Vision, Measurement Of - Research Article from Macmillan Science Library: Mathematics

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Detecting Vision Defects

The most common test for detecting vision defects is the visual acuity test. This is the well-known eye chart with a big letter E at the top. The test is conducted by having the patient stand or sit a certain distance from the chart. The person being tested covers one eye at a time and reads the smallest line of text she or he can see clearly. Each line of text is identified by a pair of numbers such as 20/15, 20/40, and so on. The first number is the distance (in feet) from the eye chart. The second number is the distance at which a person with "normal" vision can read that line. So a visual acuity of 20/40 means that a person with normal vision could read that line from 40 feet away.

Normal vision refers to average vision for the general population and is considered...

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This section contains 1,234 words
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Macmillan Science Library: Mathematics
Vision, Measurement Of from Macmillan Science Library: Mathematics. Copyright © 2001-2006 by Macmillan Reference USA, an imprint of the Gale Group. All rights reserved.
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