anatomy of the eye (click on image to enlarge)
What is Glaucoma?
Glaucoma is a condition in which the pressure inside the eye damages the cells of the optic nerve. The optic nerve transmits information from the eye to the brain to provide vision. Glaucoma affects two million Americans and is the second leading cause of blindness in the United States.
What causes glaucoma?
There are many different types of glaucoma, but most types of glaucoma have in common an abnormally high pressure inside the eye. The pressure in the eye is not directly related to blood pressure. The normal range of pressure in the eye is between 8-21 units of measurement. There is a tissue inside the eye that pumps a clear fluid (aqueous) into the eye keeping the eye from collapsing. Another tissue called the trabecular meshwork normally drains the aqueous from the eye preventing the pressure from building up. In most types of glaucoma, the drain becomes clogged or blocked resulting in an increase of the pressure inside the eye. High pressure inside the eye damages the cells of the optic nerve. In an uncommon type of glaucoma (normal tension glaucoma), the pressure measurements are within the normal range, but the optic nerve is unusually sensitive and will become damaged if the pressure is not lowered even further.
Who is at risk for having glaucoma?
About two or three percent of Americans develop glaucoma. It may occur at any age, but usually occurs after the age of forty. It appears to be hereditary and, therefore, is more common in people who have family members with glaucoma. Diabetes increases the risk of glaucoma. African-Americans develop glaucoma fifteen times more frequently than European-Americans. Another risk factor for glaucoma is uveitis and trauma…especially, blunt injury to the eye. Steroid eyedrops and injections (triamcinolone and Ozurdex) may bring out glaucoma in eyes that are predisposed.
What are the symptoms of glaucoma?
The most common type of glaucoma is “open angle” glaucoma. In its early stages, glaucoma causes no obvious symptoms. However, driving vision can be impaired early on. Moreover, if it is not detected and treated early, glaucoma eventually may cause a gradual, severe, permanent loss of vision. Rarely, visual hallucinations may occur.
A less common type of glaucoma called “angle closure” glaucoma may cause sudden pain, redness, and blurred vision. It is more often seen in far-sighted eyes. In some cases, the tendency for an acute attack of glaucoma can be predicted on examination. In such cases laser treatment and/or cataract surgery may help to “open” the angle to prevent a future attack of angle closure glaucoma.
How is glaucoma diagnosed?
The most common test for glaucoma in an eye examination is tonometry. Tonometry measures the pressure inside the eye. Most people are first suspected to have glaucoma because high pressure is found on a routine exam. Another way to diagnose glaucoma is by examination of the optic nerve inside the eye. A nerve damaged by glaucoma has an abnormal appearance called “cupping,” which may provide a clue to the diagnosis. Additionally, a formal measurement of the peripheral vision (side vision) by a visual field test usually confirms the loss of vision that may not otherwise be noticeable. A visual field test is not part of a standard exam, but is performed if glaucoma is suspected. Repeated visual field tests help to determine whether treatment has been adequate to prevent loss of vision. Finally, sophisticated computerized tests (optical coherence tomography) are available to measure the thickness of optic nerve fibers to help in the diagnosis and assess the treatment of glaucoma.
What treatment is available?
Treatment of glaucoma is directed at lowering the pressure in the eye. The first line of treatment in most cases includes prescription eye drops. There are a number of very effective eye drops that work by either opening the drain or by slowing down the pump to lower the pressure. These drops are powerful medicines that should be used exactly as prescribed to prevent blindness from glaucoma and minimize side effects from the eye drops. Side effects are not common, but may include burning, itching, redness, dry mouth, and worsening of bronchitis or asthma. It is very important to take the eye drops exactly as prescribed to prevent blindness. If eye drops fail to control the pressure, laser surgery may help. Finally, surgery performed in the operating room (trabeculectomy) may create an artificial drain to lower the pressure. After trabeculectomy patients are warned to notify the doctor urgently if the eye becomes red or appears to be infected, because infection may enter the eye after trabeculectomy and result in severe damage or blindness. In general, patients with glaucoma may require regular examinations every three to four months to preserve vision.
For more information on glaucoma contact the Glaucoma Research Foundation at 1-800-826-6693 (www.glaucoma.org).
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