2009-06-13 / Columnists

Maintaining Your Health on Mackinac

Glaucoma Threatens Normal Vision; Can Be Treated If Found Early
By Yvan Silva, M.D.

Glaucoma is a serious eye condition that results from an elevation in pressure in the eye. This is caused by a build-up of excess fluid within the eye. It affects more than 3 million people in the United States and, left untreated, the pressure can cause irreversible damage to the optic nerve, the nerve that connects the brain to the back of the eye at a spot called the optic disc. Glaucoma is a serious condition because it frequently progresses without noticeable symptoms. It leads to loss of peripheral vision, and can progress to blindness. There are various types of glaucoma, and the most common, primary open-angle glaucoma, accounts for about 90% of cases.

Blurred vision, accompanied by nausea, headaches, and halos around bright light, are symptoms that require eye examination and diagnosis. Failure of peripheral (side-vision), such as the inability to see out the side and corner of the eye or having to turn the head to see what is at the immediate right or left, is the hallmark of glaucoma.

The eye is indeed a most sophisticated organ. Globular in nature, it consists of two chambers, in front of and behind the lens. The anterior chamber, in front, is filled with watery fluid called the aqueous humor. It is produced continuously and circulated in the chamber as it drains out of the eye. The fluid nourishes the front portion of the eye. It drains through the trabecular meshwork formed of spongy tissue, through a tiny duct - the Schlemm's canal - into the bloodstream. Clogging of the trabecular network diminishes optimal drainage. A normal eye produces as much aqueous humor as it drains away, thus maintaining a normal pressure in the eye. When inefficient drainage ensues, the intra-ocular pressure increases. Both eyes are usually affected, although one may be more so than the other. The posterior chamber, behind the lens, is called the vitreous chamber, which is filled with a clear gel, the vitreous fluid. A certain optimal pressure is necessary for the eyeball to hold its shape and function.

Starting around the age of 35, a pressure check for glaucoma should be an essential part of an annual eye examination. A visual field check is done to detect peripheral vision loss. The optic disc is directly visualized through the pupil with an ophthalmoscope for signs of damage. Eyeball pressure is obtained by tonometry. These are the risk factors for glaucoma: Family history, diabetes, previous eye injury, and some rare diseases. It is the leading cause of blindness in African Americans. There is no cure, but it can be treated by lowering the pressure in the eye to prevent progressive loss of peripheral vision and further damage to the optic nerve. When a diagnosis is made, other tests may be indicated to identify, for example, the thickness of the cornea, mapping of the visual fields, and measuring the rate of drainage of fluid from the eye.

The first line of treatment usually prescribed is the administration of eye drops designed to slow production of the aqueous humor or increase the drainage. If this proves insufficient to lower the eye pressure to an optimal level, oral medications are indicated. Known as carbonic anhydrase inhibitors, acetazolamide, and metazolamide, they can be effective in achieving the desired pressure levels. Surgery is the next level of treatment. Done in the doctor's office, a laser beam is applied to the trabecular meshwork to open it up and promote drainage of the aqueous humor. There are nonlaser surgical techniques that involve making a drainage passage or placement of a small drainage tube, and these also are usually done on an outpatient basis. Eye drops may still be required after surgery, in some cases, to enhance drainage and keep the pressure under control.

When the passage to the trabecular network becomes blocked at the angle between the cornea and the iris (the colored membrane in the eye), this is usually rapid, and often requires emergency treatment. Known as angle-closure glaucoma, symptoms ensue rapidly, signifying the emergency nature of the problem. Suddenly, blurring of vision, eye pain and redness, halos around lights, and headache and nausea ensue rapidly. After rapid pre-operative treatment with medications to lower the pressure to safe levels, surgically a small hole is created in the iris (iridotomy) to create a drainage tract for the aqueous humor. Often, the procedure may be recommended for the other eye prophylactically because of the high risk of sudden angle-closure in the other eye.

Glaucoma is an insidious process in the eyes that cannot be reversed. Best monitored with eye examinations, it can be slowed or stopped before damage from increasing pressure in the eye leads to optic nerve damage and the threat of blindness.

Dr. Silva is a professor of surgery at Wayne State University and a resident of Woodbluff on Mackinac Island.

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