Blindness is usually considered as an inability to see or a complete loss of vision, although legally, a blind person may retain some vision. In contrast, visual impairment indicates a loss of vision such that there is an impact on daily living, which usually implies partial loss of vision.

There are many causes of visual impairment or blindness, and all parts of the eye (cornea, retina, lens, optic nerve) can be affected. The causes can be genetic (inherited eye diseases affecting both eyes), accidental (mechanical injury to the eyeball), inflammation of the eye tissues (uveitis), acute or extended exposure to harmful chemicals or radiation (acids, alkali, tobacco smoke, UV radiation), dietary imbalance (lack of vitamin A), medication (corticosteroids), systemic diseases (diabetes, renal failure), or simply an aging process.

The majority of visual impairments do not lead to blindness and are related to...