Abstract
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 7 infant macaques by fitting them with prism goggles on day 1 of life. The goggles were removed after 3 wks (n=2), 3 mos (n=1) or 6 mos (n=2), emulating surgical repair of strabismus in humans at 3 mos, 12 mos, and 24 mos of age, respectively. Two control monkeys wore plano lenses. After the goggles were removed, horizontal pursuit was recorded using search coils, evoked by "step–ramp" target motion. A nasal bias index (NBI) was calculated as (Sn–St )/(Sn+St), where Sn is nasally–directed and St is temporally–directed mean eye speed.
Results: :
Each animal in the 3 and 6–mos 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 mos group was 5 times greater than that in the 3 mos group, and 30 times greater than that in the 3 wk group (ANOVA, p=0.03). For 30 deg/s target motion, the NBI in the 6 mos–duration group was 4 times greater than that in the 3 mos group, and 12 times greater than that in the 3 wk group (ANOVA, p=0.05). Controls had symmetric pursuit.
Conclusions: :
Early correction of strabismus (i.e. elimination of binocular decorrelation) prevents maldevelopment of the pursuit system. These findings indicate that early correction of infantile strabismus is beneficial for brain development.
Keywords: strabismus • strabismus: treatment