Ординатура / Офтальмология / Английские материалы / The Eye Book A Complete Guide to Eye Disorders and Health_Cassel, Billig, Randall_2001

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Other Forms of Treatment

Lasers

An increasingly important tool for treating glaucoma, lasers have proven effective in both closed-angle and open-angle glaucoma.

Lasers in treating closed-angle glaucoma: Briefly, the trouble in closed-angle glaucoma is that the anterior chamber angle is narrowed or plugged by the root of the iris. As a result, aqueous fluid can’t flow from its site of production, in the posterior chamber, out of the eye through the trabecular meshwork filter in the corner of the anterior chamber angle, and it “backs up,” raising pressure within the eye.

Lasers provide a mechanical solution to the problem by making a hole, or peripheral iridectomy (PI), in the iris to improve the flow of aqueous from the posterior to the anterior chamber. It’s like providing the aqueous with a short-cut to the trabecular meshwork. The PI relieves the pressure behind the iris, deepens the shallow anterior chamber and narrowed angle, and helps aqueous exit the trabecular meshwork and enter Schlemm’s canal. Peripheral iridectomies are performed either with cutting lasers (called YAG lasers) or with burning lasers (argon lasers).

Candidates for PI include people with acute angleclosure glaucoma attacks (the sudden onset of painful glaucoma described above) and chronic closed-angle glaucoma. Occasionally PIs are also performed prophy-

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lactically (as preventive measures) on people with narrowed anterior chamber angles to preclude the sudden or gradual buildup of pressure.

A PI is painless, usually takes less than half an hour, and requires no preoperative testing or postoperative restrictions. Complications are minimal and may vary depending on the state of the eye at the time of the procedure. For example, bleeding from blood vessels in the iris is a common and usually limited occurrence after a laser PI. But in patients with an acute angle-closure attack, this complication can occur more often and may be more difficult to control. Other potential complications of peripheral iridectomies include a temporary elevation in eye pressure, inflammation of the eye (iritis), and temporary blurred vision. (As always, be sure to discuss all risks with your eye doctor before undergoing this or any form of treatment.)

Lasers in treating open-angle glaucoma: Argon lasers are also used in open-angle glaucoma. In several studies these “burning” lasers have been shown to lower intraocular pressures by as much as 10 millimeters of mercury for at least eighteen months in a statistically significant number of patients with elevated eye pressure. This effect varies greatly depending on the type of glaucoma being treated.

In this procedure, called laser trabeculoplasty, a specially designed mirrored contact lens is placed on an anesthetized cornea. The surgeon can then use a magnified slit lamp to get a good view of the trabecular meshwork. Carefully guiding the laser, the surgeon

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Image not available.

Fig. 8.7. Peripheral iridectomy

makes between fifty and a hundred “spots,” or tiny burns, on the trabecular meshwork. Exactly how these burns lower eye pressures is not known, but current thinking is that they cause the minuscule fibers of connective tissue in the meshwork to contract, opening up sieve-like spaces through which the aqueous fluid can seep into Schlemm’s canal. The treatment is painless and usually takes about half an hour.

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Complications, as with laser PIs, are rare and mainly include a short-term rise in eye pressure and the development of scar tissue in the vicinity of the trabecular meshwork (which can make the drainage problem even worse). One drawback is that the results aren’t immediate; it may take six to ten weeks before eye pressures get lower. Another is that, unfortunately, the effects don’t seem permanent; studies have found that the results last for only about five years in about 46 percent of patients. In some cases people undergo repeat laser procedures, but results have not been shown to be consistently successful.

Therefore, laser trabeculoplasty is not a first-line choice in the treatment of glaucoma. It’s usually done after medical therapies have failed to prevent advancing vision loss, or in an effort to delay the need for surgical intervention. Not infrequently patients still need some of their medications despite laser treatment. It is, however, an important treatment option in patients who aren’t good candidates for surgery.

Glaucoma Surgery

There are several surgical approaches designed to lower eye pressure. Currently, these techniques are mainly used when medical and laser treatments fail— when, in other words, IOP can’t be lowered sufficiently to halt the loss of vision.

Trabeculectomy, the most commonly performed surgical procedure for glaucoma, is basically the surgical creation of a new drain in the eye—a custom-built “trap

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door” in the sclera of the eyeball. The aqueous fluid collects under the conjunctiva, forming a “blister” of fluid, and is gradually absorbed into the circulation on the outside of the eyeball. Eventually a permanent fistula, or hole, develops at the trap door, maintaining a constant outflow of aqueous from the eye and lowering IOP with or without medication.

Note: This surgical technique is not without risks and should be performed only by those experienced in this surgery and the management of potential postoperative complications.

Surgically, a trabeculectomy tries to create a fine balance in the eye between too much and too little outflow of aqueous under a surgical tissue flap (the trap door). Thus, the days and weeks after this type of surgery can often be stormy. For example, too much filtration can initially lead to abnormally soft eyes and flat anterior chambers. If not corrected, this situation can lead to eye problems and result in permanent vision loss. The postoperative management of trabeculectomies—as the eye heals and establishes filtration through this new drain— often requires vigilance and patience by doctors as well as patients.

