Trabeculectomy
Chat Highlights
August 10, 2005

On Wednesday, August 10, 2005, Dr. Rick Wilson a glaucoma specialist at Wills, and the glaucoma chat group discussed "Trabeculectomy."

Moderator:  Welcome back to chat, Dr. Wilson.  We have several newcomers with us.  The topic tonight is "Trabeculectomy" (trab).  By the way, that's the term most searched for on our site.

Dr. Rick Wilson:  A trabeculectomy is a surgically created flap valve in the wall of the eye that allows fluid to leave the eye at a normal rate.  It is basically a hole in the wall of the eye, with a flap of the patient's sclera (the white part of the wall) sewn loosely over the hole to slow down the exit of aqueous.  A piece of iris is often removed beneath the hole to prevent the iris from getting caught in the hole.

P:  What is the difference in the meaning of the suffixes "ectomy" and "plasty?"

Dr. Rick Wilson:  "Ectomy" (as in "trabeculectomy") signifies removal of tissue; "plasty" (as in "trabeculoplasty") signifies a change made to tissue.

Moderator:  How does a trabeculoplasty change tissue?

Dr. Rick Wilson:  An argon laser trabeculoplasty (ALT) seems to burn the trabecular meshwork, stimulating the remaining live cells to divide.  The new cells are much more effective at removing the debris that builds up in the TM (trabeculr meshwork) than the original cells were.

P:  I'm confused.  Is the iris in front of the sclera or under it?

Dr. Rick Wilson:  The iris makes up the pupil.  It is inside the eye and forms the back wall of the anterior chamber of the eye.  On the side of the iris away from the pupil, the iris attaches to the inside of the sclera just behind the junction of the sclera and the clear cornea.

P:  If a trab fails after several years and there is scar tissue, would if be possible to do another trab in the same spot?

Dr. Rick Wilson:  It is possible, but quite difficult, and the results are much more unpredictable than a new trab just adjacent to the old one.

P:  Typically, about how many trabs a year would an ophthalmologist perform?

Dr. Rick Wilson:  By my third year in practice as a glaucoma specialist, I did 350 trabeculectomies by themselves, and more combined with cataract surgery.  A general ophthalmologist might do fewer than 10 trabeculectomies in a year.

P:  After my recent trab, my intraocular presssure (IOP) dropped to 1 mm Hg.  After a week, it increased 9 mm Hg, and has stayed there for about eight weeks.  I lost some vision.  Did the drop in IOP cause that?  If I must have a trab in the fellow eye, will I be likely to have a similar problem?

Dr. Rick Wilson:  Often the abnormally low IOP and the diversion of a good deal of aqueous out of the eye before it has a chance to impart oxygen and nutrients to the lens in the eye leads to an increase in the opacity of an cataract, if one is present.  Often, if that happened in one eye, it tends to happen in the other.  On the other hand, if the period of too low an IOP is avoided, perhaps there won't be a change in vision.  My average is a decrease of about a half line of vision one year after surgery.  That decrease is generally returned after cataract extraction.

P:  One of our group, who lives in the Canadian Maritimes, has been having a problem with a leaking bleb.  There's not enough good tissue remaining in the eye for any further surgery.  The contact lens didn't stop the leak.  The other day he had an autologous blood injection.  About how long will he have to wait to find out if that has stopped the leak?

Dr. Rick Wilson:  I would think it would take 10 to 20 days to make sure.

Moderator:  What is the success rates for trabs?  Does age make a difference?

Dr. Rick Wilson:  The success rate varies, depending upon the number of risk factors present.  In an elderly Caucasian patient without inflammation or previous surgery, the success rate should be about 95% IOP control, with or without medication.  Dark eyes --especially with dark skin --, previous trauma or surgery, present inflammation, and young age are risk factors for trabeculectomy failure.

P:  When do you use anti-scarring drugs during a trab?

Dr. Rick Wilson:  Most glaucoma specialists use them on almost everyone.  In older white patients who do not need too much of a drop in IOP, I use a soak of 5-FU.  In everyone else, I use a mitomycin soak for 30 seconds to 4 minutes.

P:  How many trabs can be done on an eye?

Dr. Rick Wilson:  Usually, three good trabs can be done.

P:  Doesn't removing a cataract often adversely affect a trabeculectomy?

Dr. Rick Wilson:  Less than it once did, since cataract surgery has become much less invasive, with a small wound.  Still, a cataract operation with a working trab in place is worrisome because there will be some postoperative healing of the trab.

P:  My daughter has had trabs twice.  Her IOP continues to increase.  What treatment could be tried next?

Dr. Rick Wilson:  If medicine no longer controls her IOP, and the last trab was done by a glaucoma specialist with mitomycin and still failed, then an aqueous shunt probably would be needed.

P:  Will a shunt cause her to lose more vision?

Dr. Rick Wilson:  There are risks with all surgery.  The shunt is slightly more risky than the trab, but at her age probably will not cause any vision loss.

P:  My three-year-old trab is fragile, but still working.  It is opaque, but transparent in the center.  What causes a trab to become opaque?

Dr. Rick Wilson:  Fibrosis or scar tissue.  A normal trab should not be clear and transparent, but slightly white and cloudy.  The thinning of the conjunctiva from the constant pressure of the aqueous under it does thin the conjunctiva and leave it clear.

P:  Do you consider trabeculectomy a last option after medication or an alternative to medication?

Dr. Rick Wilson:  In America we usually consider it after medicines and laser have failed.

P:  After a patient has a shunt and the shunt fails, is having a second trab even a possibility?

Dr. Rick Wilson:  Yes, I have done three of them and they worked out fairly well.  If, however, only one plate was put in with the first shunt, then another plate (shunt) can be added in the opposite upper quadrant.

P:  What is a diffuse bleb? I am staying at target pressures, but apparently the bleb is not working as well as before.

Dr. Rick Wilson:  That means the conjunctiva is mildly or moderately elevated off the sclera over a large area of the eye.  Sometimes failing blebs can be treated with a needle or blade revision.  That is surgery, but as an outpatient and with minimal outpatient visits.

P:  I have keratoconus and must wear gas permeable contact lenses.  I've heard that gas perms and trabs are not a good mix because of the risk of infection.  If I don't wear the lenses, I can't see clearly.  If I need a trab, am I just out of luck as far as ever seeing clearly again?

Dr. Rick Wilson:  An aqueous shunt offers no problems with contact lens wear.  If you have to have a trab, then your surgeon should base his conjunctival flap far up under the lid and spread the mitomycin around over a large area to get a diffuse bleb.

P:  Is it feasible to remove an epiretinal membrane and a cataract in a combined surgery after a trab?  If not, in what order should they be done?

Dr. Rick Wilson:  It is feasible and probably easier for the patient.

P:  What results can be expected from a trabeculoplasty?

Dr. Rick Wilson:  The expected decrease in IOP with both argon and selective laser trabeculoplasty is between 25 to 35 percent for patients over 60 years of age with good pigment in their trabecular meshwork, an open angle and the diagnosis of pseudoexfoliative glaucoma, pigmentary glaucoma, primary open-angle glaucoma or normal-tension glaucoma.

P:  Is a cataract inevitable after a trabeculectomy?

Dr. Rick Wilson:  If you do not have a cataract, an uncomplicated trab will not give you one.  If you have a cataract, it will progress at a faster rate.

Moderator:  Thank you, Dr. Rick Wilson.  We look forward to seeing you here in two weeks.

On August 17, Dr. Henderer discussed "Genes" in the Chat room. Click here for highlights of that meeting.

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