n. the inability to see. Lack of all light perception constitutes total blindness but there are degrees of visual impairment far less severe than this that may be classed as blindness for administrative or statutory purposes. For example, marked reduction in the visual field is classified as blindness, even if objects are still seen sharply. The commonest causes of blindness worldwide are trachoma, onchocerciasis, and vitamin A deficiency (see night blindness) but there is wide geographic variation. In Great Britain the commonest causes are age-related macular degeneration, glaucoma, cataract, myopic retinal degeneration, and diabetic retinopathy.
http://www.rnib.org/xpedio/groups/public/documents/code/InternetHome.hcsp Website of the Royal National Institute of Blind People
Subjects: Medicine and Health.