Evoked potential estimates of visual accommodation in infants.

Pattern reversal visually evoked potentials (VEPs) were recorded from infants between 2 and 5 months of age in order to measure their accommodative performance over a 9 diopter range (10-150 cm). Accommodation was stimulated by placing minus spherical lenses of increasing power in front of the infant's eyes and by changing the infant's distance from the stimulus. VEP latency measurements indicated that the infant's ability to maintain a zone of clear vision changes with age and pattern element size. For large checks (60 min arc), most 2- to 4-month old infants were able to maintain clear vision over the range of 9 diopters. When small checks (15 min arc) were used, the majority of 4- to 5-month old infants were unable by VEP measures to accommodate beyond 5-6 diopters. This decline in the infant's zone of clear vision with decreasing check size is due primarily to the relatively large depth of focus and poor visual resolution of the infant eye. In a small group of infants, accommodation was assessed both electrophysiologically by VEP recording and behaviorally using a preferential looking technique. Results indicated better accommodation by VEP estimates than by behavioral measures.