Distribution of individual macular pigment carotenoids in central retina of macaque and squirrel monkeys.

The spatial distribution of lutein (L) and zeaxanthin (Z), the structural isomers composing the macular pigment, was studied in the retinas of macaque monkeys (Macaca fascicularis) and squirrel monkeys (Saimiri sciureus). Spatial profiles of macular pigment optical density were obtained from retinal whole mounts. Then concentric annuli were microdissected from the fovea and adjacent regions of the same retinas. Each retinal segment was analyzed for carotenoids by high-performance liquid chromatography. Both L and Z reached their highest concentrations at the center of the fovea and declined monotonically with eccentricity for both primate species. This is inconsistent with a preferential association of L with rods. Macaque monkeys have a consistent pattern of more Z than L at the foveal center, like humans. Z declines more rapidly than L with eccentricity, so that L becomes dominant in the periphery. Squirrel monkeys (all male) showed striking individual differences. Some had more Z than L at the foveal center like macaques, but four of six had the reverse pattern, with more L than Z throughout the central retina. Individual differences among squirrel monkeys may be linked to their color vision polymorphisms. This suggests that a particular Z/L ratio in primate retinas may be associated with a specific cone phenotype, just as particular carotenoids are associated with specific cone types in vertebrates with cone oil droplets.