Abstract: Preparations are disclosed containing the 3R-3′R stereoisomer of zeaxanthin as a sole detectable isomer, packaged for oral ingestion by humans as a therapeutic drug or nutritional supplement. Zeaxanthin is a yellow carotenoid pigment found in the macula (in the center of the human retina), which helps protect retinal cells against phototoxic damage. The pure R-R stereoisomer can be prepared by fermenting cells, such as Flavobacterium multivorum (ATCC 55238), which do not create any detectable quantity of the undesired and potentially toxic S-S or S-R isomers, and which do not synthesize any other carotenoids. The R-R isomer can be concentrated, in large quantities and at low cost, into a viscous oily fluid containing about 5 to 20% zeaxanthin, by means of a simple solvent extraction process. This oily fluid can be mixed with a carrier such as vegetable oil and enclosed within a digestible capsule, comparable to a conventional capsule containing Vitamin E.