Macular Pigment Carotenoids and Their Roles in Human Eye Health and Diseases

Abstract

Macular pigment (MP) carotenoids lutein, zeaxanthin and their metabolites are the pigments that account for the yellow color of the human macula. The majority of MP is deposited at the fovea’s Henle fiber layer which consists of the foveal cones’ axons, and its highest concentration can reach 1 mM. MP cannot be synthesized in human or animal bodies, so vegetables and fruits generally serve as a carotenoid source. The MP uptake process is complex, with several carotenoid-binding proteins, such as glutathione S-transferase P1, StAR-related lipid transfer domain protein 3, and tubulin involved, along with the participation of some transport proteins such as HDL and scavenger receptor class B member 1. Many instruments have been invented to measure macular pigment optical density, and we discuss heterochromatic flicker photometry, fundus reflectometry, autofluorescence imaging, and resonance Raman spectroscopy. Two proposed functions of MP are photoprotection and acuity enhancement. Their protective mechanisms are thought to be the following: (1) filtering blue light to prevent the formation of free radicals, especially singlet oxygen or (2) reducing oxidation by directly quenching singlet oxygen and other reactive oxygen species. We also discuss the relationship of MP with age-related macular degeneration, macular telangiectasia type 2, and its potential to improve human visual acuity. In addition, the recent ocular carotenoid supplementation studies are reviewed in this chapter.