Glaucoma

Overview

Glaucoma is a group of diseases which cause the destruction of the tiny nerve fibers in the eye that run from the retina to the brain through the optic nerve. If left untreated, it can lead to vision loss and blindness; in fact, glaucoma is the second most common cause of legal blindness in the United States, and is the leading cause of blindness in African-Americans. It was once thought that the damage to the optic nerve was strictly attributable to high pressure in the eye. We now know that other factors must be involved, since even people with "normal" eye pressure can experience vision loss from glaucoma.

What Causes Glaucoma?

The eye constantly produces a clear fluid called aqueous that fills the anterior chamber of the eye. This fluid filters out of the anterior chamber of the eye through a drainage system that lies in a part of the eye called the angle, which is between the iris and the outer layer of the eye. This delicate balance between the production and drainage of aqueous determines the eye's intraocular pressure (IOP). Most people's IOPs fall between 8-21 mm Hg. Some eyes can tolerate higher pressures than others can.

The most common form of glaucoma is called primary open-angle glaucoma. With this type, the drainage system is open but does not function normally, causing the IOP to become elevated. Risk factors for Primary open angle glaucoma include: increased age, a family history of glaucoma, African-American heritage, nearsightedness, diabetes, regular long-term steroid/cortisone use, and history of trauma to the eye.

A far less common form of glaucoma is called acute angle closure glaucoma. This occurs when the angle where fluid drains from the eye becomes completely blocked, resulting in a sudden and dramatic rise in IOP. Acute angle closure glaucoma is a medical emergency and should be treated by an ophthalmologist immediately; otherwise, severe and permanent loss of vision will occur in just a few days.

Signs and Symptoms:

Primary open angle glaucoma is an insidious disease because it has no symptoms. Patients will not have pain nor notice any difficulty with their vision, despite the fact that irreversible damage is occurring. In fact, although approximately 2 million people in the U.S. have glaucoma, only half are aware of their disease.

Acute angle closure glaucoma does have symptoms, including:

• Extreme eye pain
• Sudden decrease in vision
• Nausea and vomiting
• Glare and light sensitivity

Detection and Diagnosis

Because glaucoma does not cause symptoms in most cases, those age 40 and over should have routine eye examinations, including measurement of intraocular pressure (IOP) and an evaluation of the optic nerve. An elevated IOP alone does not indicate the presence of glaucoma- it is only an important risk factor. Whether glaucoma develops is dependent upon the level of IOP that each individual's optic nerve can tolerate without being damaged. The examination of the optic nerve includes an analysis of the cup to disc ratio. This is a comparison of the cup (the depressed area in the center of the nerve) to the entire diameter of the optic nerve. As glaucoma progresses and the tissue of the optic nerve is destroyed, the area of cupping increases.

A crucial test to determine the presence of glaucoma, as well as to monitor the progression of the disease is called a visual field test. (Example) This test maps the peripheral vision (usually the first part of vision to be affected by the disease), and shows the extent of damage. During the test, a light shines into a bowl called a perimeter and the patient is asked to click a button when he or she sees it. Comparing visual fields over time allows the doctor to determine if the disease is controlled, or if further damage is occurring.

Another new test available is called an optic nerve head analyzer. (Example) With this test, a photograph is taken of the optic nerve and its surrounding tissue, and the thickness of the tissue is then analyzed by a computer. This test can pick up evidence of damage even before a visual field test, and may be more sensitive at demonstrating change over time.

Treatment

Although a patient will never be cured of glaucoma, treatment can usually control the disease.

Most doctors use medications (i.e. eye drops) as the first line of therapy for patients newly diagnosed with glaucoma. These eye drops lower the IOP by either causing the eye to make less fluid, or by helping increase the drainage of fluid from the eye. Some of these medications can have side effects that affect other parts of the body. It is therefore important to report any problems to your ophthalmologist, and to inform all other physicians caring for you that you use eye drops. Remember that glaucoma is a chronic disease, and that you may very well need to use these drops indefinitely.

A second option is for your ophthalmologist to perform an in-office laser procedure to help fluid drain from the eye. A new laser treatment, termed selective laser trabeculoplasty (SLT) is particularly promising in its ability to potentially reduce or eliminate the use of eyedrops in patients with glaucoma. Prior forms of laser treatment caused permanent structural changes to the drainage area, and were not particularly effective if repeated several years later if the pressure began to increase again. SLT has been found to lower intraocular pressure without causing permanent damage to the trabecular meshwork and has been found to be just as effective in eyes which were already treated with laser previously.

Conventional surgery may be necessary if the IOP cannot be controlled with medication or if the patient cannot tolerate the medications. The standard procedure is called a trabeculectomy, and creates a new opening for fluid to leave the eye.