Binocular Interactions in Glaucoma Patients With Nonoverlapping Visual Field Defects: Contrast Summation, Rivalry, and Phase Combination

Abstract

Purpose: In glaucoma, visual field defects in the left and right eye may be non-overlapping, resulting in an intact binocular visual field. In clinical management, these patients are often considered to have normal vision. However, visual performance also relies on binocular processing. The aim of this study was to evaluate binocular visual functions in glaucoma patients with intact binocular visual field, normal visual acuity, and stereoscopy.

Methods: We measured in 10 glaucoma patients and 12 age-similar controls: (1) monocular and binocular contrast sensitivity functions (CSF) using a modified quick CSF test to assess binocular contrast summation, (2) dominance during rivalry, and (3) contrast ratio at balance point with a binocular phase combination test. A mirror stereoscope was used to combine the left and right eye image (each 10° horizontally by 12° vertically) on a display.

Results: Area under the monocular and binocular CSF was lower in glaucoma compared to healthy (P < 0.001), but the binocular contrast summation ratio did not differ (P = 0.30). For rivalry, the percentage of time of mixed percept was 9% versus 18% (P = 0.056), the absolute difference of the percentage of time of dominance between the two eyes 19% versus 10% (P = 0.075), and the rivalry rate 8.2 versus 12.1 switches per minute (P = 0.017) for glaucoma and healthy, respectively. Median contrast ratio at balance point was 0.66 in glaucoma and 1.03 in controls (P = 0.011).

Conclusions: Binocular visual information processing deficits can be found in glaucoma patients with intact binocular visual field, normal visual acuity, and stereoscopy.

Figure 1.

(A) Schematic illustration of the experimental setup. (B) Illustration of the instructions given to the participant: Two frames were dichoptically displayed to the left and right eye and the subject adjusted the stereoscope to fuse the two images into a single dot with four lines. (C) Example of each visual stimulus (not to scale); from top to bottom: quick CSF test, rivalry test, and phase combination test.

Figure 2.

Boxplot with jitter of the monocular and binocular group comparisons of contrast sensitivity function (CSF) parameters, including area under the log CSF (AULCSF; A), peak sensitivity (B; log units), peak spatial frequency (C; log cpd), and β (D; log unit of cpd [to convert to octave, this number should be multiplied by log10/log2 = 3.32]), for glaucoma patients (blue) and controls (red).

Figure 3.

Percentage of time, corresponding to dominance of the better eye (orange), dominance of the worse eye (blue), and mixed percept (red) for each individual subject. Left panel corresponds to the glaucoma patients, right panel to the controls.

Figure 4.

(A) Average psychometric functions for the two groups and the corresponding individual data, showing the probability of the better eye being stronger as a function of interocular contrast ratio. (B) Boxplot with jitter of the contrast ratio at balance point. Glaucoma patients (blue) and controls (red).