Chat Highlights
When a Trabeculectomy Fails
April 4, 2001

Norma Devine, Editor

On Wednesday, April 4, 2001, Dr. Rick Wilson, a glaucoma specialist at Wills, and the glaucoma chat group discussed "When a Trabeculectomy Fails." 

Moderator:  Welcome, Dr. Rick. The topic tonight is "When a Trabeculectomy Fails."

Dr. Wilson:  Hello, gang.  

P:  Doctor Rick, what are some of the factors that cause failed trabs (trabeculectomies)?

Dr. Wilson:  Young age, inflammation, chronic use of medications, dark skin, and dark iris. 

P:  Is the chronic use of medications a factor, because the pupil becomes permanently tiny?

Dr. Wilson:  No, it's because of the effect of a low-grade chronic inflammation upon the conjunctiva, the clear covering of the eyeball.

P:   Where do Asians fall in the category of skin color?    

Dr. Wilson:  Asians are more toward the Caucasian end, which is not as far, but further than Hispanic, which is not as far as African.   

P:  How about American Indian?

Dr. Wilson:  Close to Asian.  

P:  Is it possible for a trab to last 30 or 40 years?

Dr. Wilson:  Yes, though it is not all that common.

P:  If you have a trab when you're older, is it more likely to last longer? 

Dr. Wilson:  Yes, the older the better. 

P:  I am 55.  Is that considered old or young?

Dr. Wilson:  That's relatively young.  

P:  What are the symptoms of a failing trab? 

Dr. Wilson:  The symptoms are an elevating IOP (intraocular pressure ) and a flattening bleb.

Moderator:  Does a trab usually fail soon after it is performed or much later? 

Dr. Wilson:  There is a higher incidence of failure during the first months, which decreases gradually, but never completely disappears.

P:  How long do trabs last, on average? How many times can a patient have a trab before moving to a shunt? 

Dr. Wilson:  The average trab lasts seven years or longer. There is room for three trabs, usually on the top of the eyeball.  

Moderator:  When the IOP rises and the bleb flattens, what do you do? 

Dr. Wilson:  I usually add medications again in an effort to control the IOP.  If that fails, then I perform another trab.  

P:  How often do trabs fail?   

Dr. Wilson:  Good question.  I would think the failure rate in good hands would be 10% or so at one year, with about 40% requiring medications for the IOP to be controlled. 

P:  My doctor told me he didn't think he could do another trab on me because my trab was done right in the middle of the top of my eye . Why do you think it was done that way?  

Dr. Wilson:  If the trab is done at the 12 o'clock position, then there should be room at the 2 o'clock and 10 o'clock positions for two more trabs, if there is not too much scarring from the first procedure.

P:  Does a cataract operation hasten the failure of a trab?  

Dr. Wilson:  Yes.  When the body tries to heal the cataract wound, the trabeculectomy is caught in the process and often heals some or, occasionally, even all the way.

P:  If a glaucoma patient needs both a trab and cataract surgery, would it be better to do separate operations?

Dr. Wilson:  That depends upon several factors.  

P:  When a patient needs a trab, cataract surgery and a cornea transplant, why wouldn't the doctor do the trab after the other two operations?  

Dr. Wilson:  If the glaucoma surgery is not in place or is being done at the same time, the other surgery may cause a great elevation in IOP.   I usually try to do everything at once, but others do it differently.

P:  I've just had a cataract operation and the doctor  recommended a flexible lens be used so as not to interfere with a trab, if one is required.  If a trab can be done at different areas of the eye, why use a foldable lens? 

Dr. Wilson:  A foldable lens is now used in almost all cataract surgeries performed in the United States.  Performing the cataract surgery temporally (toward the temple) would be best for glaucoma surgery later performed superiorly (at the top) on the eye. 

P:  What does "best for glaucoma surgery later performed superiorly on the eye" mean?

Dr. Wilson:  "Best" means the surgery leaves the superior conjunctiva untouched for glaucoma surgery later.

P:  Is it preferable to combine cataract surgery with a trabeculectomy because of the healing aspect?

Dr. Wilson:  Yes.  If you do the cataract surgery first, the glaucoma may become uncontrolled. If you do the trab first, the later cataract surgery may adversely affect the success of the trab.

P:  Doesn't the risk increase if cataract surgery is done at the same time as a trab?

Dr. Wilson:  Yes, but it is no different than the additive risks of  two surgeries.

P:  I had a trab and cataract surgery at the same time.  Four months later I had a detached retina.  Would the surgery have caused the detached retina? 

Dr. Wilson:  There is about a one-half percent chance of a retinal detachment anytime after a cataract operation, with or without glaucoma surgery.

P:  How long after?

Dr. Wilson:  Within a year.

P:  After a patient has had three trabs, what comes next?  

Dr. Wilson:  A shunt or a bleb revision.

P:  What is a bleb revision? How does that differ from a trab?

Dr. Wilson:  Revising a bleb means taking a poorly working trabeculectomy bleb and opening it up to work better, usually with the use of 5-FU shots or mitomycin C to retard scarring.

Moderator:   Is that called "needling the bleb?"  

Dr. Wilson:  Yes.

P:  What are the chances of a trab working on teens? Is a trab or laser the best way?  

Dr. Wilson:  Laser trabeculoplasty does not work in teens.  A trabeculectomy with mitomycin C stands a reasonably good chance of working.

P:   Why wouldn't a laser trabeculoplasty work on teens? My doctor mentioned something about healing too fast.  Is that correct?

Dr. Wilson:  No.  We don't understand how laser trabs work,  but the underlying disease process does not seem to be helped by the laser and may cause a huge IOP spike after surgery.

P:  Do you use mitomycin C in the first trab in teenagers? 

Dr. Wilson:  I use it in the first trab, but cautiously.

P:  I thought that whether or not laser would work depended on the presence of pigment in the meshwork. 

Dr. Wilson:  One needs (1) pigment, (2) the right diagnosis, such as open-angle glaucoma, pigmentary glaucoma, pseudoexfoliation or normal-tension glaucoma, (3) age, the older the better and (4) an open angle.

P:  I read in a Taiwan newspaper about a laser procedure being used there.  "Cancer-killing chemicals" are placed around the holes made by the laser. The success rate is somewhere around 80%.  Have you heard of it?  Has it been used in the U.S.?  

Dr. Wilson:  That sounds like an ab interno sclerostomy. I performed the first one in the world on a human patient years ago.  But the surgery turned out to be no better than a trabeculectomy and fell out of favor.  However, the procedure you read about could be something different.  If it is, I don't know about it.

P:  Does removing deep stitches due to IOP rising fairly soon after surgery increase the chance of failure in the first year, or is that immaterial once healing has occurred?

Dr. Wilson:  It's immaterial.

P:  Since glaucoma causes nerve damage, can that lead to Alzheimer's disease?

Dr. Wilson:  No, glaucoma damage involves only the optic nerve.   

P:  After a trabeculectomy, will the eye and the eyelid ever feel as normal as before the surgery? 

Dr. Wilson:  Probably not, if the trab is working well, although it may not be uncomfortable.

On April 11, Dr. Schmidt discussed "Antifibrosis Agents" in the Chat room. Click here for highlights of that meeting.

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