optically active

from The Collaborative International Dictionary of English v.0.48

optical activity \optical activity\ n. (Chem.)
   the ability of a chemical compound to rotate the plane of
   plane-polarized light. This is found only in chemicals whose
   molecular structure does not have a plane of symmetry, and is
   common in biochemical compounds. -- {optically active} adj.
   [PJC]

from The Collaborative International Dictionary of English v.0.48

Optically \Op"tic*al*ly\, adv.
   1. By optics or sight.
      [1913 Webster]

   2. With reference to optics.
      [1913 Webster]

   {Optically active}, {Optically inactive} (Chem. Physics),
      terms used of certain isomeric substances which, while
      identical with each other in other respects, differ in
      this, viz., that they do or do not produce right-handed or
      left-handed circular polarization of light. See {optical
      activity}.

   {Optically positive}, {Optically negative}. See under
      {Refraction}.
      [1913 Webster]