At which test distances is the ETDRS chart calibrated?

• A. 4 m, then 2 m, then 1 m
• B. 2 m, then 1 m
• C. 3 m, then 6 m
• D. 5 m, then 1 m

Answer: (A)

The ETDRS chart is designed so that the same visual acuity values (logMAR lines) can be read accurately at several standard testing distances. It is calibrated for 4 meters as the primary distance, and it also provides calibrations for 2 meters and 1 meter, allowing reliable measurement in different room sizes or for patients who are closer to the chart. Distances such as 3, 5, or 6 meters aren’t part of its standard calibration, so using those distances would disrupt the established correspondence between letter size and acuity. Therefore, the chart is calibrated at 4 meters, then 2 meters, and then 1 meter.