This means that if you're able to read the final result, you're probably a good guesser. When performing an eye exam, one eye is covered and asked to read the letters in each row aloud, starting at the top of the chart. The smallest row that can read correctly indicates the visual acuity of the eye being tested. During an eye exam, the ophthalmologist will ask you to look for the smallest line of letters you can read, and then ask you to read it.
If you can read the bottom row of letters, your visual acuity (sharpness) is very good. A young child has an eye test and doesn't know the alphabet or is too shy to read the letters aloud. But eye charts don't measure peripheral vision, depth perception, color vision, or the ability to perceive contrast. To assess your near vision, the ophthalmologist may use a small portable card called a Jaeger eye chart.
During an eye test, ophthalmologists use eye charts to measure vision at a certain distance and compare it with that of other human beings. The rotating E chart has the same scale as a standard Snellen eye chart, except that all the characters on the chart are a capital E, rotated in different 90 degree increments. There are several versions of the Snellen eye chart for people, such as young children, who cannot read the letters of the alphabet. The next time you sit in your optometrist's office chair, you'll understand why you need to read the letters on the chart in front of you and what the results mean for your vision.
In the United States, the standard eye chart location is on a wall that is 20 feet away from the eyes. The Snellen eye chart is the classic large and small letter chart that you'll typically see used by eye professionals, in schools, and in other eye testing environments. The classic example of an eye test is the Snellen eye chart, developed by Dutch ophthalmologist Hermann Snellen in the 1860s. Whenever acuity needs to be carefully evaluated (such as in an ophthalmologist's exam), or when there is a possibility that the person being examined may try to deceive the examiner (such as in a motor vehicle licensing office), equipment is used that can present the letters in a variety of random patterns.
The eye chart is used to measure visual acuity, which refers to how well you can see without glasses or contact lenses. Snellen's eye chart is read by covering one eye and reading aloud the letters on the chart, starting at the top and moving down. One of the best-known graphs associated with vision is the Snellen eye chart, designed by Dutch ophthalmologist Hermann Snellen in 1862 to measure visual acuity, how well you can see at different distances.
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