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Sara Alarcon Carrillo, Alex S. Baldwin, Mao Yu, Jiawei Zhou, Robert F. Hess; Why is stereoacuity poor in amblyopia? Evidence from a disparity noise-masking paradigm. Journal of Vision 2020;20(11):1634. doi: https://doi.org/10.1167/jov.20.11.1634.
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People with amblyopia generally have a reduced ability to use stereopsis to make depth judgements. Our understanding of this reduced ability is limited by the insensitivity of standard clinical stereo tests. These tests fail to detect residual stereo function in some amblyopic subjects. The current study employs a test designed for individuals with poor stereoacuity. The subject identifies the location of a 3D target in a random-dot display. The target is presented in stereoscopic depth using 3D shutter-glasses. We applied the equivalent noise method to determine the role of equivalent internal noise (signal to noise ratio of disparity signals) and processing efficiency (how efficiently the system processes noisy input) in amblyopic stereopsis. We tested 30 amblyopic (7 strabismic, amblyopic eye visual acuity above 20/200) and 17 control (visual acuity above 20/20) adults. Our test detected stereoacuity in 50% of amblyopic participants. Amblyopic stereoacuity thresholds (m =118 arsec) were significantly higher than those from controls (m = 57 arcsec) (t = 2.8, p < 0.05). From a linear amplifier model fit, we found higher mean equivalent internal noise in amblyopic subjects (239 arsec) compared to controls (134 arcsec) (t = 3.45, p < 0.05). The two groups did not significantly differ in the processing efficiency for the task. A multiple linear regression was performed to determine the contribution of the two factors (equivalent internal noise and efficiency) to the individual differences in amblyopic stereoacuity. The two factors accounted for 66% of the variance in stereoacuity, with differences in equivalent internal noise as the strongest predictor. This study introduced a more sensitive assessment of residual stereopsis in amblyopia and evaluated how two factors contribute to individual performance. Overall, we find that reduced amblyopic stereoability is explained by poorer input quality to the stereoscopic disparity processing mechanism.
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