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Vision

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Glaucoma

Symptoms

Open-angle glaucoma: gradual loss of peripheral vision, marked by blind spots. Symptoms only develop at the later stages of the disease. Screening exams are advised.

Closed-angle glaucoma: acute attacks involving severe eye pain, nausea and vomiting, blurred vision, and the appearance of rainbow-colored halos around lights.

When To Call Your Doctor

Contact an ophthalmologist right away if you develop symptoms of acute closed-angle glaucoma.

See an ophthalmologist for a complete eye exam every two years after age 50. (Those of African descent should start having such exams at age 40.) People with a family history of glaucoma should also have periodic exams.


What Is It?

Glaucoma is a sight-threatening disorder marked by an increase in intraocular pressure (IOP), the pressure within the eyeball. It occurs as a result of an excess buildup of aqueous humor—the clear fluid inside the eyeball that provides nutrients to and carries waste products away from the lens and cornea of the eye, the only parts of the body with no blood supply. Each day, the eye produces about one teaspoon of aqueous humor. Normally, this fluid escapes from the eye through a spongy mesh of connective tissue called the trabecular meshwork at the same rate at which it is produced. In a common type of glaucoma, production of aqueous humor appears to exceed the rate of its escape and the pressure rises.

There are two forms of glaucoma: open angle and closed angle. Open-angle glaucoma, which accounts for 90 percent of all cases, is a slow, progressive disease that produces no symptoms in its early stages. By contrast, closed-angle glaucoma is relatively uncommon and is characterized by rapid and extreme elevations of IOP, often causing acute symptoms such as severe eye pain and rapid blurring of vision. Both types of glaucoma may lead to blindness by damaging the optic nerve; however, early detection and treatment can usually control IOP and prevent severe vision loss. Most prevalent among those over age 40, glaucoma is more common in African Americans or when there is a positive family history.

What Causes It?

It is theorized that open-angle glaucoma occurs when, for reasons not completely understood, the trabecular meshwork becomes partially blocked. IOP builds up as more aqueous humor is formed, but pressure doesn’t rise high enough to cause any noticeable symptoms initially. When IOP remains elevated or continues to rise, however, fibers in the optic nerve are compressed and destroyed, leading to a gradual loss of vision over a period of years.

Closed-angle glaucoma is caused by a sudden blockage near the iris that prevents aqueous humor from reaching the trabecular meshwork. The blockage results in the rapid onset of extremely high IOP that may cause severe, permanent vision loss within a day or two.

A family history of visual-field loss due to glaucoma increases the risk of optic nerve damage. Evidence also suggests that cardiovascular disease, diabetes, and myopia (nearsightedness) increase the risk of nerve damage from glaucoma.

Prevention

While there is no way to prevent glaucoma, early detection and treatment may prevent damage to the optic nerve. See an ophthalmologist for a complete eye exam every two years after age 50. Those of African descent should start having such exams at age 40.

Diagnosis

Glaucoma is diagnosed by an eye examination which emphasizes eye pressure measurement, viewing of the optic nerve, and assessment of optic nerve function:

Tonometry (use of an instrument to apply slight pressure upon the eyeball to measure IOP).

Ophthalmoscopy (in which the pupils are dilated with eye drops so that the optic nerve may be magnified and examined with an ophthalmoscope, a lighted viewing instrument).

Perimetry (a visual-field test that determines the extent of peripheral vision).

How To Treat It

Glaucoma is a chronic disorder that cannot be cured. Open-angle glaucoma can often be treated safely and effectively by medical or surgical measures, though lifelong therapy is almost always necessary. Medications are nearly always used first. However, laser surgery is becoming a more common first option.

Eye drops are the most frequent medical treatment for glaucoma because they have fewer overall side effects than oral medications. Depending on the type, eye drops must be applied one to four times a day, regularly and on schedule, to maximize IOP control. Five types of eye drops are currently used: miotics (such as pilocarpine), beta-blockers (like timolol or levobunolol), adrenergic agonists (such as epinephrine or dipivefrin), topical prostaglandins (latanoprost), and carbonic anhydrase inhibitors (dorzolamide). Miotics (drugs that constrict the pupil) and adrenergic agonists increase the outflow of aqueous humor. Beta-blockers diminish the production of aqueous humor. Latanoprost, the newest type of glaucoma eyedrop, reduces IOP by increasing the outflow of aqueous humor. Because it works differently than other glaucoma drugs, it can be used along with a second medication to reduce IOP further. Dorzolamide drops, previously available only as tablets, decrease production of aqueous humor.

Carbonic anhydrase inhibitor pills are generally used when optic nerve damage continues or seems highly likely despite maximal topical treatment. These oral medications initially lower IOP by 20 to 30 percent on average, but significant systemic side effects (such as numbness or tingling in the extremities, malaise, and loss of appetite) and occasional serious complications (such as kidney stones, depression, diarrhea, and blood abnormalities) can limit their use.

Periodic ophthalmologic examinations are essential throughout medical therapy. These may initially be required daily or weekly for those with severe nerve damage or extreme elevations of IOP, or only every three to six months for patients with stable IOP and minimal optic nerve damage.

Surgery is successful more often than medical treatment. However, it carries a greater risk of complications, including the development of cataracts, and repeat procedures may be required. About 10 percent of those with open-angle glaucoma require surgery, when drug therapy fails or when the patient has a medical condition (such as hypertension or severe heart or lung disease) that precludes maximal drug therapy. The two most common surgical procedures—laser trabecular surgery and filtration surgery—reduce ocular pressure by opening a passage for aqueous humor.

Unless high IOP is relieved promptly during an acute attack of closed-angle glaucoma, blindness can occur within a day or two. Making a hole in the iris (iridotomy) creates a drainage path for the aqueous humor. Iridotomy in the other eye is generally recommended owing to the high likelihood that it will be involved in a future acute attack. The procedure can usually be performed with a laser.

 

From Johns Hopkins Symptoms and Remedies, the complete home medical reference. You can order this book now on our secure server.

 

 


 


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2005
WHITE PAPERS
Vision

The vision White Paper from The Johns Hopkins White Papers series is an annual, in-depth report written by Hopkins physicians.


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Johns Hopkins Symptoms and Remedies
An easy-to-use reference work that can help you pinpoint the cause of hundreds of symptoms, from abdominal pain to skin rash to swollen glands.

 

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