Functional Loss in the Magnocellular and Parvocellular Pathways in Patients with Optic Neuritis

PURPOSE. To evaluate contrast threshold and contrast gain in patients with optic neuritis under conditions designed to favor mediation by either the inferred magnocellular (MC) or parvo-cellular (PC) pathway. METHODS. Achromatic and chromatic contrast discrimination was measured in 11 patients with unilateral or bilateral optic neuritis and in 18 age-matched controls with normal vision, using achromatic steady- and pulsed-pedestal paradigms to bias performance toward the MC or PC pathway, respectively. In addition, L-M chromatic discrimination at equiluminance was evaluated using the steady-pedestal paradigm. A physiologically plausible model could describe the data with parameters ac-counting for contrast gain and contrast sensitivity in the in-ferred MC or PC pathway. The fitted parameters from the eye affected by optic neuritis were compared with those from th