The Collaborative International Dictionary of English v.0.48:

Dioptric \Di*op"tric\, Dioptrical \Di*op"tric*al\, a. [Gr. ?
   belonging to the use of the ?; ? = dia` through + the root of
   ? I shall see: cf. F. dioptrique.]
   Of or pertaining to dioptrics; assisting vision by means of
   the refraction of light; refractive; as, the dioptric system;
   a dioptric glass or telescope. "Dioptrical principles."
   --Nichol.
   [1913 Webster]

   Dioptric curve (Geom.), a Cartesian oval. See under
      Cartesian.
      [1913 Webster]