You often hear the term “20/20” when describing “perfect” vision but we thought it might be interesting to dig a little deeper and learn the history of the term and some of the scientific thinking behind its evolution. Basically it has always been explained as a person standing 20 feet away from the eye chart (or magnified to appear that way from the eye-exam chair in case the room isn’t big enough to actually be 20 feet away) being able to read the line of the letter size which a person with “normal” vision can read, when standing 20 feet away.
Snellen chartBut, what is “normal” vision? Doe it come from the statistics term “norm,” as in the norm?