Assessment of contrast gain signature in inferred magnocellular and parvocellular pathways in patients with glaucoma

Purpose: Contrast gain signatures of inferred magnocellular and parvocellular postreceptoral pathways were assessed for patients with glaucoma using a contrast discrimination paradigm developed by Pokomy and Smith. The potential causes for changes in contrast gain signature were investigated using model simulations of ganglion cell contrast responses. Methods: Foveal contrast discrimination thresholds were measured with a pedestal-A-pedestal paradigm developed by Pokorny and Smith [Pokorny, J., & Smith, V. C. (1997). Psychophysical signatures associated with magnocellular and parvocellular pathway contrast gain. Journal of the Optical Society of America A, 14(9), 2477-2486]. Stimuli were 27 ms luminance increments superimposed on 227 ms pulsed A-pedestals. Contrast thresholds and contrast gain signatures mediated by the inferred magnocellular (MC) and parvocellular (PC) pathways were assessed using linear fits to contrast discrimination thresholds at either lower or higher A-pedestal contrasts, respectively. Twenty-seven patients with glaucoma were tested, as well as 16 age-similar control subjects free of eye disease. Results: Contrast sensitivity and contrast gain signature mediated by the inferred MC pathway were lower for the glaucoma group, and reduced contrast gain signature was correlated with reduced contrast sensitivity (r 2 =45%, p