The visual acuity test is used to determine the smallest letters a person can read on a standardized chart or card held 14 - 20 feet away.
Currently, the NEI does not have a factsheet on this test.
For more information from other health sites, please visit the following webpages:
MedlinePlus, Visual acuity test
American Optometric Association, Visual Acuity: What is 20/20 Vision?