Glaucoma
What is it?
Glaucoma is a condition in which the optic nerve is damaged, usually because of increasing pressure within the eye. The damage to the optic nerve causes a loss of
vision.
Who gets it?
Over two million people in the United States have glaucoma, with 80,000 of these classified as legally blind. It is the leading cause of preventable blindness in the United States and the most frequent cause of blindness
in African-Americans, who are three times more likely to have glaucoma than the rest of the population. It is likely that glaucoma is inherited because researchers have identified at least ten defective genes that cause glaucoma. The risk of glaucoma increases with age, but it can occur in any age
group.
What causes it?
To understand how glaucoma occurs, it is helpful to have a basic understanding of the structure of the eye. The front (anterior) and back (posterior) chambers of the eye are filled with a fluid called the aqueous humor. This fluid is normally produced in the back chamber and passes into the front chamber through the pupil. The pupil is the black area in the middle of the iris, which is the colored part of the eye. The fluid moves out of the eye into the bloodstream through a drainage area located in front of the iris. This drainage area is located in the angle formed between the iris and the point at which the iris appears to meet the inside of the cornea. The cornea is a transparent dome that protects the eye and focuses light on the retina. The retina, located at the back of the eye, senses the light and converts a visual image to electrical impulses. The optic nerve carries these impulses to the brain, which translates those messages into vision. If the flow of aqueous humor is blocked somehow, intraocular pressure increases. This pressure eventually damages the optic nerve. The result is a loss of vision, or blind spots where the image from the retina isn't transmitted to the brain.
There are two main types of glaucoma.
- Open-angle glaucoma accounts for over 90% of all cases. With this type, the angle between the iris and the cornea is open, but the aqueous humor drains too slowly, creating a gradual build-up of pressure. This type of glaucoma is more common in people with diabetes or nearsightedness, and occurs more often in African Americans. A rare type of open-angle glaucoma is called normal tension glaucoma. Its cause is unknown, but it appears that the optic nerves of these patients are susceptible to damage at lower pressures than normal.
- Closed-angle glaucoma occurs when the space between the cornea and iris is narrower than normal. Anything that causes the pupil to dilate, such as dim light or eyedrops, can make the iris block the drainage of fluid. The flow of aqueous humor can become blocked due to the natural aging process, or by injury. Glaucoma can also occur as a complication of many different
diseases.
What are the symptoms?
Open-angle glaucoma produces no symptoms at first because the build-up of pressure is so gradual. As the condition progresses, however, the patient will experience a smaller field of peripheral (side) vision, headaches, and visual disturbances, such as halos around lights. Eventually, the patient may not be able to see anything to either side (tunnel vision). Open-angle glaucoma can progress to blindness.
Closed-angle glaucoma causes sudden attacks of increased pressure, resulting in blurred vision, swelling, severe pain, sensitivity to light, nausea, and halos around lights. These types of attacks need to be treated immediately. Congenital glaucoma is present at birth, with symptoms including bulging eyes, cloudy corneas, excessive tearing, and sensitivity to
light.
How is it diagnosed?
Eye care specialists diagnose glaucoma through a number of tests. Your doctor will perform a test of visual acuity by using an eye chart to measure how well you see at various distances. A test of visual field measures peripheral (side) vision. The doctor will also use eye drops to dilate your pupils so he or she can take a closer look at the inside of your eye. With the pupils dilated, an instrument called an ophthalmoscope is used to direct a beam of light into the eye and magnify the optic nerve. Your doctor will also measure intraocular pressure with an instrument called a tonometer. With this test, he or she may numb the eye with drops and then touch the cornea with a small probe. This test can also be performed by an Òeye puff,Ó which measures the resistance of the eye to a puff of air. A test called gonioscopy is often used to tell the difference between narrow-angle and open-angle
glaucoma.
What is the treatment?
While glaucoma cannot be cured, treatment can often prevent its progression and protect your remaining sight. Medicated eyedrops are usually used to treat open-angle glaucoma. The doctor may first try an eyedrop medication known as a beta blocker to decrease the amount of fluid produced by the eye. Another type of drug called a miotic might be used to increase the drainage from the anterior chamber. If medication doesn't control the pressure, surgery might be recommended to increase the drainage from the anterior chamber. A laser is used to create a hole in the iris or cut out part of the iris. The effects of surgery, however, usually do not last for more than one year.
Closed-angle glaucoma is considered a medical emergency. Treatment usually includes drinking a mixture of glycerin and water to reduce the pressure and stop the attack. Other drugs such as acetazolamide, hyperosmotic agents, a beta-blocker in eyedrop form, and pilocarpine can quickly reduce pressure. Laser surgery also can be used to make a hole in the iris so the fluid can drain and relieve pressure. However, once sight is lost due to glaucoma, it cannot be
restored.
Self-care tips
Regular eye exams are extremely important because glaucoma does have symptoms in the early stages. If you have narrow-angle glaucoma, your doctor may recommend avoiding certain medications that might aggravate the condition. If you have glaucoma, take your medication as recommended and see your eye care professional regularly.
This information has been designed as a comprehensive and quick reference
guide written by our health care reviewers. The health information written
by our authors is intended to be a supplement to the care provided by your
physician. It is not intended nor implied to be a substitute for
professional medical advice.
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