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"
(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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