Vitamin A deficiency and xerophthalmia is the major cause of blindness in young children despite intensive preventative programmes.
The WHO estimates that between six and seven million new cases of xerophthalmia occur each year, with 20% of survivors being totally blind and 50-56% partially blind. South and East Asia, parts of Africa and Latin America as well as the Middle East are the most severely affected.
Xerophthalmia has been classified by the WHO. Impaired adaptation followed by night blindness is the first effect. There is dryness and thickening of the conjunctiva and the cornea (xerophthalmia occurs as a result of keratinization).
Xerophthalmia condition appears often as a result from disease localized in the eye, from a systemic deficiency of vitamin A, trauma, or any condition in which the eyelids do not close completely. Xerophthalmia receives also other names such as Xeroma, Dry Eye Syndrome, Keratitis Sicca, or Keratoconjunctivitis Sicca.
The Schirmer's test determines whether or not the eye produces enough tears to keep it moist naturally using paper strips or of filter paper inserted into the eye for several minutes to measure the production of tears, although the exact procedure varies somewhat depending on the physician to select the proper method.
During this test both eyes are tested at the same time, the paper is inserted inside the lower eyelid and the eyes are closed for 5 minutes. After that the paper is then removed and the amount of moisture is measured. In some cases, a topical anesthetic in placed into the eye before the filter paper to prevent tearing due to the irritation from the paper.
Vitamin A is very important for maintaining good vision and in the prevention of many other eye related diseases. Diet supplements rich in vitamin A or beta-carotene should be provided in high risk areas to prevent the condition (NB vitamin A should be avoided during pregnancy because of the risk of vitamin A embryopathy).