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Rana Arham Raashid, Herbert C Goltz, Alan Blakeman, Agnes MF Wong; Simulating Amblyopic Noise: Reduction in Saccadic Adaptation in Controls. Invest. Ophthalmol. Vis. Sci. 2014;55(13):5977. doi: https://doi.org/.
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Anisometropic amblyopia patients have increased saccadic endpoint variability. We showed that they also exhibit reduced short-term saccadic gain adaptation compared to controls (Raashid et al., 2013), possibly driven by imprecise postsaccadic visuomotor errors. Here we quantify the postsaccadic error distribution difference between anisometropic amblyopia patients and controls. We apply this additional variability to the intrasaccadic target step (ISS) in controls during saccadic adaptation, and test whether their performance diminishes in response to a noisier "amblyopic" adapting step.
Five visually-normal adults performed a double-step adaptation task (±19°, followed by a mean 4° ISS back-step) during nondominant eye monocular viewing under two conditions: "consistent error" control, where the trial-by-trial ISS size was a constant 4° and "variable error", where the ISSs were distributed normally around 4.0±1.0°. We modeled the probability distribution of saccadic amplitudes to ±19° visual targets in 8 anisometropic amblyopia patients (n=1000) and 11 visually-normal controls (n=1800) viewing with their amblyopic/nondominant eye. Saccadic amplitude variance for controls was subtracted from that of patients to yield the variance of the second target step for our "variable error" condition. Percentage and time constants of adaptation were measured and compared across conditions.
Percentage adaptation within controls decreased significantly during the "variable error" condition (49±5%) compared to the "consistent error" condition (73±8%; mean ± 95% CI) during nondominant eye viewing. This adaptation magnitude decrement in controls (49±5%) was comparable to our published percentage adaptation values in anisometropic amblyopia patients during an identical "consistent error" condition with their amblyopic eye viewing (45±7%, Raashid et al., 2013). Adaptation time constants did not differ in controls between conditions (consistent: 24±13; variable: 12±7 trials), or compared to patients during the "consistent error" condition (19±7 trials).
Our preliminary findings suggest that adding exogenous spatial noise consistent with amblyopic saccadic endpoint variability to the intrasaccadic step results in reduced adaptation in healthy individuals. We suggest that postsaccadic error variability inherent in anisometropic amblyopia may be one of the predictors of impaired adaptation in these patients.
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