Source : Webster's Revised Unabridged Dictionary (1913)

Diplopia \Di*plo"pi*a\, Diplopy \Dip"lo*py\, n. [NL. diplopia,
   from Gr. ? double + the root of ? sight: cf. F. diplopie.]
   (Med.)
   The act or state of seeing double.

   Note: In crossed or heteronymous diplopia the image seen by
         the right eye is upon the left hand, and that seen by
         the left eye is upon the right hand. In homonymous
         diplopia the image seen by the right eye is on the
         right side, that by the left eye on the left side. In
         vertical diplopia one image stands above the other.

Source : WordNet®

diplopia
     n : visual impairment in which an object is seen as two objects;
         "diplopia often disappears when one eye is covered" [syn:
          {double vision}]