BINOCULAR ALIGNMENT AND VERGENCE IN EARLY INFANCY

Vergence to static targets presented at five distances between 25 and 200 cm from the subject was measured in 631 infants aged between 17 an d 120 days, Photographic images of the eyes were magnified and measure d to yield information on the monocular and binocular eye positions fo r each target, Vergence data were fit by a linear function and compare d to the vergence calculated from target distance and each infant's me asured interpupillary distance, Differences in vergence across targets were also evaluated for each subject by calculating the change in ang le of rotation for each eye, Many of even the youngest infants showed good ocular alignment both monocularly and binocularly, although the y oungest infants showed the greatest variability in vergence. However, the median difference in vergence angle between the eyes for even the youngest group was < 4 deg(6.8 prism D), and some of this difference i s attributed to versional eye movements and to slightly off-axis head position across trials, The average infant of 1-2 months showed substa ntially better vergence than has been reported in some recent studies. Apparently, oculomotor constraints are not a significant barrier to t he development of the higher forms of binocularity that begin to emerg e in the months immediately following the interval studied here, and m ay form the substrate for later developments in binocular vision.