• Courtesy of Neal H. Atebara, MD. Redrawn by C. H. Wooley.
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    Refractive Mgmt/Intervention

    Snellen letters are constructed such that they subtend an angle of 5 arcmin when located at the distance specified by the denominator. For example, if a Snellen E is 26 mm in height, it subtends 5 arcmin at 60 ft. Correspondingly, a 26-mm letter occupies the 20/60 line of the Snellen chart at the standard testing distance of 20 ft.