The most common chart used to measure visual acuity is the Snellen eye chart. The chart contains letters of graduated sizes with standardized numbers at the end of each line of letters. These numbers indicate the degree of acuity when read from a distance of 20 ft. The "E" chart can be used in the same way for illiterate or non-English-speaking patients and for children. A facsimile of a Snellen alphabet chart is pictured to the right or point here to view a facsimile of an "E" chart.

Visual acuity (i.e., clarity or sharpness of vision) is a quantitative measure commonly reflected by the term "20/20." 20/20 vision indicates a person can see the same detail from 20 feet away from an eye chart that a person with “normal” eyesight would see from 20 feet. The metric equivalent is “6/6 vision.” Visual acuity is recorded as a fraction with a numerator of 20 (i.e., distance in feet between the patient and the chart), and the denominator is recorded as the smallest complete line that the patient can read accurately without missing any letters. In practical terms, a larger denominator denotes poorer vision.

If the patient is able to read some letters on the next smaller line, indicate this by adding the number of letters read correctly on the next line (i.e., 20/25 +2). This would indicate that the patient read all of the letters in the 20/25 line correctly and two of the letters on the 20/20 line correctly. Near vision acuity is recorded as distance equivalents, such as 20/20. Distance equivalents are listed on the near vision chart, and documentation is the same as for the Snellen chart. Point here to view a facsimile of a "near" chart.