Abstract
Purpose: :
Macular pigment (MP) selectively filters short-wave light, and an expanding body of literature suggests that MP is capable of improving visual function via this mechanism. One previously posited function that has not been tested is MP’s ability to alter contrast between an object and its background, and thus alter the object’s visibility (e.g., when viewing a mid-or long-wave object against the sky). The purpose of the current investigation was to test this ecologically relevant hypothesis.
Methods: :
Alterations in contrast were assessed in Maxwellian view using a three-channel optical system. A central 1-deg disk formed by wavelengths longer than those absorbed by MP could be superimposed with a high contrast (4 cycles / deg) grating. In condition A, this central target was surrounded by a 10-deg, 460 nm annulus, which is absorbed strongly by MP. In Condition B, the 10-deg surround was composed of broadband xenon light, which is only partially absorbed by MP. In Condition C, the 10-degree surround was composed of long wavelengths not absorbed by MP. In all conditions, subjects were required to adjust the intensity of the surround, relative to the target, until the target appeared to be desaturated and/or the grating was no longer visible. MP optical density was assessed psychophysically by heterochromatic flicker photometry (HFP).
Results: :
Individuals with higher MP density required more energy to induce desaturation and reduce discriminability of the target in Condition A (p < 0.05), than in Condition B (p > 0.05), suggesting that MP alters contrast via its optical filtration properties. Effects will be compared with results for Condition C.
Conclusions: :
MP serves a variety of functions in the primate retina, including modifying the contrast and discriminability of an object against a short-wave background. This improvement seems to be due to MP’s optical filtering properties.
Keywords: macular pigment • contrast sensitivity • color vision