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K. T. Le, P. Foeller, D. Bradley, L. Tychsen, A. M. Wong; Defining the Critical Period for Smooth Pursuit Development in Infant Primates: Effects of Binocular Decorrelation. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1208.
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Infantile esotropia is typically associated with nasotemporal asymmetry of smooth pursuit, manifested as a bias favoring nasalward target motion when viewing monocularly. Earlier studies by our group have found that an optical strabismus induced in non-human primates during an early critical period of development causes smooth pursuit asymmetry when image decorrelation occurs between the first 3-12 weeks of life (equivalent of age 3-12 months in humans). The purpose of this study was to further delineate the critical period of smooth pursuit development.
Binocular image decorrelation was imposed on infant macaques by fitting them with prism goggles on day 1 of life. The goggles were removed after 3 (n=2), 6 (n=2), 9 (n=2) or 12 weeks (n=3), emulating surgical repair of strabismus in humans at 3, 6, 9 and 12 months of age, respectively. Two control monkeys wore plano lenses. Several months after goggle removal, horizontal smooth pursuit was recorded using binocular search coils and a nasal-bias index (NBI) was calculated.
Each animal in the 9- and 12-week groups developed nasotemporal asymmetry of smooth pursuit when viewing with either eye. The smooth pursuit in 3- and 6-week duration monkeys was symmetric and indistinguishable from the controls. NBI were negligible or slightly negative in the control, 3- and 6-week monkeys, but positive and substantially greater (9-14x) in the 9-and 12-week monkeys (ANOVA, p<0.05).
We further delineate the critical period of smooth pursuit development; it appears to occur between 6 and 9 weeks postnatally in monkeys. Our findings suggest that surgical repair of infantile esotropia in humans would be most beneficial before the age 6 months.
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