What is Glaucoma?
Glaucoma refers to a group of eye diseases that cause progressive damage to the optic nerve. Glaucoma is one of the leading causes of blindness in the United States. While the damage caused by glaucoma is permanent, early diagnosis and treatment usually can prevent vision-threatening loss. The key to treating glaucoma successfully is diagnosing it early, before extensive damage has occurred. In the most common form of glaucoma, open-angle glaucoma, there are no symptoms of the disease until the damage is very advanced. That is why it is important to have periodic eye check-ups, particularly if you are at high risk for developing glaucoma.
How Does Glaucoma Develop?
Aqueous humor is a clear fluid that is continuously produced inside the eye. This fluid circulates within the eye, nourishing it and removing waste products. The fluid drains from the eye through a sieve called the trabecular meshwork. From the trabecular meshwork, the fluid empties into a drainage canal, called the Canal of Schlemm, and then into the blood stream. These drainage structures are located in an area of the eye called the anterior chamber angle, where the cornea and iris come together. Fluid inside the eye does not drain into tears.
The process of making and draining fluid maintains a certain intraocular pressure necessary for the health of your eyes. Glaucoma develops when the eye's ability to drain fluid decreases. This results in a buildup of pressure throughout the eye. The increased pressure causes damage to the optic nerve, which eventually can lead to loss of vision.
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Risks for Developing Glaucoma
The following people are at high risk for developing open angle glaucoma:
- People of increasing age - while people of any age may develop glaucoma, the condition is more common in older age groups. Anyone over the age of 40 can be considered to be at increased risk for developing glaucoma
- African Americans - African Americans are eight times more likely to develop glaucoma than white Americans, and glaucoma often develops at a much earlier age in African Americans
- People with a family history of glaucoma
- People with systemic diseases, such as diabetes or heart disease
Anyone can develop glaucoma. However, close relatives of patients with primary glaucoma are more likely than the general population to develop the disease. Therefore, if you have a relative with glaucoma -- parent, grandparent, aunt, uncle, brother, sister, cousin or child -- it is especially important to have regular eye examinations. If you have glaucoma, you should tell your relatives so they can be examined. The most common type of glaucoma causes no symptoms until it is very advanced, and early diagnosis and treatment is the best way to arrest the disease and save vision.
Symptoms of Glaucoma
In most cases of glaucoma, visual loss first involves the peripheral, or side, vision. Central vision, which is what we use to look at an object directly in front of us, is usually not affected until very late in the course of glaucoma. The loss of side vision occurs very slowly. Because of this, many patients are not aware they are losing sight. A great deal of side vision can be lost before the patient is aware there is a problem. Often by the time someone notices a vision problem, the glaucoma is advanced. Vision lost due to glaucoma cannot be restored. That is why it is very important to diagnose glaucoma early and begin proper treatment.
Forms of glaucoma: open-angle and angle-closure
Primary open-angle glaucoma
This is the most common form of glaucoma. It accounts for approximately 85% of cases of adult glaucoma in the United States. In primary open-angle glaucoma, the trabecular meshwork (the drain of the eye) does not function properly, causing a buildup of pressure in the eye. This increased pressure in the eye causes damage to the optic nerve (see “What causes glaucoma?”). The damage occurs very slowly and is usually not noticed by the patient until it is very advanced. Primary open-angle glaucoma is a permanent condition that cannot be cured, but usually can be controlled with proper treatment. Primary open-angle glaucoma usually has no symptoms until there is extensive loss of vision.
This is responsible for approximately 5 to 10% of cases of adult glaucoma in the United States. It is much more common in people of Asian descent. In angle-closure glaucoma, the buildup of fluid occurs very rapidly. The iris is pushed up against the cornea so that the aqueous humor cannot get to the drain. The iris, causing the intraocular pressure to rise to high levels over a period of several hours, blocks the drain.
