1. profound, near-total, or total impairment of the ability to perceive visual stimuli. According to the World Health Organization’s international classification (1990), blindness is defined as visual acuity less than 20/400 in the better eye with best correction or a visual field less than 10° in the widest meridian in the better eye. In the United States, the criterion for legal blindness is visual acuity of 20/200 or less in the better eye with best correction or a visual field of 20° or less in the widest meridian of the better eye.

2. absence of usable vision with the exception of light perception. Major causes of organic blindness include inoperable cataract, uncontrolled glaucoma, retinitis pigmentosa, diabetic retinopathy, age-related macular degeneration, rubella, and brain injury. See also cortical blindness; functional blindness; low vision; visual impairment. —blind adj.