The development of visual acuity in infant astigmats.

Acuity for vertical, horizontal, and oblique gratings was measured in 77 infant astigmats using a preferential looking procedure. Measurements were made with the refractive error uncorrected. Most of the infant astigmats were slightly to moderately hyperopic with respect to the test distance of 50 cm. Their acuity was not significantly different from that of a group of non-astigmatic infants. Average acuity for vertical and horizontal gratings increased from 6/200 at 1 month of age to 6/24 at 1 yr. Average acuity for oblique gratings increased more slowly, so that by 1 yr of age it was only 6/33. The only infants to show reductions in acuity were those with a strong myopic focus and one infant with a very strong hyperopic focus. When this infant was tested with optical correction, acuity improved to normal levels. This suggests that meridional amblyopia develops sometime after the first year of life or that it is confined to high spatial frequencies.