In the term "20/20 vision" the numerator refers to the distance in feet from which a perso

n can reliably distinguish a pair of objects.

Twenty feet is essentially infinity from an optical perspective (the difference in optical power required to focus at 20 feet versus infinity is only 0.164 diopters). For that reason, 20/20 vision can be considered nominal performance for human distance vision.

Posted By: Arizona Bay, Jul 18, 11:59:48