Assessment of acuity in human infants using face and grating stimuli.

In a variety of ocular disorders, square-wave gratings yield more optimistic estimates of visual acuity than more complex stimuli such as letters. However, for clinical vision testing of preverbal patients, square-wave gratings are usually employed in conjunction with preferential looking procedures. We developed a complex stimulus--a schematic face--for use in preferential looking procedures. Using the method of constant stimuli, the acuities of 1-, 3-, and 5-month-old infants with normal eyes were estimated using schematic faces and square-wave gratings. Within each age group, thresholds for face and grating stimuli were not significantly different, but psychometric functions obtained with faces were significantly steeper than those obtained with square-wave gratings. This suggests that complex stimuli such as the schematic face could yield more precise acuity estimates than gratings in some pediatric eye patients.