ETDRS stands for the Early Treatment Diabetic Retinopathy Study. This landmark study helped define the standardization of eye charts and visual acuity testing, resulting in the development of these ETDRS charts. In the past, a lack of standardization resulted in uncertain test results, but with the development of ETDRS charts used in the original ETDRS study, comparing study results is far more effective. The charts use ETDRS letters, or a geometric progression in letter size from line to line, each line being of equal difficulty. The ETDRS chart format has been accepted by the National Eye Institute and the FDA, and is mandated for many clinical trials performed worldwide. It is accepted worldwide as today’s Gold Standard for accurate visual acuity measurement. They are designed for use in clinical studies and low vision evaluations where accurate and repeatable visual acuity measurements are required.