Amblyopia in astigmatic children: patterns of deficits

Abstract

Neural changes that result from disruption of normal visual experience during development are termed amblyopia. To characterize visual deficits specific to astigmatism-related amblyopia, we compared best-corrected visual performance in 330 astigmatic and 475 non-astigmatic kindergarten through 6th grade children. Astigmatism was associated with deficits in letter, grating and vernier acuity, high and middle spatial frequency contrast sensitivity, and stereoacuity. Although grating acuity, vernier acuity, and contrast sensitivity were reduced across stimulus orientation, astigmats demonstrated orientation-dependent deficits (meridional amblyopia) only for grating acuity. Astigmatic children are at risk for deficits across a range of visual functions.

Figure 1

Schematic representation of the locations at which the horizontal and vertical lines of a cross located at distance come into focus, with respect to the retina, in non-astigmatic eyes (a-c) and in eyes that have with-the-rule astigmatism (d-h) (from Harvey, 2002 and Harvey et al., 2004b, revised from Gwiazda, Mohindra, Brill, & Held, 1985).

Figure 2

Mean letter acuity for children in the non-astigmatic (NonA, n=467), hyperopic astigmatism (HA, n=155), and myopic/mixed astigmatism (M/MA, n=168) groups. Bars indicate ± 1 SEM. The NonA group had significantly better (p < 0.001) mean acuity than did both astigmatic groups.

Figure 3

Letter acuity by amount of astigmatism (scatter plot), with regression line for entire sample. Although there was considerable variability in acuity results at each level of astigmatism, letter acuity was significantly related to amount of astigmatism for the overall sample and for the HA and M/MA groups (ps < 0.001).

Figure 4

Percentage of children with right eye acuity that met the criterion for amblyopia (best-corrected letter acuity of 20/40 or worse) by age, for children in the non-astigmatic (NonA), hyperopic astigmatism (HA), and myopic/mixed astigmatism (M/MA) groups. Significantly more children in the HA and M/MA groups than in the NonA group met the criterion for amblyopia (ps < 0.001). Percentages represented by each bar reflect the following sample sizes (for NonA, HA, and M/MA respectively, the number of children meeting amblyopia criterion/total number of children): For age 4 to < 6 years, 15/82, 30/52, 20/30; For age 6 to < 8 years, 6/127, 26/60, 35/47; For age 8 to < 10 years, 3/86, 9/21, 17/25; For age 10 years and older, 13/177, 8/25, 18/70.

Figure 5

Acuity for vertical (black symbols), horizontal (white symbols), and oblique (gray symbols) gratings for children in the non-astigmatic (NonA, n=468), hyperopic astigmatism (HA, n=152), and myopic/mixed astigmatism (M/MA, n=166) groups. Bars indicate ± 1 SEM. For all three orientations, mean acuity in the NonA group was significantly better than mean acuity in the HA and M/MA groups (ps < 0.001). In comparison to results from the NonA group, both the HA and M/MA groups showed evidence of MA (ps < 0.001), with the HA group showing better acuity for horizontal than for vertical gratings, and the M/MA group showing better acuity for vertical than for horizontal gratings.

Figure 6

Vernier acuity for vertical (black symbols), horizontal (white symbols), and oblique (gray symbols) stimuli for children in the non-astigmatic (NonA, n=466), hyperopic astigmatism (HA, n=151), and myopic/mixed astigmatism (M/MA, n=165) groups. Bars indicate ± 1 SEM. For all three orientations, mean vernier acuity was significantly better for the NonA group than for the HA and M/MA groups (ps < 0.001). Neither the HA nor the M/MA group showed evidence of MA.

Figure 7

Contrast sensitivity for 1.5, 6.0, and 18.0 cy/deg sinewave gratings for horizontal and vertical stimuli for children in the non-astigmatic (NonA, n=435), hyperopic astigmatism (HA, n=135), and myopic/mixed astigmatism (M/MA, n=156) groups. Bars indicate ± 1 SEM. The NonA group had significantly better contrast sensitivity than the HA and M/MA groups for 6.0 and 18.0 cy/deg vertical and horizontal stimuli (all ps < 0.05 after Bonferroni correction), but contrast sensitivity in the astigmatic groups did not differ from that of the NonA group for 1.5 cy/deg stimuli. Neither the HA nor the M/MA group showed evidence of MA.

Figure 8

Stereoacuity for children in the non-astigmatic (NonA, n=466), hyperopic astigmatism (HA, n=153), and myopic/mixed astigmatism (M/MA, n=168) groups. Bars indicate ± 1 SEM. Children in the NonA group had significantly better stereoacuity than did children in either the HA or the M/MA group (ps < 0.001).