The Medical Minute: Glaucoma a silent threat to sight

August 27, 2003

By Shane R. Tartt, MSIV and David A. Quillen, M.D.
Penn State Milton S. Hershey Medical Center

Few things are more precious than sight. Unfortunately, millions of people each year face a silent threat to their sight that could be managed with early detection and treatment.

That threat, glaucoma, is made up of a group of disorders that can cause loss of vision. In glaucoma, pressure inside the eye is usually increased. As this happens, the delicate optic nerve is damaged, resulting in loss of vision.

The condition is a significant cause of blindness in the United States, accounting for approximately 10 percent of new cases, and is the most common cause of blindness in African-Americans. The most prevalent form is primary open-angle glaucoma, affecting nearly 2.25 million Americans.

Primary open-angle glaucoma is a chronic, slowly progressive disorder of the eye that can lead to a loss of vision. Surprisingly, and unfortunately, people with the disorder often do not notice any vision problem until late in the course of the disease, when their vision is significantly impaired.

Common factors associated with primary open-angle glaucoma include a family history of glaucoma, African-American race, older age, high degree of nearsightedness, high blood pressure and diabetes. The silent nature of the disease makes screening extremely important, especially for people with any of the common risk factors.

In glaucoma, outflow of the aqueous humor is impaired in the eye. Aqueous humor is a fluid that is constantly produced within the eye to deliver nutrients and oxygen to the front of the eye, including the clear cornea, the colored iris and the lens. The fluid leaves the eye through a structure known as the trabecular meshwork at the edge of the iris.

If the fluid is produced faster than it leaves, as in glaucoma cases, pressure builds up within the eye. The increased pressure squeezes the delicate optic nerve in the back of the eye. The millions of individual nerve fibers in the optic nerve are damaged by the pressure so they no longer carry vision from the retina to the brain. The result is gradual vision loss and potentially blindness.

To protect their vision, it is absolutely essential that people at risk for glaucoma get regular screenings and work with their eye doctor and family physician to monitor potential problems. Glaucoma is diagnosed and monitored through several simple, painless examinations. Your eye care provider can measure this pressure (intraocular pressure), which is normally in the range of 8-21 mmHg.

Treatment usually begins when pressure exceeds 21 mmHg, but might need to begin earlier, as some patients experience damage to the optic nerve with pressures in the normal range.

The extent of damage to the optic nerve can be observed directly by looking into the dilated eye with special instruments. Visual field testing may also be included to determine the development of blind spots. As the disease progresses, these areas of vision loss become larger and more numerous, and the optic nerve appears more damaged. These techniques, taken together, allow the physician to assess the amount of nerve damage, follow the disease's progress and monitor the effectiveness of treatment.

Although there is presently no treatment that can repair the damage done by glaucoma, there are many treatments than can stop the progression of the disease and fortunately, save the patient from further loss of vision. There are both medical and surgical treatments, but medical treatment is usually the first line of therapy.

Treatment includes both drops applied to the eye and medication taken by mouth. The effect of the drugs is to reduce the pressure in the eye through either decreasing production of the aqueous humor, increasing outflow of the fluid through the trabecular meshwork, or both.

Surgical treatments are designed to increase outflow and are used when medical therapy inadequately controls the pressure inside the eye. Both laser and incisional surgical approaches are used, depending on what is best suited to the patient. The benefit of treatment is monitored through checking the pressure inside the eye and looking for progression of nerve damage. Using this information, medication dosages can be altered, new drugs begun, or planning for surgery undertaken.

In the majority of cases, good control of the pressure can be achieved and progression of blindness stopped.

Because glaucoma is a major cause of blindness and patients remain asymptomatic until late in the course of the disease, the American Academy of Ophthalmology recommends that older people have comprehensive eye examinations every one to two years. Early detection of the disorder is the key to preventing vision loss. Fortunately, many treatments exist and progress is being made to help patients live with glaucoma without losing their sight.

More information on glaucoma and eye care is available at http://www.hmc.psu.edu/healthinfo/g/glaucoma.htm

(Media Contacts)

Last Updated March 19, 2009