AOA defines 20/20 vision:
20/20 vision is a term used to express normal visual acuity (the clarity or
sharpness of vision) measured at a distance of 20 feet. If you have 20/20
vision, you can see clearly at 20 feet what should normally be seen at that
distance. If you have 20/100 vision, it means that you must be as close as
20 feet to see what a person with normal vision can see at 100 feet.
20/20 does not necessarily mean perfect vision. 20/20 vision only
indicates the sharpness or clarity of vision at a distance. There are other
important vision skills, including peripheral awareness or side vision, eye
coordination, depth perception, focusing ability and color vision that
contribute to your overall visual ability.
Some people can see well at a distance, but are unable to bring nearer objects into focus. This condition
can be caused by hyperopia (farsightedness) or presbyopia (loss of focusing ability). Others can see items
that are close, but cannot see those far away. This condition may be caused by myopia (nearsightedness).
A comprehensive eye examination by a doctor of optometry can diagnose those causes, if any, that are
affecting your ability to see well. In most cases, your optometrist can prescribe glasses, contact lenses or a
vision therapy program that will help improve your vision. If the reduced vision is due to an eye disease, the
use of ocular medication or other treatment may be used.