Another risk is that in some people scar tissue may form in this artificial drain, sealing the trap door. Doctors often use medications such as 5-FU and mitomycin during or after the procedure to help avert this problem in patients considered to be at higher risk. (Doctors can tell by examining them which patients are at higher risk.)

Other, rare, complications include infection, bleeding,

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and the development of a cataract in the operated eye. Before consenting to a trabeculectomy, it’s important to weigh carefully the benefits of lowered IOP against the potential risks of the procedure.

These risks aside, the long-term results of trabeculectomies for maintaining eye pressure are good. No further progression of glaucoma can be expected in 80 percent of people after surgery, with 90 percent maintaining stable vision. As many as 40 percent of people may not ever need any medications for pressure control after the surgery, although many still require some eye drops.

What’s Best for You?

Which brings us to this question: Could we do a better job of managing glaucoma?

Traditionally in the United States, glaucoma treatment has begun with a single eye drop to lower intraocular pressure. If this does not fix the problem—if it fails to lower pressure and halt vision loss—then another eye drop is usually added to the regimen. Each drop is evaluated alone or in combination with other eye drops, as doctors struggle to find the best regimen for each patient. And even when that perfect mix is found, patients must still be carefully monitored, because—in a phenomenon frustrating to both doctors and patients— these medications often lose their effectiveness over time or the glaucoma simply becomes harder to control.

Now, on to Plan B: if eye drops don’t work to control intraocular pressure, or if the nerve fibers in the optic disc continue to deteriorate despite lowered eye pressure,

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then doctors usually consider topical or oral CAI medications. Plan C includes lasers and surgery, which are usually reserved for advanced glaucoma or for eyes that don’t adequately respond to drops and pills. But studies done in other countries have suggested that this may not be the best way to go. Instead, these studies suggest, the most effective way to control glaucoma may be to perform a surgical trabeculectomy before attempting management with medical and laser treatments. Trabeculectomy may ultimately produce better intraocular pressure control for a longer period of time, with less overall cost to the patient and with fewer side effects.

The National Institutes of Health recently began the Collaborative Investigational Glaucoma Treatment Study, or CIGTS, designed to evaluate whether newly diagnosed glaucoma patients truly are best treated by the traditional medical approach (beginning with eye drops) or by surgical trabeculectomy. The study should give us an answer to this important question within the next several years.

Also, although it’s generally accepted that IOP must be lowered in patients with glaucoma, by exactly how much is different for each patient. To make matters more complex, studies have shown that other factors, such as the level of IOP and the degree of optic disc cupping at the time of diagnosis, are also very important. It’s probably due to some of these other factors that glaucoma continues to worsen in some patients despite vigorous lowering of IOP. People with normotensive glaucoma (see above), on the other hand, seem to be more susceptible

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to developing optic nerve damage at intraocular pressures considered to be normal for the majority of the population. Even more perplexing, some people, despite elevated intraocular pressures, never seem to develop vision loss or other signs of glaucoma.

The Ocular Hypertension Study, a national prospective clinical trial, is currently studying this latter group of patients. The results of this study may give us a better grasp of the relationship of eye pressure to the development and progression of glaucoma and help us understand some of these important contributing factors.

Some Questions You May Have about Glaucoma

Can glaucoma be caused by reading too much, wearing contact lenses, or even a poor diet?

Although no one really knows why some people develop glaucoma, it definitely does not appear to be related to any of these activities. Age, family history, and race are the most significant risk factors for developing glaucoma.

Will I go blind from glaucoma?

When glaucoma is discovered early, the vast majority of people with glaucoma will not go blind from it, because of the excellent array of treatment options available today. Early detection is the key to good glaucoma management, and regular eye exams by qualified professionals are very important.

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Does glaucoma run in families?

Yes; at least, having a family history of glaucoma raises someone’s risk of developing the condition. Other factors that may make someone more prone to developing glaucoma are having diabetes, being African American (African Americans have a particularly high prevalence of glaucoma), being over age fifty-five, or being very nearsighted.

I have hypertension. Does this mean my eye pressure is high as well?

Although elevated blood pressure can cause elevated eye pressure, for most people these are two separate issues; most of the people who have elevated eye pressure don’t have it because they also have hypertension. Elevated eye pressure is also not related to any of the things we commonly think of as raising our blood pressure— increased stress, anxiety, or diet.

Can my eye pressure change from one day to the next?

Absolutely—and not only from one day to the next, but from one hour to the next! Eye pressures are usually highest in the morning. Because of this constant fluctuation, it’s important to vary the times of your eye examinations, so that your doctor can get a better overall impression of your eye pressures right after taking medications as well as some time after taking medications.

If I forget to take my drops, will this really cause me to have more problems from glaucoma?