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ETDRS was a multicenter, randomized clinical trial designed to evaluate argon laser photocoagulation and aspirin treatment in the management of patients with nonproliferative or early proliferative diabetic retinopathy.

ETDRS Scoring Method – Number of Letters The patient starts at the top of the chart and reads down until he or she reaches a row where a minimum of three letters on a line cannot be read. The patient is scored by how many letters could be correctly identified.

To compare accuracy, reproducibility and test duration for the Snellen and the Early Treatment Diabetic Retinopathy Study (ETDRS) charts, two main tools used to measure visual acuity (VA).

Definition. The ETDRS chart has been introduced as a standardized visual acuity (VA) testing chart for the Early Treatment of Diabetic Retinopathy Study (ETDRS). It uses 14 lines of 5 Sloan letter optotypes in each line in logarithmic progression.

ETDRS charts were theoretically superior to Snellen charts because interpatient differences were more accurately measured and longitudinal follow-up measurements had more consistent precision, regardless of whether the patients had high or low levels of visual acuity.

An ETDRS letter score can be calculated as follows: when 20 or more letters are read correctly at 4.0 m, the visual acuity letter score is equal to the total number of letters read correctly at 4.0 m plus 30.

The ETDRS chart is the most widely used outcome measure to assess changes in visual acuity from a therapeutic intervention. It is a modified version of the Snellen Chart and scores are based on the number of letters correctly read by a patient.