20/20 Vision

The clearness of a person's vision constitutes visual acuity. It is measured in terms of 20/20 vision, which is considered normal. It means that one can see clearly at twenty feet, what is normal for that distance. Roughly thirty-five percent of all adults have 20/20 vision without glasses.

The standard 20/20 eye test was developed in 1862 by a Dutch ophthalmologist, Dr. Herman Snellen. The Snellen eye chart is the one most commonly used today. It consists of letters or number decreasing in size at each level on the chart. The top number represents the distance a person is away from the chart (twenty feet). The bottom number represents how far away a person with normal vision can read the letters on the chart. The top number is always the same. A person with 20/10 would have superior vision.

The test is subjective in nature, requiring the cooperation of the patient. The test is performed one eye at a time, with the eye not being tested, covered. A person with 20/20 vision may not have perfect overall vision. The Snellen test does not measure other eye conditions. Difficulty to see things up close is far sightedness. Nearsightedness constitutes difficulty in seeing things far away.

Other vision skills involve depth perception, side vision, focusing ability, eye coordination and color perception. Acuity and color vision, although being done by the same cells, are different functions that do not interrelate. Thus acuity and color vision can be affected independently. Glasses, contact lenses and LASIK surgery may correct less than perfect vision.