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Keratomalacia is an eye (ocular) condition, usually affecting both eyes (bilateral), that results from severe deficiency of vitamin A. That deficiency may be dietary (i.e., intake) or metabolic (i.e., absorption). Vitamin A is essential for normal vision as well as proper bone growth, healthy skin, and protection of the mucous membranes of the digestive, respiratory, and urinary tracts against infection.
Early symptoms may include poor vision at night or in dim light (night blindness) and extreme dryness of the eyes (i.e., xerophthalmia), followed by wrinkling, progressive cloudiness, and increasing softening of the corneas (i.e., keratomalacia). With advancing vitamin A deficiency, dry, "foamy," silver-gray deposits (Bitot spots) may appear on the delicate membranes covering the whites of the eyes. Without adequate treatment, increasing softening of the corneas may lead to corneal infection, rupture (perforation), and degenerative tissue changes, resulting in blindness. In addition, in some cases, vitamin A deficiency may have additional effects, particularly during infancy and childhood.
In some developing countries, vitamin A deficiency in the diet and associated keratomalacia are a major cause of childhood blindness. In such regions, vitamin A deficiency often occurs as part of nonselective general malnutrition in infants and young children. Although rare in developed countries, vitamin A deficiency and keratomalacia may occur secondary to conditions associated with impaired absorption, storage, or transport of vitamin A, such as celiac disease, ulcerative colitis, cystic fibrosis, liver disease, or intestinal bypass surgery and any condition that affects absorption of fat-soluble vitamins.
Keratomalacia is an eye condition characterized by distinctive ocular changes due to severe vitamin A deficiency. In some affected individuals, additional effects may result from vitamin A deficiency, the severity of which tends to be inversely related to age.
Initial ocular findings commonly include impaired adjustment of the eyes to vision in the dark or dim light (impaired dark adaptation) and associated night blindness due to retinal* (i.e., rod) dysfunction. (*The retina is the light sensitive membrane upon which images are focused at the back of the eye. It contains specialized nerve cells [photoreceptors] that convert light into nerve impulses. Photoreceptors include "rods" that are sensitive to low-intensity light and thus required for night vision, and "cones" that respond to high-intensity light and colors. "Dark adaptation" is the normal increase in sensitivity of the rods to detect light available for vision in dark or dimly lit areas.)
Vitamin A deficiency leads to abnormalities in the structure and function of certain cells covering the surface of the eyes (i.e., epithelial cells). Due to such epithelial changes and inadequate tear production, affected individuals develop extreme dryness of the delicate membranes (i.e., conjunctivae) covering the whites of the eyes and inner lining of the lids (xerosis conjunctivae) and the corneas (xerosis corneae). (The cornea is the thin-walled, "dome-shaped" transparent region forming the front of the eyeball; it serves as a protective covering and helps to focus or bend [refract] light waves onto the retina at the back of the eye.) Due to abnormal dryness of the conjunctivae and the corneas (i.e., a condition known as "xerophthalmia"), there is unusual thickening and wrinkling of the conjunctivae, as well as increasing cloudiness, haziness, wrinkling, and softening of the corneas. In addition, in advanced vitamin A deficiency, foamy, silver-gray, triangular patches (Bitot spots) appear that consist of abnormal deposits of epithelial debris and secretions on the conjunctivae. Evidence suggests that Bitot spots are most likely to develop in young children with other manifestations of vitamin A deficiency.
Without adequate treatment, increasing softening of all or part of the corneas (keratomalacia) may lead to chronic infection, ulceration, and rupture (perforation) of the corneas and degenerative tissue changes (e.g., corneal protrusion and ocular shrinking [phthisis bulbi]), resulting in blindness.
As noted above, in some affected individuals, vitamin A deficiency may have additional effects. For example, retardation of mental and physical growth is a common sign in children. Vitamin A deficiency may also be associated with dryness and scaliness of the skin; decreased levels of the oxygen-carrying component of red blood cells (anemia); abnormal enlargement of the liver and spleen (hepatosplenomegaly); an increased susceptibility to certain infections (e.g., due to epithelial changes of the digestive, respiratory, and urinary tracts); and/or other findings. Evidence suggests that children with vitamin A deficiency are particularly susceptible to potential complications associated with measles.
The human body stores vitamin A mainly in the liver. Vitamin A plays a prime role in reconstituting a visual pigment (rhodopsin) within rods of the retinas that is required for night vision. It is also essential for the formation and maturation of epithelial cells and proper bone and tooth development. Sources of dietary vitamin A include fish-liver oils, liver, whole cow's milk, other dairy products (e.g., butter, cheese), egg yolks, green leafy vegetables, and yellow vegetables and fruits.
Keratomalacia is most frequently caused by prolonged dietary deprivation of vitamin A (i.e., primary vitamin A deficiency). Primary vitamin A deficiency is common in certain regions where rice is a major component of the diet (e.g., eastern and southern Asia); rice does not contain beta-carotene, which is converted by the body into vitamin A.
