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J. M. Wensveen, V. Lam, R. S. Harwerth, E. L. Smith, III; Brief Daily Periods of Unrestricted Vision Can Preserve Stereopsis in Optical Strabismus. Invest. Ophthalmol. Vis. Sci. 2007;48(13):5883.
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© ARVO (1962-2015); The Authors (2016-present)
Brief daily periods of normal vision have been shown to rescue infant monkeys from the severe amblyogenic effects of much longer periods of form deprivation. In this study we examined if brief periods of normal visual experience could preserve binocular vision in monkeys reared with optical strabismus.
Starting at 4 weeks of age, four infant monkeys were reared with 15 diopter prisms oriented base-in in front of each eye. Two monkeys wore the prism continuously, one for 4 weeks (mky-JOB) and the other for 6 weeks (mky-IGO). Two other monkeys also wore the prisms for 4 weeks (mky-JAR) or 6 weeks (mky-KER) but were allowed 2 hours of unrestricted vision each day by replacing the prisms with clear plano lenses. Four normally reared monkeys provided control data. Behavioral methods were employed to measure spatial contrast sensitivity, eye alignment, and local stereopsis. In particular, local disparity thresholds were measured using the method of constant stimuli for Gabor targets that had carrier grating spatial frequencies that were varied from 0.25 to 16 cyc/deg. The semi-intraquartile range for the resulting psychometric function was taken as the disparity threshold.
All monkeys showed normal and equal contrast sensitivities in their two eyes and no monkey demonstrated a strabismus. The monkey reared with brief daily periods of unrestricted vision during the 4 weeks of optical strabismus (mky-JAR) showed normal local stereopsis, while the monkey reared with 4 weeks of continuous strabismus (mky-JOB) showed a 10-fold reduction in local stereopsis across all spatial frequencies. The monkey reared with 6 weeks of continuous strabismus (mky-IGO) could not discriminate depth despite over 60,000 training trials, while the monkey reared with periods of normal vision during 6 weeks of prism wear (mky-KER) showed only a 1 octave reduction in stereopsis across all spatial frequencies.
Two hours of daily unrestricted vision largely preserves local stereopsis in monkeys reared with optical strabismus. During early development, the effects of normal vision are weighed more heavily than those of abnormal vision. The manner in which the effects of visual experience are integrated over time would normally reduce the likelihood that brief episodes of abnormal vision would influence binocular vision development.
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