| To standardize the measurement of visual acuity, the visual acuity needs to be performed by reading the standard Snellen Chart at a distance of 20 foot or 6 meters, or by reading the Log MARS Chart at 13 feet or 4 meters by closing each eye, one at a time and using the other eye to read from top to bottom.
What does 20/20 vision really mean?
The first 20 means the ability to read all of the letters on the "Snellen Chart" when you are standing 20 feet away. (So the first number should always be 20)
The second number means the ability to read the letters on the Snellen Chart when you are standing 20 feet away. (This number changes depending upon the ability of each individual: The higher the number, the worse the eyesight of the individual.)
20/20 vision means that the individual has standard, perfect eyesight.
20/200 mean the ability to read, while standing at 20 feet, the standardized chart equal to what normal individual can read at 200 feet.
In some countries the unit of measure is done in "meters" so the numbers could be changed into that unit of measure, for example 6/6,6/12 or 6/36. |
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