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Janice M. Wensveen, Earl L. Smith, III, Li-Fang Hung, Ronald S. Harwerth; Preserving Stereopsis During Extended Optical Strabismus. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5710.
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We examined whether brief daily periods of normal vision could preserve stereopsis in monkeys reared with an extended duration of optical strabismus.
Starting at 4 weeks of age, six infant monkeys were reared with a total of 30 prism diopters base-in split between the eyes. Two monkeys wore prisms continuously, one for 4 weeks and one for 6 weeks. Four monkeys wore prisms, but for 2 hours each day the prisms were replaced by clear plano lenses to provide normal binocular vision. The duration of treatment was 4 weeks for one monkey, 6 weeks for one monkey, and 16 weeks for 2 monkeys. Five normally reared monkeys provided control data. Behavioral methods were employed to measure spatial contrast sensitivity, eye alignment, and stereopsis with Gabor and random dot targets.
Both local and global stereopsis showed the same pattern of results. For monkeys treated for 4 weeks, continuous optical strabismus resulted in a log-unit reduction in stereopsis that was ameliorated by daily periods of normal vision. Six weeks of optical strabismus caused stereo-blindness when continuous but only a 2-fold reduction from normal disparity sensitivity when interrupted by daily periods of normal vision. Stereopsis was preserved by daily periods of normal vision in one of the two monkeys reared with optical strabismus for an extended duration of 16 weeks.
Whether strabismus is continuous or interrupted by daily periods of normal vision, longer durations of abnormal visual experience negatively impact the development of stereopsis. During early development, the effects of normal vision are weighed more heavily than those of abnormal vision, but as the duration of abnormal visual experience is extended, the integration properties may change so that the protective effects of daily periods of normal vision diminish. These results emphasize the importance of early detection and treatment of strabismus.
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