STRABISMUS (Neo-Lat., from Gk. argaika p6c, a squinting, from argailgc, strabos, crooked, from arpiotiv, strephein, to twist, turn about), or SQUINT. A well-known and common deformity which may be defined as a want of parallelism in the visual axes when the patient endeavors to direct both eyes to an object at the same time. The eye which is directed toward the object looked at is called the fixing eye, the other the squinting eye. The squint is said to be con vergent when the eye or eyes are directed toward the nose, divergent when they are directed toward the temple, and vertical when directed upward or downward. The last is often associated with con vergent squint. The divergent form is compara tively rare, and occurs most often with myopia.
Squint is of two kinds: (1) paralytic, and (2) concomitant. Paralytic squint is caused by paralysis of one or more of the ocular muscles. There is inability to move the affected eyeball away from the side toward which it is directed. When both eyes are turned toward the side to which the squinting eye is directed, the squint disappears. The head is held in a characteristic position in every variety of paralysis of the muscles of the eyeball, an attempt of nature to compensate for the squint by turning the head in such a direction that the squinting eye is directed toward objects in front of the body. There is diplopia, double vision, unless the squinting eye is the one fixed on the object. By the position of the double image, it is possible to determine which muscle is affected. The eye involved is often closed in order to avoid the second image, which is confusing in walking.
For example, a person with paralysis of the su perior oblique muscle while descending stairs sees two steps instead of one, and is often led to attempt to reach the false image, with ,disas trous results. The paralysis may be due to a lesion at any point between the cerebral cortex and the muscle. Syphilis is the most common cause; others are cold, rheumatism, and acute infectious disease. The treatment is that of the cause, exercise of the muscles. the use of prisms to relieve the diplopia, and operation as in con comitant squint if necessary. In concomitant squint there is the same deviation of the eyes in every position. and both eyes possess a normal range of movement. Squint may be alternating, in which the patient fixes with either eye; fixed ; or unilateral, in which the squint is confined to one eye; in regard to permanency it may lie con stant or periodic. In concomitant squint there is rarely double vision, one image being disre garded. 'Uncorrected errors of refraction, con genital feebleness of vision, opacities of the cornea or media, or other disease of the eye, combined with weakness of a muscle, leads to concomitant squint. for, as the sight in one eye is imperfect, there is little inducement to make the mpscular effort to keep the two parallel. The treatment includes correction of errors of refraction by glasses, exercise of the muscles by prisms, and operative methods. The last may lie division of the short tendon or advancement of that of the opposing muscle, or a combination of these procedures.