Trabeculectomies, What's New?
Chat Highlights
July 2, 2003

Norma Devine, Editor

On Wednesday, July 2, 2003, Dr. Rick Wilson, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Trabeculectomies, What's New?."

Moderator:  Good evening, Doctor Wilson.  For the benefit of newcomers tonight, please start by explaining what filtering surgery (trabeculectomy) is.  

Dr. Rick Wilson:  Newcomers should look at the graphic on our web site.  A trabeculectomy (trab) is essentially a small hole made in the wall of the eye.  A flap of sclera (the white outer coat of the eye) is sewn loosely over the hole, so that the fluid from the eye seeps slowly out under the clear conjunctiva covering of the eye.  That creates a bulge, or bleb, over the hole and flap.

Moderator:  The web site is:  http://www.willsglaucoma.org/trab.htm. It includes a photo of a bleb.

P:  What are 5-FU and mitomycin C (MMC), which are used during and after the surgery, and what are their advantages and disadvantages?   

Dr. Rick Wilson:  Mitomycin is 100 times more powerful than 5-FU. Therefore, it can be applied at the time of surgery and no further applications are needed.  5-FU is short-acting, needs to be applied at the time of surgery, and is augmented with shots over the subsequent two to three weeks.  The advantage of the 5-FU is that its effect can be modulated better just by adjusting the number of shots after surgery.  Few people, however, enjoy the shots, and there can be corneal side effects, corneal erosions, and discomfort from the medications. 

P:  What is Cat-152?  Does it prevent scarring? 

Dr. Rick Wilson:  Cat-152 (Cambridge Antibody Technology) is a human anti-TGF, beta 2m, monoclonal antibody, which is supposed to neutralize the active transforming growth factor (TGF) and decrease fibrosis (scarring).  The advantage of CAT-152 is that it would be less likely to cause the thin, white blebs so common with mitomycin.

P:  Is 5-FU, fluorouracil, the old cancer drug? 

Dr. Rick Wilson:  Yes.  Cancer drugs like 5-FU keep the most rapidly dividing cells from dividing.  In patients with cancer, the cancer cells are the ones dividing the most rapidly.  In patients with fresh wounds, the scarring cells are the ones dividing rapidly.

P:  Are there any more improvements in trabs or any expected? 

Dr. Rick Wilson:  I think that the operation, after remaining stagnant since laserable and releasable sutures were invented in the early 80's and 5-FU came along, is now starting to be more refined.  The movement from a suture line in the conjunctiva to one where the conjunctiva meets the cornea results in wider, more diffuse, less elevated blebs.  The blebs are less likely to leak and get infected.

P:  Does thickness of the cornea play a role in the decision of whether to use MMC, CAT-152, or 5-FU?

Dr. Rick Wilson:  Only when the thickness affects the pressure reading, and pushes the surgeon toward or away from surgery.

P:  Do you know what the long-term effects of CAT-152 are?  

Dr. Rick Wilson:  It's too soon to tell.  Large-scale human investigation has just begun.

P:  What indicates the use of MMC or 5-FU?

Dr. Rick Wilson:  Their use is indicated in patients who have already had a failed trabeculectomy, or in those with adverse risk factors, such as inflammation or ICE (iridio-corneal endothelium) syndrome, or in those that need a very low IOP.

P:  Which one -- 5-FU, MMC, or CAT-152 -- is least likely to cause a leaking bleb?  

Dr. Rick Wilson:  Cat-152 would, theoretically, be least likely to cause leaking, followed by 5-FU, then MMC.

P:  What are the drawbacks of using MMC? 

Dr. Rick Wilson:  There is an increased chance of success, but also an increased risk of attaining too low an IOP, or having so thin a bleb that a late leak or infection can occur.

P:  I assume the shots are in the eye.  Isn't that painful?

Dr. Rick Wilson:  The shots are under the conjunctiva, which is easy to anesthetize.  The patient feels only a slight burning sensation.

Moderator:  Are patients' fear of trabs justified?

