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Muscle Imbalances

DESCRIPTION: Strabismus is a term used to describe defects of the eye muscle system. It includes "phorias" (tendencies, or latent muscle imbalances which are controlled by the brain's efforts toward binocular vision) and "tropias"Muscle Imbalances graphic (observable deviations which the brain cannot resolve). Esotropia is the deviation of one eye toward the nose. Exotropia is the deviation of one eye toward the temporal side of the face. Hypertropia is the deviation of one eye upward. Deviations downward are very rare. Deviations may occur with either eye, alternately (e.g., alternating esotropia or alternating exotropia) or may be monocular (always the same eye). Esotropia is the most common defect, is often present at birth, but may appear as late as 4 years of age if due to accommodation; exotropia is less common in infancy and childhood and is usually intermittent. Hypertropia is the least common; and is often compensated for by head tilting. Strabismus is commonly an inherited defect (autosomal dominant) but may also be caused by paresis or secondary to other body defects.

TREATMENT: The goals of correcting strabismus are: good acuity in both eyes, good cosmetic appearance, and binocular vision. Occlusion ("patching") of the good eye forces the deviating eye to develop acuity, and should be initiated as early as possible. It is most effective before age 1, and becomes more difficult by age 5; it is ineffective beyond age 7. Early diagnosis and occlusion are the best first steps in preventing amblyopia. When no further improvement of acuity can be accomplished by patching, surgical realignment of the eye muscles is indicated (occlusion does not straighten the eyes, only improves acuity). Surgery repositions eye muscles through recession (repositioning a muscle to make it "longer") or resection (essentially "shortening" a muscle). Strabismus surgery is rarely precise; more than one opinion may be needed to achieve optimal results. Orthoptics (eye exercises) are sometimes prescribed before or after strabismus surgery, to help improve fusion; an amblyoscope may be used to measure fusion as well as to induce it.

IMPLICATIONS: Since the muscles of the eyes are responsible for coordinated movements and binocular vision, strabismus should be identified and treated as early as possible. The younger a child is, the better the prognosis. Strabismus is never "outgrown" and vision may be permanently lost if strabismus is left untreated. (see Amblyopia)

School vision screening usually happens too late to help most children with strabismus. Preschool vision screening is highly desirable. Alert parents and/or pediatricians can also recognize strabismus and should follow-up with a professional eye examination.

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