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D.M. Levi, S.P. McKee, J.A. Movshon; Visual Deficits in Anisometropia . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3184.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose To explore quantitative relationships between the degree of anisometropia and the loss of visual function, and to examine how the presence of strabismus affects visual function in observers with anisometropia. Methods We measured optotype acuity, Vernier acuity, grating acuity, contrast sensitivity and stereoacuity in 84 observers with "pure" anisometropia and 101 with strabismic anisometropia. Results Amongst anisometropes, all three "acuity" measures degrade rapidly with increases in either hyperopic or myopic anisometropia, whereas contrast sensitivity is much less degraded by anisometropia. We fit the data with an equivalent noise function to quantify how much anisometropia is required to degrade performance (relative to the fellow eye) by √2. The defocus tolerance for the three "acuity" measures is roughly 1 D, and is only slightly less for hyperopic anisometropes than myopic anisometropes. The similarity between the values for hyperopes and myopes is surprising, because previous studies and clinical experience suggest that the prevalence of amblyopia is lower with low degrees of myopic as compared with hyperopic anisometropia. Strabismic-anisometropes had a wider range of variation in visual performance, with many strabismic-anisometropes performing worse than pure anisometropes with the same degree of refractive imbalance. This is particularly evident for optotype and Vernier acuity. Moreover, a substantial number of strabismic-anisometropes show better contrast sensitivity in their non-dominant eyes than in their dominant eyes. The most striking difference between the anisometropes and the strabismic-anisometropes is in their stereoacuity. Most pure anisometropes with interocular differences less than 4 D have stereopsis, while most strabismic-anisometropes do not. Conclusions Our results show that even low degrees of interocular difference in refractive error can influence visual function, and that strabismus can exacerbate the pattern of functional loss, consistent with the notion that two distinct developmental processes determine the pattern of visual deficits in persons with amblyopia.
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