Glaucoma
Introduction
Glaucoma is an eye condition resulting from an increase of pressure in the eye. It is the second most common cause of blindness in the United States. Approximately 3 million Americans have glaucoma, and because the condition does not cause symptoms in its early stages, half of them do not know it. Another 5 million to 10 million people are at increased risk for the disorder.
What is it?
Glaucoma is an eye disease that is caused by an increase in intraocular pressure (IOP) -- this pressure gives the eyeball its round shape. The increase in IOP results from a change in the eye's ability to drain aqueous humor, the fluid circulating inside the eye.
There are two general types of glaucoma - open-angle and closed-angle (the angle refers to the point where the muscles responsible for keeping the pores open that drain the fluid meet).
The most common type is open-angle glaucoma (accounts for 90% of glaucoma cases); it is the leading cause of blindness in people of African-American descent. Normally, open-angle glaucoma is a slowly progressive (or chronic) disease that produces no obvious symptoms until its late stages. Although it usually occurs in both eyes, the disease may progress faster in one eye than the other. A smaller percentage of people develop closed-angle glaucoma, which is typically acute (occurs more suddenly) and associated with a red, swollen, and painful eye. It is usually the result of a blockage of the pores that drain eye fluid and should be treated immediately to remove the blockage to help avoid permanent vision loss.
What causes it?
The rise in intraocular pressure (IOP) that causes glaucoma results when the eye is unable to correctly drain the aqueous humor, the fluid circulating inside the eyes. The inability of the eye to drain this fluid may be due to blockage or closure of the draining pores from swelling of the surrounding tissue, problems with the muscles that open the area around these pores, or trauma or scarring from other eye diseases. There is also a hereditary component to developing this eye disease. Some medications have been linked to either causing or worsening glaucoma, but these are not thought to be the main cause of the disease. Usually, the cause of glaucoma is unknown, although some types are due to trauma or other diseases.
To understand how this increased pressure affects the eye, think of your eye as a balloon. When there is too much air blown into a balloon, pressure builds, and the balloon wall thins. Similarly, the eye's walls become weaker and weaker as the pressure increases, especially where the optic nerve is located. The optic nerve carries visual information to the brain through more than 1 million nerve fibers. As the pressure builds, the optic nerve is damaged, causing vision loss. Both types of glaucoma can lead to blindness by damaging the optic nerve. It is interesting to note that even people with normal IOP can suffer damage to the optic nerve--in fact, 25 to 30 percent of people with glaucoma do not have elevated IOP levels.
Who has it?
Glaucoma is a disease that affects all age groups. It typically occurs in people over the age of 50 years, but it can occur at any age. Up to 3 million Americans are afflicted with the disease, and it is the second leading cause of blindness in the world. Glaucoma occurs six to eight times more frequently in African-Americans than in other races, and it is the number one leading cause of blindness in African-Americans.
What are the risk factors?
Risk factors are characteristics that predispose people to developing a disease. Common risk factors for glaucoma are:
- Individuals over the age of 45
- Individuals with a family history of glaucoma
- African-Americans and Hispanics
- Individuals with diabetes, severe nearsightedness, long-term corticosteroid use, or a previous eye injury
What are the symptoms?
There are two main types of glaucoma, open-angle (which is further sub-typed into normal tension glaucoma and pigmentary glaucoma) and closed-angle. The symptoms and the time to onset of the two main types of the disease are very different.
People with open-angle glaucoma usually do not have symptoms. It is often painless and goes unnoticed until late in the disease when areas of peripheral vision are lost. If the peripheral vision continues to fade, tunnel vision may develop. Normal tension glaucoma is a subtype of open-angle glaucoma. Normal tension glaucoma, also known as "low-tension glaucoma", leads to optic nerve damage and loss of visual field in patients with a normal IOP caused by poor blood flow to the optic nerve. Another subtype of open-angle glaucoma is pigmentary glaucoma which is inherited. Pigmentary glaucoma is more common in men and appears in early adulthood. In pigmentary glaucoma the concave shaped iris creates an unusually wide angle which causes the pigment layer of the eye to rub on the lens of the eye. The rubbing motion causes the iris pigment to shed into the aqueous humor which plugs the pores and causes a clog which then increases the IOP. If open-angle glaucoma is not treated, the tunnel vision may progress into blindness. Screening performed during annual eye exams is extremely important in detecting this disease early so that treatment can be started.
