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Monika A. Formankiewicz, Charlotte-Louise R. Tucker, Sarah J. Waugh, John Siderov; Children's visual acuity charts: effects of blur and eccentricity. Journal of Vision 2009;9(8):1031. doi: 10.1167/9.8.1031.
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Crowding has a more detrimental effect on the visual acuity of strabismic amblyopes than anisometropic amblyopes, when measured with Tumbling-E patterns (Bonneh et al, 2004). Spatial vision in amblyopia can be estimated in normals by imposing increasing levels of blur and retinal eccentricity (e.g. Levi & Klein, 1982). As the detection of amblyopia in children relies on accurate assessment of visual acuity, we measured the effects of increasing blur and retinal eccentricity on visual acuity in normal adults with commercially available crowded and uncrowded children's vision charts.
High contrast optotypes, derived from common children's acuity charts, were presented on a high resolution monitor in isolation (Sheridan Gardiner letters and Kay pictures) and in configurations of commercially available crowded charts (logMAR Crowded Test, Cambridge Crowding Cards, Sonksen logMAR Test, and Kay Picture Test). These charts differ in the optotypes and crowding features used, and in the separations between them. For each chart, psychometric functions were obtained at the fovea for four levels of dioptric blur (0, 0.5D, 1D and 2D) and at four levels of retinal eccentricity (0, 1.25 deg, 2.5 deg and 5 deg in the lower field). E2 values were calculated for each chart. Four adult observers with corrected to normal vision participated.
Blur had a similar degradative effect on visual acuity across all charts (ANOVA; p[[gt]]0.10). Increasing retinal eccentricity had a greater effect on visual acuity measured with the crowded charts (Mean E2 ~1 deg) than with isolated uncrowded optotypes (Mean E2~2 deg).
Based on models of amblyopia and the above results, a greater level of visual acuity loss with crowded charts than with isolated optotypes would be expected in strabismic amblyopes, but not in anisometropic amblyopes.
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