any kind of vision loss, from temporarily weakened, low vision to blindness. "Normal" vision is 20/20 or 6/6. Individuals with superior vision can be as good as 20/10 or 6/3 which means that they can see as a young person with normal vision at twice the distance (20 feet vs 10 feet and 6 meters vs 3 meters). Vision is impaired when the best-corrected visual acuity is less than 20/40 or 6/12 in the better-seeing eye.
