Carotenoids in the retina and lens: possible acute and chronic effects on human visual performance.

(MP) that is composed of the hydroxy-carotenoids lutein and zeaxanthin. Although it appears that all humans have some quantity of these pigments within their retina, foveal concentrations tend to vary quite dramatically. This wide individual variability has prompted questions regarding possible functional consequences. At least two major nonexclusive hypotheses regarding the function of MP have been proposed. The "protection hypothesis" has received the most attention and is based on the possibility that MP could reduce the cumulative effects of damage due to light and oxygen and retard the development of age-related eye disease. The "acuity hypothesis" states that MP could improve visual resolution by absorbing short-wave light, which is easily scattered and poorly focused. In this article, we review evidence that lutein and zeaxanthin could improve human visual performance through both acute optical effects at the site of the retina and by maintaining health and functional integrity of the retina and crystalline lens.