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Trabeculectomy (filteration surgery for glaucoma)

What is trabeculectomy?

Trabeculectomy is a surgical procedure that removes part of the trabecular meshwork in the eye to relieve pressure caused by glaucoma. Trabecular meshwork is that part of the work through which the fluid in the eye drains out and helps in controlling pressure.

Why it is Done?

Trabeculectomy is the type of surgery most often used to reduce pressure in the eyes caused by open-angle glaucoma. Trabeculectomy is usually done when medication 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 is it done and what should I expect?

During trabeculectomy-sometimes also called filtration surgery-a piece of tissue in the drainage angle of the eye is removed, creating an opening. The opening is partially covered with a flap of tissue from the sclera, the white part of the eye, and the conjunctiva, the clear thin covering over the sclera. This new opening allows fluid (aqueous humor) to drain out of the eye, bypassing the clogged drainage channels of the trabecular meshwork.
As the fluid flows through the new drainage opening, the tissue over the opening rises to form a little blister or bubble, called a bleb. The bleb is located where the sclera, or white of the eye, joins the iris, the colored part of the eye. 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.

This operation often done under local anaesthetic. It takes about 45-90 minutes and you can usually go home the same day. Afterwards there is a patch over the eye. After a few hours you are discharged from the hospital and asked to return to the eye clinic the next day. The operation is usually not painful, and afterward there is usually no or slight discomfort (often relieved by over the counter pain relievers as prescribed by your doctor).

What are the risks of surgery?

The most common problem after a trabeculectomy is scarring of the opening. Scarring prevents fluid drainage from the eye and interferes with the proper function of the bleb. Antimetabolites are commonly used during surgery to prevent scarring.

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) or fluid buildup 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:

  • A cataract that is worse than it was before surgery (usual).
  • Continued changes in the nerve at the back of the eye related to glaucoma.
  • Infection

What is the main reason for failure in trabeculectomy surgery?

The main reason for failure of a trabeculectomy is that scar tissue may block the new drainage hole. Many ophthalmologists use a special chemical called an antimetabolite such as 5-Fluorouracil and Mitomycin C at the time of surgery or soon thereafter. They do this to reduce the scar tissue response and increase the success rate of filtering surgery.

The success rate of glaucoma surgery can be improved in many patients when the surgery is combined with the use of a special chemical that acts to stop scars from forming. The most widely used of these chemicals are 5-Fluorouracil and Mitomycin C. When scar tissue forms at the site of surgery, it limits the flow of fluid out of the ‘new’ drainage channel and reduces the effectiveness of the procedure.

What To Expect After Surgery?

The person does not have to be admitted to the hospital. However, children may stay in the hospital overnight following surgery. In some cases, especially when a person has poor vision in the eye not operated on, adults may stay in the hospital overnight following surgery.
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 checkup 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 and 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.

How successful is trabeculectomy surgery?

Trabeculectomy is about 90 per cent successful in terms of lowering intraocular pressure below target IOP. However, the chances of success depend on many factors. Your doctor is in the best position to discuss the chances of success in your eye.

What operation(s) can be done if I have both cataract as well as glaucoma?

In some cases, when cataracts and glaucoma coexist, the surgeon may offer you a combined procedure by removing the cataract and performing a filtering procedure at the same time. This is usually done if the cataract is thought to be causing the decrease in your vision and the glaucoma is moderately advanced.
In other cases, where the cataract is the major problem and glaucoma is well controlled, it may be possible to simply remove the cataract and not do a glaucoma operation at the same time.

Finally, if glaucoma is the main problem, and the cataract is not too advanced, glaucoma surgery may be done by itself.