From the numerous dietary carotenoids found in plasma, the primate retina selectively concentrates two xanthophyll carotenoids, lutein and zeaxanthin, in macular pigment. Trace quantities of α-cryptoxanthin and oxidized derivatives of lutein and zeaxanthin, are also present.
1 2 3 4 Two stereoisomers of zeaxanthin are found in the human retina: 3
R,3′
R-zeaxanthin (the form most common in the diet) and 3
R,3′
S-mesozeaxanthin.
5 Concentrations of lutein, and both forms of zeaxanthin peak in the fovea and decline rapidly with increasing eccentricity. Zeaxanthin predominates at the fovea and the immediate surrounding region.
3 5 6 7 Several lines of evidence support the concept that macular carotenoids may decrease the risk of age-related macular degeneration (AMD).
8 9 Risk for AMD, a major cause of blindness, has been strongly linked to greater age,
10 smoking,
11 12 and family history of AMD.
13 Increased risk for exudative AMD was associated with greater exposure to shorter wavelengths of visible light,
14 which is absorbed by macular pigment. Results in case-control studies indicated that risk for exudative AMD was reduced in those with elevated levels of lutein and zeaxanthin in diet
15 or serum,
16 but this correlation has not been observed in some population-based studies.
17 Reduced risk for drusen and pigmentary abnormalities in age-related maculopathy has also been associated with increased dietary and serum carotenoids.
18 In donor eyes with bull’s eye macular degeneration, we found that the area of preserved central retina corresponds to the area containing macular pigment.
19 Bone et al.
20 found that lutein and zeaxanthin concentrations are significantly lower in the central and rod-rich peripheral regions of donor eyes from subjects who had AMD. Both observations could be the consequence of preferential loss of rods in AMD.
21 However, using flicker rates detected preferentially by cones, Beatty et al.
22 also detected a significant reduction in macular pigment density in eyes at high risk for AMD.