Spectral sensitivities in dichromats and trichromats at mesopic retinal illuminances

Spectral sensitivity functions between 420 and 680 nm were determined by th reshold measurement at 5 deg eccentricity for deuteranopic and protanopic s ubjects at mesopic background illuminances. The results from these subjects are compared with those of normal trichromats. The functions obtained were analyzed for receptoral and postreceptoral activity. The mean curves of bo th dichromatic groups show evidence for rod activity up to a higher illumin ance level (14.98 td) than that for trichromats (4.70 td). in addition, the results indicate that S cones may be involved in detection at lower illumi nance levels in dichromats (from 0.15 td) than in normal observers (from 1. 49 td). (C) 1999 Optical Society of America [S0740-3232(99)03007-0].