How the Build Up of Aqueous Humor
Can Damage the Optic Nerve

Illustration by Bob Morreale, provided courtesy of the American Health Assistance Foundation.

Most, but not all, forms of glaucoma are characterized by high eye (intraocular) pressure. Intraocular pressure remains normal when some of the fluid (aqueous humor) produced by the eye’s ciliary body flows out freely (follow blue arrow). Aqueous humor flows from the ciliary body into the anterior chamber, out through a spongy tissue at the front of the eye called the trabecular meshwork and into a drainage canal (dark blue region next to the trabecular meshwork). In open-angle glaucoma, fluid does not flow freely through the trabecular meshwork, causing an increase in intraocular pressure, damage to the optic nerve and vision loss.

Glossary of Terms

Aqueous humor – watery fluid that nourishes the interior of the front of the eye.

Ciliary body – part of the eye, above the lens, that produces the aqueous humor.

Choroid – layer of the eye behind the retina; contains blood vessels that nourish the retina.

Cornea – the outer, transparent structure at the front of the eye that covers the iris, pupil and anterior chamber.

Fovea – the pit or depression at the center of the macula that provides the greatest visuals acuity.

Iris – the colored ring of tissue behind the cornea that regulates the amount of light entering the eye by adjusting the size of the pupil.

Lens – the transparent structure suspended behind the iris that helps to focus light on the retina.

Optic nerve – the bundle of nerve fibers at the back of the eye that carry visual messages from the retina to the brain.

Sclera – the tough outer coat that protects the entire eyeball.

Trabecular meshwork – spongy tissue located near the cornea through which aqueous humor flows out of the eye.

Vitreous – clear, jelly-like substance that fills the eye from the lens to the back of the eye.

Last Reviewed On: 11/21/08