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Purpose: Infantile esotropia is associated with nasotemporal asymmetries of pursuit during monocular viewing. The purpose of this study was to determine how the duration of binocular decorrelation, which can be strictly controlled in primates, influences directional pursuit asymmetries. Methods: Optical strabismus was created in seven infant macaques by fitting them with prism goggles on DOL 1. The goggles were removed after 3 weeks (n ϭ 2), 3 months (n ϭ 1), or 6 months (n ϭ 2), emulating surgical repair of strabismus in humans at 3, 12, and 24 months of age, respectively. Two control monkeys wore plano lenses. After the goggles were removed, horizontal pursuit was recorded using search coils, evoked by "stepramp" target motion. A nasal bias index (NBI) was calculated as (Sn Ϫ St)/(Sn ϩ St), where Sn is nasally directed and St is temporally directed mean eye speed. Results: Each animal in the 3-and 6-month-duration groups showed asymmetries of pursuit at both target speeds. The longer the duration, the more severe the asymmetry: for 15 deg/s targets, the NBI in the 6-month group was 5ϫ greater than that in the 3-month group, and 30ϫX greater than that in the 3-week group (ANOVA, P ϭ 0.03). For 30 deg/s target motion, the NBI in the 6-month-duration group was 4ϫ greater than that in the 3-month group, and 12ϫ greater than that in the 3-week group (ANOVA, P ϭ 0.05). Controls had symmetric pursuit. Conclusions: Early correction of strabismus (ie, elimination of binocular decorrelation) prevents maldevelopment of the pursuit system. These findings indicate that early correction of infantile strabismus is beneficial for brain development.

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