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In some children sight does not continue to develop
properly in one eye even though that eye is structurally normal. The
condition is called amblyopia (am-blee-oh-pee-uh) or “lazy
eye,” because the eye seems to have lost the desire to see.
What Causes Lazy Eye?
Each eye sends a slightly different visual image to
the brain. Normally, the images are similar enough to allow them to be
combines into a single image by the brain. If the two images are too
different from one another, the brain cannot combine them and the
result is double vision. Young children are able to avoid double
vision by suppressing (actively ignoring) the image from one
eye. Eventually the eye that suppresses images loses its ability to
see clearly.
Why are there two images?
The most common conditions that can cause the eyes
to send different visual images to the brain are strabismus
(misaligned eyes; one looks straight ahead while the other turns in,
out, up or down) and anisometropia (ann-eye-so-meh-troh-pee-uh)
which means that the two eyes have very different optical powers (for
example, one may be normal and the other very farsighted or have
extreme astigmatism).
Even if you can tell that your child has one of
these conditions along with poor vision, you still have no way, on
your own, of knowing whether one eye is “lazy”.
Treatment and Prognosis
Treatment must begin before school age to give the
amblyopic eye the best chance of regaining normal vision. After the
age on nine, the possibility of reversal is passed and amblyopia will
remain for life.
If the cause of the lazy eye is an optical one, it
will be treated first. Prescription eyeglasses may be necessary
(eyeglasses can be worn by infants as young as a few months old).
Although vision may improve somewhat with the glasses, it will
continue to be poorer than in the normal eye.
If the eyes are misaligned, surgery may be
necessary to straighten them. Surgical success is enhanced when the
vision in both eyes is normal so surgery will be delayed until the
amblyopia has been treated.
One the basic cause of amblyopia has been
identified and treated, a vigorous program of “patching” (covering the
good eye is necessary so that the child will use the amblyopic eye. It
will take a lot of urging and patience since you will be forcing the
child to use and eye that sees poorly. (The patching does not correct
any eye misalignment or eliminate the need for prescription eye
glasses.) When the patch is on the “good straight” eye, the amblyopic
eye straightens to the normal position for focusing. Most parents do
not realize that the “good” eye under the patch then deviates. Also,
penalization with dilating drops to blur the image in the better eye
can be used in some patients.
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