Test Details: Vitamin A is an essential nutrient required for healthy vision and skin, bone formation, immune system function, and reproduction. It is required to produce photoreceptors in the eyes and to maintain the lining of the surface of the eyes and other mucous membranes. A lack of vitamin A can affect night vision, cause eye damage, and in severe cases, lead to blindness. Too much vitamin A can be toxic, causing a range of symptoms, and sometimes leading to birth defects. Vitamin A deficiencies are primarily seen in those with malnutrition, chronic diarrheal, malabsorption disorders such as celiac disease, cystic fibrosis, or chronic pancreatitis, in the elderly, and in those with alcoholism, liver disease and blockage of the bile ducts.