Blinding has been used as an act of vengeance and torture in some instances, to deprive a person of a major sense by which they can navigate or interact within the world, act fully independently, and be aware of events surrounding them. An example from the classical realm is Oedipus, who gouges out his own eyes after realizing that he fulfilled the awful prophecy spoken of him. Having crushed the Bulgarians, the Byzantine Emperor Basil II blinded as many as 15,000 prisoners taken in the battle, before releasing them. Contemporary examples include the addition of methods such as acid throwing as a form of disfigurement. Genetic defects
People with albinism often have vision loss to the extent that many are legally blind, though few of them actually cannot see. Leber congenital amaurosis can cause total blindness or severe sight loss from birth or early childhood. Retinitis pigmentosa is characterized by decreased peripheral vision and trouble seeing at night. Advances in mapping of the human genome have identified other genetic causes of low vision or blindness. Two such examples are Bardet–Biedl syndrome . Poisoning
Rarely, blindness is caused by the intake of certain chemicals. A well-known example is methanol, which is only mildly toxic and minimally intoxicating, and breaks down into the substances formaldehyde and formic acid which in turn can cause blindness, an array of other health complications, and death. When competing with ethanol for metabolism, ethanol is metabolized first, and the onset of toxicity is delayed.
Worldwide for each blind person, an average of 3.4 people have low vision, with country and regional variation ranging from 2.4 to 5.5.By age: Visual impairment is unequally distributed across age groups. More than 82% of all people who are blind are 50 years of age and older, although they represent only 19% of the worlds population. Due to the expected number of years lived in blindness (blind years), childhood blindness remains a significant problem, with an estimated 1.4 million blind children below age 15. By gender: Available studies consistently indicate that in every region of the world, and at all ages, females have a significantly higher risk of being visually impaired than males.By geography: Visual impairment is not distributed uniformly throughout the world. More than 90% of the worlds visually impaired live in developing countries.Since the estimates of the 1990s, new data based on the 2002 global population show a reduction in the number of people who are blind or visually impaired, and those who are blind from the effects of infectious diseases, but an increase in the number of people who are blind from conditions related to longer life spans.In 1987, it was estimated that 598,000 people in the United States met the legal definition of blindness. Of this number, 58% were over the age of 65. In 1994–1995, 1.3 million Americans reported legal blindness. Society and culture
Legal definition
To determine which people qualify for special assistance because of their visual disabilities, various governments have specific definitions for legal blindness.