MEASURING VISUAL ACUITY

The Snellen eye chart is the typical eye chart used to measure visual acuity during clinical eye examinations. It contains a series of letters or numbers that become progressively smaller down the chart. The Snellen fractions, 20/20, 20/30, etc. relate to the ability to identify a letter of a certain size from a specified distance.

The ETDRS eye chart, composed of 5 letters per line, is the gold standard used in measuring visual acuity for clinical research purposes.

Charts using pictures or symbols are available to test children and those who can't read letters.