What is glaucoma?
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 spots and vision loss. Glaucoma is related to the pressure inside the eye, known as the intraocular pressure (IOP). When the aqueous humor (a clear liquid that normally flows in and out of the eye) cannot drain properly, pressure builds up in the eye. The resulting increase in IOP can damage the optic nerve and lead to vision loss.
Early detection and treatment by your ophthalmologist are keys to prevent optic nerve damage and blindness from glaucoma.
Glaucoma is the leading cause of blindness in North America, especially in older people. But sight loss from glaucoma can often be prevented with early treatment.
Open Angle Glaucoma
The most common form of glaucoma is primary open-angle glaucoma, in which the aqueous fluid is blocked from flowing back out of the eye at a normal rate through a tiny drainage system. Most people who develop primary open-angle glaucoma notice no symptoms until their vision is impaired.
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, and corneal thickness. If your risk is high, Dr. Anjema may recommend treatment to lower your IOP to prevent future damage.
Angle Closure Glaucoma
In angle-closure glaucoma, the iris (the colored part of the eye) may drop over and completely close off the drainage angle, abruptly blocking the flow of aqueous fluid and leading to increased IOP or optic nerve damage. In acute angle-closure glaucoma there is a sudden increase in IOP due to the buildup of aqueous fluid. This condition is considered an emergency because optic nerve damage and vision loss can occur within hours of the problem. Symptoms can include nausea, vomiting, seeing halos around lights, and eye pain.
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 is damaged even though the IOP is considered normal. Normal-tension glaucoma is not well understood, but lowering IOP has been shown to slow progression of this form of glaucoma.
Childhood glaucoma, which starts in infancy, childhood, or adolescence, is rare. Like primary open-angle glaucoma, there are few, if any, symptoms in the early stage. Blindness can result if it is left untreated. Like most types of glaucoma, childhood glaucoma may run in families.
Evaluation and treatment
Dr. Anjema 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, are of a particular ethnic background, or are of advanced age. Regular examinations with Dr. Anjema are important if you are at risk for this condition.
The goal of glaucoma treatment is to lower your eye pressure to prevent or slow further vision loss. Dr. Anjema will recommend treatment if the risk of vision loss is high enough to justify intervention. Treatment often consists of eye drops but can include laser treatment or surgery to create a new drain in the eye. Glaucoma is a chronic disease that can be controlled but not cured. Ongoing monitoring (up to every three to six months, but more often annually) is needed to watch for changes. Ask Dr. Anjema if you have any questions about glaucoma or your treatment.
Testing for Glaucoma
Because it has no noticeable symptoms, glaucoma is a difficult disease to detect without regular, complete eye exams.
During a glaucoma evaluation, the following tests are usually performed:
Dr. Anjema 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. Eyedrops are usually used to numb the surface of your eye for this test.
With this test, Dr. Anjema can evaluate whether or not there is any optic nerve damage by looking at the back of the eye (called the fundus). With ophthalmoscopy, Dr. Anjema uses a powerfully magnified light that magnifies up to about 15 times. This type of ophthalmoscopy is most commonly done during a routine physical examination. Ophthalmoscopy allows a better view of the fundus, even if your natural lens is clouded by cataracts.
Optical coherence tomography (OCT) is a special scan used to study the anatomy of the retina and optic nerve in fine detail. OCT testing requires dilation of the pupils but does not require a needle in the arm and does not involve touching the eye. A healthy retina is only ¼ of a millimeter thick, but it contains multiple layers of specialized cells. One layer converts light into nerve signals, another processes the nerve impulses, while another transmits these processed impulses to the brain where they are interpreted.
Sometimes photographs or other computerized images are taken of the optic nerve to inspect the nerve more closely for damage from elevated pressure in the eye.
For this test, Dr. Anjema inspects your eye’s drainage angle—the area where fluid drains out of your eye. During gonioscopy, 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, and a narrow beam of light is directed into your eye while your doctor looks through the slit lamp at the drainage angle. Drops will be used to numb the eye before the test.
Visual field test
A visual field test (perimetry test), measures all areas of your eyesight, including your side, or peripheral, vision. A visual field test can help find certain patterns of vision loss and is a key way to check for glaucoma. It is very useful in finding early changes in vision caused by nerve damage from glaucoma.
To take this painless test, you sit at a bowl-shaped instrument called a perimeter. While you stare at the center of the bowl, lights flash. Each time you see a flash you press a button. A computer records the location of each flash and whether you pressed the button when the light flashed in that location. At the end of the test, a printout shows if there are areas of your field of vision where you did not see the flashes of light. This test shows if you have any areas of vision loss. Loss of peripheral vision is often an early sign of glaucoma. Visual field testing is used together with the clinical exam and HRT testing to determine if you have glaucoma or if your glaucoma is worsening.
The Heidelberg Retina Tomograph (HRT) is a proven, essential tool for detecting and managing glaucoma and disease of the optic nerve, especially for assisting in the identification of early disease and tracking progression. The Heidelberg Retina Tomograph (HRT) is a confocal scanning laser ophthalmoscope. A laser light scans the retina in 24 millisecond sequential scans, starting above the retinal surface, then capturing parallel images at increasing depths. The stacks of images can be combined to create a three-dimensional (3-D) topographic image of the retina. Images are aligned and compared using TruTrack™ software for both individual examinations and for detecting change between examinations.
The HRT test is not covered for the assessment of glaucoma patients. The cost of the test can be claimed on your income tax return (Line 330 ). The HRT test is an optional test to you, the patient.
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. Dr. Anjema 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.