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"There was a big controversy before," says Dr. Michael A. Kass, who led the study. "Some studies showed benefits, others did not. Now there is very clear evidence that treating high intraocular pressure can help prevent glaucoma."

The study, which included more than 1,600 people at 22 medical centers across the country, showed that pressure-lowering eye drops reduced the onset of glaucoma by more than 50 percent.

All the participants had elevated fluid pressure in their eyes, but they had not started to suffer the loss of vision caused by the gradual deterioration of the optic nerve that is the hallmark of glaucoma.

Over the five years of the study, 4.4 percent of the people who got the pressure-lowering eye drops developed glaucoma, compared to 9.5 percent of those who got nothing but careful supervision.

This is important news for millions of Americans, especially older people and black people. About 2.2 million Americans age 40 and over have been diagnosed with glaucoma, and an estimated 2 million are in the early stages of the disease but have not been diagnosed.

For some unknown reason, glaucoma is more common among blacks. For that reason, they made up a quarter of the participants in the Ocular Hypertension Treatment Study, whose results are being reported in the June issue of the Archives of Ophthalmology.

The finding reinforces the standing recommendation for yearly eye examinations starting at age 60 for all Americans and at age 40 for blacks, says Kass, who is chairman of the department of ophthalmology and visual sciences at Washington University School of Medicine.

"If they have a family history of glaucoma, they should start even earlier," he adds.

The study was aimed at open-angle glaucoma, the most common form of the condition and a leading cause of blindness. Most cases occur when the fluid in the eye does not drain properly and the optic nerve suffers damage that causes narrowing of the visual field.

Eye drops that lower the pressure are used in most cases; in some, surgery is performed to improve fluid flow out of the eye.

What is impressive about the study results is that a relatively low reduction in fluid pressure produced such beneficial results, Kass says. The 50 percent reduction in glaucoma was accomplished by an average drop of just 20 percent in fluid pressure.

"A modest drop in pressure makes a big difference," he says.

But not everyone with increased pressure is a candidate for eye drop treatment, Kass says, noting that 90 percent of those in the untreated group did not develop glaucoma.

Ophthalmologists have to assess other risk factors before deciding on treatment, because "all medications have side effects," he adds.

"A person's age and race, how high the pressure is, what the optic nerve looks like, also the thickness of the cornea, since someone with a thin cornea is at high risk," are all factors, Kass says. "A person's general health status should also be considered. The doctor and patient should discuss this together to determine whether treatment is warranted."

A number of different eye drops were used in the study, and all performed about the same, Kass says. "There are lots of drops that lower pressure, so we should be able to find one that is reasonably safe for most people," he says.

Dr. Jeffrey M. Liebmann, professor of clinical ophthalmology at New York Medical College, who led the New York arm of the study, says the results "show that there should be greater emphasis on detecting people at high risk. There are many people with elevated intraocular pressure who have not yet developed glaucoma."

"Our practice is to treat only people who are at high risk for disease progression," Liebmann says. "But this study probably will decrease our threshold for treatment."

What To Do

Glaucoma is known as the "sneak thief of sight" because by the time symptoms become obvious, the damage is done. You can get detailed information about the disease from the National Eye Institute or the Schepens Eye Research Institute.