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E. M. Harvey, C. E. Clifford-Donaldson, T. K. Green, V. Dobson, J. M. Miller; Perception of Global Form in Children With Astigmatism-Related Amblyopia: A Pilot Study. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3818.
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The purpose of the present study was to determine if K and 1st grade children could reliably perform a global form (GF) task, and to determine if there is evidence of GF deficits in children with bilateral astigmatism.
Subjects were K and 1st grade children who attended school on Tohono O’odham Reservation and completed a cycloplegic eye examination (refractive error determined by autorefraction, confirmed by retinoscopy). On a second day, RE and LE best-corrected letter acuities were measured, and a test of best-corrected GF perception was conducted (monocular, RE). On each GF trial, two radial "glass pattern" stimuli (circular pattern of dots in which some percentage of dots are paired with a second dot shifted outward from center, making it appear like spokes on a wheel) were presented, and children were instructed to report which looked like a "spoked wheel". Coherence of the target patterns ranged from 100 to 20% in 10% decrements. Distractor patterns had 0% coherence. Six trials were presented at each coherence level. Threshold was the lowest coherence level at which 5/6 targets were correctly identified. Analyses included children who had no anisometropia (≥ 1.50 D sph eq) or strabismus, and who met the criteria for one of the following groups: (1) non-astigmatic control (Con) (< 1.00 D astigmatism, acuity 20/32 or better in both eyes), (2) non-amblyopic astigmatic (ANonA) (astigmatism ≥ 1.00 D, acuity 20/32 or better in both eyes), (3) amblyopic astigmatic (AA) (astigmatism ≥ 1.00 D, acuity 20/40 or worse in both eyes).
Of 97 children attempting the GF task, 3 could not complete it, and many became distracted and performed unreliably. Mean GF threshold did not differ across groups for the 67 children who met the inclusion criteria, (n, mean coherence (SD) = 39, 42.05 (13.99) for Con, 13, 40.00 (10.80) for AnonA, and 15, 36.00 (11.21) for AA).
The results suggest that astigmatism does not impact development of GF perception. However, many children had trouble performing the task reliably. Further studies, employing smaller threshold increments, fewer trials, and more child-friendly displays will determine if subtle deficits might have been missed with this experimental design.
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