Glaucoma is a disease of the optic nerve, which transmits the images you see from the eye to the brain. The optic nerve is made up of many nerve fibers (like an electric cable with its numerous wires). Glaucoma damages nerve fibers, which can cause blind areas and vision loss.
Glaucoma is pressure damage to the optic nerve. Usually, in glaucoma the pressure within the eye (“intra-ocular pressure,” or IOP) is higher than average, but glaucoma can occur at any IOP. The eye produces a clear fluid called “aqueous humor” and a tiny drain at the base of the cornea drains that fluid out of the eye. The usual reason for a pressure build-up is a partial blockage of the drain. Why a given IOP causes glaucoma damage in one person’s eye but not another’s remains a bit of a mystery.
The most common form of glaucoma is primary open-angle glaucoma. In medicalese “primary” means “we don’t know what causes it.” Probably, there is something wrong with the eye’s drain. Most people who develop primary open-angle glaucoma notice no symptoms until their vision is impaired, which is why it is so important to get regular eye exams.
Ocular hypertension is often a forerunner to actual open-angle glaucoma. When ocular pressure is above normal, the risk of developing glaucoma increases. Several risk factors will affect whether you will develop glaucoma, including the level of IOP, family history of glaucoma, and corneal thickness (people with thin corneas are more glaucoma-prone). If your risk is high, your ophthalmologist (Eye M.D.) or optometrist may recommend treatment to lower your IOP to prevent future damage.
In angle-closure glaucoma, the iris (the colored part of the eye) may come forward and completely close off the drain, blocking the flow of aqueous fluid and leading to increased IOP and optic nerve damage. In “acute” angle-closure glaucoma there is a sudden increase in IOP to a very high level, due to rapid buildup of aqueous fluid. This condition is considered an emergency, because optic nerve damage and vision loss can occur within hours of the problem. An acute attack is characterized by dull eye pain with nausea, redness and blurred, misty vision with rainbows or haloes. Angle-closure glaucoma can be “chronic” too, that is, slow in onset. An eye exam will reveal this type of glaucoma. Angle closure glaucoma is usually treated by cutting a hole in the iris with a laser. This is a simple office procedure.
Even some people with “normal” IOP can experience vision loss from glaucoma. This condition is called normal-tension glaucoma. In this type of glaucoma, the optic nerve sustains pressure damage, even though the IOP is considered statistically normal. Normal-tension glaucoma is not well understood, but lowering IOP has been shown to slow progression of this form of glaucoma.
Your doctor may tell you that you are at risk for glaucoma, if you have one or more risk factors, including having an elevated IOP, a family history of glaucoma, certain optic nerve conditions, or are of a particular ethnic background. People of African decent are prone to open-angle glaucoma; east Asians are prone to the angle-closure variety. Regular examinations with your eye doctor are important so that glaucoma doesn’t go undetected.
The goal of glaucoma treatment is to lower your eye pressure to prevent or slow further vision loss. Your doctor will recommend treatment, if the risk of vision loss is high. Treatment usually consists of laser treatment to make the eye’s drain work better and/or eye drops. Sometimes, surgery in the operating room is required to create a new drain in the eye. Glaucoma is a chronic disease that can be controlled but not cured. Ongoing monitoring (every three to six months) is needed to watch for changes and to be sure the IOP remains adequately low. Ask your ophthalmologist or optometrist, if you have any questions about glaucoma or your treatment.
Because it has no noticeable symptoms, glaucoma is a difficult disease to detect without regular, complete eye exams.
During a glaucoma evaluation, your ophthalmologist (Eye M.D.) or optometrist will perform the following tests:
- Tonometry. Your doctor measures the pressure in your eyes (intraocular pressure, or IOP) using a technique called tonometry. Tonometry measures your IOP by determining how your cornea responds when an instrument (or sometimes a puff of air) presses on the surface of your eye. Eye drops are usually used to numb the surface of your eye for this test.
