"Narrow angles" a tip-off to eyesight risk

Content provided by the Faculty of the Harvard Medical School

"Narrow angles" a tip-off to eyesight risk

Proper eye care can limit vision loss from most glaucoma — and prevent one of its most serious forms.

Glaucoma is a group of eye diseases that cause vision loss and blindness through damage to the optic nerve. Several factors contribute to its development, but the main culprit is elevated intraocular pressure, that is, pressure within the eye.

Theoretically, glaucoma can be managed and vision loss prevented or minimized with early detection and medical treatment to control intraocular pressure. But the most common form, called open-angle glaucoma, progresses so slowly and subtly that symptoms, such as blind spots and reduced peripheral vision, may go unnoticed until the disease has advanced and vision loss is inevitable.

By contrast, angle-closure glaucoma, which accounts for about 10%–15% of glaucoma in the United States, can come on suddenly and painfully and cause vision loss or blindness within hours or days. As dire as this sounds, the good news is that angle-closure glaucoma is highly preventable. For one thing, eyes that develop it have a telltale anatomical feature called “narrow angles,” which can be detected during a routine eye examination. Narrow angles means that the angle between the outer edge of the iris and the cornea is narrower, or more closed, than normal. This can affect fluid flow and thus intraocular pressure (see illustration).

Anatomy of angle-closure glaucoma In the normal eye, a fluid called the aqueous humor circulates continuously from behind the iris (the colored part of the eye) to the front, or anterior, chamber of the eye, delivering nourishment to the lens and the cells lining the cornea (the clear part of the eye). The fluid then drains out of the eye through the trabecular meshwork — the eye’s filtration system — at the junction of the outer iris and the cornea. In angle-closure glaucoma, the trabecular meshwork is obstructed by the iris, because the angle where the iris meets the cornea (sometimes referred to as the drainage angle) is narrower than normal. This slows or blocks the flow of aqueous humor out of the eye. Pressure from the aqueous humor behind the iris forces it against the trabecular meshwork.

Having narrow angles doesn’t mean that angle-closure glaucoma is inevitable. But the narrower the angle, the greater the risk, especially with increasing age. That’s why it’s important to know if you have narrow angles and to discuss with your clinician how you will be followed.

Who’s at risk for angle-closure glaucoma?

Shorter eyes — that is, farsighted eyes — are at greater risk because they tend to have a shallow anterior chamber (the fluid-filled space at the front of the eye), which narrows the angle between the iris and cornea. Risk is also age-related. In particular, the lens grows each year, becoming thicker from front to back. As the lens pushes forward, the angle between the iris and cornea narrows, and resistance to fluid flow between the iris and lens increases.

If fluid accumulates behind the iris, the iris may bulge forward and block the eye’s drainage system (the trabecular meshwork). This can precipitate an acute angle-closure attack. In such an attack, intraocular pressure skyrockets, causing severe eye pain and headache, blurry vision, eye redness, colored halos around lights, nausea, and vomiting. This is a medical emergency: Left untreated, high intraocular pressure can cause permanent damage within hours.

The goal of identifying people with narrow angles is to prevent an acute attack and to catch chronic angle-closure glaucoma — which develops more slowly — before damage occurs. Risk for angle-closure glaucoma is greater in farsighted people and in women because their eyes are smaller. Asians and Eskimos are also at increased risk because their eyes tend to have shallow anterior chambers.

How do I know if I’m at risk?

The best defense against all forms of glaucoma is regular eye examinations. Experts recommend that adults have a comprehensive eye exam at least twice in their 20s and 30s, every two to four years after age 40, and annually starting at age 60. If you have risk factors, such as a family history of glaucoma, your clinician will recommend screening more often. If you’ve been told you have narrow angles, you should have an eye examination every year, regardless of age.

During an eye exam, your vision will be tested for refractive error (farsightedness or nearsightedness). Peripheral vision will also be checked, as well as eye movement and coordination and intraocular pressure. Your clinician will examine the back of the eye with a hand-held device (an ophthalmoscope) or a slit lamp (a combination microscope and light). The slit lamp is also used to look at the structures at the front of the eye and to check for narrow angles.

What if I have narrow angles?

Not everyone with narrow angles develops angle-closure glaucoma. But a clinician can assess the risk by looking into the eye with a special lens (gonioprism) to examine the trabecular meshwork. If at least half of the trabecular meshwork is visible, you’re not at imminent risk and will be advised to have yearly exams. But if more than 50% is obscured, the next step is usually laser iridotomy to prevent an acute angle-closure attack.

Laser iridotomy is an in-office or outpatient procedure that uses an intense beam of light to create a tiny drainage hole at the outer edge of the iris. This ensures that fluid behind the iris can flow to the front of the eye and out through the trabecular meshwork. The procedure is quick and has few complications or side effects. Some inflammation may occur, which can be treated with steroid drops. Patients can usually return to work the next day.

The long-term safety of preventive laser iridotomy hasn’t been fully studied. But experts generally agree that the benefits far outweigh the risks: “It’s much safer than missing someone who potentially could have an attack of angle-closure glaucoma,” says Harvard Medical School ophthalmologist Dr. Claudia Richter. “Eyes that have those attacks are often never normal again.”

An attack is treated with medications to reduce the production of aqueous humor and increase drainage. After the eye has calmed down, laser iridotomy can be performed, usually within a few days. Because the other eye is also at risk, anyone who has an attack in one eye is routinely advised to have the procedure on the other eye.

Narrow-angle precautions

If you’ve been warned that you have narrow angles and haven’t had an iridotomy, keep the following in mind:

• Anything that dilates the pupils can trigger an acute angle-closure attack. That’s why clinicians screen for narrow angles before they administer dilating eyedrops. Certain medications can dilate the pupils, including some antidepressants and antihypertensive drugs and a number of over-the-counter cold and allergy remedies. Check drug labels for warnings about glaucoma, and consult your pharmacist or physician before taking medications or supplements of any kind.

• If you experience an upset stomach with nausea, vomiting, and a headache, cover one eye, then the other. If your vision is blurry in one eye, you may be having an acute angle-closure attack. Contact your physician immediately.

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Last updated:	August 21, 2006