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Ivy Ziqian Liu, Rana Arham Raashid, Alan Blakeman, Agnes MF Wong; The effect of anisometropic amblyopia on initiation of smooth pursuit eye movements. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):2907. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Amblyopia is a spatiotemporal visual impairment caused by abnormal visual experience early in development. Recent studies have shown that amblyopia affects visuomotor behaviors in addition to impairing sensory functions. Here we investigate the effects of anisometropic amblyopia on smooth pursuit eye movements responsible for maintaining visual acuity and stabilizing the image of moving objects on the fovea. We hypothesized that given the visual processing delays in amblyopia, there will be a significant delay in the initiation of pursuit in patients during amblyopic eye viewing
Fourteen visually normal controls and 9 people with anisometropic amblyopia were instructed to follow a red laser dot moving at ±15/s horizontally for approximately one second for a total of 40 trials. The experiment was repeated for each participant under three viewing conditions in the given order: 1) amblyopic/nondominant eye, 2) binocular, and 3) fellow/dominant eye viewing. Outcome measures were pursuit initiation latency, open-loop gain (eye/target velocity ratio 100 ms post-onset), and steady state gain (eye/target velocity ratio throughout movement).
As predicted, when viewing monocularly with the amblyopic eye, participants with anisometropic amblyopia took longer to initiate pursuit movements (203±20 ms) compared to controls viewing with their nondominant eye (183±17 ms, p=0.004). The pursuit latency in patients during binocular (168±17 ms) and monocular fellow eye (176±22 ms) viewings was comparable to controls (binocular: 172±19 ms; dominant eye: 169±15 ms respectively). Mean open-loop gains and steady state gains did not differ significantly between the two groups.
This study provides novel evidence of delayed pursuit initiation in people with anisometropic amblyopia with the amblyopic eye viewing. A comparable observation was made previously in a study involving saccadic eye movements in anisometropic amblyopia. Our findings suggest that longer initiation latencies may be due to a delay in visual processing of target motion in amblyopia. However, after smooth pursuit has been initiated, pursuit accuracy in amblyopia was equivalent to that seen in visually normal participants.
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