Nonoptical determinants of aniseikonia.

Interocular differences in apparent size (aniseikonia) are typically associated with interocular differences in refractive error (anisometropia). Aniseikonia is generally thought to reflect disparities in retinal image size that often accompany anisometropia. This assumption was examined with seven highly anisometropic subjects who were tested under conditions in which no substantial retinal image size differences were present. Using a dichoptic size matching task, consistent and large (mean = 22%) aniseikonias were found. Myopic anisometropes exhibit perceptual minification, while hyperopes demonstrate perceptual magnification when using their more ametropic eye. Both ultrasonic and fundus examinations of these subjects indicate that differential retinal growth or stretching is responsible for these findings.