CHAPTER V DEVIATIONS OF THE EYEBALL (Part 2)

we may possibly succeed in getting these images to blend and in establishing binocular single vision. It appears also that the sooner such an attempt is made after the eye starts to turn, i.e., the younger the child, the more likely we are to obtain such a result. Yet it is not certain that this power is not in abeyance sometimes in convergent strabismus, it seems to vary much in strength, and its absence does not always cause an eye to deviate. It seems probable that the two main factors in the production of the great majority of cases of convergent strabismus are absence of binocular single vision and hypermetropia, either combined or not with astigmatism, and that these always are reinforced by other fac- tors which may be held to play subordinate parts, as a rule, although in isolated cases each one of them may be paramount. Causes of Divergent Strabismus The actuating causes of divergent strabismus are not thoroughly understood, but they appear to be mechanical. The condition usu- ally appears in children about the age of ten or twelve. As a rule, we are unable to learn whether binocular single vision existed or not before one eye began to diverge, but occasionally a prior examina- tion has demonstrated its presence, perhaps that it was weak or im- perfect, and usually that the visual axes tended to diverge when the eyes were at rest, technically that the patient had exophoria. Even when binocular single vision is absent divergence does not develop until some other factor acts, and it is questionable whether it de- velops at all when this power is perfectly developed, but when the power is weak certain mechanical conditions appear to transform the exophoria into an exotropia. The most common actuating factor is a preponderance of the action of the external rectus over that of the internal. When the external rectus is too short the strabismus appears at an earlier age and the rotation of the eye inward is im- peded. The action of the external is favored over that of the in- ternal rectus by a great divergence of the axes of the orbits, and by an elongated eyeball, conditions which are apt to be present in myopia, from which the majority of these patients suffer. We may suppose also that as the demands upon the accommodation and convergence 86 DIAGNOSIS FROM OCULAR SYMPTOMS are less than normal in myopia, the internal rectus loses its strength in comparison with its opponent, which has its usual duties to per- form. Sometimes the external rectus is found to be disproportion- ately thick and strong, and it frequently happens that this muscle seems to increase in relative strength as age advances, so that an eye which converged in a child may be seen to diverge in adult life, and when the sight of an adult’s eye is impaired too much to be of use any longer divergent strabismus is apt to appear. Observations to be Made in Strabismus After noting the age of the patient, whether the strabismus is constant, intermittent, or alternating, we should measure the degree of the deviation before doing anything else. Then we should deter- mine the vision and refraction of each eye, ascertain the degree of any amblyopia that may be present, learn whether binocular single vision is frankly present, and if not try to elicit a perception of an object by both eyes at the same time, and then see if the images can be made to fuse. The greatest deviations of the eyes are to be seen in convergent strabismus, those of the divergent form are less on the average, while those of the vertical are slight. Ordinarily we perceive strabismus from the relative position of each cornea, iris, or pupil to the median vertical plane of the face, or to the horizontal plane, and we may learn by practice to estimate roughly its degree from these relative positions, or by having the patient fix on one of our fingers held at first in front of our own eye and then moved outward until the squinting eye seems to look straight into ours, but such methods depend wholly on the judgment of the examiner and are not accurate. Priestley Smith's tape measure test is a modification of the latter in the interest of accuracy, which it ap- proximates, but does not attain perfectly. An exact distance is maintained by means of a tape one meter long, one end of which is held by the patient just beneath his eye, while the other end is at- tached to a ring which is slipped over a finger of the hand of the examiner that holds an ophthalmoscope with which he reflects light into the patient’s deviating eye. Another tape marked off in de- grees is attached to the same ring and is carried over a finger of the examiner’s other hand upon which the patient fixes while it is moved outward until the reflex from the light thrown by the ophthal- moscope appears on the center of the cornea of the squinting eye. DEVIATIONS OF THE EYES 87 The number on the tape at which the moving finger stops gives the degree of strabismus. Another simple, though not absolutely accurate method is to meas- ure the degree with the aid of the strabismometer. The good eye is covered, the squinting one made to fix on a distant object, the instrument is placed on its lower lid so that zero is exactly beneath the center of the pupil, the good eye then is uncovered and caused to fix on the same object, when the degree of deviation can be read off the instrument. The same result is obtained if we make a mark on the lower lid below the center of the pupil or one edge of the cornea, in each of these positions