Senescence of foveal and parafoveal cone sensitivities and their relationsto macular pigment density

Foveal and parafoveal increment thresholds were measured for 50 observers ( 12-88 years of age) under conditions that isolated retinal mechanisms domin ated by short- (S-), middle- (M-), or long- (L-) wave-sensitive cones. Thre sholds were obtained on the plateau of the threshold-versus-intensity funct ion of each isolated mechanism and were referred to the retina by using ind ividual measurements of ocular media and macular pigment density. Age-relat ed increases in foveal thresholds, specified at the retina, were found for all three cone mechanisms. Parallel sensitivity losses for each cone mechan ism were also observed at 4 degrees and 8 degrees in the temporal retina. A significant positive correlation was found between foveal macular pigment density and the S-cone, but not the M- and L-cone, log sensitivity differen ce (0 degrees -8 degrees) specified at the retina. This relation is expecte d from the hypothesis that the macular pigment protects the photoreceptors from senescent losses in sensitivity. However, because this result is indep endent of age, it is interpreted as being due to local gain changes resulti ng from differential filtering of incident light by the macular pigment bet ween the fovea and the parafovea. (C) 2000 Optical Society of America [S074 0-3232(00)00911-X].