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Glaucoma is a condition that develops when the fluid pressure in the eye is abnormally high. This causes damage to the fibres of the optic nerve, or the nerve of vision. Some glaucoma cases may be associated with normal pressure. This condition usually occurs in older adults.
What is going on in the body?
A clear fluid called aqueous humor is constantly produced within the eye. This liquid is not the same as tears, which appear outside the eye. As new fluid is produced, an equal amount flows out of the eye. The old fluid drains out of the eye through a special filtration area at the root of the iris. The iris is the part of the eye that gives the eye its colour. A blockage in the filtration area can cause a fluid imbalance, which makes pressure build up. If this problem is not found for months or years, damage to the optic nerve will occur. The optic nerve is made up of a large number of nerve fibres. The nerve is like an electric cable containing many wires. When glaucoma damage occurs, these fibres are lost, causing blind spots to develop. The blind spots can be seen when a doctor looks into the eye. The blind spots can be plotted on a chart. This test is called a visual field test.
What are the signs and symptoms of the condition?
Because the vision loss is gradual, there may be no symptoms during the early stages. The person may not be aware of blind spots developing, and there is no pain or redness. In one type of glaucoma, called acute angle-closure glaucoma, there is a sudden rise in pressure, and the following symptoms may occur:
Most cases of glaucoma are the chronic open-angle type. In this type, there is a gradual blockage of fluid outflow over the years. This type of glaucoma is usually found during an eye examination.
- blurred vision
- severe eye pain
- nausea and vomiting
- perception of rainbow rings or halos around lights at night
What are the causes and risks of the condition?
The main cause of most glaucoma cases is fluid build up. Some cases, however, are related to injury to the eye, use of corticosteroid medications, or previous eye surgery. The risk of developing glaucoma is higher in:
The acute form of glaucoma is more common in people of Asian descent.
- older adults
- people of Aboriginal descent
- people with a family history of glaucoma
- people with diabetes
What can be done to prevent the condition?
Regular eye examinations help to spot developing glaucoma. Regular examinations will prevent loss of vision. Eye examinations with a pressure reading are recommended for the following individuals at the following time intervals:
How is the condition diagnosed?
- people of African descent or a family history of glaucoma ages 20 to 40 -- every 1 to 2 years
- ages 20 to 40 -- every 3 to 5 years
- ages 40 to 65 -- every 1 to 2 years
- those over age 65 -- every 1 to 2 years
Glaucoma is suspected when there is a high level of pressure in the eye. It is also suspected if the examination shows an abnormal optic nerve. The diagnosis is made using a combination of tests. The tests include a pressure test, which looks at the fluid-drainage area, an evaluation of the appearance of the optic nerve, and testing the visual field, or total area of visual perception, for each eye. Not every person needs all of these tests, but they should be repeated at regular intervals to find out whether or not glaucoma damage is developing over time. If there is no proof of visual loss, a person may still need to be monitored closely and given a diagnosis of "glaucoma suspect."
What are the long-term effects of the condition?
If glaucoma is not recognised and treated properly, optic nerve damage and permanent loss of vision may occur. Once vision is lost, it cannot be regained.
What are the risks to others?
There is a higher risk of developing glaucoma if there is a family history of the condition. If someone is diagnosed with glaucoma, it should be made known to other blood relatives.
What are the treatments for the condition?
Most cases of glaucoma can be controlled by using eye drops, such as timolol, latanoprost, brimonidine or dorzolamide, one or more times a day. The drops either decrease fluid production in the eye or open the fluid drainage system. More than one type of eye drop may be needed. Several new drops are available, giving doctors more choices.
Some cases of glaucoma are better managed with laser treatment. Laser treatment is directed at the drainage area at the root of the iris. This procedure can allow people to use fewer drops or none at all. If eye drops alone do not help, laser treatment plus eye drops usually controls the glaucoma.
In a few cases, surgery is needed to control the pressure. A small hole is made at the edge of the cornea, or the surface of the eye, so that fluid can filter out from underneath.
Finally, oral medications, such as acetazolamide, can be used to better manage the pressure. As with drops, oral medications must be taken regularly and continuously. Use of eye medications should be reported to all other doctors when giving health and medication history.
What are the side effects of the treatments?
Glaucoma medications may have some irritating side effects. Some drops may cause:
Pills sometimes cause:
- changes in heart rate or rhythm
- possible loss of energy
- changes in breathing, especially in people with asthma or emphysema,
- blurred vision
With surgery, serious complications are rare, but can occur. This must be discussed with the eye doctor before the operation. It is safer to operate than to allow optic nerve damage to continue.
- tingling in the fingers and toes
- decreased appetite
- possible kidney stones
- bowel irregularities
- easy bruising
How is the condition monitored?
With any type of glaucoma, routine examinations are important. Because glaucoma can get worse without the person's awareness, treatment may need to change. If the condition seems under control, examinations are usually done at least three times a year with a visual field examination annually. More frequent testing may need to be done when control seems poor. Medications for glaucoma should never be stopped or changed without first consulting the eye doctor. Early detection and proper treatment are the keys to preventing optic nerve damage and blindness.
Author: William Stevens, MD
Reviewer: HealthAnswers Australia Medical Review Panel
Editor: Dr David Taylor, Chief Medical Officer HealthAnswers Australia
Last Updated: 1/10/2001
Potential conflict of interest information for reviewers available on request