Patients usually notice blurring of vision, and the eye may become very painful. Patients often experience nausea, vomiting and headache. An attack of acute angle-closure glaucoma requires immediate medical attention. Permanent loss of vision or even blindness can occur in a matter of days without treatment.
Glaucoma may develop secondary to other conditions that affect the eye. Common causes of secondary glaucoma include injury to the eye, diabetes, inflammation in the eye and certain medications, including corticosteroid.
Acute angle-closure glaucoma usually causes severe symptoms because of the sudden rise of pressure in the eye. Some symptoms that can occur with acute angle-closure glaucoma include pain in the eye, blurry vision, halos around light, bloodshot eye, nausea, vomiting and headache.
Diagnosis of Glaucoma
The ophthalmologist uses a variety of tests to diagnose glaucoma. If glaucoma is diagnosed, these tests should continue to be performed at regular intervals to monitor the patient's condition and the effectiveness of treatment. Four main factors are evaluated in people suspected of having glaucoma:
- Intraocular Pressure - Intraocular pressure is measured by tonometry. This quick and painless technique determines if the pressure within the eye is elevated to higher than normal levels. Not everyone with elevated pressure will develop glaucoma. However, the higher the pressure, the greater the chance that a person has glaucoma or will develop glaucoma in the future. Some people can develop glaucoma even when their pressure is in the normal range. There is no pressure level that is safe for every patient. Because intraocular pressure fluctuates throughout the day, pressure may have to be measured several times. Only after careful evaluation, often requiring follow-up visits, can a "safe" pressure be determined for each individual patient.
- Anterior Chamber Angle - An ophthalmologist looks at the angle of the eye using a technique called gonioscopy. In gonioscopy, a special lens is used to examine the drainage channels in the angle of the eye. An anesthetic is used, making the technique painless. This helps the ophthalmologist determine whether a person is at risk for developing acute angle-closure glaucoma.
- Optic Nerve - Loss of vision from glaucoma results from damage to the optic nerve. By looking into the back of the eye, an ophthalmologist can see and evaluate the nerve. Drops that dilate the pupil are often needed to adequately examine the optic nerve. Periodic photographs of the nerve can help to identify damage from glaucoma. The normal optic nerve is oval and usually has a small depression in the center, called the cup. When a person has glaucoma, the cup enlarges, which is referred to as "cupping of the optic nerve.”
- Visual Fields - The vision loss in glaucoma starts in the peripheral, or side, vision. Central vision, which is what we use when we are looking straight ahead, usually is not affected until glaucoma is very advanced. Extensive loss of peripheral vision can occur before a person notices any visual problem. By the time the central vision is affected and the patient notices blurring of vision, the glaucoma is very advanced, and the loss of vision will most likely be permanent. Early loss of peripheral vision can be detected with a visual field test long before the patient becomes aware of it.
A technician may administer the visual field test, or the test may be run on a computer. The test is painless, but it can be tedious. The patient must concentrate throughout the entire exam. The patient needs to respond when a flashing or moving light is seen. The test takes approximately 30 minutes to perform and must be repeated at regular intervals as part of the management of glaucoma.
Treatment of Glaucoma
In the great majority of patients, treatment can prevent loss of vision from glaucoma. Even in advanced cases, treatment often can prevent further vision loss. Depending upon the needs of the particular patient and the type of glaucoma, treatment to lower intraocular pressure may consist of medication, laser therapy and/or surgery.
Treatment of Open-angle glaucoma
In open-angle glaucoma, the initial treatment for most patients consists of using eye drops. There are many different kinds of eye drops available to treat glaucoma. The most common drops include beta-blocker drugs (Betagan, Betoptic, Timoptic, Optipranolol, Ocupress, Betimol), prostaglandins (Xalatan, Travatan, Lumigan), and others (Trusopt, Azopt, Cosopt, Alphagan, pilocarpine). Usually, treatment begins with one medication. If the pressure is not lowered enough, a higher dose of the medication may be tried or a different medication may be added. Many of these medications can be used together to obtain an additive effect in lowering the intraocular pressure.
