Preventing Amblyopia
One definition of amblyopia is impairment of vision without detectable organic lesion of the eye. Amblyopia ex anopsia is visual impairment resulting from long disuse, as with strabismus. Sometimes called lazy eye, the causes of amblyopia include:
Strabismus causes disuse atrophy because one eye becomes preferred and the other is relatively unused. This also occurs with unequal refractive errors in the right and left eyes (at least two lines different on the vision screening chart, e.g. OD 20/20; OS 20/50).
The remaining causes of amblyopia directly block the beam of light entering the eye, therefore, little or no image reaches the retina (cataract, etc.). Normal visual input is critical while the visual (occipital) cortex of the brain is developing. The first four months of life are the most critical, but any child under ten years of age can develop disuse vision problems. Interestingly, bilateral deprivation has much less effect on cortical cells than unilateral visual deprivation.
Prevention of amblyopia which results in permanent visual impairment depends on early recognition and referral to a pediatric ophthalmologist. Surgery is indicated for many of the conditions. Eye patching is usually done prior to surgical correction of strabismus (to force use of the weak eye, the preferred eye is patched).
(Bacal D. Dont be lazy about looking for amblyopia. Contemp Pediatr 1998; 15(6):99-107)
COMMENT: School nurses do an excellent job of identifying potential vision problems. The most difficult etiology of amblyopia to identify is a subtle alterating strabismus (requiring use of the cover-uncover and the alternating cover tests).