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2. Eyeglass prescription - Wikipedia

   en.wikipedia.org/wiki/Eyeglass_prescription

   This specifies the part of the prescription designed primarily to improve far vision. In a bifocal lens, this generally indicates what is to be placed in the top segment. NV is an abbreviation for near vision. This may represent a single-vision lens prescription to improve near work, or the reading portion of a bifocal lens.

3. Trifocal lenses - Wikipedia

   en.wikipedia.org/wiki/Trifocal_lenses

   Trifocal lenses are made in similar styles to bifocals, but with an additional segment for intermediate vision above the reading section. A common style is the 7×28 flat-top or D-shaped segment, 28 mm wide, with a 7 mm high intermediate segment.

4. Dioptre - Wikipedia

   en.wikipedia.org/wiki/Dioptre

   Illustration of the relationship between optical power in dioptres and focal length in metres. A dioptre (British spelling) or diopter (American spelling), symbol dpt or D, is a unit of measurement with dimension of reciprocal length, equivalent to one reciprocal metre, 1 dpt = 1 m −1.