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Rana Arham Raashid, Herbert Goltz, Alan Blakeman, Manokaraananthan Chandrakumar, Agnes Wong; Temporal Pattern of Short-Term Saccadic Adaptation in Amblyopia. Invest. Ophthalmol. Vis. Sci. 2013;54(15):177.
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© ARVO (1962-2015); The Authors (2016-present)
Sensorimotor adaptive mechanisms maintain the accuracy of goal-directed saccades. Recently, we investigated saccadic gain adaptation in amblyopia, a disorder characterized by impairment of spatiotemporal visual processing. We found that patients adapt to a lesser spatial extent than visually normal controls (Raashid et al., ARVO 2012). Here we hypothesise that patients with amblyopia will exhibit a slower exponential temporal course of saccadic adaptation.
14 visually normal adults and 10 adult patients with amblyopia performed a double-step adaptation task (18° target step, followed by a 4° back-step), during binocular viewing and monocular viewing with the amblyopic and fellow eye (non-dominant and dominant eye in normal subjects) in three separate sessions. To quantify the time course of adaptation, the saccadic gain was modelled to decrease exponentially as a function of increasing number of trials. Individual data were fitted by the nonlinear regression equation G(t) = G0 + ΔGe−t/τ, where the time constant was given by τ number of trials. The coefficient of determination (R2) was also computed.
Most of the participants' data were fitted reliably using the exponential function, with the exception of 3 patients and 1 control who exhibited a linear decrease in gain under certain viewing conditions. Controls decreased their saccadic gain with a mean time constant of 25±16 trials with non-dominant eye viewing, 27±18 trials when viewing binocularly, and 23±14 trials with dominant eye viewing. Compared to controls, patients exhibited a similar mean time constant during amblyopic eye (30±12 trials), binocular (28±9 trials) and fellow eye (25±15 trials) viewing conditions (p=0.922). The R2 values were also comparable between controls and patients, across non-dominant/amblyopic eye (control=0.31±0.11, patients=0.25±0.07), binocular (control=0.35±0.14, patients=0.38±0.13) and dominant/fellow eye (control=0.30±0.11, patients=0.30±0.15; p=0.552) conditions.
The temporal course of adaptive changes in saccadic gain can be modelled as a decreasing exponential function in most patients with amblyopia. Among these patients, the time constants are comparable to visually normal controls, suggesting that the adapting saccadic gain in patients most likely decreases at a rate similar to controls. A larger sample size of patients will further substantiate the nature of the temporal course of adaptation in amblyopia.
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