Eye drops that reduce elevated pressure inside the eye can delay or prevent the onset of glaucoma in African-Americans at high risk for developing the disease, according to a study led by researchers at the School of Medicine and the University of Maryland Medical Center.
Michael A. Kass
The researchers said it is important to identify African-Americans with elevated eye pressure so they can receive prompt medical treatment.
The results are reported in the June issue of Archives of Ophthalmology.
“This analysis of the data revealed both good news and bad news,” said Michael A. Kass, M.D., national chair of the 22-center study and head of the Department of Ophthalmology and Visual Sciences at Washington University. “African-Americans do better when they are treated with pressure-lowering drops, but even with treatment, they tend to have a higher risk than other groups.”
Of the African-American study participants who received the pressure-lowering eye drops, 8.4 percent went on to develop glaucoma.
By comparison, 16.1 percent of the African-American study participants who did not receive the eye drops went on to develop the disease.
The African-American participants were part of a larger study called the Ocular Hypertension Treatment Study (OHTS). During the original OHTS study, 1,636 subjects between 40-80 were divided into two groups. All had elevated pressure in the eye — ocular hypertension — but did not have glaucoma, and about half were randomly selected to use eye drops daily.
The others were closely monitored by eye specialists for a minimum of five years but did not use drops.
This new analysis looked in detail at the outcomes for the 408 African-Americans who participated in the OHTS study.
Researchers also compared the African-American participants to the rest of the people in the study and found that among patients in the observation group — those who did not use pressure-lowering eye drops — about 11 percent developed glaucoma during the course of the study.
Looking at patients who received the pressure-lowering drops, the investigators found that 8.4 percent of African-Americans developed glaucoma, but only 4.4 percent of the other patients using drops developed the disease.
“We’ve known for some time that glaucoma is about four times more common in African-Americans than in Caucasians, and blindness from glaucoma is about six times more common in African-Americans,” Kass said. “This study suggests that even when treatment is identical, the risk for African-Americans is still higher, even though treatment does help.
“We believe there must be other factors that help explain the differences, but the full explanation is not available right now.”
To determine why some African-Americans are at increased risk, a team of University scientists has launched a new study that will compare gene expression in the optic nerves of African-Americans to age-matched Caucasians.
That study, funded by a five-year, $3.4 million grant from the National Eye Institute, will be headed by M. Rosario Hernandez, D.D.S., professor of ophthalmology and visual sciences.
“We believe that gene-based differences between African-Americans and Caucasians may be what underlies susceptibility to glaucoma,” Hernandez said. “We plan to test that hypothesis over the next few years by studying the behavior of human cells taken from the two groups.
“If we find that certain genes are more active in optic nerve cells from African-Americans, we also might find that those same genes are overactive in Caucasians who develop the disease, providing a potential genetic target for assessing risk.”
Hernandez and her colleagues will also compare differences in growth factors, nerve cell proliferation and cell migration in optic nerve tissues from African-Americans and Caucasians.
They will pay particular attention to the optic nerve head, the likely target of stress generated by high pressure in the eye.
“Our main goal is to determine how cells called astrocytes contribute to optic nerve degeneration in glaucoma,” Hernandez said.
“Astrocytes are the major cell type in the optic nerve, providing structural and metabolic support to the nerve fibers.”
But until Hernandez and her colleagues can identify genetic and other types of risk that make cells more vulnerable to damage from high pressure and glaucoma, researchers from the OHTS study say early detection and treatment of glaucoma is the key to a good outcome.