Comment by swixmix

Here's an example of legally blind...

  Higher Standard Deduction for Blindness
  ...
  1. You can't see better than 20/200 in the
     better eye with glasses or contact lenses, or
  2. Your field of vision is 20 degrees or less.

See https://www.irs.gov/pub/irs-pdf/p501.pdf

I believe 20/200 means you can read only the top letter, E, on vision charts.