If the eye drops are ineffective in lowering the pressure adequately, carbonic anhydrase inhibitors given in pill form (the drop form is Trusopt or Azopt) may be used. The most commonly used carbonic anhydrase inhibitors are Diamox (acetazolamide) and Neptazane (methazolamide).
Unfortunately, glaucoma medications may have undesirable side effects in some patients. Some patients are more susceptible to side effects than others. Finding the right medication for a patient involves balancing the pressure-lowering effects of the medication against the side effects. Because each patient is different, the treatment must be individualized.
There is no cure for primary open-angle glaucoma, only control through treatment. If the medication or pills are stopped, the elevated intraocular pressure will return. Therefore, it is important for glaucoma patients to use their medication faithfully. Medication may have to be altered from time to time because patients sometimes become resistant to a particular drug. For this reason, and to be certain that optic nerve damage and visual loss are controlled, regular follow-up visits to the ophthalmologist are necessary.
In some patients with open-angle glaucoma, medications are not enough to control pressure. Laser therapy or surgery is then necessary. The success of these procedures depends on many things such as the type of glaucoma, the extent of pre-existing damage, the presence of the other eye disorders and the general health of the patient.
Treatment of Angle-closure glaucoma
In angle-closure glaucoma, laser therapy or surgery is initially recommended. A relatively simple laser treatment or surgical procedure usually can prevent the condition from recurring. Afterwards, some patients with angle-closure glaucoma require no medication, while others may still need medication to control their intraocular pressure.
Prognosis for Glaucoma
Patients with glaucoma are encouraged to lead normal lives. Activities that use the eyes, such as reading, do not make glaucoma worse. There are no special dietary restrictions for people with glaucoma. Glaucoma is not contagious.
If you have glaucoma, contact your ophthalmologist immediately if you develop an eye problem that concerns you. A sudden loss of vision, eye pain or the appearance of halos around lights are few symptoms for concern. If you cannot reach your physician, go to a hospital emergency room that provides emergency eye care.
Glaucoma patients who have had surgery must contact their ophthalmologist immediately if they experience a red eye, loss of vision or pain.
As a rule, patients should follow their ophthalmologist's instructions carefully, and use the medications as directed. Medications should be used at all times. Remember to take them even when you are away from home or if you are ill. It is very important to have your prescription refilled in time so you never run out of glaucoma medication. If your pharmacist cannot refill your medicine with the old prescription, contact your ophthalmologist immediately so you can obtain a new prescription.
In rare instances, some medications used for other problems may interact with your glaucoma medication or make your glaucoma worse. Therefore, you should tell your medical doctor about your glaucoma and the medications you take. You should carry a medical emergency card in your wallet or purse and wear a medic alert that says you have glaucoma and lists your medications. Thus, in the rare event of a medical emergency, the physicians who treat you will know about your glaucoma condition.
Some medications prescribed for other conditions may carry a warning pertaining to patients with angle-closure glaucoma and not open-angle glaucoma. If you have any questions about this, ask your ophthalmologist.
The goal in the treatment of glaucoma is the preservation of sight. Fortunately, with modern medications and laser and surgical techniques, this goal is attainable for the great majority of glaucoma patients.
Because most cases of glaucoma are chronic, long-term use of medication and repeated visits to the ophthalmologist are necessary. Testing of the visual field and other examinations, including photographs of the optic nerve, must be repeated to be certain the glaucoma is under satisfactory control. The patient has a major responsibility for the treatment of his or her own disease. Sight is often lost unnecessarily because patients fail to use their medications properly or do not return for appointments.
The successful treatment of glaucoma is based on the continuing cooperation of the patient and the ophthalmologist. If you must miss an appointment with your ophthalmologist, be certain to make another appointment as soon as possible.
Under these circumstances, most patients with glaucoma can look forward to a life of good vision.