Abstract
Abstract: :
Purpose: In previous work (ARVO 2001, 2002, 2003) we have reported that among individual infants and young children, there is substantial variation in the development of both spatial vision (visual acuity, contrast sensitivity) and refractive error. However, despite significant scientific and clinical interest, the relationship between early optical error and early visual development is very poorly understood, no doubt due to the methodological and technical difficulties involved in obtaining accurate refractive estimates from individual infants and toddlers. In the present work, we employ newly developed refractive technology in an attempt to better quantify how much the early spatial limitations are accounted for by optical immaturities. Methods: Left eyes from 6–month–old (n=28) and 12–month–old (n=30) infants were refracted twice with the Welch Allyn SureSight autorefractor (without cycloplegia) and within the same session, assessed with the Teller acuity cards. For comparison, left eyes from 3–4–year–old preschoolers (n=56), 7–8–year–old children (n= 44) and young adults (n=59) were refracted, and acuity assessed (uncorrected) with either Snellen letters (adults and children) or LEA symbols (preschoolers). Results: Calculations of total absolute refractive error [|Sph| + |Cyl|], spherical equivalent, and other linear models of aggregate refractive error all revealed consistent results. As expected from traditional work, levels of visual acuity in both adults and school–age children were predicted well from the magnitude of uncorrected refractive error (all r > 0.59, all p < 0.01). However, although preschool children showed the same trend as older subjects, there was absolutely no relationship between visual acuity and refractive error in both groups of infants (range of r = –0.08 to +0.06). Conclusions: Our study is the first to examine systematically, the relationship between spatial vision and refractive error in young infants and preschoolers. In preschool children, like adults and older children, visual acuity is predicted well by optical factors. Conversely, almost none of the variation in visual acuity among individual infants is accounted for by differences in optics. Consistent with current neurological and psychophysical models of early visual development, our results suggest that infants' spatial vision is constrained almost entirely by photoreceptoral and neural immaturities.
Keywords: refraction • visual development • visual acuity