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Rana Arham Raashid, Manokaraananthan Chandrakumar, Alan Blakeman, Herbert Goltz, Agnes M. Wong; Saccadic Adaptation In Amblyopia. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5608. doi: https://doi.org/.
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Saccadic adaptation is an important motor learning mechanism that maintains the accuracy of goal-directed saccades. It is generally believed to be driven by visual error signal at the end of saccades. Amblyopia is characterized by impairment of spatiotemporal visual processing. The purpose of this study is to investigate the effects of spatiotemporal visual deficits in amblyopia on saccadic adaptation.
Study participants included 10 visually normal adults and 7 adult patients with amblyopia (5 anisometropic, 1 strabismic, 1 mixed). Participants were instructed to follow a visual target on a screen while their eye movements were recorded. Saccadic adaptation was induced experimentally using a double-step target paradigm, in which the visual target (at 18° eccentricity) was displaced toward initial fixation (by 4°) during the saccade. The experiments included a single-step pre-test, a double-step adaptation test, and a single-step post-test, performed during binocular viewing and monocular viewing with the amblyopic and fellow eye (monocular right and left eye in normal subjects) in three different sessions. Saccadic latencies and percentage change in saccadic gain were measured.
Patients with amblyopia adapted their saccadic gain (48.5±4.57%) to a lesser extent than normal subjects (71.7±3.12%) during amblyopic eye viewing (p=0.0400). Furthermore, patients with anisometropic amblyopia exhibited decreased saccadic gain adaptation than normal participants during both amblyopic eye viewing (patients=44.2±4.05%,normal=71.7±3.12%;p=0.0052) and binocular viewing (patients=45.7±4.84%,normal=73.9±3.62%;p=0.0052). Initiation of saccades was also delayed in patients during amblyopic eye viewing when compared to normal subjects (patients=231.8±8.6ms,normal=196.7±3.6ms;p=0.0330).
Saccadic gain adaptation was less robust in patients during amblyopic eye viewing. The effect was more pronounced in patients with anisometropic amblyopia who exhibited impaired adaptation during both amblyopic eye and binocular viewing. Our findings suggest that impairment of spatiotemporal visual processing in amblyopia affects saccadic adaptation, and support the hypothesis that the error signal that drives saccadic adaptation is visual in nature.
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