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Glaucoma is a group of diseases that can damage the optic nerve, which carries visual information from the back of the eye (the retina) to the brain. Damage usually results from increased pressure inside the eye (intraocular pressure). Open-angle glaucoma, the most common form of the disease, may present without symptoms and can gradually rob people of their sight if left untreated. Angle-closure glaucoma, which may be accompanied by sudden, intense pain, can come on without warning. Treatment for open-angle glaucoma must be sought immediately to preserve a person's sight.
The Glaucoma Research Foundation says almost 120,000 Americans are blind from glaucoma and at least another 3 million have the disease. Half of the people who have glaucoma don't know it.
The normal eye
Inside the front of each eye is a space called the anterior chamber (see drawing). A clear fluid (aqueous humor) normally flows in and out of this chamber, keeping nearby structures moist and nourished, and providing normal eye pressure. Fluid is produced in the ciliary body, flows through the anterior chamber and leaves the chamber at the lower angle, where the cornea and iris meet. When the fluid reaches the angle, it drains out of the eye through a spongy area (trabecular meshwork).
Open-angle glaucoma
Open-angle glaucoma is the most common type, affecting about 2.2 million Americans, mainly those older than 40. It gets its name because the angle where fluid drains out of the anterior chamber is open, but, for some reason, fluid passes too slowly through the meshwork. As fluid backs up, the pressure inside the eye rises, compressing the cells in the optic nerve. The nerve cells eventually die, resulting in permanent "blind spots," usually developing first in the peripheral (outer) areas of the field of vision. In later stages, central vision is also affected.
Normal-tension (low-tension) glaucoma
About one-third of patients with open-angle glaucoma don't have an increase in eye pressure. Normal-tension (also called low-tension) glaucoma is thought to be related in part to poor blood flow to the optic nerve or to increased sensitivity to normal eye pressure.
Angle-closure glaucoma
Angle-closure glaucoma affects nearly half a million people in the United States. It tends to be inherited, often affecting several members of a family. People of Asian descent have an increased risk of having angle-closure glaucoma. In people at risk for angle-closure, the anterior chamber is smaller than average, making the angle narrower than the normal 45 degrees. With age, the lens routinely grows larger, decreasing the angle even more. This causes pressure to build up behind the iris. If the pressure increases enough, it may force the iris against the trabecular meshwork, blocking fluid drainage. When the space becomes completely blocked, an angle-closure glaucoma attack (acute glaucoma) results.
Not all people with angle-closure glaucoma will experience an acute attack. Instead, some may develop chronic angle-closure glaucoma, where the iris gradually closes over the drain (trabecular meshwork), causing no obvious symptoms. Scars slowly form between the iris and the drain, and the eye pressure will not increase until enough scar tissue forms to cover the drainage area.
Acute (angle-closure) glaucoma
A sudden rise in eye pressure can occur within a few hours and cause severe pain. An acute attack is an emergency. If treatment is delayed, eyesight can be quickly and permanently destroyed. The trabecular meshwork can become scarred, resulting in chronic glaucoma, which is more difficult than open-angle glaucoma to control, and result in the formation of cataracts.
Many acute angle-closure glaucoma attacks occur in darkened rooms, such as movie theaters. In darkened places, the pupil dilates (increases in size) making maximum contact between the lens and the iris. This further narrows the angle, perhaps triggering an attack. The pupil also dilates when someone becomes excited or anxious. Therefore, acute glaucoma attacks may occur during periods of stress. Some drugs also can dilate the pupil and lead to an attack. These drugs include anti-depressants, cold medications, antihistamines and some drugs used to treat nausea.
Congenital glaucoma
Children with congenital glaucoma are born with defects in the angle of the eye that slow the normal drainage of fluid. These children usually have obvious symptoms such as cloudy eyes, sensitivity to light and increased tearing. If surgery is done promptly, these children have a good chance of preserving good vision.
Secondary glaucoma
Glaucoma can develop as a complication of other medical conditions, including:
- Eye surgery
- Advanced cataracts
- Eye injuries
- Some eye tumors
- Eye inflammation (uveitis)
- Diabetes
Pigmentary glaucoma is an inherited open-angle glaucoma, seen more often in men than in women, especially in nearsighted people in their 20s and 30s. These patients have an unusually wide angle, causing the iris to rub on the lens and release flakes of pigment from the iris, which blocks the meshwork and slows fluid drainage.
Exfoliation syndrome occurs in about 10 percent of the population over age 50, and is most common among people of European descent. A whitish material (exfoliation material) builds up on the lens of the eye and is rubbed off the lens by movement of the iris. Iris pigment and exfoliation material clog the meshwork, often leading to very high increases in eye pressure.
Exfoliation syndrome can lead to either open-angle glaucoma or angle-closure glaucoma, often producing both kinds of glaucoma in the same person. Although some people with exfoliation syndrome do not develop glaucoma, having the syndrome makes you six times more likely than other people to develop glaucoma.
For unknown reasons, exfoliation syndrome appears in one eye long before the other. Therefore, if you have glaucoma in one eye only, this syndrome is likely to be the cause. Since the syndrome can be detected before glaucoma develops, careful monitoring can minimize your chances of vision loss.
Long-term use of corticosteroid drugs (to treat eye inflammations and other diseases) can trigger glaucoma in some people.
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This article was reviewed and updated June 2007.
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