Abstract
Purpose: :
Previously, we established that brief daily periods of normal vision could preserve stereopsis in monkeys reared with optical strabismus. In this experiment we examine the importance of binocular concordance during the daily periods of normal vision.
Methods: :
Starting at 4 weeks of age, eight infant monkeys were reared with a total of 30 prism diopters base-in split between the eyes. Two monkeys wore prisms continuously for 4-6 weeks. Four monkeys wore prisms, but for 2 hours each day the prisms were replaced by clear plano lenses to provide concordant binocular vision. The duration of treatment was 4-6 weeks for 2 monkeys and 16 weeks for 2 monkeys. Two additional monkeys wore prisms for 16 weeks and for 2 hours each day the prisms were removed, but binocularity was disrupted by placing a diffuser lens over the right eye and a clear plano lens over the left eye. Five normally reared monkeys provided control data. Behavioral methods were employed to measure spatial contrast sensitivity, eye alignment, interocular suppression, and stereopsis with Gabor and random dot targets.
Results: :
Stereopsis was largely preserved by 2 hours of daily concordant binocular visual experience in both monkeys that were prism-reared for 4-6 weeks, and in one monkey prism-reared for 16 weeks. When binocularity was disrupted during the 2 hour daily period when the prisms were removed, stereopsis was not preserved. Interocular suppression prevented both monkeys from performing dichoptic judgments of position or depth, despite exhaustive training. One monkey showed normal monocular contrast sensitivity, and the other monkey showed moderately reduced contrast sensitivity of the eye that viewed through the diffuser.
Conclusions: :
During early visual development the effects of normal vision outweigh the effects of abnormal vision, but what constitutes ‘normal’ vision depends on whether the devleoping visual function is monocular or binocular. Binocular concordance is essential during daily periods of respite from optical strabismus for the preservation of binocular visual functions including stereopsis. Binocular concordance, however, is not essential for the maintenance of normal monocular spatial vision in monkeys.
Keywords: binocular vision/stereopsis • amblyopia • visual development