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The Two Major Surgical Procedures for Glaucoma
Trabeculectomy
Trabeculectomy has been considered the gold standard surgical procedure for treating glaucoma. It is indicated when less invasive treatments for glaucoma have failed such as medications and SLT laser treatment. It is usually performed with local anesthesia such as a retrobulbar block or peribulbar block.
An incision is made in eh conjunctiva which is the outer tissue layer covering over the sclera or white portion of the eye. The incision is usually made at the 12:00 position under the upper eyelid. A partial thickness flap in made in the sclera and dissected into the peripheral cornea. The flap is retracted and an opening is made into the eye. A portion of the trabecular meshwork and surrounding tissue is removed. Many times a peripheral iridectomy or opening is made in the iris. The flap is sutured back in place to in a manner that allows a small amount of fluid to exit the eye. The conjunctiva incision is closed in a water type manner. The fluid will drain from the eye and collect under the conjunctiva where is will be absorbed. Antimetabolites such as 5-Fluorourcil or Mitomycin C may be used to keep the opening from scarring closed. Antibiotic and anti-inflammatory eye drop medications are prescribed.
Complications
- Flat Bleb – usually means there is a leak in the conjunctiva and will need to be treated.
- Flat Anterior Chamber – the anterior has not formed either due to too much fluid draining from the eye or the eye is not producing enough fluid.
- Blebitis – infection.
- Hypotony – low eye pressure.
- Suprachoroidal Hemorrhage – rupture of an artery inside the eye
- Cataract Formation – the eye surgery can cause a cataract to develop much faster.
- Encapsulated Bleb – The conjunctiva forms a scar around the area of the trabeculectomy.
- Choroidal Detachment – fluid expands in the choroid under the retina usually due to low eye pressure.
- Bleeding – hemorrhage in the anterior chamber which usually resolves on its own.
Success Rate of Trabeculectomy
The long-term results of trabeculectomy show that the success rate is 90%. Nearly 65% of patients have their glaucoma controlled without medications. About 10% of patients need a repeat of the operation. About 2% per year of patients have their trabeculectomy fail. There is a nearly 10% of infection in the bleb in the lifetime of a patient post trabeculectomy. Trabeculectomy is the most common surgical procedure for glaucoma.
Tube Shunt Surgery for Glaucoma
Shunts were originally used in people who had a trabeculectomy that had failed, had conjunctival scarring where a trabeculectomy could not be done, neovascular glaucoma, patients with chronic inflammation, or other eye disorders. Some eye surgeons prefer treating glaucoma that is not well controlled with medications or laser with placing a tube or shunt in the eye to drain the fluid as their first choice of surgery. These tubes or shunts are made of silicone or polypropylene material that is well tolerated by the body. They come in different sizes, designs, valves, and non-valve types. The non-valved shunts are Molteno, Baerveldt, Eagle Vision shunts, and Shocket. Valved shunts are Ahmed shunts.
Types of Shunts
Shunts with Valves
The term valve refers to the shunt limiting the flow of fluid out of the eye. This limiting of the flow is to control the amount of lowering the valve will allow. This is the most common type of shunt used and is called Ahmed valve shunt. There is a limit to how low the eye pressure can be lowered by this shunt. Many times, patients will still need glaucoma eye medications to lower the eye pressure to the appropriate level.
Shunts without Valves
Shunts without valves maybe used as well. These shunts require some scarring to take place to limit the amount of fluid that is drained from the eye. Sutures are used that limit the flow of fluid until the scarring has occurred. The suture may be a type that dissolves over time and a permanent type of suture may be removed 4 to 6 weeks after the surgery. These devices tend to lower the eye pressure better that valved shunts.
Shunts Differences
Valved shunts lower the pressure less than non-valved shunts but non-valved shunts have more complications. Which shunt the eye surgeons uses may depend on their preference or the type of glaucoma present or the amount of eye pressure lowering that is needed.
Glaucoma Shunt Surgical Procedure
A conjunctival incision is made in most cases in a superior quadrant in the area between the eye muscles. The plate or reservoir shunt is placed between the rectus eye muscles with the anterior edge of the shunt approximately 8 to 10 mm posterior to the cornea. Once the shunt has been placed in the proper position, it is sutured in place with non-absorbable sutures. This is an important step so that the shunt will not move after the surgery.
After the reservoir is secure, the tube leading to the reservoir is laid across the cornea and the tube is cut with a bevel opening toward the cornea. The tube should be cut so that the tube will extend into the anterior chamber by 2 to 3mm. A 23-gauge needle is used to create the track which the tube will go through into the anterior chamber. The tube may be secured to the sclera with an absorbable suture. The tube is covered with a patch graft to prevent any erosion of the tube through the conjunctiva. The graft may be sclera, fascia lata, pericardium. dura, and/or cornea. The patch graft is sutured in place. The tube may be placed under a partial scleral flap as well. After the shunt is placed, the conjunctiva is placed back over the shunt and sutured in place.
Complications
- Flat Anterior Chamber – the anterior has not formed either due to too much fluid draining from the eye or the eye is not producing enough fluid.
- Hypotony – low eye pressure.
- Suprachoroidal Hemorrhage – rupture of an artery inside the eye.
- Cataract Formation – the eye surgery can cause a cataract to develop much faster.
- Choroidal Detachment – fluid expands in the choroid under the retina usually due to low eye pressure.
- Bleeding – hemorrhage in the anterior chamber which usually resolves on its own.
- Corneal Edema – If the tube is placed too close to the cornea, the cornea will become swollen with loss of vision.
- Hypertensive Episode – The eye pressure may dramatically increase after surgery between 1 to 6 weeks after the surgery. This is more common in valve shunts.
- Valve Malfunction – rare. It is important to prime the shunt at the time of surgery to prevent this complication.
- Scleral Perforation – Sclera too thin.
- Tube-Related Problems – If the tube is place too close to the cornea, it will cause the cornea to decompensate resulting in corneal edema. If the tube is placed too close to the iris, it will cause inflammation by rubbing on the iris. The tube can be plugged with blood, fibrin, iris, or vitreous.
- Tube Erosion – The tube can erode through the conjunctiva over the shunt either early or over time. This needs to be repaired very quickly to prevent any infection. A new patch graft needs to be placed to protect the eye.
- Tube Movement – The reservoir and tube may move and be expulsed.
- Strabismus – The eye muscles that move the eye can be altered by the placement of the shunt.
Shunt Results
The success rate for both types of shunt procedures in around 90%.
Which Glaucoma Procedure?
There are two camps in the United States where a portion of eye surgeons prefer a trabeculectomy as their primary surgical procedure for glaucoma and another group of eye surgeons prefer a shunt procedure as their primary surgical procedure for glaucoma. The type of glaucoma surgery that is best for you is based on many factors such as type of glaucoma, level of eye pressure after the surgery, condition of the conjunctiva, and eye surgeon preference.
JAMES E. CROLEY III, M.D.
Dr. James E. Croley III is a board-certified ophthalmologist and the founder of the Cataract & Refractive Institute of Florida. He graduated magna cum laude from Cumberland College before attending medical school at the University of Miami and completing his residency at the University of Alabama Eye Foundation Hospital. Additionally, he studied at Stanford University where he gained further education in advanced ophthalmology techniques. Dr. Croley is a member of the American Academy of Ophthalmology and the Florida Society of Ophthalmology.