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S. Song, D. M. Levi, D. G. Pelli; Can "Equivalent Eccentricity" Account for Two Measures of Performance in the Amblyopic Visual System?. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4883.
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The similar visual performance of the normal periphery and the amblyopic fovea is well documented. Here we ask whether an equivalent-eccentricity model can explain the reduced acuity and increased crowding in the central field of amblyopes.
We measured both isolated and flanked letter acuity at 5 different eccentricities, from the fovea to 10 degrees in the lower visual field of six amblyopic and two normal observers. We separately estimated equivalent eccentricity for both kinds of acuity. The equivalent eccentricity is the eccentricity in the normal retina that yields the same acuity.
Both isolated and flanked letter acuity in amblyopic eyes are most severely impaired at the fovea and practically normal in the periphery. Almost all amblyopes showed much greater impairment for flanked than for isolated letters in the fovea of the amblyopic eye, indicating strong crowding in the fovea. The equivalent eccentricity of the amblyopic fovea ranges from 0.6 to 7.1 (median 3.7) degrees.
The fair agreement of equivalent eccentricity estimated by two different methods suggests that equivalent eccentricity provides a reasonable account of acuity and crowding in amblyopia.
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