A gradual, painless increase in the fluid pressure inside the eye
- Rare under the age of 40; more common over the age of 60
- Sometimes runs in families; more common in people of African descent
- Gender and lifestyle are not significant factors
Chronic glaucoma is also known as open-angle glaucoma. The condition causes a gradual deterioration of sight due to a progressive build-up of fluid pressure inside the eye (often over a period of years) causing nerve damage. There are often no symptoms until late in the disease, and loss of vision is permanent. The condition can lead to total blindness, but early treatment can prevent damage. Both eyes are usually affected, although the condition may be more severe in one eye.
What are the causes?
Fluid is continually secreted into the front of the eye to nourish the tissues and maintain the shape of the eye. Normally, this fluid drains away through the trabecular meshwork, a sieve-like structure at the back of the angle that is formed between the iris and the edge of the cornea (called the drainage angle).
However, in chronic glaucoma, a gradual blockage develops in the meshwork. Although the drainage angle remains open, fluid is prevented from draining normally, and the pressure in the eye gradually rises. The increasing fluid pressure progressively damages the nerve fibres situated in the light-sensitive retina at the back of the eye and in the optic nerve, which carries nerve signals from the retina to the brain, causing loss of vision.
The underlying reason for the problem in the drainage system is not yet fully understood. Genetic factors may be involved and the condition sometimes runs in families. It is also more common in people of African descent. There is also an increased risk of developing chronic glaucoma if you are very shortsighted (see Myopia).
What are the symptoms?
Chronic glaucoma often has no symptoms until late in the disease, by which time it is probable that your vision has been permanently affected. During the later stages, the symptoms may include:
Bumping into objects because of loss of the outer edges of vision (peripheral vision).
Eventual blurring of objects that are straight ahead.
Always consult your doctor promptly if you notice a change in your vision. Because the risk of chronic glaucoma increases beyond middle age, everyone over the age of 40 should be tested for the condition every 2 years. If you are in a high-risk group, you should be tested regularly whatever your age.
How is it diagnosed?
Chronic glaucoma can be detected at an early stage during a routine eye examination. Ophthalmologists often use a technique known as tonometry to measure the pressure inside the eye. The retina will also be examined using ophthalmoscopy. This is a technique that will reveal damage to the optic nerve resulting from the high pressure. Your ophthalmologist will also perform a visual field test to check for loss of peripheral vision.
What is the treatment?
If chronic glaucoma is diagnosed early, eyedrops to reduce the pressure in the eye will probably be prescribed (see Drugs for glaucoma). You will probably have to continue using these eyedrops for the rest of your life.
If the condition is advanced, or if eyedrops do not lower the pressure sufficiently, surgery may be needed to make a drainage channel in the white of the eye (see Trabeculectomy). In another surgical technique, called laser trabeculoplasty, a laser beam is used to increase flow through the trabecular meshwork, allowing fluid to drain away. Both procedures decrease pressure in the eye and reduce further loss of vision. If the condition affects only one eye, the other will probably also need treatment eventually.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.
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