Vitamin A is actually a family of substances called retinoids that includes retinol, retinal, and retinoic acid. These are called preformed vitamin A because they are in a form that your body readily uses. Retinol is the most usable of the three forms and can be converted to both retinal and retinoic acid in your body.
Vitamin A is essential for vision. The carotenoids, lutein and zeaxanthin, are also important for your eyes and may help prevent cataracts and age-related macular degeneration (AMD). Unfortunately, AMD is usually the culprit when individuals age 60 or older experience blindness.
Milk is an excellent source of vitamin A. Carrots provide beta-carotene, which can be converted to vitamin A in your body. Eggs and spinach are good sources of lutein and zeaxanthin.