Rapid contrast adaptation in glaucoma and in aging

PURPOSE: The visual system rapidly adapts to contrast changes, often with each fixation. One key anatomical site underpinning contrast adaptation is the retinal ganglion cell dendrites, where degenerative changes occur in glaucoma. This study investigated the effects of early glaucoma and aging on rapid contrast adaptation.

METHODS: Contrast detection and discrimination thresholds were measured in central vision for briefly presented (94 ms) Gabor patches with and without adaptation to 50% contrast Gabor patches (1000 ms). Fourteen people with glaucoma (aged 58-77 years), 17 age-similar controls (aged 50-72 years), and 19 younger adults (aged 20-31 years) participated. Detection thresholds were measured at various time points (47, 106, 200, 400, 600, and 1000 ms) post adaptation. Discrimination thresholds were measured post adaptation relative to a reference contrast below (30%), equivalent to (50%), or above (70%) the adaptor.

RESULTS: The glaucoma group demonstrated elevated unadapted detection (P < 0.0001) and discrimination (P = 0.01) thresholds relative to age-similar controls. In normal observers, aging elevated unadapted thresholds (detection: P < 0.0001; discrimination: P < 0.0001). At 47 ms post adaptation, the glaucoma group demonstrated reduced effects of adaptation relative to controls (P = 0.009). Adaptation was also reduced when the reference contrast (50%) was equivalent to the adaptor (P = 0.02). Aging did not alter adaptation of normal observers.

CONCLUSIONS: Glaucoma alters rapid contrast adaptation while aging does not. Contrast adaptation is key to visual processing in natural visual environments. Our results imply that glaucoma produces abnormalities in natural visual experiences in central vision.