Every how many rows signifies a halving or doubling of visual acuity level on the ETDRS chart?

Every how many rows signifies a halving or doubling of visual acuity level on the ETDRS chart?

• A. 2 rows
• B. 3 rows
• C. 4 rows
• D. 5 rows

Answer: (B)

On the ETDRS chart, each row represents a 0.1 change in logMAR. A doubling or halving of visual acuity corresponds to a change by a factor of 2, which on the logMAR scale is log10(2) ≈ 0.301. Since each row is 0.1 logMAR, about three rows accumulate to a 0.301 change. So every three rows signify a doubling (when improving) or halving (when worsening) of visual acuity. For example, going from 20/40 (logMAR 0.30) to about 20/20 (logMAR 0.00) spans roughly three rows, reflecting a twofold improvement in acuity.

On the ETDRS chart, each row represents a 0.1 change in logMAR. A doubling or halving of visual acuity corresponds to a change by a factor of 2, which on the logMAR scale is log10(2) ≈ 0.301. Since each row is 0.1 logMAR, about three rows accumulate to a 0.301 change. So every three rows signify a doubling (when improving) or halving (when worsening) of visual acuity. For example, going from 20/40 (logMAR 0.30) to about 20/20 (logMAR 0.00) spans roughly three rows, reflecting a twofold improvement in acuity.