20/20 Vision: What Is It
Posted: Wednesday, November 04, 2009
by David Kisling
Fort Collins Eye Doctors-Dr Kisling
We often hear the expression 20/20 vision. We all know it means perfect vision, but do we know why?
The term 20/20 vision comes from a test that doctors performed on millions of people and determined what they could see from each eye at a distance of 20 feet away. Once that vision field was determined, everyone else was measured by it. 20/20 vision is perfect vision for a human who can see what the normal person can see from 20 feet away.
This is the way vision is measured. Compared to a human, a hawk has 20/2 vision. This means the hawk can see what a normal human can see at 2 feet away while he is 20 feet away. Wow! That is impressive. There are some people who have 20/10 vision, which makes their vision better than the average human.
Eye exams use eye charts to determine your vision by placing letters in a pyramid shape with the biggest letter on top and smaller letters on each row. Each row is marked with the vision acuity of the patient. When asked to reach each line, your vision is marked at the line above the last line that you cannot read. So if when reading the chart you get to line 20/60 and cannot read that line, you are then marked at 20/40 vision.
This exam is universal and is given to children as young as pre-school age all the way up to the elderly. As long as you know your letters or numbers you can take the test. Children's eye exams may involve pictures versus numbers or letters. The optometrist can best asses your vision with a test like this. It is simple, yet accurate. Remember to get regular eye exams at least every two years and to take good care of your eyes in between eye exams and all through the year.
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