Vitamin A is one of the most vital vitamins for the overall health of our body. Also known as retinol, it plays an essential role in the formation of rhodopsin, a photoreceptor pigment in the retina of the eye. It also helps in maintaining the epithelial tissues that line most internal organs, glands, and the body's surfaces. It’s our liver that stores about 80-90% of vitamin A thus its deficiency can be due to liver disorder. Therefore to check the lack that can even lead to death in kids, the doctor suggests the vitamin A test.