"The fundamental question we asked was whether you can delay or prevent people from developing glaucoma," 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. "There are millions of people in the United States -- and in other countries -- who are at risk of developing glaucoma because they have high pressure in their eyes. This study provides the first good evidence that treating those people may delay, or possibly even prevent, the blinding eye disease, glaucoma."
The study, called the Ocular Hypertension Treatment Study (OHTS), examined 1,636 people between the ages of 40 and 80. All had elevated pressure in the eye -- ocular hypertension -- but did not have glaucoma. About half (817) were randomly selected to use eye drops each day. The other patients (819) were closely monitored by eye specialists for a minimum of five years. Patients who received treatment were given commercially available, pressure-lowering eye drops, either a single type of drop or a combination of more than one. The drops reduced pressure in the eye by approximately 20 percent.
"I think it is very significant that reducing pressure in the eye by only 20 percent reduced risk by as much as it did," Kass says. "A modest drop in pressure makes a big difference."
Open-angle glaucoma is the most common form of glaucoma and one of the leading causes of blindness in the United States. It is the number one cause of blindness among African Americans and affects a total of about 2.2 million Americans age 40 and over. As many as 2 million more may have the disease, but they have not been diagnosed. Because glaucoma rarely has early symptoms, by the time they experience vision problems, most people already have significant, irreversible damage.
As with heart disease, diabetes and high blood pressure, glaucoma develops over many years. The idea of attacking glaucoma before damage could occur has been an attractive one, but there was no clear evidence to support this approach. The current study addressed this issue by clearly identifying factors that put people at risk for the disease.
Several risk factors are associated with the development of glaucoma, including older age and African descent, particular characteristics in the anatomy of the optic nerve, and thinness of the cornea.
Fluid regularly flows into and out of the eye. High pressure results when that fluid drains too slowly. Between 3 and 6 million Americans have elevated eye pressure and are at risk for open-angle glaucoma. Approximately 1.5 million people in the United States who have elevated eye pressure but do not have glaucoma already are being treated with medications that lower intraocular pressure, but prior to this study, there was no convincing evidence that the treatment has any long-term benefit. These findings change that.
"During the five-year study period, we found that only 4.4 percent of the study patients who received the eye drops developed glaucoma," says Mae E. Gordon, Ph.D., director of the OHTS Coordinating Center and professor in the Department of Ophthalmology and Visual Sciences and the Division of Biostatistics at Washington University School of Medicine. "By comparison, 9.5 percent of the study participants who did not get pressure-lowering drops developed glaucoma."
Although high pressure in the eye is a strong risk factor for glaucoma, patients aren't considered to have the disease until they also have damage to their optic nerve. The damage causes loss of peripheral (side) vision. As glaucoma worsens, a patient's field of vision gradually narrows, and they can become almost blind. But if the disease is detected early through a comprehensive eye exam, glaucoma usually can be controlled and serious vision loss prevented. The American Academy of Ophthalmology recommends comprehensive eye exams for all people over 60 and for African Americans over 45. African Americans are three to four times more likely to develop glaucoma than Caucasians. Because of that high risk, 25 percent of the participants in the OHTS were African American.
Even though drops succeeded in reducing the rate of glaucoma, Kass believes not all patients with high eye pressure should automatically receive treatment. "Before simply putting a patient on drops, doctors need to consider the patient's general health status, their individual risk factors and their life expectancy," he says. "It's important to remember that even in the study group that did not receive treatment, 90 percent of the people did not develop glaucoma."
Because some eye drops cause side effects and because daily treatment can be inconvenient and expensive, Kass believes some patients may want to opt for close observation rather than active treatment. He says doctors should use the results of this study as only one of several factors when designing a treatment strategy for an individual patient.
"The availability of many different types of pressure-lowering eye drops will allow eye-care professionals to choose the safest regimen for each individual patient," he says. "We found no increase in health problems among patients who received eye drops, but different regimens of drops are more appropriate to some patients than others, depending upon individual risk and the general health of the patient."
Kass says researchers hope to continue the study to determine the long-term benefits of treatment and to improve accuracy of the early diagnosis of glaucoma. But now that the initial phase is complete, those participants who were randomly assigned to receive observation rather than eye drops will be offered eye drop medication.
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. Through its affiliations with Barnes-Jewish and St. Louis Children's hospitals, the School of Medicine is linked to BJC HealthCare.