Visual acuity (VA) is acuteness or clearness of
vision, especially form vision, which is dependent on the sharpness of the retinal focus within the
eye and the sensitivity of the interpretative faculty of the brain.
[1]
VA is a
quantitative measure of the ability to identify black symbols on a white background at a standardized distance as the size of the symbols is varied. It is the most common clinical measurement of visual function. 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.
So you are ok. About closed branches, just go to the oasc and hope for the best, and make sure you put down all the branches you are interested in. If you want to fly, but are also interested in ABM, dont apply to flying exclusively. This will increase your chances. Beware adding branches that you are not interested in, or dont research, they will be able to tell.