Blindness is the condition of lacking the sense of sight. There is a distinction between being totally blind and legally blind; the category of the legally blind includes many people with some degree of vision, even if only sufficient to distinguish light and dark. Blind people themselves refer to those with the sense of sight as "sighted". Other people included in discussions of and services for the blind are:
The most common treatable causes of blindness in the world today are cataracts followed by trachoma (caused by chlamydia trachomatis) and onchocerciasis (river blindness). Prior to the disease's eradication, corneal scarring caused by smallpox had been one of the commonest causes of blindness. Other common causes of blindness include Vitamin A deficiency, other childhood diseases and congenital problems.