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J. M. Stringham, B. R. Hammond, Jr., M. Engles; The Glare Hypothesis of Macular Pigment Function. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2146.
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Discomfort and reduced visual performance due to glaring light conditions are common complaints for most individuals. Past studies have shown that macular pigment (MP, the yellow screening pigments in the inner layers of the fovea) reduces discomfort due to glare. In this study we evaluated whether MP was related to visual performance under glare conditions.
36 healthy subjects participated (age range 18-41). Spatial profiles of MP optical density (MPOD) were measured using heterochromatic flicker photometry (HFP) with a Newtonian-view macular densitometer. Photostress recovery and grating visibility under veiling conditions were assessed in a Maxwellian view optical system. For the veiling glare experiment, subjects fixated a 1 deg.-diameter disk containing a black and white 100% contrast grating stimulus. The intensity of an annulus (the glare source) with an 11 deg. inner and 12 deg. outer diameter was adjusted by the subject until the grating stimulus was no longer seen. This was done for six narrow-band wavelengths (from 440 nm to 620 nm) and a broad-band xenon-white. For the photostress recovery experiment, the time required to detect a 1 deg.-diameter grating stimulus (detailed above) after a 5-second exposure to a 2.5µW/cm2, 5 deg.-diameter disk was recorded. The wavelength of the test stimulus ranged from 420 nm to 640 nm, and a xenon-white stimulus was also used. Subjects were tested under central viewing and eccentric viewing (10 deg. temporal retina) conditions.
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 veling glare functions were well-described by the photopic spectral sensitivity function (V).
MP is strongly related to improved visual function under glare conditions, prompting the question of whether increasing MP density through supplementation would reduce some of the deleterious effects of glare.
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