It is estimated that over two million Americans have some type of glaucoma — and half of them do not know it.
Glaucoma is a serious yet frequently misunderstood disease. It is not a form of cancer, it is not contagious or life-threatening, and it seldom leads to blindness when diagnosed and treated early. Although it cannot be cured, it can usually be controlled. There are several types of glaucoma. This article covers the most common type, open-angle glaucoma.
The eye receives its nourishment from a clear fluid that circulates inside the eye called aqueous humor (not related to tears produced outside of the eye). As this fluid is constantly produced, it must also be constantly returned to the bloodstream through the eyes’ drainage canal, which is called the trabecular meshwork.
In the case of open-angle glaucoma, something has gone wrong with the drainage canal. When aqueous fluid cannot drain fast enough, the pressure inside the eye begins to build. This excess fluid pressure pushes against the delicate optic nerve which connects the eye to the brain. If the pressure remains too high for too long, irreversible vision loss can occur.
In the early stages, a person will not experience any symptoms. There is no pain or outward sign of trouble. Glaucoma usually occurs in both eyes, but extra fluid pressure often begins to build on only one eye at first. The early visual changes are very slight and do not affect the central vision but, over time, parts of the peripheral vision (the top, sides, and bottom areas of vision) can be lost.
Tonometry is used to measure eye pressure. After applying numbing drops, the tonometer is pressed against the eye and its resistance is measured and recorded. Although regular monitoring of the pressure is important, eye pressure can vary at different times of the day. Some optic nerves can be damaged by relatively low pressures while other optic nerves may not be damaged by relatively high pressures. Therefore, to be safe and accurate, other tests are usually performed.
Ophthalmoscopy is used to examine the shape and color of the optic nerve. Using eye drops to dilate the pupil, an ophthalmoscope is used to magnify and light up the inside of the eye. If the optic nerve appears to be cupped or is not a healthy pink color, additional tests will be run.
Perimetry is a test that maps the field of vision. Looking straight ahead into a white, bowl-shaped area, patients indicate when they are able to detect lights as they are brought into their field of vision. This map allows the doctor to see any pattern of visual changes caused by the early stages of glaucoma.
Gonioscopy is used to check whether the angle at which the iris meets the cornea is open or closed. This helps the doctor determine if he or she is dealing with open-angle glaucoma or narrow-angle glaucoma. About 90 percent of glaucoma patients have open-angle glaucoma. To control glaucoma, your doctor will use one of three basic types of treatments: medicines, laser surgery, or filtration surgery. The goal of treatment is to lower the pressure in the eye.
Medicines come in pill and/or eye drop form. They work by either slowing the production of aqueous fluid within the eye or by improving the flow through the drainage meshwork. To be effective, most glaucoma medications must be taken one to four times every day, without fail. Most of these medications have some undesirable side effects. Your doctor will attempt to find a medication that controls your pressure with the least number of side effects. Medicines should never be stopped without consulting your doctor and you should notify all of your other doctors about the medications you are taking.
Laser surgery attempts to treat the drainage canal. Requiring only numbing eye drops, the laser beam is applied to the trabecular meshwork resulting in an improved rate of drainage. When laser surgery is successful, it may reduce the need for daily medications.
Filtration Surgery is performed when medicines and/or laser surgery are unsuccessful in controlling eye pressure. During this microscopic procedure, a new drainage channel is created to allow aqueous fluid to drain from the eye.
Glaucoma can occur in people of all races and at any age. The likelihood of developing glaucoma increases if you are African-American, if you have a relative with glaucoma, if you are diabetic, if you are very nearsighted, or if you are over 35 years of age.
Even with modern treatments, glaucoma is one of the leading causes of preventable blindness. Everyone should be checked for glaucoma around age 35 and again at age 40. Those considered to be at higher risk, including persons over the age of 60 should have their pressure checked every year or two. With early detection and treatment, vision can be preserved and patients are able to lead normal lives.
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