The component of gaze selection/control in the development of visual acuity in children.

Visual acuity was tested for 180 eyes of 90 children in four age groups using three types of test charts. Subjects read the same 10 high-contrast letters in Snellen (line) format, as isolated-letter flash cards, and as repeat-letter flash cards. Group mean line and group mean isolated-letter acuity showed similar progressive improvements with age. A subgroup of 24 of 50 eyes of 4- to 5-year-olds (15 of 25 subjects) and 3 of 50 eyes of 6- to 7-year-old (2 of 25 subjects) had low Snellen acuity. Of this low-acuity subgroup of 27 eyes, 10 scored above average for their age group on the repeat-letter chart. We concluded that abnormal lateral interactions were not the explanation for the immaturity of Snellen acuity in these 10 eyes. We suggest that an important factor in the low acuities of these 10 eyes is delayed development of the selection and/or control of gaze direction. Some eyes with excellent Snellen acuity showed high crowding. For example, there were five such eyes in the oldest group. We suggest that the excellent acuities of at least two of these eyes are limited by minor inaccuracies in gaze selection and/or control rather than by lateral interaction.