Despite impaired binocular function, binocular disparity integration across the visual field is spared in normal aging and glaucoma

Abstract

Objective: To examine how binocularly asymmetric glaucomatous visual field damage affects processing of binocular disparity across the visual field. Design: Case-control study. Participants and Controls: A sample of 18 patients with primary open-angle glaucoma, 16 age-matched controls, and 13 young controls. Methods: Participants underwent standard clinical assessments of binocular visual acuity, binocular contrast sensitivity, stereoacuity, and perimetry. We employed a previously validated psychophysical procedure to measure how sensitivity to binocular disparity varied across spatial frequencies and visual field sectors, i.e. with full-field stimuli spanning the central 21° of the visual field, and with stimuli restricted to annular regions spanning 0°-3°, 3°-9° or 9°-21°. Main Outcome Measures: We verified the presence of binocularly asymmetric glaucomatous visual field damage by comparing—between the two eyes—the mean deviation values obtained from the Humphrey Field Analyzer (HFA) 24-2 test. To assess the spatial-frequency tuning of disparity sensitivity across the visual field of patients and controls, we fit disparity sensitivity data to log-parabola models and compared fitted model parameters. Lastly, we employed disparity sensitivity measurements from restricted visual field conditions to model different possible scenarios regarding how disparity information is combined across visual field sectors. We adjudicated between the potential mechanisms by comparing model predictions to the observed patterns of disparity sensitivity with full-field stimuli. Results: The interocular difference in HFA 24-2 mean deviation was greater in glaucoma patients compared to both young and age-matched controls (ps=.01). Across participant groups foveal regions preferentially processed disparities at finer spatial scales, whereas periphery regions were tuned for coarser scales (p<.001). Disparity sensitivity also decreased from the fovea to the periphery (p<.001) and across participant groups (ps<.01). Finally, similar to controls, glaucoma patients exhibited near-optimal disparity integration, specifically at low spatial frequencies (p<.001). Conclusions: Contrary to the conventional view that glaucoma spares central vision, we find that glaucomatous damage causes a widespread loss of disparity sensitivity across both foveal and peripheral regions. Despite these losses, cortical integration mechanisms appear to be well preserved, suggesting that glaucoma patients make the best possible use of their remaining binocular function.