The values indicated in the "sphere" and "cylinder" columns of an eyeglass prescription specify the optical bent of the lenses in diopters, abbreviated D. The cutting edge the character of diopters, the extended the lens refracts or bends light. A diopter is the convertible of the focal length in meters. If a lens has a focal length of 1/3 meters, it is a 3 diopter lens.
Stacking lenses combines their power. A +1 diopter lens combined with a +2 diopter lens forms Eyeglass Lens Replacement a +3 diopter system.