logmar

Convert visual acuity between logMAR, Snellen, and decimal. Pure arithmetic, zero dependencies.

npm install logmar

const la = require("logmar");

la.snellenToLogmar("20/40");  // 0.301
la.logmarToSnellen(0.3);      // "20/40"
la.snellenToLogmar("6/12");   // 0.301  (metric Snellen, same acuity)
la.decimalToLogmar(0.5);      // 0.301
la.logmarToDecimal(0.0);      // 1  (20/20)

API

• snellenToLogmar("20/40") / logmarToSnellen(0.3, base=20)
• decimalToLogmar(0.5) / logmarToDecimal(0.3)
• snellenToDecimal("20/40") / decimalToSnellen(0.5, base=20)

logMAR = −log₁₀(decimal acuity); Snellen m/x has decimal m/x. 20/20 = 0.0 logMAR = 1.0 decimal; larger logMAR is worse acuity. logmarToSnellen rounds the denominator to the nearest whole line.

Licence

MIT.