**1. Introduction**

Decades of research have indicated that abundant intake of carotenoid-rich food is correlated with the reduced risk of several age-related ocular diseases, for example, age-related macular degeneration (AMD) and diabetic retinopathy (DR). To date, among more than 1000 carotenoids discovered in nature, about 50 have been identified in the human diet [1]. However, only 25 dietary carotenoids and 9 of their metabolites have been found in human plasma, of which lutein, its stereoisomers zeaxanthin and meso-zeaxanthin are highly concentrated in the human retina [2].

Lutein is one of xanthophyll carotenoids (oxygen-containing carotenoids) which exist in the dark green leafy vegetables, yellow fruits and vegetables, and egg yolk [1]. Since animals are

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

not able to produce lutein, they need to depend on the dietary consumption. After absorption of lutein with fat, it is attached to the lipoprotein and then transported into the circulation; subsequently, with the serum concentration of 0.2 μm, lutein reached throughout the body and accumulated in the eye, especially in the retina, to serve certain biological functions [3]. In the human eye, the distribution of lutein varies. Lutein is found in higher quantities within the peripheral retina, retina pigment epithelium (RPE), choroid and ciliary body while exhibiting low concentrations in the iris and lens [2].

According to the most updated data from WHO, 253 million people suffer from vision impairment, and 81% people who are blind or have moderate or severe vision impairment are aged 50 or above [4]. A large number of studies have indicated that lutein plays an important role in decreasing the risk of AMD, the leading cause of blindness in the elderly people in the developed countries [5, 6]. Clinical trials have demonstrated that lower concentration of lutein in retina and serum was observed in DR patients when compared with patients without diabetes [7]. Moreover, DR patients receiving lutein and zeaxanthin supplements have shown improvement in visual acuity and contrast sensitivity, indicating a possible benefit in delaying the onset and development of DR [7]. In this chapter, we will introduce the background information of lutein, summarize its functions in the normal eye, and discuss the effects of lutein in age-related eye diseases.
