Trabeculectomy
Chat Highlights
November 1, 2006

On Wednesday, November 1, 2006, Dr. Rick Wilson, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Trabeculectomy."

Moderator:   Welcome back to chat, Dr. Wilson. Before we start to discuss the topic, “Trabeculectomy,” please tell us how your recovery from knee-replacement surgery is going.

Dr. Rick Wilson:  My knees are doing quite well. I walked around my block twice today.  My ankles and right hip didn't like it all that much, but I'm much more mobile than I was before surgery, with less pain.  Thanks for asking.

Moderator:  That’s good to hear. Many patients have been asking about your progress. If you’re ready, please begin by describing a trabeculectomy.

Dr. Rick Wilson:  A trabeculectomy is a small hole made through the wall of the eye underneath a flap of sclera, the tough white coat of the eye.  The flap is loosely sewn down to allow the flow of fluid to seep out slowly, with resistance. The fluid that passes through the hole is captured underneath the conjunctiva, the clear outer layer of the eye, which is carefully sewn back together in a water-tight fashion.

P:   The word “trabeculectomy” is often abbreviated as “trab”, but “trab” can mean “trabeculoplasty,” “trabeculotomy,” or “trabeculectomy.”  How do those procedures differ?

Dr. Rick Wilson:  A trabeculoplasty, in which a laser is used, changes the shape of the trabecular meshwork (TM).

A trabeculotomy opens the inner wall of Schlemm's canal (the channel that takes fluid from the eye after it passes through the trabecular meshwork into the eye) by creating an opening in the TM. That reduces resistance to fluid leaving the eye.  A trabeculotomy is usually used in children under the ages of one-and-a half years.

In a trabeculectomy, the trabecular meshwork is removed by making the hole through the eye wall, with a scleral flap over it.  Nowadays, the trabecular meshwork is often not removed when the hole is made, but it is still called a trabeculectomy.

P:  Thank you! For years I've been trying to get an answer to why it's called an "ectomy", when nothing is removed (as in an appendectomy or a tonsillectomy).

Dr. Rick Wilson:  A piece of sclera is still removed to make a hole the fluid goes through, but the piece may not contain any trabecular meshwork.

P:  What is the success rate for a trabeculectomy?

Dr. Rick Wilson:  The success rate for a trabeculectomy in a patient over 70 years of age, who is white and has no inflammation or previous surgery, should be 60 to 70% without the addition of medications, and over 90% IOP (intraocular pressure) control with the addition of medications.

If the patient is younger, has very dark skin, is African-American, or has intraocular inflammation, the success rate decreases.

P:  Can anything be done to improve the success rate of trabeculectomies?

Dr. Rick Wilson:  Many things have been tried over the years, but the main agents that work are topical steroids, 5-FU, and mitomycin.  The steroids slow down healing and scarring.  The 5-FU more drastically slows down healing and scarring.  Mitomycin either inhibits the cells that cause scarring or kills them, depending upon the dosage.

P:  When and how are 5-FU and mitomycin used?

Dr. Rick Wilson:  Mitomycin and 5-FU are placed on an absorbent pledget (a small pad) and positioned where the trabeculectomy will be performed.  The pledget is left in place for a variable amount of time and then removed. If the effect is not enough, 5-FU shots can be given in the post-operative period, but more mitomycin is not applied.

P:  Can a trabeculectomy be performed on an eye that has a shunt in it?

Dr. Rick Wilson:  Yes, but there has to be enough conjunctiva that can be elevated off the sclera to form a pocket for the fluid to drain into once it passes through the sclera.

P:  Will the shunt tube obstruct use of the trabeculectomy instrument?

Dr. Rick Wilson:  Many patients who have had shunts have extensive conjunctival scarring that may prevent the performance of a trabeculectomy.

P:  Is bleeding from a trabeculectomy likely to plug a shunt?

Dr. Rick Wilson:  A trabeculectomy would have to be made in a different quadrant of the eye than where the shunt tube was placed.  Bleeding can block the tube, but usually this is only for the short term.

P:  If cataract surgery and a trabeculectomy are combined, are the risks increased?  Should they be combined?

Dr. Rick Wilson:  A complication of trabeculectomy, hypotony (too low an intraocular pressure), is much less common when both procedures are combined.  The procedure for trabeculectomy is not much affected by the addition of cataract surgery.  Since cataract surgery has become almost minimally invasive, fewer cataract and glaucoma procedures are being done at the same time.  The usual indications for doing both at once are too high an IOP in an eye with a visually significant cataract, or a patient on multiple medications with significant glaucoma damage who needs a cataract extraction.

P:  What can be done to save a trabeculectomy that has scarred over even with the use of mitomycin C?

