Abstract
Purpose :
Uncorrected myopia and astigmatism result in reduced stereoacuity. However, previous studies have used tests that are broadband in their spatial frequency content. We developed a new stereoacuity test using narrow-band Gabor stimuli to evaluate depth perception at different spatial scales, from coarse to fine stereopsis. The present study aimed to characterize the impact of non-directional myopic blur and directional astigmatic blur on the spatial frequency tuning of stereopsis.
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 of or behind) relative to the Gabor references. Four young adult observers with normal vision were tested. Positive spherical and cylindrical lenses (i.e., +1.00 DS and +1.00 D x 90) were used to induce myopic and astigmatic refractive errors, respectively, in the two eyes. Appropriate plus lens powers were added to the distance correction in order to minimize ocular accommodation at the viewing distances (0.5 m, 1 m, and 2 m).
Results :
The stereoacuity versus spatial frequency function was essentially the inverse of a typical contrast sensitivity function, with the optimum spatial frequency at around 7.5 cyc/deg. The induced spherical and astigmatic blur degraded stereoacuity selectively and substantially at high spatial frequencies, shifting the optimum frequency to lower spatial frequencies. Interestingly, stereopsis for low spatial frequency targets was only mildly affected in both refractive conditions. On average, at a given spatial frequency, stereothresholds were significantly elevated by 18% more with spherical defocus compared to astigmatic defocus.
Conclusions :
Using a new stereoacuity test, we characterized the effects of uncorrected myopia and astigmatism on depth perception at different spatial scales. Both types of refractive errors affected stereoacuity similarly over a range of spatial frequencies, but myopic defocus led to a greater degradation in stereoacuity compared to astigmatic defocus.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.