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Paul E. Foeller, Dolores V. Bradley, Lawrence Tychsen; Ocular Following Response in Macaque Monkeys with Infantile Strabismus. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4855.
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© ARVO (1962-2015); The Authors (2016-present)
Newborn monkeys reared viewing non-corresponding binocular images develop the infantile strabismus syndrome in a few weeks. Here we measure development of the ocular following response (OFR) after different durations of non-correspondence.
Eight infant macaques were fitted with prism goggles at age 3 wks to induce image non-correspondence. The goggles were removed after 3 wks (n=2), 6 wks (n=2), 9 wks (n=2) or 12 wks (n=2). At age 1 year the monkeys were trained to perform visual tasks and eye movements were recorded using eye coils. Horizontal OFR was evoked by ramp motion (5-75 deg/sec) of a large-field (45 deg x 45 deg) display of random dots (each subtending 1-3 deg arc) 50 msec after a centering-saccade. Exposure to horizontal dot motion was limited to 200 msec followed by a blanking of the display for 500 msec. Ramp motion direction and velocity were randomized.
The shortest-duration monkeys (3 wks) regained normal eye alignment and exhibited symmetric pursuit/OFR. In contrast, the intermediate and long-duration monkeys (6, 9 and 12 wks) exhibited persistent heterotropias and pursuit/OFR asymmetries. The severity of the OFR asymmetry increased with increasing duration. For each group, a nasal bias index (NBI) was calculated as (Vn - Vt) / (Vn + Vt) x 100 [Vn = nasally-directed and Vt = temporally-directed mean eye velocity]. The 3 wk monkeys had a NBI of -4.0. The 6 wk, 9 and 12 wk monkeys had NBIs of 13, 34 and 44, respectively.
Longer durations of binocular decorrelation in infancy cause greater maldevelopment of the OFR. These results reinforce the importance of restoring normal eye alignment in infancy within a short period of time.
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