A logMAR chart is a chart consisting of rows of letters that is used by ophthalmologists, orthoptists, optometrists, and vision scientists to estimate visual acuity.
To calculate the score, take the row number where they got all four correct (0.3), count the number of letters below that that they got correct (4) and multiply this by 0.025 = 0.10. This is then subtracted from 0.23 to give the LogMAR score of 0.20.
Uncover the science behind LogMAR visual acuity, the advanced method for precisely measuring and tracking vision changes. Learn why it’s crucial for eye care.
In logMAR notation, lower scores correspond to better vision, and as acuity becomes worse, the value of the logMAR increases. For every line of logMAR change there is 0.1 Δ, and for each letter there is 0.02 Δ.
LogMAR is approximately normally distributed. That means you can calculate means, SDs, t-tests, whatever, to your heart’s desire. As the first analysis step, convert everything to LogMAR. After analysis, one can convert back to Snellen or decimal notation to reach the pertinent audience.
Usage: In addition to interactive use of the calculator, links to the calculator may contain either logMAR or Snellen values that will be automatically evaluated.
With the transition to reading with the logarithmic scale (LogMAR), the threshold of 6/9 remains the baseline for preschool and school children, but it is now expressed with a logarithmic value to achieve a more accurate and comparable vision test result.
Unlike traditional Snellen charts, LOGMAR charts utilize a logarithmic scale, providing more precise and evenly spaced measurements across the visual acuity spectrum. This logarithmic progression offers greater sensitivity in detecting subtle changes in vision, particularly at higher acuity levels.
The final LogMAR score is calculated by considering the smallest line read and then subtracting or adding based on the number of letters correctly or incorrectly identified on subsequent lines.
