The Absorption, Storage, and Transport of Ocular Carotenoids and Retinoids.

Carotenoids, yellow and red pigments found abundantly in nature, play essential roles in various aspects of human physiology. They serve as critical molecules in vision by functioning as antioxidants and as filters for blue light within the retina. Furthermore, carotenoids are the natural precursors of vitamin A, which is indispensable for the synthesis of retinaldehyde, the visual chromophore, and retinoic acid, a small molecule that regulates gene expression. Insufficient levels of carotenoids and retinoids have been linked to age-related macular degeneration and xerophthalmia, respectively. Nevertheless, the mechanisms by which the eye maintains carotenoid and retinoid homeostasis have remained a mystery. Recent breakthroughs identified the molecular players involved in this process and provided valuable biochemical insights into their functioning. Mutations in the corresponding genes disrupt the homeostasis of carotenoids and retinoids, leading to visual system pathologies. This review aims to consolidate our current understanding of these pathways, including their regulatory principles.