Vanderbilt University Register : ASK THE EXPERTS

ASK THE EXPERTS

Q: What does "20/20" mean in terms of eyesight, and, if it's considered ideal, how can contact lens companies claim their products can allow a person to see at 20/15?

A: The notation 20/20 indicates that the eye can resolve at 20 feet a standardized object designed to be seen at 20 feet. If the eye is 20/15, then it can see at 20 feet a standardized object designed to be seen at 15 ft. If the eye sees 20/30, it needs to be at 20 feet to resolve a standardized object designed to be seen at 30 feet, and so on. 20/20 is accepted as "normal," but in fact, many people see at least 20/15 and some 20/10. Australian Aboriginals, for example, frequently have vision in the 20/15-to-20/10 range unaided. As hunter-gathers living in a flat land, they need superb distance vision to survive. So, this is probably due to natural selection. There are also theoretical reasons why an eye, with appropriate laser reshaping of the cornea -- the principal refracting of the surface of the eye -- might see 20/5. Contact lenses also alter the refraction of the eye and thus allow the eye to see better. So with many contact lens wearers, better than 20/20 eyesight is achievable.

Source: Denis M. O'Day
George Weeks Hale Professor or Ophthalmology and Visual Sciences, and chair of the department

-- Adrienne Spain

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