Chromatic and achromatic loss of sensitivity in glaucoma

Abstract

Purpose: Loss of both chromatic and achromatic sensitivity in glaucoma has been shown, however, the relative loss is unknown. We aim to quantify and establish which of these systems is affected most in glaucoma.Methods: Earlier experiments have shown that thresholds for detection of coherent motion of colour‐defined, spatially structured stimuli are not affected by dynamic luminance contrast noise. We used these results to design stimuli conditions that isolate chromatic and achromatic mechanisms. We studied 13 subjects with Primary Open Angle Glaucoma (POAG) with mean age of 70 years, 17 control subjects with a mean age of 68 years and 13 young normal subjects with a mean age of 31 years. Contrast thresholds were measured using a 4‐alternative, forced‐choice procedure involving discrimination of motion direction. Achromatic and chromatic sensitivities were measured, the latter along the tritan and protan confusion axes, foveally and at 8° eccentricity.Results: There were statistically significant differences between the three subject groups. Comparison of the control and POAG groups revealed a loss of sensitivity in the POAG group. Achromatic sensitivity thresholds increased 1.4‐fold (both at the fovea and at 8°), whereas chromatic thresholds increased 1.8‐ (B/Y) and 1.5‐fold (R/G) at the fovea and 2.0‐ (B/Y) and 1.6‐fold (R/G) at 8°. Comparison of the control and young groups reflected the ageing effects. Achromatic sensitivity showed 1.5‐fold reduction (both fovea and 8°), but the chromatic loss was more severe: 3.5‐ (B/Y) and 3.0‐fold (R/G) at the fovea, and 3.6‐ (B/Y) and 3.2‐fold (R/G) at 8°.Conclusions: The results confirm that the B/Y channel is most affected in glaucoma, but both chromatic and achromatic mechanisms are affected by ageing and glaucoma.