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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 usually caused by high pressure inside the eye, known as 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.
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 the glaucoma ia advanced and vision is impaired.
Ocular hypertension, or high pressure in the eye, is a risk factor for developing actual 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 lOP and family history. If your risk is high, your ophthalmologist may recommend treatment to lower your IOP to prevent future damage.
Early in the disease process of glaucoma, individual nerve fibers in the eye's optic nerve are damaged, causing a thinning of the nerve fiber layer. Techniques have been devised to help measure the thickness of the nerve fiber layer. A nerve fiber layer analysis can help diagnose early glaucoma and is also used tctinonitor disease progression.
During a glaucoma evaluation, your ophthalmologist will perform the following tests:
Tonometry. Your ophthalmologist 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.
Gonioscopy. For this test, your ophthalmologist inspects your eye’s drainage angle--the area where fluid drains out of your eye. During gonioscopy, you sit ia 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 the 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 the numb the eye before the test.
Ophthalmoscopy. With this test, your ophthalmologist can evaluate whether or not there is any optic nerve damage by looking at the back of the eye (called the fundus). There are two types of ophthalmoscopy: direct and indirect. With direct ophthalmoscopy, your ophthalmologist uses a small flashlight-like instrument with several lenses that magnifies up to about 15 times. This type of ophthalmoscopy is most commonly done during a routine physical examination. With indirect ophthalmoscopy, the ophthalmologist wears a headband with a light attached and uses a small handheld lens to look inside your eye. Indirect ophthalmoscopy allows a better view of the fundus, even if your natural lens is clouded by cataracts.
Visual field test. The peripheral (side) vision of each eye is tested with vcisual field testing, or perimetry. For this test, you sit at a bowl-shaped instrument called a perimeter. While you stare at the center of the bowl, lights flash. This test shows if you have any areas of vision loss. Loss of peripheral vision is often an early sign of glaucoma.
Photography. Sometimes photographs or other computerized images are taken of the optic nerve to inspect the nerve more closely for damaged from elevated pressure in the eye.
Special imaging. Different scanners may be used to better 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 will discuss which tests are best for you.