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C-S Kee, L-F Hung, Y Qiao, R Ramamirtham, JA Winawer, J Wallman, EL Smith; Temporal Constraints on Experimental Emmetropization in Infant Monkeys . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2925.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:The developing eyes of several species including monkeys compensate for hyperopic defocus imposed by minus lenses so that the eyes become functionally emmetropic while wearing the lenses (myopic without the lenses). Results from both chicks and tree shrews show that the duration and timing of the periods of lens-wear greatly influence the degree of lens-compensation. To investigate the temporal integration properties of this experimental model of emmetropization in primates, we examined the effects of brief daily interruptions of lens wear on the ocular compensation for minus lenses in infant monkeys. Methods:Beginning at about 3 weeks of age, -3 D lenses were secured in front of both eyes of 18 infant rhesus monkeys. In the absence of full accommodation, these lenses would produce hyperopic defocus. Six of these monkeys wore the lenses continuously during the 12 hr of light each day. For the other monkeys, the -3 D lenses were removed for brief, 15-minute periods 4 times each day. During these periods these monkeys viewed through either zero-powered lenses (plano group, n=6) or +4.5 D lenses (+4.5 D group, n=6). Three monkeys reared with binocular plano lenses and 16 normal monkeys served as controls. The ocular effects were assessed periodically by cycloplegic retinoscopy, keratometry, and A-scan ultrasonography. Results:As expected, most (5 of 6) animals that wore the -3 D lenses continuously exhibited clear evidence of compensatory axial myopia. In contrast, most (5 of 6) of the monkeys wearing plano lenses during the brief interruptions of minus lens wear either exhibited growth patterns similar to normal monkeys or became relatively hyperopic. However, unlike previous findings in chicks, in which brief plus-lens-wear had a stronger effect than plano lenses (Winawer et al., ARVO, 2000), 5 of the 6 monkeys in the +4.5 D group exhibited compensatory myopic growth. Conclusion: Brief periods of unrestricted vision block the myopic growth otherwise produced by long daily periods of hyperopic defocus. Thus, the temporal integration properties of the primate emmetropization mechanism would reduce the likelihood that long periods of near-viewing would cause myopia, as long as occasional periods of normal vision occurred.
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