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K. Lam, P. Foeller, D. Bradley, L. Tychsen, A. M. Wong; Defining the Critical Period for Eye Alignment Development in Infant Primates: Effects of Binocular Decorrelation. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1984.
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Earlier studies by our group have found that an optical strabismus induced in non-human primates at birth causes a permanent large-angle esotropia 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 eye alignment development.
Binocular image decorrelation was imposed on 12 normal infant macaques (Macaca mulatta) 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), 12 (n=3), or 24 weeks (n=3), emulating surgical repair of strabismus in humans at 3, 6, 9, 12, and 24 months of age, respectively. Two monkeys wore plano lenses and served as controls. Several months after the goggles were removed, eye alignment was recorded using binocular search coils during automated single and alternate-cover testing. Alignment in each cardinal position was measured during steady fixation to assess concomitance.
The longer the duration of image decorrelation, the greater the magnitude of resultant concomitant esotropia. Only physiological (< 2 deg) heterophorias were detected in the control, 3-wk and 6-wk-duration groups. The 9-wk, 12-wk, and 24-wk-duration monkeys exhibited larger-angle estropias (9 - 12 deg).
Longer durations of binocular decorrelation in infancy cause greater maldevelopment of the vergence system manifested as larger-angle esotropia. Our findings suggest that surgical repair in infantile esotropia in humans would be most beneficial before the age of 6 months, and supports early correction of infantile strabismus.
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