Glaucoma - Causes

Aqueous humor is produced by tissues in the front of the eyeball. Aqueous humor brings nourishment to the cornea and lens. It also maintains the proper pressure inside the eyeball. Proper pressure is necessary for the eyeball to maintain the correct shape. The amount of pressure produced by aqueous humor is called the intraocular ("inside the eye") pressure (IOP).

Aqueous humor drains out of the eyeball through a network of tiny tubes also located in the front of the eyeball. Glaucoma develops when the flow of aqueous humor is altered. In some cases, the fluid is produced too rapidly. In other cases, it is not removed from the eyeball fast enough. In either case, too much aqueous humor collects in the eyeball. The fluid causes pressure that pushes on blood vessels in the retina of the eye. The retina is a thin membrane at the back of the eyeball. It receives light rays that pass through the eyeball and transmits them to the optic nerve. Over time, excess pressure in the eye can damage cells in the retina and optic nerve. The cells die and the optic nerve is no longer able to carry messages to the brain. A person's vision is reduced.