Of the more than 600 types of carotenoids that exist in nature only 2 are found in the retina, accumulating in the macula lutea which is responsible for central vision. These carotenoids—lutein and zeaxanthin—help to filter or protect the retina from blue light or sunlight radiation that is harmful to the eyes, protect retina cells from damage, and defend against free radicals.
In addition to marigold flowers and goji berries, which are known to be the best natural food sources, lutein and zeaxanthin can also be found in corn, eggs, carrots, kale, cauliflower, amaranth, spinach, peas, pistachios, broccoli, morning glory, cucumber (including the peel), avocado, and pumpkin. Lutein and zeaxanthin are non-provitamin A carotenoids, meaning they are not converted into vitamin A like beta-carotenes are. This means they can be used immediately by the body and so not accumulate in the body when taken in excess.