vitamin A

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Nutritional sources of vit A

Good sources of retinol or preformed vitamin A are liver, fish-oils, egg, yolk and dairy products. Human and other animals convert carotenoids to retinol and its metabolites, or they obtain preformed vitamin A in foods of animal origin or in nutritional supplements.
Vitamin A in vision

In the retina, retinaldehyde functions as the prosthetic group of the light-sensitive opsin proteins, forming rhodopsin vitamin A helps protect the surface of the eye (cornea), it is essential for good vision.
Studies show vitamin A eye drops are effective for the treatment of dry eyes. In fact, one study found that over-the-counter lubricating eye drops containing vitamin A were as effective for the treatment of dry eye syndrome as more expensive prescription eye drops formulated for dry eye relief.
Vitamin A eye drops also have been shown effective for the treatment of a specific type of eye inflammation called superior limbic keratoconjunctivitis.Because beta-carotene is converted into vitamin A in the body, it's likely this provitamin an offers similar eye benefits as the pre-formed retinol type of vitamin A, though more research is needed to confirm this.
And researchers at Columbia University Medical Center found that a synthetic, altered form of vitamin A might be able to slow the progression of Stargardt's disease, an inherited eye disease that causes severe vision loss in young people.
When given to mice with the same genetic defect as humans with Stargardt's disease (also called juvenile macular degeneration), the modified vitamin A inhibited the growth of clump-like deposits in the retina called "vitamin A dimers" that are associated with degenerative changes and vision loss.
The National Eye Institute has awarded the researchers a $1.25 million grant to further investigate the link between vitamin A dimers and various retinal degenerations, which could lead to new approaches to treat these diseases.


What foods provide vitamin A?
Vitamin A is found naturally in many foods and is added to some foods, such as milk and cereal. You can get recommended amounts of vitamin A by eating a variety of foods, including the following:

Beef liver and other organ meats (but these foods are also high in cholesterol, so limit the amount you eat).
Some types of fish, such as salmon.
Green leafy vegetables and other green, orange, and yellow vegetables, such as broccoli, carrots, and squash.
Fruits, including cantaloupe, apricots, and mangos.
Dairy products, which are among the major sources of vitamin A for Americans.
Fortified breakfast cereals.

source:
https://www.allaboutvision.com/nutrition/vitamin_a.htm
https://ods.od.nih.gov/factsheets/VitaminA-Consumer/