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Title: Effect of induced astigmatic blur on the spatial frequency tuning of stereopsis
Authors: Tran, K
Bui, J
Yang, E
Moghtaderi, A
Ngo, C
Chat, S
Kee, CS 
Levi, D
Li, R
Issue Date: 2015
Source: American Academy of Optometry Annual Meeting 2015, New Orleans, USA, 7-10 October, 2015 How to cite?
Abstract: Purpose: It is well known that uncorrected astigmatism results in reduced stereoacuity. However, previous studies have used tests that are broadband in their spatial frequency content. The present study aimed to understand the effects of astigmatism on the spatial frequency tuning of stereoscopic depth perception.
Methods: The visual stimulus consisted of two horizontally separated square blocks, one presented to each eye. Each block contained a Gabor target patch surrounded by four Gabor reference patches. Binocular disparity was introduced by shifting the two Gabor targets in opposite directions, and a haploscope was used to enable binocular fusion. Stimulus spatial frequency ranged from 1-20 cyc/deg. The visual task was to determine the stereoscopic depth of the Gabor target (in front/behind) relative to the four references. Three young adult observers with normal visual acuity were tested. Plus cylindrical lenses were used to induce astigmatic blur in the two eyes. Appropriate plus lens powers were added to the distance correction in order to prevent accommodation for the viewing distances. Stereothresholds were measured for a range of against-the-rule astigmatism: from 0 to 2D.
Results: The stereoacuity versus spatial frequency function is basically the inverse of a typical contrast sensitivity function, with the optimum spatial frequency at 5-10 cyc/deg. Increasing the astigmatic blur degrades stereo thresholds selectively at high spatial frequencies, gradually shifting the optimum frequency to lower spatial frequencies. Interestingly, stereopsis for low frequency targets was only mildly affected even with high astigmatism. As expected, with-the-rule astigmatism did not remarkably affect stereoacuity.
Conclusions: Here we show that astigmatic blur results in spatial frequency specific losses of stereopsis. These findings have clinical implications for understanding both the sparing of coarse stereopsis and the deficits in fine stereopsis in meridional amblyopia.
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