A year ago during a routine eye examination doctors found a tiny blind spot in Gwendolyn Brown's left eye. The Temple Hills resident said she had noticed no change in her sight.

The spot was an early sign of glaucoma, an eye disease that strikes without warning and is a leading cause of blindness in the United States, especially for blacks.

"Glaucoma is truly a silent thief," said Brown, 41, who is black. "I had no signs that anything was wrong -- no pain or loss of vision." Her annual checkups had shown that her sight was good.

Glaucoma accounts for more than 12 percent of all reported cases of blindness, according to the National Eye Institute.

And a recent review of data on blindness collected in 14 states during the 1960s indicates that blacks develop glaucoma at a rate eight to 16 times higher than whites, and often get the disease at an earlier age.

"There may be a genetic difference among blacks that causes them to be more prone to glaucoma, just as they are more prone to high blood pressure, but we don't yet know," said Dr. Alfred Sommers, an ophthalmologist at the Wilmer Institute of Johns Hopkins University who is conducting a five-year study of glaucoma in the Baltimore area.

"We do know that the nature of glaucoma is that we have to find people affected with the disease early enough before much vision is lost," he said.

Dr. Roger Mason, director of glaucoma services at Howard University Hospital, said he sees about five new glaucoma patients a week, but there are no reliable estimates on the number of people with the disease in Washington area.

A random sampling of patients who came to the Wilmer Institute for eye disorders showed that blacks made up 49 percent of all patients at the clinic, but 82 percent of patients with glaucoma, Sommers said.

Glaucoma occurs when the natural fluids constantly produced in the eye do not drain away, but instead collect and exert pressure behind the eyeball, eventually destroying the optic nerves, which carry visual messages to the brain and allow sight, Mason said. The damage is irreversible.

Gwendolyn Brown, like many glaucoma sufferers, takes prescribed eyedrops twice a day to keep the pressure at normal levels and prevent further loss of vision, according to Mason, her doctor.

"Most patients do not feel any symptoms," Mason said, "so the best way to detect the disease is to have regular checkups after age 40, and perhaps earlier if you are black and have a family history of the disease."