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Visual acuity test
Make it clearer
The visual acuity test looks for one thing only: the smallest letters you can manage to read. It uses a standardized chart, the Snellen chart, that grid of letters that get smaller line by line, or a card, placed about 6 meters away.
It is done very simply. You cover one eye with your palm, a piece of paper or a small paddle, and read aloud the smallest line you can make out. Then it is repeated with the other: one eye at a time, because what we want to know is how each one sees on its own. If the person cannot read letters, as with a young child, numbers, lines or pictures are used.
The result is written as a fraction, and that is the part that confuses people. The fraction compares two distances: yours on top and that of normal vision below. The top number is the distance you are standing from the chart. The bottom one is the distance at which a person with normal vision could read that same line. That is why 20/20 is considered normal: you read at 6 meters what a person with normal vision would read at 6 meters.
In brief
The visual acuity test determines the smallest letters someone can read on a Snellen chart at 6 meters.
You cover one eye and read aloud the smallest line you can make out; then the other eye. Anyone who cannot read letters is tested with pictures.
The result is a fraction: your distance on top and, below it, the distance at which normal vision would read that line; 20/20 is normal.
The fraction compares two distances: yours and that of normal vision.
Sources (1)
- MedlinePlus, U.S. National Library of MedicineVisual acuity test, MedlinePlus Medical EncyclopediaPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
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