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Alistair Curd, Karen Hampson, Edward Mallen; Suppression in the accommodative response to short-duration changes in dioptric stimulus. Invest. Ophthalmol. Vis. Sci. 2013;54(15):4262.
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To investigate whether suppression of the accommodation response (AR) would be observed when a dioptric stimulus performed a step-change, followed by an inverted step-change within the latency time for AR. Results would be relevant to models of accommodation and nearwork.
A monocular adaptive optics apparatus displayed a target to participants, and accommodation was recorded using a Shack-Hartmann wavefront sensor. A deformable mirror rapidly changed the dioptric stimulus provided by the target. The baseline vergence of the target was −2D at the eye. An initial step-change in the stimulus was followed by a second, inverted step, before the stimulus returned to the baseline. Initial steps were of 1D or 2D in either direction; intervals between the steps ranged from 0.05s to 0.5s. The stimulus settings were randomised in order. The six participants (aged 21-26) observed every stimulus condition five times, through their dominant eye. A Badal optometer arrangement was used to eliminate a size cue and audible cues from the system were masked with auditory input through headphones. Timings of the first change in the stimulus were randomised.
Whether accommodation was responding to the first or second change in the stimulus affected the peak AR (p<0.05 with t-tests, correcting for multiple comparisons). For 0.2s intervals between the changes in stimulus, accommodation and disaccommodation responses were suppressed when responding to the first step change, relative to the second (p<0.05). These mean decreases in the peak AR were 0.13D, 0.18D and 0.10D for 2D disaccommodative (DS) and 1D and 2D accommodative stimuli (AS), relative to the baseline (from peaks of 0.31D, 0.45D and 0.37D, respectively). 1D DS from the baseline required a longer interval between steps (0.25s) to elicit a response than did 2D DS, 1D AS and 2D AS. Changes in stimulus with intervals between 0.4s and 0.5s also significantly affected AR (p<0.05).
The accommodation system responds to changes that occur and are subsequently inverted well within its latency period.The response to the initial change in stimulus can be suppressed by a second change well within the latency. Changes in stimulus during onset may also affect the AR. During the latency, information from 200ms from the first change in stimulus, onwards, is used to determine the AR. Information prior to this is used, but less influential.
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