What is the meaning of eyesight 2020?

Answer 1

In the term "20/20 vision" the numerator refers to the distance in feet from which a person can reliably distinguish a pair of objects. The denominator is the distance from which a person with standard VA (that is, with 20/20 vision) would be able to distinguish them-the distance at which their separation angle is 1 arc minute. The metric equivalent is 6/6 vision where the distance is 6 meters. 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; 20/40 vision can be considered half that acuity for distance vision and 20/10 vision would be twice normal acuity. The 20/x number does not directly relate to the eyeglass prescription required to correct vision; rather an eye exam seeks to find the prescription that will provide at least 20/20 vision.