Source : Webster's Revised Unabridged Dictionary (1913)

Mydriatic \Myd`ri*at"ic\, a.
   Causing dilatation of the pupil. -- n. A mydriatic medicine
   or agent, as belladonna.

Source : WordNet®

mydriatic
     n : a drug that causes the pupil of the eye to dilate; used to
         aid eye examinations [syn: {mydriatic drug}]