Brief Daily Periods of Unrestricted Vision Can Prevent Form-deprivation Amblyopia

Abstract

Abstract: : Purpose: Early in life continuous monocular form deprivation can produce very severe amblyopia. The purpose of this study was to determine the effects of brief daily periods of unrestricted vision on the development of form-deprivation amblyopia in infant monkeys. Methods: Unilateral form deprivation was produced by rearing 18 infant rhesus monkeys with a diffuser spectacle lens in front of one eye and a clear plano lens in front of the fellow eye. The lens-rearing regimen was initiated at approximately 3 weeks of age and continued until the animals were 4 months old. During the treatment period, 3 infants wore the diffuser lenses continuously. For the other form-deprived infants, the diffusers were removed each day and replaced with a clear plano lens for periods of 1 (n=5), 2 (n=6) or 4 hours (n=4). Lens removal occurred near the mid-point of the normal 12-hour lighting cycle. When the animals were approximately 18 months of age, operant psychophysical methods were used to measure spatial contrast sensitivity functions for each eye. The degree of amblyopia was quantified by the interocular ratio of the areas under the contrast sensitivity functions for the non-treated and treated eyes. Control data were obtained from 4 monkeys that were reared with plano lenses in front of both eyes and 4 normal animals. Results: Continuous form deprivation produced nearly a 10-fold reduction in spatial vision. Only one hour of unrestricted vision each day was sufficient to reduce the degree of amblyopia by over 50% and with 4 hours of unrestricted vision there were virtually no interocular differences in contrast sensitivity. Conclusions: In terms of spatial vision development, the effects of normal and abnormal visual experience are not weighted equally. Instead, relatively short daily periods of unrestricted vision effectively counteract the amblyogenic consequences of much longer daily periods of monocular form deprivation.

Keywords: amblyopia • visual development • spatial vision