Source : Webster's Revised Unabridged Dictionary (1913)

Lens \Lens\ (l[e^]nz), n.; pl. {Lenses} (-[e^]z). [L. lens a
   lentil. So named from the resemblance in shape of a double
   convex lens to the seed of a lentil. Cf. {Lentil}.] (Opt.)
   A piece of glass, or other transparent substance, ground with
   two opposite regular surfaces, either both curved, or one
   curved and the other plane, and commonly used, either singly
   or combined, in optical instruments, for changing the
   direction of rays of light, and thus magnifying objects, or
   otherwise modifying vision. In practice, the curved surfaces
   are usually spherical, though rarely cylindrical, or of some
   other figure. Lenses

   Note: Of spherical lenses, there are six varieties, as shown
         in section in the figures herewith given: viz., a
         plano-concave; b double-concave; c plano-convex; d
         double-convex; e converging concavo-convex, or
         converging meniscus; f diverging concavo-convex, or
         diverging meniscus.

   {Crossed lens} (Opt.), a double-convex lens with one radius
      equal to six times the other.

   {Crystalline lens}. (Anat.) See {Eye}.

   {Fresnel lens} (Opt.), a compound lens formed by placing
      around a central convex lens rings of glass so curved as
      to have the same focus; used, especially in lighthouses,
      for concentrating light in a particular direction; -- so
      called from the inventor.

   {Multiplying} {lens or glass} (Opt.), a lens one side of
      which is plane and the other convex, but made up of a
      number of plane faces inclined to one another, each of
      which presents a separate image of the object viewed
      through it, so that the object is, as it were, multiplied.
      

   {Polyzonal lens}. See {Polyzonal}.

Crystalline \Crys"tal*line\ (kr?s"tal-l?n or -l?n; 277), a. [L.
   crystallinus, from Gr. ????: cf. F. cristallin. See
   {Crystal}.]
   1. Consisting, or made, of crystal.

            Mount, eagle, to my palace crystalline. --Shak.

   2. Formed by crystallization; like crystal in texture.

            Their crystalline structure.          --Whewell.

   3. Imperfectly crystallized; as, granite is only crystalline,
      while quartz crystal is perfectly crystallized.

   4. Fig.: Resembling crystal; pure; transparent; pellucid.
      ``The crystalline sky.'' --Milton.

   {Crystalline heavens}, or {Crystalline spheres}, in the
      Ptolemaic system of astronomy, two transparent spheres
      imagined to exist between the region of the fixed stars
      and the primum mobile (or outer circle of the heavens,
      which by its motion was supposed to carry round all those
      within it), in order to explain certain movements of the
      heavenly bodies.

   {Crystalline lens} (Anat.), the capsular lenslike body in the
      eye, serving to focus the rays of light. It consists of
      rodlike cells derived from the external embryonic
      epithelium.

Source : WordNet®

crystalline lens
     n : biconvex transparent body situated behind the iris in the
         eye; it focuses light waves on the retina [syn: {lens}]