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Roger W. Li, Kevin Gustafson, Sandy Chat, Dennis Levi; Towards Establishing A New Treatment Protocol For Improving Stereovision In Patients With Amblyopia. Invest. Ophthalmol. Vis. Sci. 2012;53(14):3893.
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Reduced visual acuity in amblyopia can be substantially improved with perceptual learning, and the effects sometimes generalize to improved stereoacuity (Li et al., 2004-2011). Our current experiment isaimed at investigating the residual plasticity of stereopsis in those "previously treated" amblyopic patients.
Seven adults with non-strabismic amblyopia participated in this study. All of them had already completed an earlier course of perceptual learning treatment and showed improvements in visual acuity. In this experiment, they were required to practice a stereo discrimination task repetitiously over a period of months. The visual stimulus consisted of two horizontally separated square blocks, one presented to each eye. Each block contained a target Gabor patch surrounded by four reference Gabor patches. Binocular disparity was introduced by shifting the two target Gabors in opposite directions (controlled by 2 interleaved staircases), and a haploscope was used to enable binocular fusion. The position and phase of each Gabor patch was randomly jittered to eliminate any possible monocular cues. The visual task was to determine the stereoscopic depth of the target Gabor (crossed disparity: in front of / uncrossed disparity: behind) relative to the four references. We also trained seven normal observers for comparison.
All amblyopes showed a rapid, and very substantial improvement in stereoacuity, by as much as a factor of 3-8. We found those who initially presented with higher thresholds needed a longer period to reach plateau performance, and the time taken to reach the plateau levels was roughly proportional to the stereothreshold deficit.
Here we show that practicing a stereo discrimination task can improve stereoacuity in adult amblyopic patients. Importantly, this new technique might be useful, in combination with other vision training egimens, to induce binocular plasticity and boost the already improved stereoacuity in previously treated amblyopes.
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