What is glaucoma?

Glaucoma is an ocular disease characterized by optic nerve damage which results in loss of peripheral vision in the early stages of the disease which, if left untreated, can progress to blindness.

What is the prevalence of glaucoma?

Glaucoma is a common cause of blindness in the United States and the most frequent cause of blindness among African Americans. Almost 900,000 people in the United States have some visual impairment as a result of glaucoma. Between 80,000 and 120,000 Americans are currently legally blind from glaucoma. Approximately 5,000 individuals become blind from glaucoma each year. Approximately 2.25 million Americans 40 years or over have primary open angle glaucoma. Because glaucoma causes a very slow and painless loss of vision, one half of the Americans with glaucoma are not aware of their disease.

What causes optic nerve damage in glaucoma?

The intraocular pressure (IOP) of the eye is felt to be the cause of optic nerve damage in most types of glaucoma. The level of intraocular pressure is determined by the rate of intraocular fluid (aqueous) production by the secretory gland (ciliary body) and the rate of fluid (aqueous) outflow by the drainage canal (trabecular meshwork). In most people the intraocular pressure generally measures between 10 and 21 (mm Hg). In individuals who have an abnormality or blockage of the drainage canal, the fluid cannot drain properly and thus the intraocular pressure may become elevated greater than 21mm Hg. The more elevated the intraocular pressure, the greater the risk of developing nerve damage.

There are two possibilities as to how the optic nerve is damaged by the intraocular pressure. In the mechanical theory, the intraocular pressure is thought to directly compress the optic nerve fibers, causing a slow loss of the individual nerve cells. In the vascular theory, the intraocular pressure is felt to indirectly cause nerve cell death by compressing the vessels and reducing the blood flow to the optic nerve cells. Many scientists feel that both mechanisms contribute to optic nerve damage.

How does the IOP relate to glaucoma?

Glaucoma occurs when optic nerve or nerve cell damage results. People who have elevated intraocular pressure (i.e. >21mm Hg) are at a greater risk of developing glaucoma; however, many individuals who have elevated intraocular pressure do not have glaucoma. Although elevated intraocular pressure does not always indicate glaucoma, it is considered a risk factor for its development.

Although people who have intraocular pressures in the normal range (10 - 21) are at less risk of developing glaucoma, it is still possible to occur. Individuals with glaucoma and who have intraocular pressures in the normal range are said to have normotensive glaucoma or low tension glaucoma. Many of these people have vascular or blood circulation problems, making their optic nerve more susceptible to damage at lower pressure levels.

What causes the pressure elevation?

In most people, the elevated IOP occurs as a result of an obstruction of the drainage channel. The exact way in which this happens determines the type of glaucoma an individual is diagnosed as having.

In primary open angle glaucoma, which is the most common type, age usually causes the channels to become less efficient in draining the fluid. Your doctor's examination will show no obvious abnormality of the drainage canal, as the damage is on a microscopic level.

In other forms of glaucoma, your doctor's examination may reveal a cause of the obstruction, such as pigment (pigmentary glaucoma), inflammation (inflammatory glaucoma), or abnormal vessels (neovascular glaucoma), to name a few.

In angle closure glaucoma, the base of the iris (colored part of the eye) has moved forward to block the drainage canal. Although this form is more rare than open angle glaucoma, it may progress rapidly to painful blindness in a matter of days if not treated.

How does glaucoma affect vision?

Usually in the early stages of most types of glaucoma, small unnoticeable blind spots (scotomas) occur in the peripheral vision. If the disease progresses, the blind spots enlarge, then coalesce eventually, resulting in tunnel vision. At this stage, the center sight may still be normal (20/20). Ultimately, if not treated, even central vision may be lost, resulting in irreversible blindness.

What are the symptoms of glaucoma?

Unfortunately, with most types of glaucoma, the individual does not notice the early blind spots, as they painlessly and gradually form. It is usually not until central vision is affected that people are aware of a problem.

In the rare occurrence of angle closure glaucoma, a sudden onset of pain and loss of vision may occur. Symptoms may also include halos around lights, blurry vision, a red eye, headache, facial pain, or nausea. If these symptoms occur, immediate medical attention should be sought.

How is glaucoma diagnosed?

Your eye physician will need to perform a variety of tests in order to diagnose glaucoma.

The intraocular pressure (IOP) is measured with a tonometer and determines the risk of developing glaucoma.

The drainage canal (trabecular meshwork) is examined with a special lens (goniolens) to observe for an obstruction.

The optic nerve is evaluated for damage and possibly photographed.

The peripheral vision is measured with a visual field perimeter to search for blind spots.

After the evaluation, your doctor may diagnose you as having glaucoma if damage to the optic nerve or visual field is discovered. If no damage is found but one or more risk factors are present, a diagnosis of glaucoma suspect may be entered.

What are the risk factors for glaucoma?

As previously mentioned, the higher the intraocular pressure the greater the risk of glaucoma. The incidence of glaucoma has also been found to be higher in African Americans, diabetics, and in people who have cardiovascular disease. Blunt trauma to the eye can also predispose one to developing glaucoma.

Angle closure glaucoma more frequently occurs in Caucasian women who are farsighted.

It should be noted, however, that the absence of risk factors does not necessarily mean that glaucoma will not occur.

How is glaucoma treated?

There are three ways to treat glaucoma: medicine, laser, and surgery.

In the United States most people diagnosed with glaucoma are initially treated with medications or laser first, then surgery if the disease cannot be controlled.

There are a variety of medicines available to lower the intraocular pressure, and, hopefully stabilize the disease. Beta blockers (timolol, levobunolol, metipranolol, optipranolol, and betaxolol) lower the intraocular pressure by reducing the fluid formation. Miotics (pilocarpine, carbachol, and echothiophate) lower the intraocular pressure by opening the drainage channels. Adrenergic agonists (epinephrine, dipinalyl epinephrine, apraclonidine) and carbonic anhydrase inhibitors (acetazolamide, methazolamide, dorzolamide) also lower the intraocular pressure by reducing fluid secretion. A new medication, latanoprost, lowers intraocular pressure by enhancing fluid drainage.

A laser treatment may be performed in place of, or following, medical treatment. Argon laser trabeculoplasty (ALT) has been shown to be relatively safe and effective in lowering the intraocular pressure. Some individuals may have an excellent initial lowering of the IOP, but with time the IOP may become elevated again.

In the United States, surgery is performed, usually in cases of glaucoma that do not respond to medical or laser treatment, or it may be the initial form of treatment in individuals who present with advanced glaucoma.

As with all medicines and procedures, there are risks as well as benefits. Any reactions or concerns should be directed to your primary eye care provider.

Does treatment cure glaucoma?

No. Whenever optic nerve damage and vision loss occurs, this cannot be reversed. However, treatment can stabilize sight to prevent further loss of vision. Most patients who have glaucoma will continue to need treatment and monitoring for their entire life.