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J.B. Shelton, E.M. Harvey, V. Dobson, J.M. Miller, C.E. Clifford; Performance of Children With Astigmatism–related Amblyopia on the ‘Pelli–Levi Dual Acuity Chart’ . Invest. Ophthalmol. Vis. Sci. 2005;46(13):5644.
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Purpose:Pelli, Levi, and Chung (Journal of Vision, 2004) suggested their new "Pelli–Levi Dual Acuity Chart" may diagnose amblyopia in subjects with anisometropia and/or strabismus. The chart is similar to a Snellen acuity chart except that white noise is added to one half of the chart, allowing visual sensitivity to be broken down into two factors: equivalent noise and efficiency. Because amblyopic eyes in their study had decreased efficiency when compared to non–amblyopic eyes, Pelli et al predicted that amblyopic eyes will score one to two lines worse on the noise versus no–noise portion of the chart, while normals will show no difference in acuity between the two portions of the chart. We studied a sample of elementary school children with a high prevalence of bilateral astigmatism–related amblyopia to determine whether the Dual Acuity Chart distinguished these amblyopes from non–amblyopes. Methods:Subjects were 63 second and third grade children, all members of a Native American population with a high prevalence of astigmatism–related amblyopia. Their visual acuity was measured with the ETDRS chart (Precision Vision, Inc.) while wearing best correction, determined by cycloplegic autorefraction and confirmed by retinoscopy. Each child also underwent right eye (RE) best–corrected acuity testing with the Dual Acuity Chart. Results:Based on RE best–corrected ETDRS acuity we categorized children as astigmatic amblyopes (RE ≥ 2.00 D cyl and 20/40 or worse) or non–amblyopes (RE < 1.00 D cyl and 20/20 or better). We excluded children with anisometropia > 1.50 D spherical equivalent. Mean difference in number of lines correct on the no–noise versus noise portion of the chart was 3.33 lines for amblyopes (N = 8) and 2.75 lines for non–amblyopes (N = 27) (t(33) = –1.20, p = 0.24). Conclusions:The Dual Acuity Chart did not distinguish between astigmatic–amblyopes and non–amblyopes. The results suggest the nature of the deficits associated with astigmatism–related amblyopia may differ from those due to anisometropic or strabismic–amblyopia. However, the poor performance in noise by amblyopes and non–amblyopes alike suggests that cognitive or visual system immaturity may have increased variability in measurements, thereby decreasing our ability to detect significant differences between amblyopes and non–amblyopes.
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