The term 20/20 vision refers to the distance from which people's vision is tested in relation to the size of the text that can be read from that distance. Calculate the quality of an individual's vision with information from a practicing optometrist in this free video on eye health.
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I'm Doctor Jim Kirkconnell of Bellevue Eye Care Center in Nashville, Tennessee. We all hear this term, 20/20 vision, but what does it mean and where did it come from? Well, there's a Doctor Snellen who invented this term 110 years ago, and we still use his terminology today. The first 20 refers to a 20 foot viewing distance, which is considered optical infinity. In fact, anything further away than seventeen feet is considered a distance finding. And the second number 20 is the standard size of a certain letter, and acuity or checking your vision, is considered a recognition task. You have to recognize what the letters are. And so from 20 feet, a 20-sized letter is 8.75 millimeters tall. That's what it is, I didn't invent it. Now if you see 20/40, that means that it has to be twice as big as that in order for you to recognize what it is. If you see 20/200, then you're seeing something that is 8.75 centimeters, ten times bigger than 20/20. That's how big you have to have something to look at in order to recognize what it is. So the first number is the viewing distance on the top, and then you have the slash, and the second number's that size that the letter is. In Europe, they use 6 meters, but again, we're going to limit ourselves to what it is here in the U.S.