- Gonioscopy. For this test, your doctor inspects your eye’s drainage angle – the area where fluid drains out of your eye. During goinoscopy, you sit in a chair facing the microscope used to look inside your eye. You will place your chin on a chin rest and your forehead against a support bar while looking straight ahead. The goniolens is placed lightly on the front of your eye, while your doctor looks through the microscope at the drainage angle. Drops will be used to numb the eye before this test.
- Ophthalmosocopy. With this test, your doctor can evaluate whether or not there is any optic nerve damage by looking at the back of the eye (called the fundus). A good fundus exam under 3D, high magnification is the best screening method to catch glaucoma. The pupils should be dilated for this exam.
- Visual field test. For this test, you sit at a bowl-shaped instrument called a perimeter . It shows you lights of varying intensity at various points in your field of vision. Each time you see a flash, you press a button. A computer records your response to each flash. The computer tells your eye doctor if the sensitivity to light is decreased at any of the points. Abnormalities in this test can indicate that you may have lost some vision already from glaucoma. Often, the visual loss is too subtle for you to notice, but the machine can detect very subtle changes.
- Photography. Sometimes photographs or other computerized images are taken of the optic nerve to record their appearance of your optic nerves. That way, as your eye doctor follows you over the years, he or she can look at the photos and compare them to how your nerves look now, to see if there is any increased glaucoma damage. Many doctors take the photos periodically as a way to detect subtle changes.
- Special imaging. Different scanners may be used to determine the configuration of the optic nerve head or retinal nerve fiber layer.
Each of these evaluation tools is an important way to monitor your vision to help ensure that glaucoma does not rob you of your sight. Some of these tests will not be necessary for everyone. Your ophthalmologist or optometrist will discuss which tests are best for you. Some tests may need to be repeated on a regular basis to monitor any changes in your vision caused by glaucoma.
Glaucoma: People of African and Hispanic Ancestry Are at Higher Risk
If you are of African or Hispanic ancestry and especially if you have a known family member with glaucoma, you are at a higher risk for vision loss from this eye disease.
Primary open-angle glaucoma is the leading cause of blindness among people of African ancestry, occurring at a rate of four times higher than among Caucasian patients. It also occurs about 10 years earlier among people of African ancestry than among Caucasians and develops more rapidly. Studies show that in the United States, African Americans between the ages of 45 and 64 are approximately 15 times more likely to go blind from glaucoma than Caucasians with glaucoma in the same age group. Primary open-angle glaucoma is also the leading cause of blindness among people of Hispanic (and especially Mexican) ancestry, occurring at a rate approaching that of people of African ancestry.
It is not clear why people of African ancestry have higher rates of open-angle glaucoma and subsequent blindness. One factor may be that they are more susceptible to developing elevated IOP earlier in life, which is thought to contribute to optic nerve damage and eventual vision loss. There also may be anatomical factors in the eye that are in play.
Glaucoma causes no symptoms early in its course--you will not experience pain or vision changes while it is developing. The best way to protect yourself and your family members against vision loss from glaucoma is by being aware of your higher risk of developing this disease and by having regular eye examinations for glaucoma at appropriate intervals.
Recommended intervals for a comprehensive eye evaluation in people of African ancestry are as follows:
- 20 to 29 years of age: every 3 to 5 years;
- 30 to 64 years of age: every 2 to 4 years;
- 65 years and older: every 1 to 2 years
It is also recommended that people of Hispanic ancestry have regular, comprehensive eye evaluations. This is especially important after age 60.
If you are diagnosed with glaucoma, please make sure to tell your family members and urge them to have an eye exam for glaucoma.
Here are some resources for more information on glaucoma:
The Glaucoma Foundation
80 Maiden Lane, Suite 1206
New York, NY 10038
Phone: 1-800-GLAUCOMA (452-8266)
The National Eye Institute
2020 Vision Place
Bethesda, MD 20892-3655
Prevent Blindness America
The American Academy of Ophthalmology
P.O. Box 7424
San Francisco, CA 94120-7424