Meridional Amblyopia in 3- to 5-Year-Old Native American Children with Astigmatism >/= 1.50 Diopters

Abstract

Abstract: : Purpose: To determine whether meridional amblyopia (MA) is present in astigmatic preschool-aged children. Methods: Monocular (right eye) grating acuity for horizontal and vertical gratings was measured using the Teller acuity card procedure in 494 3- to 5-year-old children who were enrolled in the Tohono O'odham Nation's Head Start program in the fall of '97, '98, '99, and 2000. Prevalence of astigmatism ≷1.5 D was 31% in right eyes of these children. Axis was with-the-rule in all astigmatic eyes (i.e., in the absence of correction, horizontal gratings were focused in front of vertical gratings in these eyes). Children were tested in trial frames containing best correction, as determined by cycloplegic refraction just prior to testing. MA was defined as log(acuity for horizontal gratings) minus log(acuity for vertical gratings). Results: There was no difference in the mean MA for astigmatic vs non-astigmatic eyes. However, eyes with myopic or mixed astigmatism (i.e., those in which horizontal gratings were focused myopically in the absence of correction [n=69]) were 4.8 times more likely to show better acuity for vertical gratings than for horizontal gratings, whereas eyes with simple or compound hyperopic astigmatism (i.e., eyes that could accommodate to focus both grating orientations in the absence of correction [n=86]) showed equal likelihood of better acuity for horizontal gratings as for vertical gratings (X₂=10.3. p<0.01), similar to results for the group of non-astigmatic eyes. Conclusions: The results provide evidence that MA is present in astigmatic preschool children who have myopic or mixed with-the-rule astigmatism, but not in children who have hyperopic astigmatism. This is likely to be related to differences in uncorrected vision in these two types of astigmats: hyperopic astigmats have the ability to accommodate to bring either horizontal or vertical lines into focus, whereas myopic and mixed astigmats cannot accommodate to eliminate blur of horizontal lines at distance. Thus, the ability to use accomodation to bring distant stimuli of different orientations into focus at least some of the time may provide enough clear visual input across stimulus orientation to deter the development of MA in young children with hyperopic astigmatism.

Keywords: 325 astigmatism • 623 visual development: infancy and childhood • 620 visual acuity