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List of All Topics
Glaucoma
Introduction
Glaucoma is sometimes called the silent thief because it can slowly steal your sight before you realize anything's wrong. It's a leading cause of vision loss.
The most common form of glaucoma, primary open-angle glaucoma, develops gradually, giving no warning signs. Many people aren't even aware they have an eye problem until their vision is extensively compromised.
Glaucoma is not just one disease, but a group of them. The common feature of these diseases is damage to the optic nerve, usually accompanied by an abnormally high pressure inside your eyeball.
The optic nerve is a bundle of more than a million nerve fibers at the back of your eye. It's like an electric cable made up of thousands of individual wires carrying the images from the inside back wall of your eyeball (retina) to your brain. Blind spots develop in your visual field when the optic nerve deteriorates, usually starting with your peripheral (side) vision. If left untreated, glaucoma may lead to blindness in both eyes.
Fortunately, medical advances have made it easier to diagnose and treat glaucoma. If detected and treated early, glaucoma need not cause even moderate vision loss. But having glaucoma does mean regular monitoring and treatment for the rest of your life.
Signs and symptoms
Glaucoma occurs in several types, and signs and symptoms vary depending on the type of glaucoma you have.
Primary open-angle glaucoma progresses with few or no symptoms until the condition reaches an advanced stage. As increased eye pressure continues to damage your optic nerve, you lose more and more of your peripheral vision. If glaucoma is left untreated, you can develop tunnel vision and eventually lose all sight. Open-angle glaucoma usually affects both eyes, although at first you may have vision loss in just one eye.
Acute angle-closure glaucoma develops suddenly in response to a rapid rise in eye pressure. Permanent vision loss can occur within a day of the attack, so it requires immediate medical attention. An attack often happens in the evening or in a darkened room when the light is dim and your pupils have become relatively dilated. Pain may be severe. Signs and symptoms include:
- Blurred vision
- Halos around lights
- Reddening of the eye
- Severe eye pain
- Nausea and vomiting
Causes
Internal pressure in your eye, called intraocular pressure, allows your eye to hold its shape and function properly. Intraocular pressure is like air in a balloon — too much pressure inside the balloon affects its shape and may even cause it to pop. In the case of your eye, too much pressure can damage the optic nerve.
Fluids inside your eye help maintain the intraocular pressure. These fluids are the vitreous, which fills the vitreous cavity at the back of your eye, and the aqueous humor, which fills the anterior chamber at the front of your eye. Aqueous humor is continuously produced and circulated through the anterior chamber before draining out of your eye. This continuous flow of fluid nourishes the lens and the cornea and also removes unwanted debris. A healthy eye produces aqueous humor at the same rate that it drains fluid, thus maintaining a normal pressure.
Your eyes' drainage system
Aqueous humor exits your eye through a drainage system located at the angle formed where the iris and the cornea meet. Here it passes through a sieve-like system of spongy tissue called the trabecular meshwork and drains into a channel called Schlemm's canal. The fluid then merges into your bloodstream.
When the drainage system doesn't function properly — for example, if the trabecular meshwork becomes clogged — the aqueous humor can't filter out of the eye at its normal rate, and pressure builds within your eye. For reasons that doctors don't completely understand, increased eye pressure is often associated with gradual damage to the nerve fibers that make up the optic nerve .
Types of glaucoma
- Primary open-angle glaucoma
. This form, also called chronic open-angle glaucoma,
accounts for most cases of the disease. Although the drainage angle
formed by the cornea and the iris remains open, the aqueous humor drains
too slowly. This leads to fluid backup and a gradual buildup of pressure
within your eye. Damage to the optic nerve is so slow and painless that
a large portion of your vision can be lost before you're even aware of a
problem.
The exact cause of primary open-angle glaucoma remains unknown. It may be that the aqueous humor drains or is absorbed less efficiently with age, but not all older adults get this form of glaucoma. About 2 percent of Americans older than age 40 have elevated eye pressure. For Americans older than 70, the number is 8 percent. - Angle-closure. Angle-closure glaucoma, also called
closed-angle glaucoma,
is a less common form of the disease. This type of glaucoma is a medical
emergency that can cause vision loss within a day of its
onset.
It occurs when the drainage angle formed by the cornea and the iris closes or becomes blocked. Many people with this type of glaucoma have a very narrow drainage angle, which may be an abnormality from birth. As you get older, your lens becomes larger, pushing your iris forward and narrowing the space between the iris and the cornea.
