https://visionaware.org/your-eye-condition/what-is-legal-blindness/

1: A visual acuity of 20/200 or less in the better-seeing eye with best conventional correction (meaning with regular glasses or contact lenses).

Snellen Eye ChartThis is a 20/200 visual acuity measurement, correlated with the Snellen Eye Chart.
If you can only read line 1 (the big “E”) from 20 feet away while wearing your regular glasses or contact lenses, the doctor records your vision (or visual acuity) as 20/200 with best correction.
Update: In 2007, the Social Security Administration updated the criteria for measuring legal blindness when using newer low vision test charts with lines that can measure visual acuity between 20/100 and 20/200. Under the new criteria, if a person’s visual acuity is measured with one of the newer charts, and they cannot read any of the letters on the 20/100 line, they will qualify as legally blind, based on a visual acuity of 20/200 or less.
Part 2 of the U.S. definition of legal blindness states this about visual field:


#2: OR a visual field (the total area an individual can see without moving the eyes from side to side) of 20 degrees or less (also called tunnel vision) in the better-seeing eye.