and measure the distance between them in millimeters. One great advantage of both the tape measure and the strabismometer tests is that they can be used even with very young children. With older and intelligent patients a much more accurate meas- urement can be obtained with a perimeter and a small electric light. The patient fixes the central spot of the instrument while the ex- aminer passes the light, together with his own eye, along the arc until the light reflex appears on the center of the cornea of the squinting eye; the perimetric reading gives the angle of strabismus plus or minus the angle y, which remains to be determined. The good eye is covered and the squinting one fixed on the central spot, close to which the light is brought. If the light reflex is on the center of the cornea when the light and the central spot coincide, there is no angle y; if it is not we move the light to the right or left until the reflex is central and determine the angle from the de- gree of the are on which it rests. If it is to the temporal side of the eye the angle y is positive and its degree is to be added to that of the strabismus already obtained; if it is to the nasal side it is nega- tive and must be subtracted. A prism test is possible only when binocular vision is present. A red glass is placed before one eye and, when diplopia is main- tained, one prism after another is slipped into place with their bases in the direction opposite to that of the squint until one is found with which the images are fused, or exactly superimposed; one half of the degree of this prism is the degree of the angle of strabismus. This test is of particular value in a few cases in which the angle y is so large that a strabismus is counterfeited. A case in point is that of a man who desired to have an operation performed to correct a slight deviation of his eyes which really constituted somewhat of a 88 DIAGNOSIS FROM OCULAR SYMPTOMS deformity, but this test revealed that he had binocular single vision, orthophoria, and that his angle y was unusually large. MUSCULAR PARESIS A patient with paresis of one or more of the extrinsic muscles of the eye has a secondary deviation that is much greater than the primary, impairment of motility in the direction of the affected muscle or muscles, diplopia with vertigo and faulty orientation if the paresis is recent, and sometimes an abnormal position of the head. The paresis may be due to disease of the muscular tissue itself, to a lesion in the orbit, or to one that compromises the nerve supply anywhere along the course of the nerve, or in the brain. It may vary from extremely slight, when there is no apparent deviation, to total paralysis, and may affect a single muscle, a group, or all of them. When the paresis is very slight the only symptom may be diplopia when the eyes are turned far toward the limit of the binocular field of fixation in the direction in which the affected muscle is called most strongly into action. In such a case we need to learn which muscle is at fault. If the patient sees double only when he looks far to the left we know that either the right internal rectus, or the left external rectus is acting badly, as they are the two muscles which take part in this movement of the eyes. To ascertain which of the two is affected we place a red glass before one eye and have him look at a light placed far to the left, when he will see one red and one white light. If the red glass is in front of his right eye and the red light is to the left of the other the diplopia is crossed, the eyes diverge, and therefore the right internal rectus is paretic, but if the red is to the right of the white light the diplopia is homony- mous, the eyes converge, and therefore the left external rectus is too weak to perform its duty completely. We must be on our guard against a hysterical diplopia of this nature that is met with occa- sionally. A lady exhibited diplopia at the extreme right of the field, and had been operated on several times for heterophoria. She was known to be suffering from hysteria, and finally this was demon- strated to be the origin of her muscular troubles by obtaining diplo- pia at the extreme right, then slowly carrying the light upward and then across the upper limit of the field to the extreme left while the diplopia was maintained throughout without change, a phe- DEVIATIONS OF THE EYES 89 nomenon that could be accounted for by no possible combination of muscular defects. When a patient complains of diplopia, vertigo, and an inability to determine which of the two images he sees is the true one, or carries his head twisted to one side to do away with these annoyances, we have to note whether one eye deviates in any direc- tion when his head is in its normal position, whether the diplopia is crossed or homonymous, in which eye and in what direction the sec- ondary deviation appears, and the position of the head when this is abnormal. If we know the actions of the individual muscles, singly and combined, we can deduce from these symptoms which one or ones are affected, but it is of little use to try to memorize the al- most numberless combinations that may take place. If the patient holds his head erect, but turned to one side, and has diplopia when he looks straight forward with his head in its normal position, either the external rectus of the eye on the side toward which the head is turned, or the internal rectus of the other, must be paretic, because these two muscles are relieved greatly from duty in that position of