What is Glaucoma?

Glaucoma is a disease that damages the eyes optic nerve. The optic nerve is connected to the retina — a layer of light-sensitive tissue lining the back of the eye and is made up of many nerve fibers, like an electric cable is made up of many wires. It is the optic nerve that sends signals from your retina to your brain, where these signals are interpreted as the images you see.

In the healthy eye, a clear fluid called aqueous (pronounced AY-kwee-us) humor circulates inside the front portion of your eye. To maintain a constant healthy eye pressure, your eye continually produces a small amount of aqueous humor while an equal amount of this fluid flows out of your eye. If you have glaucoma, the aqueous humor does not flow out of the eye properly. Fluid pressure in the eye builds up and, over time, causes damage to the optic nerve fibers.

Glaucoma can cause blindness if it is left untreated. Only about half of the estimated three million Americans who have glaucoma are even aware that they have the condition. When glaucoma develops, usually you don't have any early symptoms and the disease progresses slowly. In this way, glaucoma can steal your sight very gradually. Fortunately, early detection and treatment (with glaucoma eye drops, glaucoma surgery or both) can help preserve your vision.

Narrow Angle Glaucoma (NAG)

Also called closed-angle or angle-closure glaucoma -- the drainage space is cramped, so when the iris dilates (enlarging the pupil) it sometimes blocks the drainage channels, raising the pressure.

A clear fluid called aqueous (or aqueous humor) fills the anterior chamber, a small compartment between the iris (colored part of the eye) and the cornea (clear window covering the iris). Aqueous is produced and circulated in the eyeball to supply essential nutrients to the eye and keep a gentle pressure within it, like a balloon or tire.

The pressure is maintained within a tight range by a control system that balances aqueous production and drainage. Aqueous drains through the trabeculum and Schlemm's Canal, channels located near the "angle," a wedge-shaped space in the anterior chamber that encircles the iris where it meets the edge of the cornea.

People with NAG have anatomically narrow angles, which makes it easier for the drainage channels to be blocked, particularly by the iris.

Open Angle Glaucoma (OAG)

This is the most common type. It is particularly dangerous because there are no symptoms -- no pain or other warning that you are losing vision -- until it is too late.

In open-angle glaucoma, a microscopic blockage gradually develops in the drainage mechanism, preventing aqueous from leaving the eye easily. Since aqueous continues to be produced, the pressure within the eye steadily builds up (over months to years). If the pressure stays much above a normal level, the delicate blood supply and nerve fibers in the optic nerve will be damaged.

Since OAG causes no symptoms, it is frequently detected only during a routine eye examination. As part of the exam, the pressure within your eyes will be checked by a painless test called tonometry. An elevated pressure is a sign that you may have glaucoma, but pressure alone will not tell if you do have glaucoma or that the pressure needs treatment.

Open-angle glaucoma is usually a lifelong problem. Never assume that you have been cured, and do not stop treatment unless you have been told to do so. Left untreated, this disease can cause total blindness. On the other hand, proper treatment and regular checkups can help you to preserve your precious eyesight for the rest of your life.

Secondary glaucoma is caused by ("secondary to") some other eye condition or disease. One eye or both may be affected, and it can occur at almost any age.

Secondary glaucoma can be caused by many different eye problems that lead to blocked drainage and cause a pressure buildup. These include inflammations of certain eye structures (uveitis), eye injuries (which tear the drainage structures), bleeding in the eye, growth of abnormal blood vessels (as from diabetes), and prolonged use of steroids.