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Glaucoma

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GLAUCOMA

DEFINITION

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Glaucoma is a disorder of the eye in which the optic nerve is damaged. The optic nerve carries light messages from the eye to the brain. Left untreated, glaucoma can result in loss of vision.

DESCRIPTION

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Over two million people in the United States have glaucoma. About eighty thousand of these individuals are legally blind because of the disorder. Glaucoma is the leading cause of preventable blindness in the United States. The condition is about three times as common among African Americans as among whites. The risk for glaucoma increases rapidly with age, but the condition can affect any age group, including newborn infants and fetuses.

Glaucoma is actually a class of disorders. More than twenty different forms of the condition have been identified. They all develop in a similar way, however. The amount of aqueous (pronounced a-kwee-us) humor, a watery fluid that fills the inside of the eyeball, begins to build up. As more of this fluid collects, it places greater pressure on all parts of the eye, including the optic nerve. Eventually the excess pressure destroys the nerve.

The many forms of glaucoma are grouped into two large categories: open-angle glaucoma and closed-angle glaucoma. Open-angle glaucoma is a progressive disease. That is, it gets worse over time if not treated. At first, only a few nerve cells in the optic nerve are destroyed. Blind spots develop in areas where those nerve cells are located. Over time, more and more nerve cells are destroyed. A larger and larger area of vision is lost. Eventually, a person may lose his or her sight completely.

Closed-angle glaucoma happens very quickly. Some type of accident or change in the eye causes aqueous humor to build up very suddenly. The effects of glaucoma appear in a very short time.

CAUSES

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Aqueous humor is produced by tissues in the front of the eyeball. Aqueous humor brings nourishment to the cornea and lens. It also maintains the proper pressure inside the eyeball. Proper pressure is necessary for the eyeball to maintain the correct shape. The amount of pressure produced by aqueous humor is called the intraocular ("inside the eye") pressure (IOP).

Aqueous humor drains out of the eyeball through a network of tiny tubes also located in the front of the eyeball. Glaucoma develops when the flow of aqueous humor is altered. In some cases, the fluid is produced too rapidly. In other cases, it is not removed from the eyeball fast enough. In either case, too much aqueous humor collects in the eyeball. The fluid causes pressure that pushes on blood vessels in the retina of the eye. The retina is a thin membrane at the back of the eyeball. It receives light rays that pass through the eyeball and transmits them to the optic nerve. Over time, excess pressure in the eye can damage cells in the retina and optic nerve. The cells die and the optic nerve is no longer able to carry messages to the brain. A person's vision is reduced.

SYMPTOMS

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There are usually no noticeable symptoms of open-angle glaucoma. The loss of vision occurs very slowly, often over a period of years. If only one eye is affected, the other eye takes over the task of seeing for both eyes. The person with glaucoma does not realize that vision is being affected. Eventually, however, loss of vision becomes severe. The patient becomes aware that a problem exists. By this time, the glaucoma is more difficult to treat.

Glaucoma: Words to Know

Aqueous humor:

A watery fluid that fills the inside of the eyeball, providing nourishment to the eye and maintaining internal pressure in the eyeball.

Blind spot:

An area on the retina that is unable to respond to light rays.

Cornea:

The tough, transparent tissue that covers the front of the eyeball.

Intraocular pressure (IOP):

The amount of pressure caused by aqueous humor inside the eyeball.

Laser:

A device for producing very intense beams of light of a single color.

Optic nerve:

A nerve at the back of the eyeball that carries messages from the retina to the brain.

Retina:

A thin membrane at the back of the eyeball that receives light rays that pass through the eyeball and transmits them to the optic nerve.

Tonometer:

A device used to measure intraocular pressure in the eyeball.

The symptoms of closed-angle glaucoma are more obvious. A person may experience blurred vision, severe pain, sensitivity to light, and nausea. The cornea, the transparent tissue at the front of the eye, becomes cloudy. Closed-angle glaucoma is a medical emergency and requires immediate treatment.

DIAGNOSIS

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Glaucoma is usually diagnosed during a routine visit to an eye specialist. Because of its mild symptoms, patients are less likely to visit a doctor about the condition.

The fastest test for glaucoma is a measurement of the IOP. The eye specialist first numbs the patient's eye with eye drops that have a yellow coloring. The pressure inside the eyeball is then measured with an instrument called a tonometer (pronounced toe-NAHM-etter). The test takes only a few seconds and provides a fast diagnosis of glaucoma.

