Carotenoids (xanthophylls) have been proposed to play various roles in biological systems, including limiting chromatic aberration at the fovea of the retina and quenching of 1O2. Beta carotene, the precursor of vitamin A, can act as a free radical trap at low oxygen tension. Studies of postmortem human retinas have shown that carotenoids make up the yellow pigment in the macula. Two carotenoids, lutein and zeaxanthin, are present in the macula and located in the Henle fiber layer. In humans, zeaxanthin is concentrated primarily in the fovea, whereas lutein is dispersed throughout the retina. Interestingly, little beta carotene is present in the human eye. Furthermore, carotenoids are present only in the retina and are absent from the RPE. In the peripheral retina, lutein and zeaxanthin are concentrated in rod outer segments and may act as antioxidants to protect against short-wavelength visible light. Figure 14-3A shows the localization of antioxidants in the human macula and peripheral retina, and Figure 14-3B shows their localization in a cross section of the peripheral retina.
Chew EY, Clemons TE, Agrón E, et al. Long-term effects of vitamins C and E, beta-carotene, and zinc on age-related macular degeneration. AREDS report no. 35. Ophthalmology. 2013;120(8):1604–1611.
Khachik F, Bernstein PS, Garland DL. Identification of lutein and zeaxanthin oxidation products in human and monkey retinas. Invest Ophthalmol Vis Sci. 1997;38(9):1802–1811.
Excerpted from BCSC 2020-2021 series: Section 2 - Fundamentals and Principles of Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.