The easiest way to think about 20/20 is that it means that the eye can see at 20 feet what the average, healthy eye can see at 20 feet. It would follow that 20/200 (poor) vision means that the eye can see at 20 feet what an average, healthy eye can see at 200 feet, or that an eye that sees 20/10 (exceptionally well) sees at 20 feet what an average, healthy eye can see at 10 feet.
Having 20/20 vision does not necessarily mean that your eyes are healthy. The presence of glaucoma or many other eye conditions may not affect central visual acuity until late in the disease. Healthy eyes, though, usually do see 20/20 or better.
If an eye does not see 20/20, it is up to the ophthalmologist to determine the cause. It is also important to test each eye individually.
Did you also know? The standard eye chart used by most doctors today is known as the Snellen Eye Chart, developed by Dutch ophthalmologist Herman Snellen in 1862.
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Most people would think it was some sort of grading system for the clarity of one's vision. 20/20 would be a perfect score if it were a pop quiz! Thanks for the fast fact, by the way. Please post more!
Posted by: Karina Chiodo | May 30, 2011 at 12:16 PM
In some other countries, 20/20 isn't used because they don't use the imperial system. Instead, it's 6/6 as in 6 metres.
Posted by: eye surgery risks | December 18, 2011 at 10:39 PM