If glaucoma is suspected, the eye specialist can then examine the back of the patient's eye for possible damage or changes. The specialist uses an ophthalmoscope (pronounced ahf-THAL-muh-skope) for this purpose. An ophthalmoscope is a device that shines light on the retina. The eye specialist is able to see if the retina and optic nerve are damaged in any way.

TREATING GLAUCOMA

An interesting footnote in the history of medicine is the role played by the study of the eye, ear, nose, and throat. These parts of the body are now regarded as important special fields of medicine. However, until the nineteenth century, they were not regarded as legitimate topics of medical study. They were left to "quacks." A quack is someone who treats human disease without having adequate medical preparation.

Thus, the first scientific discussion of glaucoma appeared around 1850. At that time, the German physician Albrecht von Graefe (1787–1840) described a surgical method for treating glaucoma.

He tells of operating on patient's whose vision was "perfectly restored in all cases."

At about the same time, drugs were being developed for treatment of the disorder. The first such drugs were actually discovered by Christian missionaries. The missionaries were introduced by native people to plants that had the effect of reducing the worst symptoms of glaucoma. Those plants were later found to contain a chemical known as physostigmine. Nearly a century later, the great black American chemist Percy Julian (1899–1975) discovered a way to make physostigmine synthetically in the laboratory. Physostigmine has now largely been replaced by other drugs for the treatment of glaucoma.

Visual tests can also be used to find blind spots in the patient's field of vision. The patient is asked to look at cards with various geometric patterns on them. Difficulty in seeing any one part of a pattern tells the eye specialist where a blind spot may be.

TREATMENT

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Glaucoma may be treated with either medication or surgery. Medication is usually tried first. The drugs used are substances that reduce intraocular pressure. In general, they either decrease the rate at which aqueous humor is produced in the eye, or they increase the rate at which it is drained off. All of the medications used for glaucoma have side effects. Various individual drugs and combinations of drugs may have to be tried to see which works best for any one patient.

Some patients do not respond well to medication. In such cases, surgery may be necessary. The purpose of surgery is to open up the canals through which aqueous humor drains out of the eye. The surgery is often done with lasers.

Surgery is usually quite effective in solving glaucoma problems. However, its effects may not last very long. In many cases, surgery is required again in a year or less.

Alternative Treatment

Some vitamins and minerals are thought to reduce intraocular pressure. These include vitamins C and B₁ (thiamine) and chromium and zinc.

Research suggests that marijuana reduces IOP. However, there is some dispute as to whether the drug should be used for this purpose. Researchers are currently weighing the advantages of using marijuana to relieve the symptoms of glaucoma against public concerns about the drug.

PROGNOSIS

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About half of the people who develop glaucoma are not aware of their condition until fairly late in the course of the disorder. Many of these individuals will lose part or all of their vision. Vision loss caused by glaucoma cannot be repaired. Patients who are diagnosed with glaucoma usually respond to treatment. The prognosis for those individuals is very good.

PREVENTION

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Researchers currently do not know the factors that cause glaucoma. As a result, there is no way to prevent the disorder. However, it is relatively easy to diagnose glaucoma in its early stages. The best preventive step is to have regular eye checkups. A normal part of those checkups is a tonometer test for glaucoma. Early detection of glaucoma can prevent the most serious consequences of the condition.

FOR MORE INFORMATION

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Books

Marks, Edith, and Rita Montauredes. Coping with Glaucoma. Garden City Park, NY: Avery, 1997.

Trope, Graham E. A Patient's Guide to the Disease. Toronto: University of Toronto Press, 1997.

Organizations

American Academy of Ophthalmology. P.O. Box 7424, San Francisco, CA 94120–7424. (415) 561–8500. http://www.eyenet.org/aao_index.html.

Glaucoma Research Foundation. 490 Post Street, Suite 830, San Francisco, CA 94102. (415) 986–3162; (800) 826–6693. http://www.glaucoma.org.

Prevent Blindness America. 500 East Remington Rd., Schaumburg, IL 60173. (800) 331–2020. http://www.prevent-blindness.org.

Web sites

"Ask NOAH About: The Eye." NOAH: New York Online Access to Health. [Online] http://www.noah.cuny.edu/eye/eye.html#G (accessed on October 20, 1999).

Titcomb, Lucy. "Treatment of Glaucoma." http://www.pharmacymag.co.uk/glau.htm (accessed on April 29, 1998).

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