By Jim Stringham0
Lutein and the two zeaxanthin isomers, RR-zeaxanthin (3R, 3’R-zeaxanthin) and RS-zeaxanthin (“mesozeaxanthin,” 3R, 3R’S-mesozeaxanthin) are the only three carotenoids found in the eye, specifically in the macula of the retina. RR-zeaxanthin and mesozeaxanthin are both considered zeaxanthin. They are obtained via the diet, and concentrated in the central retina (termed the macula—the region of the retina responsible for highest visual performance). The location of their respective areas of deposition is highly specific: lutein is the dominant carotenoid in the peripheral macula, RR-zeaxanthin in the mid-peripheral macula and mesozeaxanthin at the center of the macula.

Each of these carotenoids plays an important role in protecting the retina and enhancing visual performance. The characterization and functions of lutein and RR-zeaxanthin are well known, and the science behind these two xanthophylls has grown at a steady rate.

Mesozeaxanthin historically had been incorrectly coupled with RR-zeaxanthin as an impurity or its isomer, and the measurement of mesozeaxanthin in serum and foods had largely been ignored until awareness of its specific role in the eye emerged. Each of the macular carotenoids is a powerful antioxidant with specific targets. Mesozeaxanthin is the most potent of the three, followed by RR-zeaxanthin, which is twice as potent as lutein in quenching free radicals. The protective role of lutein focuses on the cellular membrane. Mesozeaxanthin is located at the very center of the macula, the focal point of visual function. Its central location and stronger antioxidant potential make mesozeaxanthin critical in protecting the most at-risk tissue with the highest metabolic rate and light exposure, and it also provides the best protection for the lipid membrane.

A mixture of the three macular carotenoids at a ratio of 1:1:1 has been shown to quench singlet oxygen more effectively than any of the three individually. Mesozeaxanthin and RR-zeaxanthin are perpendicular to the cell membranes to better protect the lipid membrane from oxidation, and also to absorb similar wavelengths of high-energy light.
Lutein is parallel, perpendicular to and oriented near the surface of the cell membrane, making it a better filter of blue light. However, because lutein and the zeaxanthin isomers absorb different wavelengths of light, together, the three absorb a broader spectrum of high energy light….
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source: Natural Product Insider