ETDRS Vision Test Charts - Leading LogMAR Chart Producers

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March 06, 2024

ETDRS (LogMAR) Vision Test Charts

ETDRS is a type of visual acuity test that was developed as part of a large study of diabetic patients, called Early Treatment Diabetic Retinopathy Study. The test has a number of advantages over the previous types of acuity test, specifically the Snellen and Sloan tests. The ETDRS test incorporates equal acuity steps between testing lines, so that from row to row, the letter size changes by an equal 0.1 log unit per line. This equal change between lines creates different acuity levels than found on the previous tests, such as 20/16 vs 20/15 and 20/32 vs 20/30. This equal step on a logarithmic scale is the reason the test is often also referred to as a LogMAR test. In addition to equal steps between rows, the letters on each row are also spaced equally on a log scale. ETDRS tests are available for letters, numbers and symbols. And back-lit charts are available to standardize the testing luminance.