What is 20/20 vision and why is it praised?

20/20 refers to "normal" visual acuity at distance. There are people, usually younger ones, who can see more sharply than that at distance. In general, the higher the second number (the denominator), the worse the distance vision.

But bear in mind if you hear somebody bragging about having 20/20 vision:

1)You don't know if that ratio is being applied to binocular vision (both eyes together) or just one eye at a time.

2)It says absolutely nothing about near vision. While in an effort to simplify things some eye doctors will refer to "20/20 near vision" that really doesn't mean anything exact.

3)It is typically measured at 100% contrast: jet black letters against bright white background. Most of the real world is not that way.

4)The ratio is often bandied about without specifying whether it is being measured with no correction (contact lenses or glasses) or whether it is uncorrected.

These issues do not render the term "20/20" useless by any means, but do require some further context to truly be applicable to a patient's unique situation.

Written by J. Trevor Woodhams, M.D. - Chief of Surgery, Woodhams Eye Clinic