Which chart is regarded as the gold standard for measuring visual acuity?

Which chart is regarded as the gold standard for measuring visual acuity?

• A. ETDRS
• B. Snellen
• C. Bailey-Lovie
• D. Pelli-Robson

Answer: (A)

Visual acuity is measured most reliably when the chart uses letters that are equally difficult and progresses in fixed, small steps. The ETDRS chart achieves this with a logMAR scale, five letters per line, and equal 0.1 logMAR increments between lines. This design gives highly consistent, repeatable results and minimizes variations introduced by different letters or line lengths, making it ideal for comparing results across clinics and for research. Because of its standardized letter set and scoring, the ETDRS chart became the reference standard in major trials and eye care practice. The other charts don’t provide the same level of standardization. The Snellen chart, though common in clinics, uses variable letter sizes per line and uneven step progression, which reduces precision and cross-clinic comparability. The Bailey-Lovie chart also uses a logMAR approach, but ETDRS refined and standardized the format further to maximize consistency. The Pelli-Robson chart, on the other hand, measures contrast sensitivity rather than high-contrast acuity, so it doesn’t assess acuity in the same way.

Visual acuity is measured most reliably when the chart uses letters that are equally difficult and progresses in fixed, small steps. The ETDRS chart achieves this with a logMAR scale, five letters per line, and equal 0.1 logMAR increments between lines. This design gives highly consistent, repeatable results and minimizes variations introduced by different letters or line lengths, making it ideal for comparing results across clinics and for research. Because of its standardized letter set and scoring, the ETDRS chart became the reference standard in major trials and eye care practice.

The other charts don’t provide the same level of standardization. The Snellen chart, though common in clinics, uses variable letter sizes per line and uneven step progression, which reduces precision and cross-clinic comparability. The Bailey-Lovie chart also uses a logMAR approach, but ETDRS refined and standardized the format further to maximize consistency. The Pelli-Robson chart, on the other hand, measures contrast sensitivity rather than high-contrast acuity, so it doesn’t assess acuity in the same way.