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Glaucoma

Description

An in-depth report on the causes, diagnosis, treatment, and prevention of glaucoma.

Surgery

If medications do not control eye pressure, or if they create intolerable side effects, surgery may be necessary in a small percentage of people with chronic glaucoma. It may be particularly helpful for patients with pseudoexfoliation glaucoma.

The standard procedures are usually one of the following:

• Filtration surgery (trabeculectomy). This procedure opens the full thickness of the drainage area.
• Laser trabeculoplasty. This procedure partially opens the drainage area. It does not reduce pressure to the extent of trabeculectomy but it has fewer adverse effects.

African Americans may respond better to initial laser surgery than to conventional trabeculectomy, while the opposite may be true in Caucasians. Some experts now recommend that, in most circumstances, African Americans should start with laser surgery and Caucasians who have no serious medical problems should have trabeculectomy first.

In addition, a number of experimental and less invasive procedures are under development.

Filtration Surgery (Trabeculectomy)

The Procedure. Filtration surgery has been used for more than 100 years with only minor modifications. It employs conventional surgical techniques known as full-thickness filtering surgery or guarded filtering surgery (trabeculectomy).

• The surgeon creates a sclerostomy , a passage in the sclera (the white part of the eye) for draining excess eye fluid.
• A flap is created that allows fluid to escape but which does not deflate the eyeball.
• The surgeon may also remove a tiny piece of the iris (called an iridectomy ) so that fluid can flow backward into the eye.
• A small bubble called a bleb nearly always forms over the opening, which is a sign that fluid is draining out. Although surgeons aim for a thick bleb, which poses less risk than a thin one for later leakage, paradoxically the ideal operation would have no bleb at all.

The procedure has a high success rate. About 50% of patients no longer need medication after surgery. Thirty-five to 40% of those who still need medication have better control of their glaucoma.

A new instrument called a trabectome has allowed for a less invasive type of trabulectomy surgery The trabectome procedure appears to be a safe and simple way to lower eye pressure. It can be performed before a traditional trabulectomy, if needed. Results from a small study, presented at the 2005 meeting of the American Academy of Ophthalmology, showed that the new approach successfully reduced eye pressure in 90% of patients with open-angle glaucoma.

Side Effects. Many of the serious side effects or complications that occur with filtration surgery involve blebs (blister-like bumps).

• Bleb Leaks and Infections. Blebs, particularly thin ones, commonly leak. Leakage can occur early on or sometimes as late as months or years after surgery. Untreated, such leaks can be serious and even cause blindness. Late-onset leakage significantly increases the risk for infection as well as a number of other serious conditions, including bleeding, a flattening of the eye ball, and harmful inflammation. Surgical repair is the most effective way of managing leaking blebs, although drug therapies, pressure patching, and other nonsurgical techniques may be tried first. Due to the dangers of leaking blebs, experts recommend lifelong monitoring after surgery. Unfortunately, the incidence of late-onset leaking blebs is increasing due to the use of drugs used in filtration surgery to prevent scarring, another complication.
• Scarring. In up to 20% of cases, scars form around the incision, closing up the drainage channels and causing pressure to rebuild. These scars are formed from fibroblasts , which are immature collagen cells that form at the surgical site. Scarring is a particular problem in young patients, African Americans, patients who have taken multiple drugs, have had an inflammatory disease, or have had cataract surgery. Releasing the surgical stitches used in the procedure may help prevent scarring and pressure build-up. A second procedure called bleb needling sometimes can open up the scarred area and restore drainage. With this technique, the tip of a very fine hypodermic needle is used carefully to cut loose the particles closing off the drainage area. A new technique that does not require sutures may prove to be effective and have fewer complications.
• Cataracts. The procedure is highly associated with the development of cataracts over time. Because cataracts are associated with glaucoma anyway, it is not entirely clear whether the cataracts are caused by the surgery or would develop in any case.

Supportive Medication for Preventing Scarring. Specific drugs, usually mitomycin C, are often used in conjunction with the procedure to prevent scarring and closure. A large review of studies of mitomycin C supported its effectiveness in increasing surgical success in nearly all patients. Fluorouracil (5-FU) appears to be similar in effectiveness but has a high risk for complications and is not used as often as in the past.

Laser Trabeculoplasty

The Procedure. Laser trabeculoplasty involves the following steps:

• The procedure uses an instrument, usually a YAG laser, to burn 80 - 100 tiny holes in the drainage area.
• A tiny scar forms, which increases fluid outflow.
• The procedure takes 15 minutes, causes almost no discomfort, and has very few complications.

In a 2-year study, laser surgery of the trabecular meshwork reduced pressure by a third in 70 - 97% of patients. Patients still need to take anti-glaucoma eye drop medications every day.

Laser surgery is not a cure. Within 2 - 5 years, about half of patients need either additional surgery or new medications.

Complications. In about 35% of patients, pressure increases after surgery. In most cases it is temporary, but in rare cases the increased pressure is permanent and vision loss can occur. Use of the drug apraclonidine (Iopidine) or pilocarpine can help prevent this elevated pressure. About a third of patients also develop adhesive-like substances called peripheral anterior synechiae that cause the iris to stick to part of the cornea.

Drainage Implants (Tube Shunts)

Drainage implants, also known as tube shunts, may be used to drain fluid in certain cases, such as if glaucoma is not responsive to any standard procedure or is caused by certain conditions. A 2007 study suggested that tube shunts work better than filtration surgery (trabulectomy) for some patients. In the study, patients who received tube shunts had more stable IOP over the course of a year than patients who underwent trabulectomy.

