Blindness
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 three major causes of blindness in the world are cataract , trachoma , and glaucoma , accounting for over 70 percent of all cases of sightlessness. Cataract is an opacity, or cloudiness, in the normally clear lens of the eye that interferes with vision.