Dr. Rick Wilson:  Most patients, when presented with the information  I give them (which is  also available on the website and must be provided for the benefit of lawyers), think the surgery must be worse than the treatment they are currently receiving.  Usually, however, the surgery is not suggested unless the doctor can see progressive loss.  The loss usually is undetected by the patient.  Therefore, the risk of the surgery constitutes a small, but acute, risk, compared to a nearly 100% long-term risk without surgical control of IOP (intraocular pressure).

P:  I have ICE syndrome and had a trabeculectomy with MMC last year.  I have a cataract and will need surgery sometime in the future. My doctor says he will use MMC again for that surgery.  Will the surgical site be in the same place as the surgically created bleb?  How great is the risk of the trab failing as a result of cataract  surgery?

Dr. Rick Wilson:  Usually, the incision will not be in the same place as the first trab, if a second trab is performed at the same time as the cataract surgery.  If a second trab is not performed, the risk of having to repeat the trabeculectomy is about 5 to 10%, but the chance of having to be back on some medication is about 40%.  Those are general figures, and your doctor may do better or worse than that.

P:  If a bleb leaks too much, how is that fixed?

Dr. Rick Wilson:  Sometimes just injecting some of the patient's blood into the bleb will block up the hole and thicken the bleb enough to increase the intraocular pressure (IOP) 2 to 4 mm Hg.  If that doesn't work, a patch of conjunctiva can be taken from below the cornea and transplanted over the bleb.

P:  When MMC is used, would a leaky bleb be caused by the thinness of the bleb, or by the tightness of the stitches?

Dr. Rick Wilson:  The pressure of the fluid coming out of the eye is often concentrated over the bleb, thinning it, like when you blow bubbles with bubble gum.  Such thinning may take years.

P:  What is so bad about filtering surgery that glaucoma patients are first treated, sometimes for decades, with drops that cause problems and aggravation?  

Dr. Rick Wilson:  In the United Kingdom they operate much earlier than we do.  It may have to do with the national health system, where the cost to the patient is not as big a deal.  We have evolved to use drops first.  With the advent of prostaglandins, people now do seem to do as well with drops as with surgery, on the basis of comfort and visual fields.  That was shown in the Collaborative Initial Glaucoma Treatment Study (CIGTS).  

P:  I had a trabeculectomy during an acute-angle attack. Scar tissue has closed off the drain. My doctor says I have 70% damage to my optic nerve.  My IOP is still in the 20s.  I need more surgery to reduce the pressure to the low teens.   Can a revision be done instead of another trabeculectomy?

Dr. Rick Wilson:  Revisions are tough to do and unpredictable, unless you have some bleb to needle.  A new trab at an adjacent site is more predictable and more likely to work.

P:  My mom's doctor has recommended that she have combined cataract and glaucoma surgery.  Her optic nerve is badly damaged and she is almost legally blind.  From your web site, I learned what cataract surgery entails, but I don't know what the doctor means by glaucoma surgery. He said he didn't know what's behind the cataract, but the combined surgery might improve her vision.  Do you think a combined glaucoma and cataract surgery would help?  

Dr. Rick Wilson:  The glaucoma surgery is almost certainly a trab if he is a glaucoma specialist.  If it isn't a trab, I would get a second opinion from a glaucoma specialist.  If you mom can see bright colors and identify them correctly through the cataract, and has central vision -- even if only a small island -- she will often see better after the cataract extraction in the small areas she can still see through.

P:  How many trabs are possible in the same eye?  

Dr. Rick Wilson:  Usually three, occasionally four.  

P:  In your experience, what is the lifetime of a bleb?  What is the lifetime of a bleb that has already had a patch?

Dr. Rick Wilson:  It used to be said that trabs lasted seven years on average.  I think we are doing better than that now, but I can't say by how much, as it is a continually moving target.  Having a patch cuts down the lifetime of the bleb in many cases, but not all.

P:  My doctor at the Yale Eye Center says you are an extraordinary doctor.  I have been helped so much by these chats and your candid discussions. Thank you so much!  

Dr. Rick Wilson:  You are quite welcome.  Goodnight.

End of highlights for July 2, 2003.

On July 9, Dr. Wilson discussed "Ocular Diseases and Glaucoma" in the Chat room. Click here for highlights of that meeting.

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