In addition, keratomalacia is common with certain malnutrition disorders resulting from insufficient consumption of protein and energy (i.e., protein-calorie malnutrition, such as kwashiorkor). In such cases, vitamin A deficiency may result from dietary deprivation as well as defective storage and transport of vitamin A.
Infants and children who are allergic to milk or are given dilute formula may also be at risk for vitamin A deficiency and associated keratomalacia. (Whole cow's milk and breast milk are adequate sources of vitamin A.)
Vitamin A deficiency and keratomalacia may also occur secondary to certain diseases or conditions characterized by insufficient conversion of beta-carotene to vitamin A or impaired storage, absorption, or transport of vitamin A (secondary vitamin A deficiency). For example, impaired vitamin A absorption or storage may occur with chronic intestinal disorders, such as ulcerative colitis; sprue or celiac disease; cystic fibrosis or other disorders characterized by pancreatic insufficiency and associated malabsorption; or intestinal bypass surgery (duodenal bypass). Impaired storage or absorption of vitamin A may also be associated with infection of the small intestine (giardiasis); partial obstruction of the small intestine at birth; obstruction of the bile ducts; or liver disease, such as internal scarring and impaired functioning of the liver (cirrhosis). (For further information on such conditions, please choose "colitis," "celiac," "cystic fibrosis," or "giardiasis" as your search term in the Rare Disease Database.)
Keratomalacia occurs most commonly in developing countries due to prolonged dietary deprivation of vitamin A or protein-calorie malnutrition. As noted above, keratomalacia is a major cause of blindness in young children in such areas. In developed countries, vitamin A deficiency most frequently occurs when there is interference with vitamin A intake, absorption, or transport.
Keratomalacia may be diagnosed based upon a complete patient history; thorough clinical evaluation, including eye examination; blood studies (e.g., assessment of beta-carotene and vitamin A levels); and additional specialized tests. Eye examination should include evaluation of the external appearance of the eyes, visual acuity, eye movements, and visual fields; the use of an illuminated microscope to view the conjunctivae, corneas, and other regions of the eyes (slit-lamp examination); measures of dark adaptation to help to detect night blindness; and/or additional diagnostic assessments (e.g., to exclude other possible causes of night blindness). In addition, evaluation may include microscopic examination of scrapings of surface cells from the eyes.
In some cases, other diagnostic studies may also be conducted to help exclude or confirm possible secondary causes of vitamin A deficiency and keratomalacia. In addition, in some instances, a trial with appropriate therapeutic doses of vitamin A may confirm a diagnosis.
The treatment of vitamin A deficiency and associated keratomalacia includes vitamin A supplementation, with dose levels and length of treatment determined by the severity of the deficiency and other factors. However, prolonged daily administration of high doses must be avoided, particularly for infants, since toxicity (i.e., hypervitaminosis A) may result. (In infants and young children, manifestations of acute vitamin A toxicity due to large doses may include increased intracranial pressure, drowsiness, nausea, vomiting, and other abnormalities. Chronic hypervitaminosis A, which may result from excessive doses for several weeks or months, may be characterized by irritability; lack of appetite; dry, itchy skin; hair loss; cracked lips; generalized weakness; tender swelling of the bones; increased intracranial pressure; liver enlargement; and/or other abnormalities.) In addition, because vitamin A may cause birth defects if given in high doses during pregnancy, extreme caution must be taken in treating women in their childbearing years. Experts advise that vitamin A doses should not exceed two times the recommended daily allowance (RDA) for women who are pregnant or breastfeeding (i.e., lactating).
In addition, in cases in which keratomalacia occurs secondary to impaired vitamin A absorption, storage, or transport, treatment also includes appropriate therapeutic measures to help manage or correct the underlying disorder or condition.
In some cases, the treatment of keratomalacia may include the administration of antibiotic drops or ointments to treat secondary infections, the use of other appropriate eyedrops, and/or additional measures. Other treatment for this disorder is symptomatic and supportive.
Measures to prevent vitamin A deficiency and keratomalacia include ensuring proper nutrition through a balanced diet that contains adequate protein and vitamin A or carotenes. In some cases, routine preventive (prophylactic) vitamin A supplementation may also be required, such as for individuals with impaired vitamin A absorption, storage, or transport. In developing countries where keratomalacia is a major cause of blindness, regular prophylactic vitamin A supplementation is recommended for children at appropriate doses as determined by age and other factors.
In addition, infants who are allergic to milk should be provided with adequate vitamin A within substitute formulas. (Parents should speak with pediatricians concerning appropriate measures to ensure that their children are receiving sufficient levels of vitamin A and other necessary nutrients within their diets.)
Experts also advise administration of appropriate doses of vitamin A for children who are at risk for vitamin A deficiency and who develop certain viral infections, such as measles.
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Report last updated: 2008/04/21 00:00:00 GMT+0