The Early Treatment in Diabetic Retinopathy Study Chart Compared with the Tumbling-E and Landolt-C

Abstract

Visual acuity (VA) is a measure of the visual system’s ability to resolve fine detail and is expressed using the logarithm of the minimal angle of resolution (logMAR), which depends on the angular size of critical detail in optotypes. Charts originally developed for the Early Treatment in Diabetic Retinopathy Study (ETDRS) and subsequently refined have become the gold standard in ophthalmology research and are based on the design principles of Bailey and Lovie; they have logarithmic scales, 5 optotypes per line, and geometric progression in letter size and spacing. The letter size on each line is 1.2589, or 0.1 log units, times bigger than those on the next line and optotypes are the 10 Sloan letters (C, D, H, K, N, O, R, S, V, and Z).