Blindness, total or partial inability to see because of disease or disorder of the eye, optic nerve, or brain. The term blindness typically refers to vision loss that is not correctable with eyeglasses or contact lenses. Blindness may not mean a total absence of sight, however. Some people who are considered blind may be able to perceive slowly moving lights or colors.
The term low vision is used for moderately impaired vision. People with low vision may have a visual impairment that affects only central vision—the area directly in front of the eyes—or peripheral vision—the area to either side of and slightly behind the eyes. Some people with low vision are able to function with their remaining sight while others need help to learn to use their sight more efficiently with training and special tools.
The term blindness is used somewhat misleadingly to designate certain visual conditions. Color blindness, for example, does not reduce visual acuity and should more accurately be called color-perception deficiency. Color blindness occurs almost exclusively in males, and the most common form is the inability to differentiate between certain shades of red and green. Night blindness, the inability to see in low levels of light, is commonly associated with a lack of vitamin A in the diet or with inherited diseases such as retinitis pigmentosa, a condition involving progressive degeneration of the eye’s retina and abnormal deposits of pigment.