Vitamin A deficiency and the eye.

Vitamin A deficiency is the leading cause of childhood blindness worldwide. It is most prevalent in developing countries, with the World Health Organization estimates of approximately 228 million children affected by moderate to severe deficiency. At greatest risk are the malnourished children born to vitamin A–deficient mothers, particularly if they are affected concurrently by other biological stressors, such as diarrhea or measles. Although rare in the United States, vitamin A deficiency has been known to occur as a result of poor dietary intake, liver diseases, and gastrointestinal malabsorption. The spectrum of ocular disease arising from vitamin A deficiency is known as xerophthalmia. Ocular changes include conjunctival and corneal drying (xerosis), corneal ulceration and melting (kerotomalacia), night blindness (nyctalopia) and retinopathy. In addition to its importance in the function of the eye, vitamin A is necessary for proper immune function. Vitamin A deficiency is associated with a high degree of morbidity and mortality, mainly because affected children are more susceptible to respiratory and intestinal infections.