ABSTRACT
I. INTRODUCTION Chemical and biological properties of carotenoids are described in several reviews (1-5). It is known that about 600 distinct compounds are identified as naturally occurring carotenoids (6). They include cyclic hydrocarbon carotenoids (carotenes), acyclic hydrocarbon carotenoids (lycopene), and oxygenated hydrocarbon carotenoids (xanthophylls). The distribution of each carotenoid is quite different in the tissues and organs of humans (7-9). Major carotenoids in the human plasma are lutein, zeaxanthin, β-cryptoxanthin, lycopene, α-carotene, and β-carotene (10). The necessity of carotenoids for normal visual function referring to their provitamin A activity has long been known. However, also the role of a carotenoid itself in eye tissue, namely in the retina, has been intensively studied. It was demonstrated that the two polar substances, lutein and zeaxanthin, are the major carotenoids in the eye (11). They are concentrated throughout the whole retina; however, their highest concentration is at the locus of sharpest vision, the macula, forming the macular pigment. Handelman et al. (11) showed the carotenoid concentration in the macula to be fivefold higher compared with the peripheral retina. Lutein is the major carotenoid in the peripheral retina, whereas zeaxanthin becomes more and more dominant approaching the foveal center.
