Glaucoma refers to certain eye diseases that affect the optic nerve and cause vision loss. Most, but not all, of these diseases typically produce elevated pressure inside the eye, called intraocular pressure (IOP). Normal IOP is measured in millimeters of mercury and can range from 10-21 mm Hg. An elevated IOP is the most important risk factor for the development of glaucoma.
Elevated IOP is sometimes called ocular hypertension. If your doctor diagnoses ocular hypertension, it does not mean you have glaucoma, but it does mean you are at a higher risk for developing the condition, and you should see an ophthalmologist (a medical doctor who specializes in eye care and surgery) frequently.
Half of the people with glaucoma are usually unaware of it until a serious loss of vision has occurred.
Many factors are associated with an increased risk of developing glaucoma, some of which are elevated IOP, a family history, ethnic background, and older age.
The two main types of glaucoma are angle closure and open angle.
- In angle-closure glaucoma, the normal drainage canals within the eye are physically blocked. Angle-closure glaucoma can be acute (sudden) or chronic (long-lasting). In acute angle-closure glaucoma, a sudden increase in IOP occurs because of the buildup of fluid known as aqueous humor. Acute angle-closure glaucoma is considered an emergency because optic nerve damage and vision loss can occur within hours of the onset of the problem. Chronic angle-closure glaucoma may cause vision damage without symptoms.
- In open-angle glaucoma, the drainage system remains open. Open-angle glaucoma also may cause vision damage without symptoms.
- Normal (or low) tension glaucoma is an unusual and poorly understood form of the disease. In this type of glaucoma, the optic nerve is damaged even though the IOP is consistently within a range usually considered normal.
- Childhood glaucoma is rare and starts in infancy, childhood, or adolescence. It is similar to open-angle glaucoma, and few, if any, symptoms are present in the early stage. Blindness can result if it is left untreated. Like most types of glaucoma, this childhood form is thought to be inherited.
- Congenital glaucoma is a type of childhood glaucoma that usually appears soon after birth, although it may be delayed until later in the first year of life. Unlike childhood glaucoma, though, congenital glaucoma often has noticeable signs that may include tearing, light sensitivity, and cloudiness of the cornea. This type of glaucoma is more common in boys and can affect one or both eyes.
- Secondary glaucoma refers to an increased IOP that is a result of a structural problem within the eye. This secondary type may be the result of injury to the eye or other medical conditions. This form of glaucoma is different because treatment is aimed at treating the underlying cause as well as lowering the increased pressure within the eye.
Glaucoma involves increased pressure within the eye. In the normal eye, a clear fluid called aqueous humor is produced in the rear chamber and flows through the pupil into the front chamber. Once in the front part of the eye, the fluid drains out of the eye through an area called the canal of Schlemm. Aqueous humor provides structural support, oxygen, and nutrition to tissues within the eye.
- Increased IOP results from either increased production or decreased drainage of aqueous humor. The resulting increase in pressure within the eye may eventually damage the optic nerve. This increase in IOP is by far the most common risk factor for vision loss due to glaucoma, but it is not the only factor involved.
- For many years, it was believed that high IOP was the primary cause of optic nerve damage in glaucoma. Now we know that even people with normal IOP can experience vision loss from glaucoma. On the other hand, some people with high IOP never develop the optic nerve damage of glaucoma. Therefore, other factors may affect the optic nerve even when IOP is within the normal range.
- Elevated IOP is still considered a major risk factor for glaucoma, though, because studies have shown that the higher the IOP is, the more likely the optic nerve will be damaged.
- No one knows why certain ethnic groups, such as African Americans, have higher rates of glaucoma that lead to blindness. Primary open-angle glaucoma is the leading cause of blindness among African Americans and Alaska Natives, occurring 6-8 times more often than in whites, often in the earlier stages of life.
Most people with glaucoma do not notice symptoms until they begin to have significant vision loss. As optic nerve fibers are damaged by glaucoma, small blind spots may begin to develop, usually in the peripheral or side vision. If the entire optic nerve is destroyed, blindness results.
Other symptoms usually are related to sudden increases in IOP, particularly with acute angle-closure glaucoma, and may include blurred vision, halos around lights, severe eye pain, headache, abdominal pain, nausea, and vomiting.
When to Seek Medical Care for Glaucoma
Call your doctor right away if you have severe eye pain or a sudden loss of vision, especially loss of peripheral or side vision.
Many of the medications used to treat glaucoma may have side effects, which may include stinging or redness of the eyes; blurred vision; headache; or changes in heartbeat, pulse, or breathing. Most side effects are not serious and go away without difficulty. Not everyone will experience side effects from glaucoma medications, but notify your doctor if you experience any of them.
With angle-closure glaucoma, a rapid buildup of IOP may lead to blurred vision, severe eye pain, headache, abdominal pain, or nausea and vomiting. While angle-closure glaucoma is rare, it is a serious form of the disease and, unless treated quickly, can result in blindness. If you have these symptoms, you should seek medical attention immediately for evaluation and treatment in order to prevent permanent vision loss.
