Visual Acuity Testing

Visual acuity (VA) is the measure of the eye's ability to resolve detail at a given distance. The Snellen fraction (e.g., 20/20) compares the patient's acuity to a standard: the numerator is the test distance (20 feet) and the denominator is the distance at which a normal eye can read that line. LogMAR (Logarithm of Minimum Angle of Resolution) provides a more linear and statistically valid scale. ETDRS charts use logMAR principles with equal letter spacing and are the gold standard for clinical trials.