di·op·ter /daɪˈɑptɚ/
  屈光度
  di·op·ter /daɪˈɑptɚ, ˈdaɪˌɑp-/ 名詞
  Di·op·ter Di·op·tra n.  An optical instrument, invented by Hipparchus, for taking altitudes, leveling, etc.
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  diopter
       n : a unit of measurement of the refractive power of a lens
           which is equal to the reciprocal of the focal length
           measured in meters