Whether the narrow drainage angle is an abnormality from birth or a result of aging, as this angle narrows, the iris gets closer to the trabecular meshwork. If it gets too close, the aqueous humor can't exit through the trabecular meshwork, resulting in a buildup of fluid and an increase in eye pressure.
Angle-closure glaucoma can be chronic (progressing gradually) or acute (appearing suddenly). The acute form occurs when the iris is forced up against the trabecular meshwork and completely blocks the drainage of the aqueous humor.
Angle-closure glaucoma is more common among farsighted people. Normal aging also may cause angle blockage.
If you have a narrow drainage angle and your pupils become dilated, the angle may close and cause a sudden increase in eye pressure. This attack of acute angle-closure glaucoma requires immediate treatment. Although an acute attack often affects only one eye, the other eye is at risk of an attack as well.
Several factors can cause your pupils to dilate, including darkness or dim light, stress or excitement, and certain medications. These medications include antihistamines, tricyclic antidepressants and eyedrops used to dilate your pupils. However, dilating eyedrops may not cause the angle to close until several hours after the drops are put in your eyes. - Secondary. Both open-angle and angle-closure glaucoma can be primary or secondary conditions. They're called primary when the cause of the condition is unknown. They're called secondary when the condition can be traced to a known cause, such as an injury or an eye disease. Secondary glaucoma may be caused by a variety of medical conditions, medications, physical injuries, and eye abnormalities or deformities. Infrequently eye surgery can be associated with secondary glaucoma.
- Low-tension.
Low-tension glaucoma
is a poorly understood, though not uncommon, form of the disease. In
this form, eye pressure remains within what is ordinarily thought to be
the normal range, but the optic nerve is damaged nevertheless. Why this
happens is unknown.
Some experts believe that people with low-tension glaucoma may have an abnormally sensitive optic nerve or a reduced blood supply to the optic nerve caused by a condition such as atherosclerosis, a hardening of the arteries caused by accumulation of fatty deposits (plaques) and other substances. Under these circumstances even normal pressure on the optic nerve seems to be enough to cause damage.
Treatment
The treatment of glaucoma is aimed at reducing intraocular pressure by improving aqueous outflow, reducing the production of aqueous, or both. Doctors accomplish these treatment goals with eyedrops, systemic medications, laser treatment, surgery, or a combination of treatments.
If your doctor determines that you have elevated intraocular pressure , an excavated optic disk and loss of visual field, you'll likely be treated for glaucoma. If you have only slightly elevated eye pressure, an undamaged optic nerve and no visual field loss, you may not need treatment, but your doctor may advise more frequent examinations to detect any future changes. If you have signs of optic nerve damage and visual field loss, even if your eye pressure is in the normal range, you may need treatment to lower eye pressure further, which may help slow the progression of glaucoma.
Glaucoma can't be cured, and damage caused by the disease can't be reversed. But with treatment, glaucoma can be controlled. Eyedrops, oral medications and surgical procedures can prevent or slow further damage.
Prevention
Until recently, there was no proven way to prevent glaucoma. But a large multicenter trial, supported by the National Eye Institute, found that when glaucoma eyedrops were given daily to people with elevated eye pressure (above 24 mm Hg), they reduced eye pressure an average of 22 percent. More important, the researchers discovered that daily use of eyedrops can reduce the risk of developing glaucoma by nearly half in blacks with elevated eye pressure.
Another study found that cholesterol-lowering medications reduced the risk of open-angle glaucoma, especially for people who already have cardiovascular disease. Although this may be an added benefit for those already taking these medications to reduce their cholesterol levels, more studies need to be done to confirm the reduction in risk of glaucoma.
Frequent monitoring
Regular checkups can help detect the disease in its early stages before irreversible damage has occurred. As a general rule, have eye exams every two to four years if you're between the ages of 40 and 65, and every one to two years if you're older than 65.
Your doctor will likely recommend more frequent monitoring if you're at increased risk of developing glaucoma. For example, a family history of glaucoma puts you at increased risk of developing glaucoma and is a reason for more frequent monitoring. You may also need even more frequent checkups if you have received a diagnosis of abnormally high intraocular pressure or have a history of serious eye injury
Information obtained from National Institute of Health