Macular pigments: their characteristics and putative role.

The macular pigments (MP) absorb light in the blue-green region of the visible spectrum and comprise two carotenoids, lutein and zeaxanthin. In humans the concentration of MP varies widely across the normal population. There are two (not mutually exclusive) proposed roles for MP: to improve visual function and to act as an antioxidant and protect the macula from damage by oxidative stress. In this article we review the origin, spectral characteristics and ocular distribution of MP and also discuss the effect MP has on central visual function and the techniques available for measurement of MP optical density in vivo. Finally, we review the evidence for both proposed physiological roles of MP. Considering the first of these, we conclude that although MP might improve visual function in theory, to date there is no firm evidence that higher levels of MP are correlated with enhanced measures of visual performance. There is a growing body of evidence that has highlighted associations between macular disease and low levels of MP, most particularly with age-related macular degeneration (AMD) and with risk factors for AMD. However, all findings to date are associative only and there is no direct evidence for high MP levels conferring a protective effect. Increased dietary intake of MP gives rise to increased levels of serum and retinal MP. This, taken together with the associative evidence of low MP levels in disease, indicates that a potential, and perhaps serendipitous, therapeutic strategy for macular disease exists. We conclude, however, that the potential protective properties of MP will only be fully evaluated by undertaking longitudinal studies that follow initially healthy participants through to the development of macular disease.