The Collaborative International Dictionary of English v.0.48:

Glaucoma \Glau*co"ma\, n. [L., fr. Gr. glay`kwma, fr. glayko`s
   light gray, blue gray.] (Med.)
   Dimness or abolition of sight, with a diminution of
   transparency, a bluish or greenish tinge of the refracting
   media of the eye, and a hard inelastic condition of the
   eyeball, with marked increase of tension within the eyeball.
   [1913 Webster]

WordNet (r) 3.0 (2006):

glaucoma
    n 1: an eye disease that damages the optic nerve and impairs
         vision (sometimes progressing to blindness); "contrary to
         popular belief, glaucoma is not always caused by elevated
         intraocular pressure"