How large is each step between lines on the ETDRS chart in logMAR terms?

How large is each step between lines on the ETDRS chart in logMAR terms?

• A. 0.2 log units
• B. 0.1 log units
• C. 0.3 log units
• D. 0.05 log units

Answer: (B)

The ETDRS chart is designed so that each line represents a fixed, uniform change in acuity on the logMAR scale. Moving from one line to the next corresponds to a 0.1 logMAR difference, so each step between lines is 0.1 logMAR. Within a line, each letter typically carries 0.02 logMAR, and with five letters per line that adds up to 0.10 logMAR per line. This precise, consistent spacing is what makes ETDRS measurements more reproducible than other charts.

The ETDRS chart is designed so that each line represents a fixed, uniform change in acuity on the logMAR scale. Moving from one line to the next corresponds to a 0.1 logMAR difference, so each step between lines is 0.1 logMAR. Within a line, each letter typically carries 0.02 logMAR, and with five letters per line that adds up to 0.10 logMAR per line. This precise, consistent spacing is what makes ETDRS measurements more reproducible than other charts.