The pattern of visual deficits in amblyopia

Abstract

Amblyopia is usually defined as a deficit in optotype (Snellen) acuity with no detectable organic cause. We asked whether this visual abnormality is completely characterized by the deficit in optotype acuity, or whether it has distinct forms that are determined by the conditions associated with the acuity loss, such as strabismus or anisometropia. To decide this issue, 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. Optotype acuity accounts for much of the variance in Vernier and grating acuity, and somewhat less of the variance in contrast sensitivity. Nevertheless, there are differences in the patterns of visual loss among the clinically defined categories, particularly between strabismic and anisometropic categories. We used factor analysis to create a succinct representation of our measurement space. This analysis revealed two main dimensions of variation in the visual performance of our abnormal sample, one related to the visual acuity measures (optotype, Vernier, and grating acuity) and the other related to the contrast sensitivity measures (Pelli-Robson and edge contrast sensitivity). Representing our data in this space reveals distinctive distributions of visual loss for different patient categories, and suggests that two consequences of the associated conditions--reduced resolution and loss of binocularity--determine the pattern of visual deficit. Non-binocular observers with mild-to-moderate acuity deficits have, on average, better monocular contrast sensitivity than do binocular observers with the same acuity loss. 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.

Spatial Resolution for Feature Binding Is Impaired in Peripheral and Amblyopic Vision

“…tions (P Ͼ 0.05), and each factor significant at P Ͻ 0.02; ANOVA between amblyopic eyes and dominant eyes in amblyopic observers gives P ϭ 0.02 for interaction eye task with no other significant interactions (P Ͼ 0.05), and each factor significant at P Ͻ 0.03]. Interestingly, JS was our only amblyopic observer with residual stereovision, and previous studies have reported that amblyopes with residual stereo-competence often show transfer of the deficit in their amblyopic eye to the dominant eye (Ho et al 2005;McKee et al 2003). Our results are consistent with these previous reports in that JS is the only subject that shows conjunction impairment in both eyes.…”

“…The earliest physiological effects of amblyopia are seen in V1 (Kiorpes and McKee 1999;McKee et al 2003), and they generally occur before foveal specialization in the retina is complete at ϳ4 yr of age (Youdelis and Hendrickson 1986). Interestingly, the peripheral retina appears to develop much more rapidly than the fovea.…”

Relationship Between Anisometropia, Patient Age, and the Development of Amblyopia

“…59 The observation that anisometropic amblyopia is associated primarily with loss of high spatial frequency contrast sensitivity, with resultant defects in steroacuity and summation, has also been demonstrated by other investigators. 56,60,61 The high spatial frequency contrast sensitivity defects in anisometropic amblyopes are important clinically. Friendly and colleagues 62 tested the visual acuity of 32 orthotropic anisometropic amblyopic children using Teller visual acuity tests and compared them to the results of acuity testing using Bailey-Lovie-Ferris charts.…”

Improving the performance of the amblyopic visual system

“…dense unilateral cataract results in severe loss), and to the age at which the amblyogenic factor occurred. Precisely how these factors interact is as yet unknown, but it is evident that different early visual experiences result in different functional losses in amblyopia (Mckee et al 2003), and a significant factor that distinguishes performance among amblyopes is the presence or absence of binocular function.…”