A person is considered legally blind when all that person can read, at best, is the 20/200 line on the eye chart (usually the top "E") from a distance of 20 feet, or if the person's visual acuity is better than 20/200 but has a field of vision narrowed to 20 degrees or less (as in "tunnel vision"). Most CCTV users are legally blind and have a visual acuity ranging from 20/100 to 20/800.