<unk>  <unk>  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.<unk>  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<unk> ried. It is the most common clinical measurement of<unk>  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<unk>  would be able to distinguish them--the distance at which their separation angle is 1 arc minute. The metric equivalent is 6/6 vision. 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<unk>  for distance vision and 20/10 vision would be twice normal<unk> . 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 20/20 vision.
Visual acuity
Refractive index
Intraocular pressure
Binocular vision
Renal function
Fundal height
Glaucoma classification
Dosimetry