Loss of transparency of the crystalline lens of the eye, due to changes in its delicate protein fibres. At an advanced stage, the front part of the lens becomes densely opaque, but the cataract never causes total blindness. Almost everyone over 65 has some degree of cataract. Regular exposure to ultraviolet light increases the risk. Other causes include injury to the eye, particularly if a foreign body enters the lens. Cataract is common in people who have diabetes mellitus. Long-term use of corticosteroid drugs may contribute to cataract development. Congenital cataract may be due to an infection of the mother in early pregnancy, especially with rubella, to the toxic effects of certain drugs in pregnancy, or be associated with Down’s syndrome or galactosaemia. Onset of symptoms is almost imperceptible, although night driving may be affected early on. There is slow, progressive loss of visual acuity. The person may become shortsighted and notice disturbances in colour perception. When vision has become seriously impaired, cataract surgery is performed to remove the lens.


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