others, while having no effect upon the deviation, it will do away with the s mptoms. In esophoria (particularly in convergence excess) the y total amount of hyperopia and astigmatism (determined Under a mydriatic) should be prescribed and the glasses worn, constantly. In exophoria (particularly convergence insufficiency) the myopia present should be fully corrected, and the concave glasses worn for near as well as for distance. On the other hand, it is often proper to more or less under correct hyperopia or presbyopia coexisting with convergence insufficiency.

In ophthalmoplegia interna it is often necessary to prescribe a convex glass for the affected eye to supplement its lost accommodation.

3. Exercise, tonics, and other corroborant measures are frequently required in debilitating affections, neurasthenia and hysteria, which by causing a temporary enfeeblement of the muscles either produce a deviation directly or, in case one is already present, interfere with its proper compensation.

4. The bromids may be of use in certain cases of spasm. Other remedies, such as strychnin, electricity, etc., which are supposed to act directly upon the muscles or nerves, are of little value, except in so far as they improve the general nutrition. The same may be said with even more force of electricity and eserin in ophthalmoplegia interna.

5. Exercise of the prism convergence (so called adduction) with prism, base out, is often useful in exophoria (particularly convergence in sufficiency), but often fails. Exercise with prisms, base in, in esophoria is of' no service.

Prisms for continuous wear may be useful, particularly in slight and stationary vertical deviations. Their employment in lateral deviations is to be avoided, except as a temporary measure, since prisms, base in, tend to produce con vergence insufficiency, and prisms, base out, a convergence excess, so that in both cases they ultimately increase the deviation which they are designed to correct.

6. The muscles may be exercised, not only by means of prisms, but also by making forced movements of the eyes in different directions, UP, down, right, and left; by making forced movements of convergence in looking at near objects; by forcing the eyes to overcome a natural diplopia of small amount; and by forcing the eyes to move so as to unite the images of two objects which are some distance apart. These orthoptic exercises, as they are called, should not be kept up for more than a few minutes at a time, but ma be repeated several times a day.

7. An operation is to be done only when the symptoms are marked and when it is apparent that all other measures will fail. In structural and insertional muscular anomalies an operation is generally indicated, and does good service. In paretic and spastic deviations it is indicated only when we are assured that the condition has become stationary. In convergence and divergence anomalies it is usually indicated when the deviation is marked and when correction of the refraction after long trial has afforded no relief. In all cases the rule is to perform tenotomy of an over acting muscle and advancement of one that is under acting, provided always that the latter is capable of acting at all. The specific operations to be employed are

(a) In esophoria (or convergent squint), when due to over action of one or both interni or to convergence excess, tenotomy of one or both interni ; when due to weakness of the externi or to divergence insufficiency, advancement of one or both externi combined, especially if there is overaction of convergence or over action of the interni, with tenotomy of the latter.

(b) In exophoria, when due to over action of one or both externi or to divergence excess, tenotomy of the externi; when due to convergence insufficiency or to actual insufficiency or paresis of one or both interni, advancement of the latter, combined, if necessary, with tenotomy of the externi.

(c) In non comitant hyperphoria, when due to weakness of the superior or inferior rectus, advancement of the weak muscle; when due to over action of the superior or inferior rectus, tenotomy of the over acting muscle; when due to weakness ( ' paresis) of the superior oblique, tenotomy of the inferior rectus of the other eye; when due to over action of the superior oblique, advancement of the inferior rectus of the other eve; when due to weakness of the inferior oblique, tenotomy of the superior rectus of the other eye; and when due to over action of* the inferior oblique, advancement of the superior rectus of the other eye. A comitant hyperphoria is generally best remedied by tenotomy of the superior rectus of the higher eye.

In performing either a tenotomy or advancement the precise amount of the deviation should be measured (when possible by the phorometer) before and during the operation, the latter being done in successive steps, and its effect gradually increased until just the desired amount of correction is obtained. As the ultimate effect is somewhat less than the primary, it is advisable in operations upon the lateral muscles' (especially advancements) to produce an over effect of about 30.' An exception is in the convergent squint of young persons, in which we prefer to leave a slight amount of convergence, so as to prevent a possible over correction later, and in large deviations, in which the best plan is to divide the operation between the two eyes.

In the author's experience the best results are secured if the tenotomy is performed by the open method, the incision being made in the middle of the tendon, near its insertion, and carried gradually up and down until the tests show that the fibers are sufficiently detached. A bandage is not applied in the case of a simple tenotomy, and the patient is encouraged to use his eyes for distant vision directly after the operation, for then the directive influence of binocular fixation, exerted upon the tissues when they are still plastic, tends to make the eyes assume their proper position with regard to each other.' In advancement a bandage is required to prevent sudden movements of the eye, which would produce loosening of the sutures.

If an excessive over correction is produced, the surplus should be at once removed by inserting a suture and making the proper traction.

Back to Resources