LogMAR

LogMAR stands for the logarithm of the minimum angle of resolution. It is a scale used to quantify visual acuity in ophthalmology and optometry. The minimum angle of resolution (MAR) is the smallest detail a person can distinguish; logMAR equals log10(MAR in arcminutes). In practice, lower logMAR values indicate better vision.

LogMAR charts, such as the ETDRS chart, present letters in lines with equal steps in logMAR. Each line differs by 0.1 logMAR, and each letter is worth 0.02 logMAR. A common scoring rule is that acuity is the logMAR value of the last line on which the patient identifies at least three of five letters correctly. In general, 0.0 logMAR corresponds to 20/20 vision, while higher positive values indicate worse acuity; negative values denote better-than-standard acuity (for example, about -0.1 logMAR ≈ 20/16).

Compared with Snellen charts, logMAR is more linear and precise, providing uniform increments and facilitating statistical analysis. This makes it widely used in research, clinical trials, and longitudinal monitoring of visual function.

History and usage: The logMAR concept was introduced in 1976 by Bailey and Lovie to create a standardized, scalable measure of acuity. The standardized ETDRS-style logMAR chart design became widely adopted in ophthalmology and optometry in the late 20th century and remains a common tool for documenting visual acuity in clinics and studies.