Billy R. Hammond

Cigarette Smoking and Retinal Carotenoids: Implications for Age-related Macular Degeneration

The foveal region of the retina has a yellow pigmentation composed primarily of the carotenoids lutein and zeaxanthin. Past studies have shown that cigarette smoking depresses carotenoid concentrations in the blood. This is the first report on the effects of cigarette smoking on carotenoids in the retina. Macular pigment optical density (MP) was measured psychophysically by comparing foveal and parafoveal sensitivities to light of 460 and 550 nm. General dietary patterns, smoking frequency (cigaretts/day) and personal data were collected by questionnaire. Thirty-four smokers and 34 nonsmokers were compared. Subjects were matched with respect to age, sex, dietary patterns and overall pigmentation (i.e., eye, skin and hair color). The smoking group had a mean MP of 0.16 (SD = 0.12) compared to a mean MP of 0.34 (SD = 0.15) for nonsmokers (P < 0.0001). MP density and smoking frequency were inversely related (r = -0.498 P < 0.001) in a dose-response relationship. A variety of evidence suggests that MP protects the macula from actinic damage both passively (by screening potentially harmful short-wave light) and actively as an antioxidant (e.g., by quenching reactive oxygen species). If smoking causes a reduction in MP density, then smokers may be at risk. Epidemiologic data identifying smoking as a risk factor for the neovascular form of age-related macular degeneration are consistent with this hypothesis.

Sex Differences in Macular Pigment Optical Density:: Relation to Plasma Carotenoid Concentrations and Dietary Patterns

Sex differences in macular pigment (MP) optical density (measured psychophysically) were examined. Concentrations of lutein and zeaxanthin (L and Z) (non-separated) and beta-carotene (BC) in the blood were determined using reverse phase high-performance liquid chromatography. Dietary intake of L and Z, BC, fat, and iron were estimated by questionnaire. Males had 38% higher MP density than females (P < 0.001) despite similar plasma carotenoid concentrations and similar dietary intake (except for fat). Dietary intake of carotenoids, fat and iron, as well as plasma concentrations of L and Z were positively related to MP density in males. Conversely, only plasma L and Z was related to MP density for females, and dietary fat was negatively related to MP density. Sex differences in protection of the retina by MP and in the relationship between the retina, blood and diet could be a factor in the incidence of retinal diseases, especially age-related macular degeneration.

Macular pigment: influences on visual acuity and visibility.

There is increasing evidence that the macular pigment (MP) carotenoids lutein (L) and zeaxanthin (Z) protect the retina and lens from age-related loss. As a result, the use of L and Z supplements has increased dramatically in recent years. An increasing number of reports have suggested that L and Z supplementation (and increased MP density) are related to improved visual performance in normal subjects and patients with retinal and lenticular disease. These improvements in vision could be due either to changes in the underlying biology and/or optical changes. The optical mechanisms, i.e., preferential absorption of short-wave light, underlying these putative improvements in vision, however, have not been properly evaluated. Two major hypotheses are discussed. The acuity hypothesis posits that MP could improve visual function by reducing the effects of chromatic aberration. The visibility hypothesis is based on the idea that MP may improve vision through the atmosphere by preferentially absorbing blue haze (short-wave dominant air light that produces a veiling luminance when viewing objects at a distance).

The glare hypothesis of macular pigment function.

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°-diameter disk containing a black and white 100% contrast grating stimulus. The intensity of an annulus (the glare source) with an 11° inner and 12° 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°-diameter grating stimulus (detailed above) after a 5-s exposure to a 2.5 &mgr;W/cm2, 5°-diameter disk was recorded. Both central and eccentric (10° 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 (V&lgr;). Conclusions. MP is strongly related to improvements in glare disability and photostress recovery in a manner consistent with its spectral absorption and spatial profile.