True or False: With the ETDRS chart, there is a constant increment of size increase regardless of testing distance.

True or False: With the ETDRS chart, there is a constant increment of size increase regardless of testing distance.

• A. True
• B. False
• C. Not applicable
• D. Both

Answer: (A)

The main idea is that the ETDRS chart uses a logMAR scale with equal steps between lines. Each line is 0.1 logMAR larger than the one before, which translates to a fixed, proportional increase in letter size and difficulty. Because logMAR measures angular resolution, those steps are defined in perceptual terms, not in fixed physical sizes. The chart is designed to be used at a standard testing distance (typically 4 meters), so the size progression matches the intended angular sizes at that distance. Therefore, there is a constant increment in the difficulty from line to line, independent of distance, as long as you test at the chart’s standard distance. If distance were changed without adjusting size, the angular size would shift and the step relationships wouldn’t hold as intended.

The main idea is that the ETDRS chart uses a logMAR scale with equal steps between lines. Each line is 0.1 logMAR larger than the one before, which translates to a fixed, proportional increase in letter size and difficulty. Because logMAR measures angular resolution, those steps are defined in perceptual terms, not in fixed physical sizes. The chart is designed to be used at a standard testing distance (typically 4 meters), so the size progression matches the intended angular sizes at that distance. Therefore, there is a constant increment in the difficulty from line to line, independent of distance, as long as you test at the chart’s standard distance. If distance were changed without adjusting size, the angular size would shift and the step relationships wouldn’t hold as intended.