Trabeculectomy (filtration surgery) is a common surgery performed to reduce eye pressure in patients with open-angle glaucoma. Trabeculectomy is usually done when other treatments for glaucoma have failed to adequately lower eye pressure. The goal of this surgery is to lower eye pressure to prevent further loss of vision from glaucoma.
During trabeculectomy surgery a new drainage passage is created to filter fluid from the eye. This new opening allows aqueous humor, the fluid inside the eye, to drain out of the eye, bypassing the trabecular meshwork, the clogged drainage passages present in people with glaucoma. The new drainage opening is covered by the sclera, the white part of the eye, and the conjunctiva, the clear thin covering over the sclera. As the fluid flows through the new drainage opening, the tissue over the opening forms a little blister or bubble, called a bleb. The bleb is located where the sclera, the white of the eye, joins the iris, the colored part of the eye, and is hidden underneath the upper eyelid. The fluid is then absorbed into the bloodstream. It does not flow out onto the surface of the eye and is completely separate from the tear drainage system, the lacrimal system. The bleb does not alter the appearance of the visible part of the eye. During office visits after surgery, the doctor evaluates the bleb to make sure that fluid is still draining out of the new drainage opening. Sometimes the doctor will massage the bleb to increase the flow of fluid.
Trabeculectomy significantly lowers eye pressure in 80-90% of patients and as a result loss of peripheral vision is stopped or significantly slowed. On average, trabeculectomy surgery continues to lower pressure for 10 years. For some it may last as long as 30 years; in others it may last only a few months. Some people may need additional treatment or surgery over time.
Trabeculectomy is less likely to be successful in African Americans, diabetics and people who have had previous eye surgery.
Generally, trabeculectomy surgery is performed on an outpatient basis. It is performed under local anesthesia in which medicine is administered intravenously to relax the patient. A numbing shot is administered under the eye to prevent pain and eye movements during surgery. The surgery takes about 30 minutes, although the whole pre and post-operative process may take a few hours.
Immediately after surgery, the eye is patched, and an eye shield, a hard covering, is placed over the eye. The doctor’s assistant will remove these the following day. Until this time the patient does not require any eye medications in the operated eye. On the day of surgery and for at least 2 weeks patients need to avoid any activity that might jar the eye, such as bending, lifting, or straining. Additionally, the eye shield should be worn at night for 2 weeks in order to avoid any external pressure on the eye.
On the day after surgery, it is normal for the vision to be extremely blurry after the eye patch and shield are removed. It is also normal for the eye pressure to range anywhere from zero to 30 on the first day after the operation, as it takes a few days for the filter to function optimally. At this time, instructions will be given regarding post-operative eye drops. For most patients this will include Pred Forte drops for 4-6 weeks and an antibiotic drop for 1-2 weeks. All other should be discontinued in the operated eye.
Post-operative visits will take place with the doctor about once a week for four weeks. During this time, anti-scarring injections may be performed or stitches may be cut to adjust the flow of fluid. Usually there is mild discomfort after trabeculectomy surgery. Pain is not typical and should be brought to the doctor’s attention immediately.
The most common problem after trabeculectomy surgery is scarring of the filtration site. Scarring prevents fluid drainage from the eye and interferes with the proper function of the bleb. Mitomycin-C, anti-scarring medicine, is commonly used during surgery to prevent scarring. Post-operatively 5-fluorouracil, additional anti-scarring medicine, can be injected into conjunctiva, the thin tissue covering the eye, to prevent scarring.
Other complications of this surgery include, but are not limited to, blurring of the vision for several weeks (usual), worsening of pre-existing cataract, infection (rare), bleeding (rare) and droopy eyelid (rare). In certain instances, the surgery can result in eye pressures that are too low. In these cases, injections to the eye or additional surgery may be necessary to regulate the pressure.