The optic nerves of American blacks may be more susceptible than those of whites to internal eye pressures associated with glaucoma, say the authors of a new Johns Hopkins study.
The study identified a dramatic difference in the prevalence of the blinding disease in blacks.
American blacks have the disease at a rate four to five times higher than whites, investigators at the Dana Center for Preventive Ophthalmology at the Hopkins Wilmer Eye Institute saidtoday in JAMA, the Journal of the American Medical Association.
The researchers, who examined a large multiracial population in East Baltimore, also found that rates of the disease increase with age and by age 70, one in eight blacks have glaucoma, compared with one in 50 whites.
Glaucoma occurs when fluid pressure inside the eye increases and irreversibly damages the optic nerve, causing vision loss and sometimes blindness. The disease is more common in people older than 35, the very nearsighted and diabetics. Blindness from glaucoma is largely preventable.
American blacks may have a vulnerability for this disease tied to the inability of their optic nerve to withstand damage from the buildup of fluid, Dr. Alfred Sommer said yesterday.
"The differences in the rates between blacks and whites appear unrelated to social and economic status or to access or use of eye-care services," said Sommer, the principal investigator in the East Baltimore study.
The study involved the examination from January 1985 to November 1988 of 5,308 people --2,395 black and 2,913 white -- 40 or older.
Using rigorous vision and eye tests, the researchers found that rates of glaucoma among blacks ranged from 1.23 percent for those age 40 to 49 to 11.26 percent for those 80 and older. In comparison, rates for whites ranged from 0.92 percent for 40- to 49-year-olds to 2.16 percent for those 80 and older.
About half of the 100 black and 32 white glaucoma patients gleaned from the 5,308 participants were unaware they had glaucoma, while the rest were receiving treatment.
"The report provides convincing evidence that blacks, particularly older blacks, are at a considerably higher risk of developing primary open angle glaucoma than whites," said Dr. Larry E. Rich of Oregon, in an accompanying editorial in JAMA. This kind of glaucoma, often referred to as POAG, is seen in most cases in the United States.
Dr. Carl Kupfer, director of the National Eye Institute of the U.S. Department of Health and Human Services, said, "The Baltimore eye survey has now provided the most conclusive information to date on the increased risk of American blacks to this insidious, blinding eye disease. . . . The findings that are being announced today are highly significant."
An estimated 3 million Americans have glaucoma, which is symptomless in its early stages, and 10 million are at greater than average risk, experts say.
"Many people who have the disease remain unaware because peripheral or side vision usually is affected first and people don't ordinarily think of shutting one eye and testing the other to see if they can detect any loss of their side vision," said Sommer. "But I think we might just ask them to do that."
The higher-risk groups must be motivated and educated that this is a disease that could cause them to go blind and they would not know it by themselves until it is too late, he said.
"If they are black, they should begin to have a comprehensive eye examination every two years no later than 35 to 40 years of age."