X-Chrom lens (See Contact Lenses.)
Xerophthalmia is a disease caused by a vitamin A deficiency. It may occur as a result of malnutrition, protein deficiency, or diarrhea. Early symptoms of the disorder include night blindness, conjunctivitis, and tearing. It is the second leading cause of blindness in the world and the leading cause of blindness in children in underdeveloped countries. Although found worldwide, the disease is most concentrated in Southern Asia and Northern Saharan Africa. Children under the age of six are at the greatest risk. The disease causes fundamental changes in the cornea, conjunctiva, and anterior segments of the eye, which can lead to blindness. In severe cases, the cornea is perforated and aqueous fluid is lost. As a result, the anterior chamber flattens, the iris adheres to the cornea, and the eyeball is destroyed. Xerophthalmia can be detected during a corneal examination or by electroretinogram, a method impractical in field work. Treatment of the disease consists of megadoses of vitamin A (200,000 IU) orally, coupled with a protein- and calorie-rich diet, and treatment of any accompanying systemic infection. The vitamin A dosage may be administered twice a year as a preventative measure. Other preventatives include enrichment of a commonly ingested staple as tea or sugar with a tasteless form of vitamin A, nutritional education, and improvement in the diet – all of which are impossible without foreign aid.