Closed-angle glaucoma, sometimes known as acute glaucoma, differs from open-angle in that the symptoms typically occur suddenly (although not always). The symptoms may include blurred vision, formation of halos around lights at night, pain and redness in the eye, and swelling and clouding of the cornea (the typically clear and transparent coating layer of the outer eyeball). The pain experienced can be so intense that it may cause nausea and vomiting or a headache. Symptoms like this need to be evaluated in the emergency department as soon as possible to prevent permanent eye damage.
How is it treated?
Currently, there is no cure for glaucoma, but treatment can control the progression of the disease. The primary goal of treatment is to prevent further damage to the eye by lowering intraocular pressure (IOP) and to ultimately prevent blindness. Treatment of glaucoma may include medications, surgery, or a combination of medication and surgery.
For open-angle glaucoma, topical eye medications (eyedrops, gels and ointments) are often used early in the disease followed by oral medications or surgery. Surgery is frequently used in individuals who do not experience adequate lowering of intraocular pressure by the medications or in individuals who experience unwanted side effects from using medications. For closed-angle glaucoma, laser surgery is often performed before a doctor prescribes medications, but glaucoma medications may also be given after the surgery.
Topical beta-blocking eye medications are commonly used as initial therapy for the treatment of open-angle glaucoma. Additional agents may be added to the beta-blocker if the intraocular pressure (IOP) remains elevated. The choice of the second medication often depends on how well the drug is tolerated, how well it works, and its ease of use. It is important to know that up to four different topical medications may be needed to treat glaucoma.
There are several types of topical medications that are used for the treatment of glaucoma. These medications work to lower intraocular pressure (IOP) by either decreasing the amount of aqueous fluid the eye makes or by helping the aqueous fluid drain from the eye. The topical eyedrops, gels or ointment may cause burning, stinging, or redness when instilled into the eye, although these side effects are usually tolerable. If you have problems using one topical eye medication, tell your doctor or pharmacist because using a different drug or dosage may be possible.
Medications can be taken by mouth when topical eye medications are not effective at controlling or reducing intraocular pressure (IOP). Medications taken by mouth may also be used alone or in combination with topical eye medications to lower the pressure. Often, patients experience more side effects with the medications taken by mouth than with topical eye medications.
Helping Yourself
Treating glaucoma involves proper use of your topical eye medications (i.e. eyedrops, gels, or ointments), which includes knowing the correct way to use topical eye medications as well as understanding the prescribed dose. To learn more about how to properly use your eyedrops, return to our "Drug Library" tab and click on the "Using Medicines" link.
Using your medication exactly as directed is important to prevent loss of vision. Unwanted side effects may also result when your medication is not used as your health care provider has instructed.
Several medications can worsen glaucoma. Therefore, it is very important to inform your doctor or pharmacist of any prescription and nonprescription medications you are taking.
A new device is now available to self-monitor intraocular pressure (IOP) at home. This device, called the Proview Eye Pressure Monitor, may be useful in patients who want to take an active role in management of their glaucoma. Measuring and recording IOP on a regular basis will help to note any changes that should be discussed with your ophthalmologist. This device is available without a prescription. Discuss the use of this device with your ophthalmologist to determine whether IOP self-monitoring would be beneficial for you.
What is on the horizon?
Although the present generation of medications for glaucoma can help control the disease, most have side effects, and none, so far, can provide a cure. As a result, research is ongoing, as scientists attempt to devise more effective tactics to fight the disease.
