Eye drops that reduce elevated pressure inside the eye can delay or possibly prevent the onset of glaucoma in African Americans at higher risk for developing the disease, researchers have found. This makes it more important to identify African Americans at higher risk for developing glaucoma so they can receive prompt evaluation for possible medical treatment. These results are reported in the June 2004 issue of Archives of Ophthalmology.
Scientists found that 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 vision loss. Of the African American study participants who received the eye drops, 8.4 percent developed glaucoma. By comparison, 16.1 percent of the African American study participants who did not receive the eye drops developed glaucoma. The study was funded by the National Eye Institute (NEI) and the National Center on Minority Health and Health Disparities (NCMHD), two components of the Federal government's National Institutes of Health.
The results of this study, called the Ocular Hypertension Treatment Study (OHTS), are a followup to initial results released two years ago. In those findings, researchers discovered that treating people with elevated eye pressure could delay or prevent the onset of glaucoma. At that time, results for the subgroup of African Americans trended in the same direction, but were not conclusive.
Primary open-angle glaucoma affects about 2.2 million Americans age 40 and over, half of whom 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.
"This is the first study to recruit large numbers of African Americans to examine the benefit of pressure-lowering eye drops to prevent or delay the onset of glaucoma," said Paul A. Sieving, M.D., Ph.D., director of the NEI. "The results underscore that African Americans over age 40 should receive a comprehensive dilated eye exam at least once every two years to see if they are at higher risk for glaucoma."
These results do not imply that every African American with high eye pressure requires treatment, according to Eve Higginbotham, M.D., chair of the Department of Ophthalmology at the University of Maryland Medical Center and first author of the journal article. "When determining treatment, doctors should take into account several risk factors, including specific anatomical characteristics of the optic nerve and the cornea," Dr. Higginbotham said. "While African Americans participating in the 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."
Dr. Higginbotham suggested that before determining treatment, the doctor and patient should also discuss the patient's health status and life expectancy, and the burden of daily treatment, including cost, inconvenience, and possible side effects.
Elevated eye pressure results when the fluid that flows in and out of the eye drains too slowly, gradually increasing pressure inside the eye. It is estimated that between three and six million people in the U.S. are at increased risk for developing primary open-angle glaucoma, representing between four and seven percent of the population above age 40. In this study, ocular hypertension was defined as pressure of 24 mm Hg or greater in at least one eye.
The OHTS studied more than 1600 people, including 408 African Americans, 40-80 years of age who had elevated eye pressure but no signs of glaucoma. Half were assigned daily pressure-lowering eye drops, and the other half were assigned to observation (no medication). In the medication group, the number of African Americans participants developing glaucoma was significantly lower (8.4 percent) compared to the observation group (16.1 percent).
"The study also confirms that the risk for developing glaucoma is higher among African Americans compared with others," said Michael Kass, M.D., of the Washington University Department of Ophthalmology and Visual Sciences and chair of the study. "A number of risk factors may be contributing to the increased prevalence of visual impairment from glaucoma in African Americans. These include a family history of glaucoma; earlier onset of the disease compared to other races; later detection of the disease; and economic and social barriers to treatment."
Glaucoma is a leading cause of blindness in African Americans, said John Ruffin Ph.D., director of the NCMHD. "Glaucoma is almost three times as common in African Americans than Whites," Dr. Ruffin said. "However, if glaucoma is detected and treated early in its progression, it can usually be slowed and serious vision loss can be delayed."
Dr. Ruffin said Medicare covers an annual dilated eye examination for people at higher risk for glaucoma. This important preventive benefit defines higher risk as people with diabetes; those with a family history of glaucoma; and African Americans aged 50 and older.
In addition to support from the NEI and NCMHD, the Ocular Hypertension Treatment Study was supported by Research to Prevent Blindness and Merck Research Laboratories. The study was conducted at 22 clinical centers across the country. A list of study centers and principal investigators is attached.