the head, and we know the condition to be paresis rather than paralysis because the function of the muscle is not abolished. To determine which muscle is at fault we use the same test as when the paresis is so slight that diplopia appears only when the eyes are turned to the extreme limit of the field, except that we place the light directly in front of him. If the red glass shows that the diplopia is homonymous the internal rectus is paretic, if the diplopia is crossed the external rectus is too weak. We con- firm the results of this test by covering the eyes alternately and ob- serving the deviation and the movement of adjustment to fix the light as these appear in each; the sound eye has the greater or secondary deviation and makes the longer excursion in order to fix, as has been explained. Thus we learn which eye, and whether its external or its internal rectus, is affected, even when the paresis is so slight that the deviation can scarcely be seen and the patient is able to secure binocular single fixation by a simple rotation of the head. When the paresis is more marked, and when paralysis is present, the eye deviates away plainly from the affected muscle, its move- ment toward it is restricted when it tries to follow a moving object, the secondary deviation of the sound eye is enormous, and the diag- nosis is easy. 90 DIAGNOSIS FROM OCULAR SYMPTOMS When a patient inclines his head on one shoulder, lowers his chin and rotates it toward the same side, taking the position of torticollis, we should think of a possible paralysis or paresis of either the su- perior oblique of the eye on the opposite side from that to which the head inclines, or the inferior rectus of the other. Such a condi- tion certainly is present if the patient has vertical diplopia when the head is held erect. One of the two images is tilted and the vertical distance between them increases as he looks down. The diplopia in paralysis of the superior oblique is slightly homonymous, that in paralysis of the inferior rectus is slightly crossed, and in both the upper end of the lower image tilts toward the upper, so the pictures produced by these two conditions resemble each other closely. The differentiation is made through observation of the secondary devia- tion, which takes place in the sound eye and leaves the diagnosis made by exclusion. Whether the paresis is sufficient or not to cause the patient to assume the extreme degree of torticollis, we have to con- sider the exact direction of the secondary deviation, which is down- ward and slightly outward in paresis of the inferior rectus, down- ward and slightly inward in paresis of the superior oblique, and the limitations of movement, which are most marked downward and inward in the former, downward and outward in the latter. When a patient goes about with his chin raised and his head tilted a little to one side in order to avoid a vertical diplopia in which the upper image is tilted, its upper end leaning away from the other, he has a paralysis or paresis of either a superior rectus or an inferior oblique. Crossed diplopia points to the rectus, homony- mous to the oblique, but it is crossed sometimes in paresis of the latter, perhaps because a latent exophoria has been made manifest. We exclude one eye by observation of the secondary deviation, which is always in the good one, and differentiate between the two muscles by noticing the excursions of the other. If it lags behind when the patient looks up, up and in, and especially up and out, the superior rectus is at fault, while if the eye rises freely up and out, but lags badly when it tries to move up and in, the inferior oblique is paretic. The following table, copied from Duane, is of great assistance in locating the affected muscle in cases of slight paresis as soon as we have become sufficiently familiar with the abbreviations, so that their interpretation does not entail too great a mental effort. The abbre- viations mean :— DEVIATIONS OF THE EYES 91 E, eyes; R, turned to the right; L, turned to the left; u, turned up; d, turned down; DH, homonymous diplopia; DX, crossed diplopia; DR, Vertical diplopia with the image belonging to the right eye below; DL, Vertical diplopia with the image belonging to the left eye below; > greatly, increasing progressively and fast. Thus the abbreviation Ku & r DL > greatly means a vertical diplo- pia with the image belonging to the left eye below which increases progressively and fast when the eyes are turned up and to the right, literally eyes up and right, diplopia left increasing. DIPLOPIA PARESIS OF Er. DH > greatly Er. DX > greatly El. DH > greatly El. DX > greatly Eu & r. DL > greatly Eu & r. DR > greatly Eu & |. DR > greatly Eu & |. DL > greatly Ed & r. DR > greatly Ed & r. DL > greatly . DR > greatly . DL > greatly right external rectus left internal rectus left external rectus right internal rectus right superior rectus left inferior oblique left superior rectus right inferior oblique right inferior rectus left superior oblique right superior oblique left inferior rectus When all of the muscles supplied by the third nerve are paralyzed we first notice ptosis. After we lift the lid we see that the eye is drawn outward and a little downward by the unaffected externus and superior oblique, that there is a slight degree of exophthalmos, that the pupil is dilated, and that it does not react to light. The power of accommodation is lost and the diagnosis is made quickly and easily. When the same picture is presented except that the eye looks