logMARbased

logMARbased refers to visual acuity assessments that use the logMAR scale as the primary scoring metric. The logMAR scale is derived from MAR, measured in arcminutes; logMAR = log10(MAR).

In practice, acuity tests such as the ETDRS chart present letters in equal-contrast, incremental steps. On ETDRS, each correctly identified letter improves acuity by 0.02 logMAR; each line consists of five letters, totaling 0.10 logMAR per line. The total logMAR score equals the sum of the letter scores; a lower score indicates better acuity. A score of 0.00 logMAR corresponds to normal 20/20 acuity; negative scores imply acuity better than 20/20, while positive scores indicate reduced acuity.

Advantages include an approximately equal-interval scale, enabling robust statistical analyses and sample size planning; high test-retest reliability under standardized conditions; and widespread adoption in research and clinical practice, with ETDRS and other logMAR-based charts providing normative data.

Limitations: Requires controlled testing conditions (distance, illumination, letter size); may be less intuitive to patients compared with Snellen fractions; conversions to familiar Snellen values can introduce confusion.

Applications: measurement of refractive outcomes, monitoring diseases, clinical trials, and vision research; preferred in ophthalmology and optometry due to precision and comparability across studies.