Cornea xerophthalmia

Avitaminosis A results in the loss of night vision nyctalopia). Furthermore, the removal of vitamin A from the diet causes the cornea of the eye to dry out xerophthalmia). However, excessive intake of vitamin A can result in severe and even fatal toxicity. 

Impotence Night blindness Retardation of growth Xerophthalmia Increased visuel threshold Dryness of cornea Yes FAT-SOLUBLE p-Carotene not acutely toxic, but supplementation is hot recommended Excess vitamin A can increase incidence of fractures... 

DEFICIENCY Vitamin A deficiency results in night blindness and xerophthalmia (dry cornea and conjunctiva, sometimes with ulceration of the cornea). Nonocular changes may also occur dry skin and mucous membranes. Deficiency may result from poor dietary intake, or poor absorption, as from bowel disease, or a defect in bile flow that causes fet malabsorption. Poor protein intake may result in a reduced level of the transport protein that carries vitamin A in the blood stream. 

Two retinoids, retinoic acid and retinal, appear to have most of the biochemical functions attributed to vitamin A Retinoic acid is required for cell differentiation and is the ligand for two families of nuclear receptors, RAR . y and RXR 0 y. These receptors are part of a family of superreceptors that include the steroid hormones and cholecalciferol. Vitamin A deficiency can lead to a variety of symptoms depending on the age of the deficient person. The most serious syndrome is keratomalacia, which results in desiccation, ulceration, and xerophthalmia of the cornea and conjunctiva. It is one of the leading causes of blindness in infants and children. 

Nutritional vitamin A deficiency causes xerophthalmia, a progressive disease characterized by night blindness, xerosis (dryness), and keratomalacia (comeal thinning), which may lead to perforation xerophthalmia may be reversed with vitamin A therapy. However, rapid, irreversible blindness ensues once the cornea perforates. Vitamin A also is involved in epithelial differentiation and may have some role in corneal epithelial wound healing. There is no evidence to support using topical vitamin A for keratoconjunctivitis sicca in the absence of a nutritional deficiency. 

Vision can also be impaired because of xerophthalmia (from the Latin words for dry and eye), another manifestation of a vitamin A deficiency. In this condition, the conjunctiva (the covering of the eye) dries out, the cornea becomes inflamed, and the eyes become ulcerated. It may progress to blindness in extreme deficiency of vitamin A. Xerophthalmia is a very common disease in infants and undernourished children in those parts of the world where the deficiency is prevalent but it may be prevented by including in the diet a good source of vitamin A. 

Extreme vitamin A deficiency over a long period of time may cause xerophthalmia, characterized by the following stages (1) the cornea (the transparent membrane that coats the outer surface of the eye) becomes dry, then inflamed... 

The term describing keratinization and cloudiness of the cornea caused by a vitamin A deficiency. Xerophthalmia occurs most frequently in undernourished infants and children in India, the Middle East, Southeast Asia, and parts of Africa and South America, in areas where the diet is lacking in whole milk, butter, and green or yellow vegetables. Vitamin A should be administered immediately to persons with xerophthalmia in order to arrest the disease and prevent the loss of sight... 

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