Glaucoma Surgery: Filtration Surgery (Trabeculectomy)

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 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.

The Procedure. Filtration surgery has been used for more than 100 years with only minor modifications. It uses 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 without deflating 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.
• As the fluid flows through the new drainage opening, the tissue over the opening nearly always rises to form a little blister or bubble, called a bleb, this 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. During office visits after surgery, the doctor looks at the bleb to make sure that fluid is still draining out of the new opening. Not all blebs have to be easily seen to work.

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 newer 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.

What to Expect After Surgery?

The person does not have to be admitted to the hospital. But children may stay in the hospital overnight following surgery. And in some cases, your doctor may recommend that you stay in the hospital.

Right after surgery, antibiotics may be applied to the eye. Also, antibiotics may be injected under the lining of the eyelid (conjunctiva). After surgery, the eyelid is usually taped shut, and a hard covering (eye shield) is placed over the eye.

The person wears a dressing over the eye during the first night after surgery and wears the eye shield at bedtime for up to a month. Corticosteroids are usually applied to the eye for about 1 to 2 months after surgery to decrease inflammation in the eye.

People who have a trabeculectomy without being admitted to the hospital usually have a check-up the following day with their eye specialist.

Any activity that might jar the eye needs to be avoided after surgery. People usually need to avoid bending, lifting, or straining for several weeks after surgery.

After surgery, people who have problems with constipation may need to take laxatives to avoid straining while trying to pass stools. Straining can raise the pressure inside the eye, increasing the risk of damage to the optic nerve or bleeding.

Usually there is mild discomfort after a trabeculectomy. Severe pain may be a sign of complications. If you have severe pain after a trabeculectomy, call your doctor immediately.

Why It Is Done?

Trabeculectomy is used to treat open-angle glaucoma and chronic closed-angle glaucoma. Trabeculectomy is usually done when medicine treatment for glaucoma has failed to reduce the pressure in the eyes enough to prevent damage to a person’s eyesight.

Trabeculectomy is not the first surgery used for treating babies who have congenital glaucoma.

How Well It Works?

The new opening created by trabeculectomy allows fluid to gather under the tissue that lines the eyeball (conjunctiva), where it is absorbed into the bloodstream.

This procedure has been shown to reduce IOP and the need for medical treatment.¹But many people need another trabeculectomy surgery or other treatments for glaucoma. Trabeculectomy is less likely to be successful in:

• African Americans.
• Children who have congenital glaucoma.
• People who have difficult-to-control glaucoma in which new blood vessels grow on the iris (neovascular secondary glaucoma).
• People who have diabetes.
• People who have had previous eye surgery.

The long-term effectiveness of trabeculectomy surgery in preventing loss of vision from glaucoma is less certain. It is not a cure, and visual field loss can continue despite surgery

Early and Late Complications

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, doctors 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. Scarring is a particular problem in young patients, African-Americans, and 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.
• 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.

Other complications of this surgery that may develop soon after surgery include:

• Severe blurring of vision for several weeks (usual).
• Bleeding in the eye.
• Extremely low pressures in the eye, which may result in blurred vision that results from clouding of the lens (cataract), fluid build-up under the nerve layer in the eye (retina).
• Sudden, permanent loss of central vision. This risk depends in part on how much central vision had been lost before surgery.
• Infection in the eye.
• High pressure in the eye, causing the space in the front part of the eye (anterior chamber) to collapse (malignant glaucoma). This is rare.

Late complications after a trabeculectomy may include:

• Continued changes in the nerve at the back of the eye related to glaucoma.
• Infection.
• Droopy eyelid (a very slight droop of the eyelid is common).

What to Think About

Trabeculectomy is the most frequently used surgery to treat glaucoma. If you are having this type of surgery, talk with your doctor about its possible risks and benefits for you.

Very low pressures in the eye, infection in the bubble created by the surgery (bleb), clouding of the lens (cataracts), or swelling of the clear covering (corneal oedema) over the coloured part of the eye (bullous keratopathy) can sometimes occur.

Scarring of the opening after surgery is the most common problem with trabeculectomy. The risk of scarring is decreased when corticosteroids are used after surgery. 5-fluorouracil may be used to prevent scarring. If bleb failure continues to be a problem, a plastic drainage device called a seton may be placed in the eye to help drain fluid.

Trabeculectomy may be combined with surgery to remove a cataract.

Stitches placed during surgery may be cut after surgery if fluid is not draining well from the eye. Your doctor may ask you to massage the bleb to help the fluid drain