Keratomalacia Health Dictionary

A fat-soluble vitamin essential for normal growth, for the formation of bones and teeth, for cell structure, for night vision, and for protecting the linings of the respiratory, digestive, and urinary tracts against infection.

Vitamin A is absorbed by the body in the form of retinol. This is found in liver, fish-liver oils, egg yolk, dairy produce, and is added to margarines. Carotene, which the body converts into retinol, is found in various vegetables and fruits.

Vitamin A deficiency is rare in developed countries. In most cases, it is due to malabsorption. Vitamin A deficiency may also result from long-term treatment with certain lipid-lowering drugs. Deficiency is common in some developing countries due to poor diet. The first symptom of deficiency is night blindness, followed by dryness and inflammation of the eyes (see xerophthalmia), keratomalacia, and eventually blindness. Deficiency also causes reduced resistance to infection, dry skin, and, in children, stunted growth.

Prolonged excessive intake of vitamin A can cause headache, nausea, loss of appetite, skin peeling, hair loss, and irregular menstruation. In severe cases, the liver and spleen become enlarged. Excessive intake during pregnancy may cause birth defects. In infants, excessive intake may cause skull deformities, which disappear if the diet is corrected.

The drug tretinoin (a derivative of vitamin A) is used to treat severe acne.... vitamin a

An eye disorder in which vitamin A deficiency causes the conjunctiva and cornea to become abnormally dry. Without treatment, xerophthalmia may progress to keratomalacia, a condition in which severe damage is caused to the cornea.... xerophthalmia

The transparent thin-walled dome that forms the front of the eyeball. The cornea is joined at its circumference to the sclera (white of the eye); the black pupil and the coloured iris are visible beneath it. The main functions of the cornea are to help focus light-rays on to the retina at the back of the eye and to protect the front of the eye. It is kept moist by tears produced by the lacrimal gland and the mucus- and fluid-secreting cells in the eyelids and conjunctiva. cornea, disorders of Injuries or diseases affecting the cornea, the outer shell of the eyeball. Injuries include corneal abrasions, which sometimes become infected and progress to a corneal ulcer. Penetrating corneal injuries can cause scarring, which may lead to impairment of vision. Chemical injuries can result from contact with a corrosive substance and require immediate flushing of the eye with water.

In actinic keratopathy, the outer layer of the cornea is damaged by ultraviolet light. In exposure keratopathy, damage is due to reduced protection by the tear film and blink reflex. The cornea can also be infected by viruses, bacteria, and fungi, the herpes simplex virus being especially dangerous. True inflammation of the cornea (called keratitis) is uncommon as the cornea contains no blood vessels.

Other disorders include: keratomalacia as a result of vitamin A deficiency; keratoconjunctivitis sicca (dry eye); corneal dystrophies such as keratoconus; and oedema, in which fluid builds up in the cornea and impairs vision.

Rare congenital defects include microcornea (smaller cornea than normal) or megalocornea (bigger than normal) and buphthalmos, or “ox-eye’’, in which the entire eyeball is distended as a result of glaucoma.

Degenerative conditions of the cornea such as calcium deposition, thinning, and spontaneous ulceration occur mainly in the elderly, and are more common in previously damaged eyes.... cornea

Many eye disorders are minor, but some can cause loss of vision unless treated. (See also cornea, disorders of; retinal detachment.)

Squint is sometimes present at birth. Rarely, babies are born with microphthalmos. Other congenital disorders that affect the eye are nystagmus, albinism, and developmental abnormalities of the cornea and retina.

Conjunctivitis is the most common eye infection and rarely affects vision. Trachoma or severe bacterial conjunctivitis can impair vision. Corneal infections can lead to blurred vision or corneal perforation if not treated early. Endophthalmitis (infection within the eye) can occur as a result of eye injury or infection elsewhere in the body.

Narrowing, blockage or inflammation of the blood vessels of the retina may cause partial or total loss of vision.

Malignant melanoma of the choroid is the most common cancerous tumour of the eye. Retinoblastoma is a cancerous tumour of the retina that most commonly affects children.

Various vitamin deficiencies (particularly of vitamin A) can affect the eye. This may lead to xerophthalmia, night blindness, or, ultimately, keratomalacia.

Uveitis may be caused by infection or an autoimmune disorder such as ankylosing spondylitis and sarcoidosis.

Macular degeneration of the retina is common in the elderly, as is cataract.

Glaucoma, in which the pressure inside the eyeball becomes raised, can lead to permanent loss of vision. In retinal detachment, the retina lifts away from the underlying layer of the eye.Ametropia is a general term for any focusing error, such as astigmatism, myopia, or hypermetropia. Presbyopia is the progressive loss with age of the ability to focus at close range. Amblyopia is often due to squint.... eye, disorders of

combining form denoting abnormal softening of a tissue. Example: keratomalacia (of the cornea).... malacia

(nyctalopia) the inability to see in dim light or at night. It is due to a disorder of the cells in the retina that are responsible for vision in dim light (see rod), and can result from dietary deficiency of *vitamin A. Vitamin A deficiency may progress to cause *xerophthalmia and *keratomalacia. Night blindness may be caused by other retinal diseases, e.g. *retinitis pigmentosa. Congenital stationary night blindness is characterized by poor night vision from early childhood that does not get worse, in association with *nystagmus. Compare day blindness.... night blindness