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 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 because it only indicates one aspect, the clarity of vision at distance. There are other important visual skills, including peripheral awareness (side vision), eye coordination, depth perception, focusing ability and color vision that contribute to your overall visual ability.
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 or contact lenses 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.