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Glaucoma

Description

An in-depth report on the causes, diagnosis, treatment, and prevention of glaucoma.

Outlook

Worldwide, glaucoma ranks as one of the leading causes of blindness. Even if people with glaucoma do not become blind, vision can be impaired. In developed countries, most people get treatment in time to preserve their vision. Even so, glaucoma causes between 3 - 6% of blindness cases in Caucasians, and even more cases in African Americans.

In a 20-year study of Caucasian patients with glaucoma, blindness in at least one eye occurred in 27% of patients and blindness in both eyes occurred in 9% of patients. The blindness rates in African Americans are most likely higher. In fact, glaucoma is the leading cause of blindness in African Americans. Despite this higher prevalence, this ethnic group receives surgical treatment at half the rate of Caucasians.

Outlook for Primary Open-Angle Glaucoma

The Process Leading to Vision Loss. Chronic glaucoma is often called “the silent thief of sight," because the afflicted person has no warning sign, no hint that anything is wrong. Untreated, the destruction develops slowly over time:

• Over years or decades, the increased pressure compresses nerves at the back of the eyes.
• Glaucoma gradually destroys first the outer fibers of the optic nerve, which reduces peripheral vision (the top, sides, and bottom areas of vision), but not central vision.
• By the time a person notices that peripheral vision has been lost, permanent damage has already occurred.
• If the eye pressure remains high, the destruction can progress until tunnel vision develops, and the person is only able to see objects that are straight ahead.
• The last nerve fibers destroyed are those responsible for central vision; if this occurs, the glaucoma victim becomes totally blind.

Although there is no cure for open-angle glaucoma, a number of treatments are available that lower intraocular pressure and slow progression of vision loss.

Risk Factors for Vision Loss. Estimates of progression rates in vision deterioration range from 9 - 30% over a 2 - 7 year period.

According to a study on patients with elevated IOP, for every 1-mm Hg increase in IOP, there is a 10% higher risk of disease progression. A very elevated IOP (above 30 mm Hg) is certainly hazardous. An elevated IOP that is below 30 mm Hg, however, is not necessarily the most important factor in determining the risk for disease progression. Some evidence suggests that frequent and large daily fluctuations in intraocular pressure, not simply high IOP, are associated with the greatest risk for loss of vision. Having normal-tension glaucoma with optic nerve damage also carries a high risk for progression, even if eye pressure is reduced.

In any case, factors other than IOP play a role in increasing the chances for progression and vision loss in patients with slightly elevated IOP and normal tension glaucoma:

• Both eyes affected
• Pseudoexfoliation (PEX) syndrome. PEX occurs when proteins produced in the eye flake off the outer layer of the lens and collects in the drainage angle.
• Bleeding in a specific region called the peripapillary nerve fiber layer
• Thin corneas. (People who have thick corneas and elevated IOP may only need to be monitored if they have no other risk factor for vision loss.)
• Larger cup-to-optic disc ratio. (The cup of the optic disc is the center portion, which enlarges as nerve damage progresses.)

Non-eye related factors associated with disease progression include being elderly, African American, female, or having a history of migraines.

Severity of Acute Closed-Angle Glaucoma

Acute closed-angle glaucoma is a medical emergency; if the high pressure is not reduced within hours, it may permanently damage vision. Anyone who experiences its symptoms should immediately contact an ophthalmologist or go to a hospital emergency room.

• Review Date: 3/3/2007
• Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital.

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