Researchers are trying to identify various tests, procedures and medications that may provide health care professionals with more information regarding the causes, treatment and prevention of glaucoma. In addition, researchers are looking at the influence of genes on glaucoma.
Research is currently being done to develop glaucoma treatments that can be used less often. The current medications for glaucoma have to be used several times a day. This complex dosing schedule discourages patients from using their medication correctly; decreasing the benefits they should obtain from the medication. Once-a-week preparations are currently being developed to simplify the dosing schedule for the treatment of glaucoma.
Currently, the New York Glaucoma Research Institute has several ongoing studies. The Institute is reviewing the use of ultrasound biomicroscopy (UBM), a procedure that researchers anticipate will provide for a more accurate diagnosis of glaucoma. Optical coherence tomography (OCT) is another procedure being studied. This procedure is being investigated to aid health care professionals to gain a better understanding of the development of glaucoma, as well as allow for earlier detection of the disease. Other areas of research include confocal scanning laser ophthalmoscopy and tissue culture, which will evaluate the optic nerve and provide insight into how to strengthen the optic nerve once affected by glaucoma.
There is a new interest in research targeting stem cell therapies to treat glaucoma. Researchers now believe that there is a potential for using stem cells as a renewable source of replacement cells and tissue to treat glaucoma. It is believed that adult stem cells will work by replacing retinal ganglion cells, the cells that die in glaucoma.
Memantine (Namenda), a medication that has been used to treat Parkinson's disease and dementia, and glatiramer (Copaxone), a medication used in patients with multiple sclerosis, are being considered for glaucoma treatment by researchers. Researchers believe Namenda and Copaxone may be able to protect the optic nerve from too much glutamate. Without glutamate, calcium cannot enter the nerve cell. Therefore, the nerve cells are protected from excess amounts of calcium, which can be toxic to the cell. The greatest advantage of Namenda and Copaxone is that they are able to accomplish this without interfering with the normal function of the cell. This ability to protect the cell from calcium and still allow normal cell function may someday make memantine and copaxone first-line medications for the treatment of glaucoma. At this time, no definitive studies have been done to assess the effectiveness and safety of these medications in glaucoma patients.
A new type of drug is being researched that could help stop or slow vision loss from glaucoma. The drug is called aminoguanidine and works by slowing the action of NOS-2, an enzyme that makes nitric oxide. This drug has been shown in animals to slow down and possibly prevent the loss of retinal ganglion cells (RGCs), the crucial nerve cells that are important to sight.
References
Lesar TS, Fiscella RG, and Edward D. Glaucoma. Pharmacotherapy: a physiologic approach. 6th ed. Dipiro JT, Talbert RL, Yee GC, et al., eds. The McGraw-Hill Companies, Inc; 2005:1713-26.
Ackerman SJ. Guarding against glaucoma. URL: http://www.fda.gov/fdac/features/995_glaucoma.html. Available from the internet. Accessed June 2005, June 2006, April 2007, and April 2008.
The Glaucoma Foundation Home Page. URL: http://www.glaucoma-foundation.org. Accessed June 2005, June 2006, April 2007, and April 2008.
Glaucoma Research Foundation Home Page. URL: http://www.glaucoma.com. Accessed June 2005, June 2006, April 2007, and April 2008.
American Glaucoma Society. URL: http://www.glaucomaweb.org. Accessed June 2006, April 2007, and April 2008.
Medline Plus: Glaucoma. URL: http://www.nlm.nih.gov/medlineplus/glaucoma.html. Accessed June 2006, April 2007, and April 2008.
Glaucoma Health Condition Last Updated: April 2008
Note: The above information is intended to supplement, not substitute for, the expertise and judgment of your physician, pharmacist, or other healthcare professional. It is not intended to diagnose a health condition, but it can be used as a guide to help you decide if you should seek professional treatment or to help you learn more about your condition once it has been diagnosed.