Infant interocular acuity differences and binocular vision.

Monocular acuity, binocular acuity, and stereopsis were assessed with preferential-looking techniques in a sample of 114 normal infants aged 0-11 months in order to examine developmental trends in: (1) interocular differences in acuity, (2) test-retest reliability, (3) the relationship between monocular and binocular measures of acuity, and (4) the relationship between interocular differences in acuity and stereopsis. Mean interocular acuity difference was largest during months 0-5 (approximately 1 octave) and decreased to approximately 0.5 octaves by months 9-11. Test-retest reliability was constant throughout months 0-11 (0.5 octaves). The superiority of binocular acuity over monocular acuity was evident after the 6th month. The presence or absence of stereopsis during months 3-5 was directly related to the magnitude of interocular acuity differences. These age trends suggest that the third to fifth months of life may represent a period of binocular competition in the human visual system which, during normal development, culminates in small interocular acuity differences and the onset of binocular function, including stereopsis.