An Introduction to Glaucoma
Glaucoma is a group of diseases sharing certain features, commonly including high pressure within the eye (intraocular pressure), damage to the optic nerve, loss of peripheral (side) vision, and possibly blindness.
Nearly 3 million people have glaucoma. Approximately 80,000 Americans become blind each year because of it. The condition causes another 900,000 people to lose partial vision.
However, with early treatment, you may be able to protect your eyes against serious vision loss.
The cornea is the clear outer covering of the eye. Separating it from the iris (the colored part) is the anterior chamber, a space filled and inflated by aqueous humor. This clear fluid (unrelated to the tears which bathe the outside surface of the cornea) starts in the ciliary body just behind the iris. It circulates in the anterior chamber, nourishing the eye's delicate tissue and keeping it from collapsing. To maintain equilibrium, the aqueous humor drains through a porous tissue in the angle in front of the iris, where it meets the cornea, called the trabecular meshwork.
If the aqueous humor cannot drain properly, either because the drainage canals become clogged (as in
open angle glaucoma) or because the iris is pushing against the cornea (as in angle closure glaucoma), it backs up, putting pressure on the gel in the vitreous cavity at the center of the eye. Eventually, the building pressure affects the delicate optic nerve at the rear of the eye. Since the optic nerve transmits visual images to the brain, any damage to it reduces vision.
The optic nerve is a bundle of more than one million nerve fibers. It connects the retina to the brain. The retina is the light-sensitive tissue at the back of the eye. A healthy optic nerve is necessary for good vision.
Different Types of Glaucoma
The types of this condition include:
- Open angle glaucoma (also known as chronic glaucoma)
- Angle closure glaucoma (also known as acute glaucoma, narrow angle glaucoma, or closed angle glaucoma)
- Low tension glaucoma
- Normal tension glaucoma
- Congenital glaucoma
- Secondary glaucoma
- Pigmentary glaucoma
- Neovascular glaucoma.
Open angle is by far the most common form of this condition.
Glaucoma is a leading cause of blindness in the United States. However, researchers are not sure of the exact cause or causes of the condition. They do know that although anyone can get it, some people are at higher risk than others. The risk is higher in the following people:
- African Americans over the age of 40
- Everyone over age 60, especially Mexican Americans
- People with a family history of glaucoma
- People with diabetes.
Among African Americans, studies show that glaucoma is:
- Five times more likely to occur in African Americans than in Caucasians
- About four times more likely to cause blindness in African Americans than in Caucasians
- Fifteen times more likely to cause blindness in African Americans between the ages of 45 and 64 than in Caucasians of the same age group.
(Click Causes of Glaucoma for more information.)
Glaucoma symptoms can develop in one or both eyes. The specific symptoms will depend on the type of glaucoma a person is experiencing.
Open Angle
For
open angle glaucoma, a person usually shows no symptoms in the beginning. For this type, there is no pain, and vision stays normal.
However, as the condition progresses, a person with open angle glaucoma may notice the following symptoms:
- Gradual failure of side vision (object in front may be clear, but objects to the side may be missed)
- Narrowed vision
- Blindness.
Angle Closure
Symptoms of acute angle closure glaucoma may seem the opposite of open angle glaucoma, erupting in a sudden, violent attack.
In angle closure glaucoma, the fluid at the front of the eye cannot reach the angle and leave the eye. The angle gets blocked by part of the iris. People with this type of glaucoma have a sudden increase in eye pressure.
Angle closure glaucoma symptoms include:
- Severe pain
- Nausea
- Redness of the eye
- Blurred vision.
If you have these possible symptoms of angle closure glaucoma, you need to seek treatment immediately. This is a medical emergency. If your doctor is unavailable, go to the nearest hospital or clinic.
Many people may know of the "air puff" test or other tests used to measure eye pressure during an eye examination. However, this test alone cannot detect glaucoma; while elevated eye pressure means that you are at risk for developing it, it does not necessarily mean that you have it
(see Glaucoma and Eye Pressure). A person has glaucoma only if the optic nerve is damaged. If you have increased eye pressure but no damage to the optic nerve, you do not have it.
A diagnosis is most often made through a comprehensive eye exam that includes the following:
- Visual acuity test
- Visual field test
- Dilated eye exam
- Tonometry
- Pachymetry.
Although there is no cure, glaucoma can usually be controlled. The most common treatments are:
Medications
Medication may come in the form of eye drops or pills. Some drugs are designed to reduce pressure by slowing the flow of fluid into the eye. Others help to improve fluid drainage.
For most people with glaucoma, regular use of medications will control the increased fluid pressure. However, these drugs may stop working over time. They may also cause side effects. If a problem occurs, the eye care professional may select other medications, change the dosage, or suggest other ways to deal with the problem.
Laser Surgery
During laser surgery, a strong beam of light is focused on the part of the anterior chamber where the fluid leaves the eye. This results in a series of small changes, which makes it easier for fluid to exit the eye. Over time, the effect of laser surgery may wear off. Patients who have this form of surgery may need to continue taking medications.
Surgery
Traditional
glaucoma surgery can also help fluid escape from the eye, and thereby reduce the pressure. However, surgery is usually reserved for patients whose pressure cannot be controlled with eye drops, pills, or laser surgery.
Protection Against Glaucoma
Studies have shown that the early detection and treatment of glaucoma, before it causes major vision loss, is the best way to control the condition. If you fall into one of the high-risk groups, make sure to have your eyes examined through dilated pupils every two years by an eye care professional.
Effective January 2002, Medicare helps pay for a dilated eye exam every year for:
- African Americans age 50 and older
- People who have a family history of glaucoma
- People who have diabetes.
