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While most people are familiar with the term 20/20 vision, everyone does not understand its real meaning. Consequently, a brief overview may help.
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 vision does not mean perfect vision. It only indicates the sharpness or clarity of vision at a distance. There are other important vision skills, among them peripheral awareness or side vision, eye coordination, depth perception, focusing ability and color vision that contribute to one's overall vision ability.
If a person has 15/15 vision, it does not mean that the individual's vision is better than one who has 20/20. It simply means normal sharpness of vision at 15 feet just as 20/20 indicates normal acuity at 20 feet. For consistency, optometrists in the U.S. use 20 feet as the standard to express sharpness of vision. Other countries express visual acuity in their own way. In Britain, for example, optometrists express visual acuity in meters (6/6 is considered normal).
Visual acuity is affected by many factors. Therefore, some people have less than 20/20 vision. Less than optimum clarity may result from vision conditions like nearsightedness, farsightedness or astigmatism or from eye diseases.
Clarity of vision does vary with distance. Some people can see well at a distance but are unable to bring nearer objects into focus. This condition can be caused by farsightedness or presbyopia (a loss of focusing ability). Others can see items that are close but cannot see those far away. This condition may be caused by nearsightedness.
A comprehensive eye examination by a doctor of optometry should identify causes, if any, that are affecting an individual's ability to see well. In most cases, the optometrist can prescribe glasses, contact lenses or a vision therapy program that will help improve vision. If the reduced vision is due to an eye disease, the use of ocular medication or othertreatment by an ophthalmologist may be required.
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