Facts About Open-Angle Glaucoma
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 3 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 people
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 to detect
glaucoma.
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 disease 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 antiglaucoma drugs
enter the bloodstream, 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 gain 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, patients with
open-angle glaucoma in the future should enjoy an even greater range of
treatment options that will help spare them progressive loss of vision.
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