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Suzanne P. McKee; The pattern of visual functions in human amblyopia. Journal of Vision 2005;5(12):40. https://doi.org/10.1167/5.12.40.
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Amblyopia is usually defined as a deficit in optotype (Snellen) acuity without a detectable organic cause. Is amblyopia completely characterized by the deficit in optotype acuity, or does it have distinct forms that are determined by the conditions associated with the acuity loss, such as strabismus or anisometropia? To answer these questions, we measured optotype acuity, Vernier acuity, grating acuity, contrast sensitivity, and binocular function in 427 adults with amblyopia or with risk factors for amblyopia, and in a comparison group of 68 normal observers. Our results showed that there are distinctive patterns of functional loss in amblyopia. Factor analysis revealed two main dimensions of variation in visual performance, one related to visual acuity and one related to visual sensitivity. These dimensions separate three broad groups of abnormal observers, similar to the those traditionally associated with strabismus, anisometropia, or strabismus-anisometropia. However, the pattern of loss does not depend on presumed etiology, but rather on whether the abnormal observer retains binocular function in the central visual field. Non-binocular observers with mild-to-moderate acuity deficits have better monocular contrast sensitivity than do binocular observers with the same acuity loss. Surprisingly, some non-binocular observers have supernormal sensitivity in their non-preferred eye. Despite their superior contrast sensitivity, non-binocular observers typically have poorer optotype acuity and Vernier acuity, at a given level of grating acuity, than those with residual binocular function. Our results confirm earlier findings of differences between strabismic and anisometropic amblyopes and suggest that two consequences of the associated conditions, namely reduced visual resolution and the loss of binocular vision, determine the differences among amblyopic categories.
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