Category A - full version without watermark 720x576 (check terms and conditions at www.teledesign.de) The version with watermark is for free to embed. Glaucoma refers to a group of diseases that affect the optic nerve and involve loss of retinal ganglion cells in a characteristic pattern. It is a type of optic neuropathy. Raised intraocular pressure is a significant risk factor for developing glaucoma . Untreated glaucoma leads to permanent damage of the optic nerve and resultant visual field loss, which can progress to blindness. Intraocular pressure is a function of production of liquid aqueous humor by the ciliary processes of the eye and its drainage through the trabecular meshwork. Aqueous humor flows from the ciliary processes into the posterior chamber, bounded posteriorly by the lens and the zonule of Zinn and anteriorly by the iris. It then flows through the pupil of the iris into the anterior chamber, bounded posteriorly by the iris and anteriorly by the cornea. From here the trabecular meshwork drains aqueous humor via Schlemm's canal into scleral plexuses and general blood circulation.  In open angle glaucoma there is reduced flow through the trabecular meshwork; in angle closure glaucoma, the iris is pushed forward against the trabecular meshwork, blocking fluid from escaping.