The influence of simulated visual impairment on distance stereopsis

Abstract

The intricate interrelationships between visual acuity (VA) and stereopsis depend on an array of factors, incorporating the nature of vision impairment, its manifestation (monocular versus binocular), and the classification of stereopsis test symbols used. The objectives of this study were to methodically dissect these multifaceted interactions by simulating a diverse range of vision loss conditions. Thirty medical students with normal vision were subjected to simulated vision loss through opacification and blurring methodologies. Stereopsis was assessed at a distance using both contour-based and random-dot-based symbols under equal binocular and varied monocular VA conditions. In this study, opacification consistently affected stereopsis more than blurring at equivalent VA reductions. However, this difference was absent in contour-based symbols under binocular vision impairment conditions. Significant differences in stereopsis emerged between monocular and binocular vision within the opacification contour-based groups. These differences were less evident in the opacification and blurring groups using random-dot-based patterns. In terms of symbols, the contour-based test demonstrated superior results to the random-dot-based test, particularly under decreased VA. In sum, the method of VA reduction and the choice of stereogram significantly impact distance stereopsis outcomes. This understanding can guide clinical assessments of stereopsis in individuals with varying visual impairments.

Figure 1.

Schematic diagram of distance stereopsis inspection.

Figure 2.

Schematic diagram of a phoropter modified for testing purposes. (A) A pair of circularly polarized lenses, modified with −0.12DC astigmatic lens auxiliary accessories (indicated by the blue arrows). The astigmatic lenses originally located behind the attachment have been replaced with circular polarizing films. Polarizers' orientations are calibrated to align optimally with the 3D display when set on the 180° axis, consequently providing the best 3D display effect. (B) Two magnetic strips affixed to the backplate of the phoropter (indicated by the green arrows). During the examination, these magnetic strips facilitate the attachment of opacification cards of varying concentrations (indicated by the purple arrows) to the area behind the peephole, thereby allowing modifications of the inspection conditions as required.

Figure 3.

3D simulation diagram of the visual target. (A) Contour-based symbols: This diagram represents the first-grade test page with predetermined disparities of 39 pixels (stereo circle positioned to the right), 26 pixels (stereo circle located at the bottom), and 13 pixels (stereo circle positioned at the top). (B) Random-dot−based symbols: This diagram showcases one of the third-grade test pages with established disparities of 11 pixels (stereo circle situated at the bottom), 10 pixels (stereo circle positioned at the top), and 9 pixels (stereo circle located to the left).

Figure 4.

Flow chart of three-level menu stereopsis inspection.

Figure 5.

Flow chart of test in blurring.

Figure 6.

Flow chart of test under opacification.

Figure 7.

Trend curves are characterized by the relationship between stereoacuity and different VA levels simulated by the opacification and fogging (blurring) methods. (A) Monocular VA decreases with random-dot-based stereograms. (B) Binocular VA decreases with random-dot-based stereograms. (C) Monocular VA decreases with contour-based stereograms. (D) Binocular VA decreases with contour-based stereograms. Stereopsis values were transformed to log arcsec values for visualizing. Datapoints and error bars represent the median and quartile of the stereopsis, respectively.

Figure 8.

Trend curves are characterized by the relationship between stereoacuity and different decreased monocular and binocular VA levels. (A) Opacification method with random-dot-based stereograms. (B) Fogging (blurring) method with random-dot-based stereograms. (C) Opacification method with contour-based stereograms. (D) Fogging method with contour-based stereograms. Stereopsis values were transformed to log arcsec values for visualizing. Datapoints and error bars represent the median and quartile of the stereopsis, respectively.

Figure 9.

Trend curves are characterized by the relationship between stereoacuity tested with random-dot-based and contour-based stereograms at different VA levels. (A) Opacification method with monocular VA decrease. (B) Opacification method with binocular VA decrease. (C) Fogging (blurring) method with monocular VA decrease. (D) Fogging method with binocular VA decrease. Stereopsis values were transformed to log arcsec values for visualizing. Datapoints and error bars represent the median and quartile of the stereopsis, respectively.