The glare hypothesis of macular pigment function

Abstract

Purpose: Discomfort and reduced visual performance due to glaring light conditions are common complaints for most individuals. Past studies have shown that macular pigment (MP) reduces discomfort due to glare. In this study, we evaluated whether MP was related to visual performance under glare conditions.

Methods: Thirty-six healthy subjects participated (age range, 18 to 41). Spatial profiles of MP optical density were measured using heterochromatic flicker photometry with a Newtonian-view macular densitometer. Photostress recovery and grating visibility under veiling conditions were assessed in a Maxwellian-view optical system. Both experiments used six monochromatic lights (from 440 to 620 nm) and a broadband xenon white. For the veiling glare experiment, subjects fixated a 1 degrees diameter disk containing a black and white 100% contrast grating stimulus. The intensity of an annulus (the glare source) with an 11 degrees inner and 12 degrees outer diameter was adjusted by the subject until the grating stimulus was no longer seen. For the photostress recovery experiment, the time required to detect a 1 degrees -diameter grating stimulus (detailed above) after a 5-s exposure to a 2.5 microW/cm2, 5 degrees -diameter disk was recorded. Both central and eccentric (10 degrees temporal retina) viewing conditions were assessed.

Results: MP at 30' eccentricity ranged from 0.08 to 1.04 OD, and was found to dramatically reduce the deleterious effects of glare. Visual thresholds under glare conditions were strongly related to MP density (e.g., r = 0.76, p = 0.0001 when using white light). Photostress recovery time, after exposure to xenon-white light, was significantly shorter for subjects with higher MP levels (r = -0.79, p = 0.0001). Both photostress recovery and veiling glare functions were well-described by the photopic spectral sensitivity function (Vlambda).

Conclusions: MP is strongly related to improvements in glare disability and photostress recovery in a manner consistent with its spectral absorption and spatial profile.