Glaucoma Exams and Tests
Many different methods are used to measure pressure within the eye. Other tests determine whether you have glaucoma and how advanced your glaucoma may be. Most diagnostic tests need to be repeated on a regular basis to follow the presence or progression of glaucoma.
- Air puff test: The "air puff" test is the most common. This test is a way to measure the IOP without having to actually touch the eye. For this test, you sit in front of a machine with your chin resting on a brace. The eye doctor points a small jet directly at your eye. This jet then delivers a quick puff of air onto the surface of your eye. By measuring the response of the eye to the puff of air, the doctor can make a rough estimate of the intraocular pressure. This is a good screening test for elevated IOP, but it is not very accurate.
- Direct tonometry: Direct tonometry on the surface of the front part of the eye is a much more accurate measurement of IOP. It, however, requires greater skill and expertise to perform. A sensor is placed gently on the surface of an anesthetized eye, and a very accurate IOP is measured.
- Dilation: An examination to inspect the back of the eye through dilated (widened) pupils is required to diagnose glaucoma. To do this, drops are put into the eyes to enlarge, or dilate, the pupils. This allows the eye doctor to see more of the inside of the eye. An eye doctor can recognize a characteristic divot or depression in the optic nerve at the back of the eye caused by damage from the elevated eye pressure. This enlargement is called "cupping" of the optic nerve and means the condition may be relatively advanced.
- Perimetry: Another test, perimetry, is used to determine the presence of defects within the visual fields, particularly vision to the side (called your peripheral vision). Because people with glaucoma tend to lose their vision from the outer edges to the center, checking peripheral vision is very important. In perimetry, a machine is used to test your peripheral vision. You are asked to look at a series of blinking lights. By recording when you see the lights, an accurate map of your peripheral vision can be made. If you have glaucoma, you will have decreased peripheral vision. This test can be performed to follow the progress of your glaucoma or to determine the severity of the initial diagnosis.
Self-Care at Home for Glaucoma
Your doctor may prescribe medication to lower your IOP. The only way to make sure that these medications work is to take them as prescribed.
Medical Treatment for Glaucoma
Treatment is designed to lower the IOP by reducing production or increasing outflow of aqueous humor. Depending on the type of glaucoma, medications or surgery are used. IOP usually can be lowered using different medications in the form of eyedrops (see How to Instill Your Eyedrops) and oral or IV medications.
Beta-adrenergic blocking agents, alpha-adrenergic agonists, and prostaglandin analogues are some of the most commonly used medications.
- Beta-blockers, such as timolol (Timoptic), can reduce the amount of aqueous humor produced.
- Alpha-adrenergic agonists, such as brimonidine (Alphagan), decrease the production of aqueous humor and also improve the drainage of aqueous humor.
- Another group of drugs called prostaglandin analogs have recently been used. One that may be prescribed is latanoprost (Xalatan). They work near the drainage area within the eye to increase the secondary route of aqueous humor outflow in order to lower IOP.
In certain cases, surgery may be required.
- If you have angle-closure glaucoma, an operation called an iridotomy may need to be done. During an iridotomy, a drainage hole is created in the iris in order to relieve the increased pressure inside the eye. This technique can be performed using a laser; therefore, an incision in the eye is not needed. You may choose to have an iridotomy after an acute episode of angle-closure glaucoma or to prevent an attack of angle-closure glaucoma.
- Medication normally does not work well for congenital glaucoma, so surgery is usually required.
- Other types of surgery that are performed to help glaucoma include trabeculoplasty, cyclophotocoagulation, and filtering. All of these procedures try to ease the drainage of aqueous humor in the affected eye or eyes to decrease IOP. For more information on these procedures, consult your eye doctor.
Before leaving the hospital or your doctor's office, you should make sure you have information concerning the following:
- Medications - When and how they should be taken
- Signs and symptoms - What symptoms to look for that suggest medication failure, side effects, or other problems
- Limitations - What activities you must refrain from and for how long
- Follow-up - When to set up an appointment with your doctor for follow-up examination and to repeat the visual field test
In most cases, the best prevention for glaucoma is early detection. If detected early, vision loss and blindness may be prevented. Anyone older than 20 years should have a glaucoma screening. Periodic eye examinations are indicated for the rest of your life to help prevent and identify glaucoma, especially if you have certain risk factors such as being an African American or having a family history of glaucoma.
Although glaucoma cannot be cured, it can be controlled. People with glaucoma need to have regular eye examinations and usually need to continue treatment for the rest of their lives.
- Untreated acute glaucoma results in permanent vision loss. Untreated chronic glaucoma can progress to blindness within several years.
- Early diagnosis and treatment usually results in excellent success and vision is saved. The outcome for congenital glaucoma varies depending on the age that symptoms are detected and the child’s response to therapy.
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Medically reviewed by William Baer, MD; Board Certified Ophthalmology
"Open-angle glaucoma: Epidemiology, clinical presentation, and diagnosis"