Glaucoma is an umbrella term, which covers a group of diseases with a characteristic pattern of optic nerve damage. The optic nerve is the bundle of nerve fibers at the back of the eye that carry visual messages from the retina to the brain. There are many types of glaucoma classified by clinical exams. The most common one is primary open-angle glaucoma (POAG). Patients with POAG most commonly experience no symptoms at all until the disease progresses to an advanced stage. The most common symptoms of advanced disease include side vision loss and diminished quality of vision, which can significantly impair daily activities, including driving. The current available treatments have been proven effective in slowing down the disease, but not in reversing optic nerve damage.
In order to avoid such irreversible visual debilitation, it is important to have your eyes examined for glaucoma by an eye doctor, especially if you carry some of the known risk factors, such as family history of the disease. It is crucial to have some basic understanding of the tests for glaucoma so that you can make an informed decision about your treatment options under the guidance of your doctor. Some of the tests are outlined below.
Increased eye pressure is the most important risk factor for glaucoma. It is considered as one of the “vital signs” when you visit your eye doctor. You can think of high eye pressure as a risk factor for glaucoma just like high blood pressure is a risk factor for stroke. The eye pressure test is called tonometry, and the most common method is known as “applanation,” in which a tiny instrument contacts the surface of the eye after it is numbed with an eye drop. It is painless and quick, but does require your cooperation. Knowing this is helpful because if you are not fully relaxed at the time of measurement, the reading can be misleading.
Corneal Thickness and “Angle” Tests
Some other contact tests include a corneal thickness test (pachymetry) and an “angle” test (gonioscopy). They are absolutely necessary and are included in the “vital signs” of the eye exam.
Cornea Thickness Test (Pachymetry)
Pachymetry painlessly measures the thickness of the cornea with a small probe after the eye is numbed with an eye drop. A thin cornea may contribute to artificially low eye pressure readings, and a thick cornea may contribute to pressure readings that are higher than they actually are. The cornea thickness measurement provides crucial information for your doctor to tailor your treatment.
Angle Test (Gonioscopy)
Gonioscopy is another test performed by your doctor with a hand held goniolens. Some doctors refer that lens as an “exam contact lens.” The doctor will barely touch the gonioscopy lens to the numbed cornea. The procedure is simple, quick, and does not hurt. It is similar to using mirrors in a periscope to see areas that are not otherwise visible to the naked eye. Once the gonioscopy lens is in contact with the cornea, it will allow the eye doctor to see the “angle.” The “angle” is the area where the cornea (the clear part in the front of the eye) meets the iris (the colored part of the eye). The “angle” is also where the trabecular meshwork is located. Under normal circumstances, the majority of the fluid that is created inside the eye must exit the eye by passing through the trabecular meshwork. If the trabecular meshwork is visible on gonioscopic examination, doctors call this an “open” angle. If the trabecular meshwork is blocked by scar tissue or the iris, it is called a “closed” angle.
Visual Field Test
The visual field test is considered a functional test, and allows your doctor to tell you if you have lost any field of vision from glaucoma, how much you have lost, and can help determine the rate of disease progression, which in turn will help to tailor the treatment. Your doctor will be able to tell you how severe your disease is based on this test.
Although the test is not painful, and it only takes a few minutes for each eye, if you are overly anxious or tired, you may not be able to perform the test reliably. Also, the test may require some learning experience, and therefore may need to be repeated. There is no special preparation for the test, or any need to remove your contact lenses. The visual field test needs to be repeated periodically, although the frequency may vary significantly depending upon your specific situation.
Glaucoma Imaging Tests
The glaucoma imaging tests are a reliable way for your doctor to monitor glaucoma progression. The tests are non-invasive and involve no radiation. Your pupils will be dilated using eye drops, and then the doctor will photograph your optic nerve with a digital camera, or use other technologies to map your optic nerve. Regardless of the modality your doctor chooses, the results become immediately available, which can be projected on a computer screen for discussion.
Rachel Kuchtey, M.D., Ph.D. Assistant Professor Glaucoma and Anterior Segment Surgery Vanderbilt Eye Institute
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