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Billy R. Hammond, Jr., Bill Smollon, Billy R. Wooten; Compensation For Variation In Macular Pigment Optical Density Across Individuals. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3634.
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Even when the same quanta enter the eyes of different individuals, light incident on the photoreceptors themselves differs greatly, particularly for short-wave visible light. This is due to the presence of significant intraocular absorption by chromophores such as the intraretinal macular pigments (MP). Past data has shown that peak S-cone sensitivity and color perception (for the Y-B opponent system) is constant across the retina. These findings imply that the visual system must compensate, in some part, for variation in MP filtering. The question of whether the visual system also compensates for MP filtering across individuals, however, has not been specifically tested. When all things are equal, does an individual with high levels of MP have different perceptions (e.g., sensitivity to the color blue) than an individual with low MP? This study addressed this question.
35 subjects were tested. Yellow (Y, 581 nm)/blue (B, 490 nm) and red (R, 600 nm)/green (G, 501 nm) cancellation functions were obtained. MP optical density at 460 nm was measured using heterochromatic flicker photometry.
Hue-cancellation ratios for the R-G opponent system (501-600) were strongly related (r2 = 0.66) to MP density. This effect was linearly related to MP amount as shown by a slope near one and an intercept near zero (Y = 1.09X - 0.10; under photopic conditions). In contrast, MP was not linearly related to hue cancellation ratios (490/581) for the Y-B system (Y = 0.61X - 0.23; under photopic conditions).
The amount of green light (501 nm) needed to reach a perceptual white when mixed with red was linearly related to MPOD suggesting no compensation within the R-G opponent system for MP filtering. In contrast, the amount of blue light (490 nm) needed to reach a perceptual white when mixed with yellow was not linearly related to MPOD suggesting only partial compensation for MP density across subjects (as opposed to past studies that have found complete compensation when testing across retinal sites of the same individual). Our data also show that the locus for unique green also tends to shift towards longer wavelengths with higher levels of MP density. Taken together, these data suggest that compensation for MP density is relegated to specific visual mechanisms (the Y-B system) and that this correction occurs at post-receptoral sites.
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