Dr. Rick Wilson:  A needle or tiny knife can be inserted between the sclera and the conjunctiva to try to remake the pocket for the fluid to drain into.  Mitomycin or 5-FU can be injected into that pocket to try to keep it from scarring back down.

P:  I've been told that 5-fluorouacil doesn't really work, and it can cause other eye damage (especially for smokers).  Can you comment?

Dr. Rick Wilson:  Mitomycin is 100 times more powerful than 5-FU, so 5-FU does not work in all cases. 5-FU, if used on multiple occasions, can cause usually temporary corneal erosions (very similar to abrasions without the trauma).

P:  How can a patient keep from sneezing and hiccupping for weeks after surgery?

Moderator:  When I feel a sneeze coming on, I press and hold the area above my upper lip, just under my nose, to stop the sneeze.

P:  My questions concerns the Trabectome.  Can Trabectome surgery be performed on an eye that has a shunt?  Will the shunt tube obstruct use of the Trabectome instrument?  Is bleeding from the Trabectome surgery likely to plug the shunt?

Dr. Rick Wilson:  The Trabectome is a unit that makes a trabeculotomy from the inside instead of from the outside.  The more problems an eye has, it seems the less likely a Trabectome is going to work.  The Trabectome surgery can be done in an eye with a shunt, but not right where the tube is located. It is unlikely that blood will block up the tube for long. The problem is that if the eye needed a shunt in the first place, it may have too severe a problem for the Trabectome to be as effective as needed.  The results, however, are variable, so -- depending upon circumstances -- it may be prudent to try the Trabectome, as it has been an extremely safe procedure.

P:  Does a trabeculectomy eliminate the need for eyedrop medication? If so, for how long?

Dr. Rick Wilson:  It used to be said that 50% of trabeculectomy patients did not need drops for a year or more, and the IOP was controlled, on average, for seven years.  Another 40 to 45 % of patients could be controlled on eyedrops after a trabeculectomy when they weren't before. Now, with the use of 5-FU and mitomycin, the success rate is higher and the duration of success is longer.

P:  I had successful trabeculectomies 10 and 13 years ago.  These past years few years, however, my peripheral vision has deteriorated quickly for no apparent reason.  Doctors have been baffled, as the pressures have been stable and constantly under control.  Could you shed any light on that?  I have tried alternatives, such as blood circulation therapy with some success.

Dr. Rick Wilson:  Each patient has an individual level of IOP control.  If you have serious nerve damage, your IOP may well need to be below 12 mm Hg, and for advanced damage in the single digits, to be "under control".  If you are losing vision, you are obviously not under control.  What has your IOP been during this period?

P:  That is the strange thing, as my pressures have been below 15 mm Hg and usually below 12 mm Hg. I also have a home pressure monitor.

Dr. Rick Wilson:  A study out of Bascom Palmer years ago showed that a group of post-operative patients with IOPs that averaged 15 mm Hg had 50% of the patients progress over five years.  As a general rule, if you are getting worse with IOPs between 12 and 15 mm Hg, you need an IOP in the 8 to 10 mm Hg range.  It could be that your IOP is fluctuating much higher on awakening and no one knows, or your blood pressure is dropping too low at night to give your optic nerves adequate blood flow.  For the most part, however, if a patient is getting worse at some IOP, we try to drop it by 35% more.

P:  I have heard that some doctors who did not have success with mitomycin or 5-FU are trying Avastin (bevacizumab) to prevent scarring and keep trabs open.  Do you know anything about the use of Avastin in treating glaucoma?

Dr. Rick Wilson:  It has worked at least for a short term in patients with neovascular glaucoma.  We are developing a study at Wills to study it, so I can't give you any first-hand information.

P:  You mentioned that inflammation is not good for surgery.  My eyes are always bloodshot from meds.  Are my eyes inflamed?

Dr. Rick Wilson:  The surface of the eye is inflamed and your vessels are probably dilated from the use of a prostaglandin like Lumigan, Travatan, or Xalatan.  That does decrease the success of surgery to some extent.  Mitomycin is usually able to overcome the problem of mild inflammation from the use of glaucoma drops and deliver adequate IOPs with surgery that was done well.

P:  When medication is failing to lower pressure in normal-tension glaucoma to the single digits and vision is continuing to deteriorate, are SLT or ALT a good alternative to a trabeculectomy?

Dr. Rick Wilson:  Yes, if you are over 60 years old, have a significant amount of pigment in your trabecular meshwork to absorb the energy of the laser, and have an open angle to get the laser energy to the trabecular meshwork.

Moderator: Thank you, Dr. Wilson.  Goodnight from all of us.

Dr. Rick Wilson:  Good night, everyone.

On November 15, Dr. Wilson discussed "Shunts" in the Chat room. Click here for highlights of that meeting.

Click here for the most recent glaucoma chat highlights and links to the chat archives.

Click here for upcoming glaucoma chat events.