Candidates. Success rates are highest (75% pressure control over 5 - 7 years) in appropriate patients. Drainage implants may be useful in the following conditions:

• Glaucoma caused by swelling in the iris
• Glaucoma caused by abnormal vessel formations
• Iridocorneal endothelial (ICE) syndrome

The Procedure. In general, the procedure involves:

• An implant, most commonly a 1/2 inch silicone tube, is inserted into the eye's front chamber (anterior). The Molteno implant used with mitomycin C is currently the most effective approach, with reported success rates of 80%. Other implants, such as the Ahmed implant, may have fewer complications.
• The tube drains the fluid onto a tiny plate that is sewn to the side of the eye.
• Fluid collects on the plate and then is absorbed by the tissues in the eye.

Complications. Complications include:

• Hypotony (very low eye pressure) is a serious complication that has been reduced using better techniques and improved implants.
• Cataracts, detached retina, breakdown of the cornea, and bleeding are potentially significant complications.
• There is also a risk for eye movement disorders, such as strabismus (crossed eyes) or diplopia (double-vision).

The implant often becomes blocked and repeated operations are needed. Some researchers are studying the use of a drug called tissue plasminogen activator (tPA) to open up tubes that have been blocked by blood or blood factors. (This so-called clot-busting drug is normally used to break up blood clots during heart attacks.) In one 2002 study, tPA prevented such blocks in 89% of eyes. Unfortunately, significant complications rates were high (11%).

Nonpenetrating Surgical Techniques: Deep Sclerectomy and Viscocanalostomy

Deep sclerectomy and viscocanalostomy are less invasive techniques than filtering surgery that leave the anterior chamber (front of the eye) intact and avoid creation of blebs.

In deep sclerectomy, the surgeon removes a deep piece of the sclera (the white part of the eye), part of the trabecular meshwork, and the front of Schlemm's canal (the vessels that return fluid into the bloodstream).

• In both deep sclerectomy and viscocanalostomy, the surgeon first creates a flap in the outer part of the sclera (the white part of the eye) and then removes a deep piece of the sclera underneath. This opens up Schlemm's canal (the vessels that return fluid into the bloodstream) and exposes a layer above the anterior chamber called Descemet's membrane. A space has also been created between the inner and outer layers of the sclera.
• In deep sclerectomy, this space now serves as a tiny reservoir for aqueous fluid that flows through the membrane and pools here. The fluid then flows out without the surgeon having to open the anterior chamber (as in standard filtering surgery).
• In viscocanalostomy, the surgeon typically injects gel-like materials into the ends of Schlemm's canal in order to enlarge the canal for fluid outflow and lower IOP. The tiny reservoir is sewn tightly up.

Many variations are under investigation. In general, the procedures have fewer complications afterward than standard filtering surgery, although they require excellent surgical skill. Nonpenetrating techniques do not lower IOPs as much as conventional surgery does, however. In time, however, these nonpenetrating techniques are expected to be as effective as filtration surgery.

Treatment for Patients with both Glaucoma and Cataracts

Cataracts and Glaucoma. For patients with both glaucoma and cataracts, experts recommend the following:

• In patients with cataracts and poorly controlled glaucoma, a two-step procedure for both eye conditions is needed. Typically the patient will first have a trabeculectomy for glaucoma, followed by cataract surgery such as phacoemulsification (lens removal through ultrasound). Fluid leakage and the presence of blood in the back chamber of the eye are potential complications of this combined procedure.
• Phacoemulsification is sometimes combined with viscocanalostomy in a procedure called phacoviscocanalostomy. A 2006 study suggested this approach is safe and effective. The study followed patients for 7 years after they underwent phacoviscocanalostomy and found that no serious complications occurred.
• In patients who have cataracts plus either closed-angle glaucoma or open angle glaucoma that is stabilized with medication, the cataract may be able to be extracted and medication continued for the glaucoma.

A major 2002 analysis suggested that the combined approach generally offers better control over eye pressure for patients with both cataracts and glaucoma. However, it is still unclear which specific type of surgical procedure works best. [For descriptions of cataract surgery, see In-Depth Report #26: Cataracts.]

Laser Cyclophotocoagulation (or Cycloablation) for End-Stage Glaucoma

Diode laser transscleral cyclophotocoagulation (TSCPC), also called laser cycloablation, reduces aqueous production by destroying the muscles that control the lens for near and far vision ( the ciliary body ). There is a chance of vision loss with this procedure, so it is reserved for people with end-stage glaucoma or those who fail to benefit from any other therapies. Nevertheless, researchers continue to explore the possibilities for this effective procedure, especially for people who may not have access to expensive medications. Studies have suggested it may even be suitable as first-line surgery for some patients.

Surgery for Acute Closed-Angle Glaucoma

For an acute closed-angle glaucoma attack, emergency microsurgery is usually necessary after reducing pressure with medications.

Iridotomy or Iridectomy. Either laser (iridotomy) or conventional (iridectomy) surgery may be used. With either procedure an ophthalmologist makes a tiny opening in the iris to let the aqueous humor flow out more freely. Because acute glaucoma commonly occurs later in the other eye, surgeons will often recommend surgery in the unaffected eye to prevent a second attack.

Laser iridotomy almost never requires hospitalization, and postsurgical treatment includes only aspirin and eye drops. It has almost completely replaced conventional surgery, which requires anesthesia and hospitalization.

Vision will be blurred, and recovery can take 4 - 8 weeks. Once surgery has been performed, such patients can usually use previously restricted anticholinergic medications, such as antihistamines and certain antidepressants, with safety.

Phacoemulsification and Intraocular Lens Implantation. Phacoemulsification and intraocular lens implantation, a procedure ordinarily used for cataracts, may prove to be beneficial for some patients with acute angle-closure glaucoma requiring surgery. [For descriptions of phacoemulsification and intraocular lens implantation, see In-Depth Report #26: Cataracts.]

• Review Date: 3/3/2007
• Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital.

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