strabismus(redirected from tropia)
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strabismus(strəbĭz`məs), inability of the eyes to focus together because of an imbalance in the muscles that control eyeeye,
organ of vision and light perception. In humans the eye is of the camera type, with an iris diaphragm and variable focusing, or accommodation. Other types of eye are the simple eye, found in many invertebrates, and the compound eye, found in insects and many other
..... Click the link for more information. movement; also called squint. It is a consequence of weakness or uneven development of one or more of the six small muscles that surround the eye. One or both eyes may be affected. Horizontal strabismus is caused when the eyes do not move together laterally; this condition is known as cross-eye if the eye turns inward or walleye if the eye turns outward. Vertical strabismus results when the eye rolls upward or downward in its socket. There is also torsional strabismus in which the eyes do not rotate together about their optical axes. Strabismus is usually present at birth and becomes apparent early in infancy, but it may also result from illness or injury. Because the condition results in perception of a double image, there is a tendency to use only one eye. It is important that treatment be started as soon as possible to prevent loss of sight in the unused eye. Corrective therapy includes exercise that strengthens eye muscles and prescription of corrective lenses. Sometimes a patch is placed alternately on each eye so that neither is allowed to become completely unused. If necessary, the eye muscles may be shortened or lengthened surgically.
deviation of the visual axis of one of the eyes from the common point of fixation, leading to a loss of binocular vision. Two types are distinguished: concomitant and paralytic strabismus.
Concomitant strabismus, in which the deviating eye always follows the movement of the other eye and the angle of divergence of their visual axes remains constant, is observed predominantly in children (up to 2 percent). Its causes have not been conclusively elucidated. Strabismus may be accommodative, owing to anomalies of refraction and disturbances of eye accommodation, or nonaccommodative. Accommodative strabismus disappears upon administration of drops of atropine in the eye and use of corrective lenses: nonaccommodative strabismus is distinguished by extreme persistence. Strabismus may be constant or periodic, unilateral (when only one eye deviates) or alternating, and convergent (when the deviating eye moves toward the nose) or divergent (when the deviating eye moves toward the temple); the eye may simultaneously deviate upward or downward as well.
In approximately half the cases of concomitant strabismus some decrease in acuity of vision is noted in the deviating eye. The treatment of nonaccommodative strabismus is manifold, employing both various exercises for the eyes on special instruments (synoptophores, amblyoscopes) and operations directed toward weakening the stronger eye muscle or strengthening its antagonist.
Paralytic strabismus originates with paralysis of the oculomotor muscles as a result of disease of the central nervous system (infection, hemorrhage). It is characterized by limited mobility of the paralyzed eye, double images, and a different deflection angle of either eye. Treatment is directed at the disease causing the strabismus; sometimes vision can be restored by special operations on the eye muscles.
REFERENCEMnogotomnoe rukovodstvo po glaznym bolezniam, vol. 3, book 1. Moscow, 1962. Pages 237–355.
M. L. KRASNOV