Facts About Open-Angle Glaucoma
Glaucoma: Primary Open Angle
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Open-angle glaucoma is the most common form of glaucoma, an eye disease that is a leading cause of blindness in the United States and the number one cause of blindness in Blacks. Although early treatment can substantially reduce the likelihood of severe vision loss or blindness, many people at higher risk for blindness from glaucoma are unaware of the importance of early detection, or are not having their eyes examined on a regular basis for the disease. Increased public awareness of the potential benefits of a regular, comprehensive eye examination with dilated pupils is crucial to reduce the enormous social and personal costs of open-angle glaucoma.
How does open-angle glaucoma affect the eye?
In a normal eye, aqueous humor–a clear, nutrient-rich fluid–passes continuously through the pupil and into a small space at the front of the eye, called the anterior chamber. As it leaves this area, the aqueous humor flows to the periphery of the chamber, or angle, where it exits through a complex channel system and drains into blood vessels in and near the sclera, the white outer coat of the eye.
In an eye with open-angle glaucoma, the aqueous humor drains too slowly through the channel system, creating a chronic rise in fluid pressure inside the eye. This elevated pressure may gradually interrupt the metabolic processes of cells in the optic nerve, leading to a progressive destruction of nerve fibers that are essential for vision.
Open-angle glaucoma is so called because the angle of the anterior chamber is open to aqueous humor outflow. It is the slow drainage of aqueous humor through the drainage system that increases fluid pressure. Conversely, in angle-closure glaucoma, part of the iris suddenly obstructs the angle and blocks the aqueous humor from reaching the drainage system. This causes a very painful rise in intraocular pressure, and requires emergency medical attention.
How many Americans have open-angle glaucoma?
Approximately three million Americans have open-angle glaucoma–but about half are unaware of it. Glaucoma accounts for over 4.5 million visits to physicians each year.
What is the cost of blindness from open-angle glaucoma?
It is estimated that as many as 120,000 Americans are now blind from the disease. Based on this estimate, blindness due to open-angle glaucoma costs the U.S. government over $1.5 billion annually in Social Security benefits, lost income tax revenues, and health care expenditures.
Who is at risk?
Although open-angle glaucoma can affect anyone, it is most prevalent in Blacks over age 40 and anyone over age 60. As people grow older, age-related changes in the eyes make them more susceptible to open-angle glaucoma.
The National Eye Institute-supported Baltimore Eye Survey shows that by age 70, about one in 50 Whites will have the disease. In Blacks, the problem is more severe. For example:
Blacks are three to four times more likely to develop open-angle glaucoma than Whites.
Open-angle glaucoma develops earlier in Blacks–around age 40–than in Whites, and progresses more rapidly. By age 70, one in eight Blacks has the disease.
Open-angle glaucoma is a leading cause of blindness among Blacks. In fact, Blacks are about six times more likely to become blind from the disease than Whites.
What are the symptoms of the disease?
At its onset, open-angle glaucoma usually has no symptoms. There is no pain, no blurring of vision, and no ocular inflammation to alert someone that they have the disease. But, as open-angle glaucoma progresses, it will slowly and insidiously begin to destroy peripheral vision. It is at this point that most people seek treatment, but tragically, vision that has already been lost from glaucoma cannot be restored.
How is glaucoma detected?
The most reliable way to detect open-angle glaucoma is through a comprehensive eye examination with dilated pupils–which when indicated, includes a visual field test.
To dilate, or enlarge, the pupils, the eye care professional places medicated drops into the eye. By so doing, the practitioner can better examine the back of the eye for early signs of disease, such as optic nerve damage, before noticeable vision loss occurs.
Tonometry is a common and painless test to measure intraocular pressure. In this test, an eye care professional uses an instrument called a tonometer to measure the fluid pressure in the anterior chamber. However, because elevated fluid pressure is only one characteristic of open-angle glaucoma, tonometry does not always indicate whether or not a person has the disease. In fact, many people with elevated fluid pressure never develop any form of glaucoma, while people with seemingly “normal pressure” during an examination will develop the disease. For this reason, tonometry should be viewed as one important component of the overall examination for glaucoma, but should not be the only test used for glaucoma detection.
When indicated, a visual field test, also called perimetry, is used by the eye care professional to measure the patient’s field of vision. This test is particularly important because it can detect a patient’s early loss of peripheral vision, a sign of open-angle glaucoma.
The National Eye Health Education Program recommends that people at higher risk undergo an eye examination through dilated pupils at least once every two years.
How is glaucoma treated?
Glaucoma treatment is aimed at controlling the eye’s fluid pressure, as a means of slowing the disease’s progression. Such treatment does not cure the disease. Most doctors use medications for newly diagnosed glaucoma; however, new research findings show that laser surgery is a safe and effective alternative. Open-angle glaucoma treatments include:
Medications: Several medications, in the form of eyedrops or pills, are available either to enhance fluid drainage or decrease the eye’s production of aqueous humor. Unfortunately, because anti-glaucoma drugs enter the blood system, they can cause various side effects such as headaches and respiratory problems. When such side effects occur, patients should consult with their eye care professional about alternative treatment regimens.
Laser Surgery: Glaucoma treatment using an argon laser has proved beneficial in preliminary studies. In this form of treatment, a high-energy beam of light is directed onto the trabecular meshwork–part of the anterior chamber’s drainage system–and approximately 100 tiny burns are made on its surface. The burns stretch the existing holes in the meshwork for better fluid drainage. Laser surgery, however, may be effective for only a short time and usually is used in conjunction with drops or pills.
Surgery: Several procedures may be performed to improve drainage flow, such as a trabeculotomy, goniotomy, and trabeculectomy. All of these involve making a small hole in the anterior chamber through which fluid can leave the eye. Although these procedures have a fairly high success rate, they are generally reserved until medical therapy is no longer effective.
What research is being conducted on glaucoma?
National Eye Institute-supported researchers are now studying the aging eye to delineate the exact sequence of biochemical events that cause open-angle glaucoma. By so doing, a clearer and more effective strategy can be developed to treat the disease. For example, long-term steroid treatment of ocular inflammation can cause an increase in fluid pressure. To understand this effect better, scientists recently developed a research model to study, step-by-step, how steroids influence intraocular pressure. In another study, these same investigators identified the major steroid-induced protein and cloned its gene. In the future, the researchers will attempt to clarify the biochemical switch(es) regulating these genes and glean greater insight into elevated fluid pressure, a feature common to all glaucomas.
Basic studies are also being conducted to learn more about the mechanisms of aqueous humor inflow and outflow, glaucomatous tissue changes in the optic nerve, and the dynamics of trabecular meshwork cells.
Studies are being conducted to streamline current surgical procedures, improve surgical wound healing, understand the possible role of nutrition in preventing open-angle glaucoma, and improve diagnostic techniques.
Through continued laboratory and clinical research, open-angle glaucoma patients should enjoy an even greater range of treatment options in the future that will help spare them progressive loss of vision.
September 1999
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