Contour interaction in the preschool child.

Preschool children show poorer visual acuity when tested with multiple optotypes than when tested with isolated optotypes. This difference in performance could be the result of contour interaction or the greater distractions imposed by a multiple optotype display, which may be beyond a young child's ability. To differentiate between these alternatives, isolated and surrounded visual acuity were measured in children aged 2 to 7 years by pairing a Landolt C with an O. The surrounded optotypes were identical to the isolated optotypes with the exception of the flanking bars located at 2.5 times the minimum angle of resolution (MAR) of the optotype. A two-alternative forced choice interleaved paradigm was used to measure surrounded and isolated visual acuity defined as 75% correct. When the test demands were equated by measuring isolated and surrounded acuity using a single optotype, poorer visual acuity was obtained with surrounded optotypes. This suggests that preschool children, like adults, show contour interaction.