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Abstract
Retinal carotenoids lutein and zeaxanthin are found in high concentration in macula lutea of the neural retina, where they are termed macular pigment (MP). There are multiple hypotheses for MPs function in retinal tissue, based largely on lutein and zeaxanthins known antioxidant and light absorption properties. The protective hypothesis, the most widely tested of these hypotheses, suggests that MP is capable of protecting vulnerable retinal tissue from actinic damage and oxidative stress over the lifespan. The two least explored hypotheses, the visual function hypothesis and the neural efficiency hypothesis, suggest that MP is capable of influencing visual function via an optical mechanism and / or via a direct influence on central nervous tissue, both inside and outside the neural retina. In the latter case, MP may be capable of serving as a biomarker of lutein and zeaxanthin embedded in the frontal and occipital cortices. The purpose of the present investigation was to provide further examination of the visual function hypothesis and to provide a first test of the neural efficiency hypothesis.