glaucoma

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of a group of eye diseases characterized by abnormally high intraocular fluid pressure, damage to the optic disk, and gradual loss of vision.

from The Century Dictionary.

• noun In pathology, a condition of increased tension or fluid-pressure within the eyeball, with progressive diminution of clearness of vision, and an excavation of the papilla of the optic nerve, resulting (unless properly treated) in blindness. Also called glaucosis.
• noun [capitalized] [NL. (Ehrenberg).] A genus of ciliate infusorians, of the group Colpodina. G. scintillans is an example.

from the GNU version of the Collaborative International Dictionary of English.

• noun (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.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun pathology An eye disease or disorder that is defined as a characteristic optic neuropathy, or disease of the optic nerve, possibly, if untreated, leading to damage of the optic disc of the eye and resultant visual field loss due to lack of communication between the retina and the brain, which can lead to blindness.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an eye disease that damages the optic nerve and impairs vision (sometimes progressing to blindness)