 | Eye Drops May Delay or Prevent Glaucoma in African-Americans
Embargoed until 3 p.m. CT, Monday, June 14
St. Louis, June 14, 2004 — 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 University of Maryland Medical Center and Washington University School of Medicine in St. Louis.
The researchers say that means 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 2004 issue of Archives of Ophthalmology.
“This analysis of the data revealed both good news and bad news,” says 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 School of Medicine. “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.”
Daily pressure-lowering eye drops reduced the development of primary open-angle glaucoma in African-Americans by almost 50 percent. Primary open-angle glaucoma is the most common form of glaucoma and one of the nation’s leading causes of blindness.
Of the African-American study participants who received the 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 subjects were part of a larger study called the Ocular Hypertension Treatment Study (OHTS). The new results are a follow up to initial results released two years ago. In those earlier findings, researchers discovered that treating people with elevated eye pressure could delay or prevent the onset of glaucoma. At that time, results for African-Americans trended in the same direction, but now investigators have been able to separate out data from the African-American participants in the national study and consider their risks as a group.
During the original OHTS study, 1,636 subjects between the ages of 40 and 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 each day. 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 subjects to the rest of the subjects 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. But the percentage of African-Americans who did not receive drops and developed the disease was 16.1 percent.
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 says. “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.”
The study suggests there may be anatomical differences that explain some of the increased risk. For instance, some African-American patients have thinner corneas and a slightly different anatomical appearance to the optic nerve than other populations. Eve Higginbotham, M.D., first author on this study and head of the Department of Ophthalmology at the University of Maryland Medical Center, says those differences should be considered when prescribing treatment for African-American patients at risk for glaucoma.
To determine why some African-Americans are at increased risk, a team of Washington 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 at Washington University School of Medicine.
“We believe that gene-based differences between African-Americans and Caucasians may be what underlies susceptibility to glaucoma,” Hernandez says. “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 colleagues also will 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 says. “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. Both for African-Americans and for members of other ethnic groups, this latest study reaffirms that drops can slow the progression of the disease.
“When determining treatment, doctors should take into account several risk factors, including the specific anatomical characteristics of the optic nerve and the cornea,” Higginbotham says. “While African-Americans participating in our study were more likely than others to have these specific physical characteristics, the study results underscore the importance of measuring these ocular risk factors rather than relying solely on the race or ethnicity of the individual.”
Primary open-angle glaucoma
Primary open-angle glaucoma affects about 2.2 million Americans age 40 and over. Half of them are not aware they have the disease. Vision loss from glaucoma occurs when the optic nerve is damaged. In most cases, elevated eye pressure, also called ocular hypertension, contributes to this damage. This causes gradual loss of peripheral (side) vision.
As the disease progresses, the field of vision gradually narrows and blindness can result. Glaucoma has no early symptoms, and by the time people experience problems with their vision, they usually have a significant amount of optic nerve damage. However, if detected early, glaucoma can usually be controlled and serious vision loss prevented. Comprehensive dilated eye examinations are recommended at least once every two years for African Americans over age 40 and all people over age 60.
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Higginbotham EJ, Gordon MO, Beiser JA, Drake MV, Bennett GR, Wilson MR, Kass MA. The Ocular Hypertension Treatment Study: Topical medication delays or prevents primary open-angle glaucoma in African American individuals.
Archives of Ophthalmology, June 2004, pp. 813-820.
The Ocular Hypertension Treatment Study was sponsored by the National Eye Institute (NEI) and the National Center on Minority Health and Health Disparities (NCMHD) of the National Institutes of Health (NIH). The study also was supported by Research to Prevent Blindness and Merck Research Laboratories.
The full-time and volunteer faculty of Washington University School of Medicine are the physicians and surgeons of Barnes-Jewish and St. Louis Children's hospitals. The School of Medicine is one of the leading medical research, teaching and patient care institutions in the nation, currently ranked second in the nation by U.S. News & World Report. Through its affiliations with Barnes-Jewish and St. Louis Children's hospitals, the School of Medicine is linked to BJC HealthCare. |