In simple terms, glaucoma is a buildup of fluid inside the eye. It's the leading cause of blindness among adults in the United States, and estimates are that one of every seven persons is a victim. Your eyes are essentially hollow globes filled with a constantly circulating fluid that must drain out of the eye as more fluid is pumped in. When the passages that allow fluid to drain become clogged or blocked, the fluid pressure can build and eventually cause damage to the optic nerve. That buildup of pressure is called glaucoma. Of the two types of glaucoma, open-angle and acute-(or closed) angle. The latter is far more serious and represents only about 10 percent of total glaucoma cases.

The Risks of Glaucoma

Because open-angle glaucoma, the more common version of the disorder, usually develops gradually and without symptoms, regular eye exams are important in detecting the disease before it damages your eyesight. If detected at an early stage and treated promptly, glaucoma can be controlled with little or no further vision loss. People of all ages can develop glaucoma, but it most frequently occurs in those who are more than 40 years of age. People of African-American heritage are also at greater risk, as are those with a family history of glaucoma, those who are very nearsighted and those who have diabetes.

Acute or closed-angle glaucoma can develop more quickly and may be accompanied by symptoms such as blurred vision, a loss of side vision, appearance of colored rings around the eyes, and pain or redness in the eyes. A combination of any of these symptoms necessitates an immediate eye examination.

Preparation for the Examination

Before the examination, patients will be asked to supply their address and telephone numbers, insurance information, names of other doctors, list of medications being taken, and past medical records if available. Some doctors ask patients to bring to the exam all medications currently being used. Because a glaucoma exam includes dilating the eyes, it's a good idea to bring sunglasses to wear during the trip home.

The Examination

The exam usually begins with a visual acuity test and refraction to determine how well you can see with and without eyeglasses or contact lenses. Then, it moves on to more specialized procedures, which allow the doctor to determine whether the disease has already caused damage to the eye.

Introacular Pressure Test
Because glaucoma is caused by pressure inside the eye, the first and most important test in determining whether the disease may be a problem is a test for intraocular pressure (IOP). This test is conducted with one of two types of tonometer. The applanation tonometer involves the use of a pressure-sensitive tip that is placed gently against the eye, while the air puff tonometer directs a gentle puff of air toward the eye. The applanation procedure is considered to be more accurate and will probably be used in most glaucoma examinations.

Visual Field Test
A visual field or perimetry test measures the ability of your eye to see straight ahead and to the side (peripheral vision). During a visual field test, one eye is temporarily covered and the patient is asked to look straight ahead at a fixed space.

There are two kinds of tests. In a moving target test, the targets are moved from the side, where they are not visible, towards the center of vision until the patient sees them. This test can be done with either a black screen on the wall or with a large bowl-shaped instrument.

The other is fixed target test, called computerized static perimetry. It uses small points of light that appear bright or dim but do not move. During this test, a patient sits in a chair facing either a bowl-shaped instrument or a computer screen.

The visual field examination is important in detecting many disorders of the eye, optic nerve and brain. One of the early symptoms of glaucoma, for instance, is the appearance of "blind spots" that can be detected by a visual field test.

Another important part of any glaucoma examination is called ophthalmoscopy. During this test, your doctor will place drops in the eye to dilate the pupil (make it larger), allowing a bigger "window" through which to examine the interior of the eye. The doctor looks inside the eyes, using a magnifying instrument called an opthalmoscope. Of particular interest during an examination for glaucoma is the retina, the thin membrane that covers about two-thirds of the inside back of the eye. The retina acts like the lens of a camera, receiving images and transmitting them to the brain via the optic nerve. Because glaucoma pressure can damage the retina and or the optic nerve, a careful examination of this area is critical.

Gonioscopy is test by which the doctor uses a contact lens with mirrors to evaluate the anterior chamber angle of the eye. This is the area where aqueous fluid filters out of the eye, and it is not visible except with the gonioscopy procedure. If an angle is very narrow, it may close off causing risk of a pressure increase, which can damage the eye. This test is especially important in differentiating between narrow or closed angle glaucoma. Gonioscopy also allows the doctor to examine the trabecular meshwork, a sponge-like portion of the eye, out of which fluids drain in order to maintain proper fluid pressure.

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