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J.A. Movshon, S.P. McKee, D.M. Levi; The Pattern of Visual Deficits in Amblyopia . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3182.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose Amblyopia is usually defined as a deficit in optotype (Snellen) acuity without a detectable organic cause. But 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? Methods 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. Results Measurements of optotype acuity capture much of the variance in the other functional measurements of acuity, and somewhat less of the variance in measures of contrast sensitivity. Factor analysis reveals two main dimensions of variation in visual performance in observers with abnormal vision, 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 the two in combination. However, the pattern of loss does not depend on the presumed etiology, but rather on whether an 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. Moreover, some non-binocular observers have supernormal sensitivity in their non-preferred eyes, even if their acuity is below normal. We attribute this superiority to the reorganization of afferent connections to visual cortex. 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. This pattern is similar to that reported to differentiate strabismics and anisometropes in previous studies of smaller groups of amblyopes. We attribute the "pattern acuity" deficits in non-binocular observers to functional losses in cortical areas downstream of V1. Conclusions Our results show that there are distinctive and systematic variations in the pattern of functional loss in amblyopia. We suggest that two distinct developmental processes determine the differences among different types of amblyopes.
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