Shunt Surgery
Chat Highlights
July 10, 2002

Norma Devine, Editor

On Wednesday, July 10, 2002, Dr. Rick Wilson, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Shunt Surgery."

Moderator:  Welcome, Dr. Rick. Our topic tonight is "Shunt Surgery." Please tell us what a shunt is and what it does.

Dr. Rick Wilson:  It is a plastic tube that shunts fluid from the inside of the eye to a plate that keeps the body's tissues from scarring around the end of the tube and closing it off.  The size of the plate is roughly proportional to the amount of fluid that will be absorbed into the surrounding tissue once the shunt hits a steady state.

P:  How often does hypotony (too low an IOP) occur after shunt surgery?  One doctor told me that the eye would “deflate like a basketball.”  That sounded horrible to me, like I might lose the eye.  But patients who have had shunt surgery tell me that hypotony sometimes occurs after surgery, but then the intraocular pressure (IOP) goes back up.  What permanent damage does hypotony do?

Dr. Rick Wilson:  Hypotony is unusual with shunt surgery in healthy eyes that have normal aqueous production. The usual problem is too high an IOP, which requires medication for control.

P:  Which patients are at more risk for developing hypotony?

Dr. Rick Wilson:  Patients with chronic inflammation in the eye, and patients with diabetes that can cut down on the blood supply and the amount of aqueous the eye makes are two types of patients that might end up with too low an IOP.  The other common cause is patients that have had laser cyclo-destruction of the ciliary body to reduce IOP.

P:  Would hypotony after a trab predispose a patient to hypotony after shunt surgery?

Dr. Rick Wilson:  Unless you fall into one of the three categories I mentioned, hypotony is much less common with a shunt.

P:  Are shunts all the same size?

Dr. Rick Wilson:  The shunts are usually one-size-fits-all, so some may drain too much for some patients and not enough for others.

P:  Can shunt surgery be performed after trabeculectomies?

Dr. Rick Wilson:  Yes, and it usually is.

P:  Is shunt surgery ever combined with other surgery, such as cataract surgery?

Dr. Rick Wilson:  It can be, but that is a rare operation. Shunt surgery would more likely be combined with a retinal procedure or a corneal graft.

P:  Of the six available implants -- Ahmed, Baerveldt, Molteno, Krupin-Denver, Schocket, glaucoma pressure regulator -- which are currently the most popular?

Dr. Rick Wilson:  The Baerveldt is probably the most popular among glaucoma specialists.  The Ahmed is the easiest to implant, so is more popular among surgeons who have less experience dealing with the common problems following glaucoma surgery.  The Molteno has the longest track record, and no shunt has ever been found to give better results.  It requires surgery in both superior quadrants, which takes longer.  That is probably why the other two, Ahmed and Baerveldt, have gained such popularity.

P:  What are the risks of shunt surgery?

Dr. Rick Wilson:  The main risk is the drop in IOP that accompanies the Ahmed after it is implanted.  The Ahmed has a valve that is variably successful in preventing hypotony.  The other shunts (except for the Krupin, which is rarely used anymore) do not have a valve; the surgeon uses a dissolvable suture to tie off the tube leading from the eye.  The shunt doesn't really work until three to five weeks after surgery, when the suture dissolves.  By then, scar tissue has built up around the reservoir of the shunt, so hypotony should only be a short-term problem.

P:  How long do shunts last?

Dr. Rick Wilson:  Shunts are like trabeculectomies. The success rate gradually decreases with time.

P:  Why would a vitrectomy be done during shunt surgery?  If a water-type fluid replaces the vitreous jelly, why doesn't the shunt drain out that fluid?

Dr. Rick Wilson:  The vitrectomy removes vitreous, the jelly-like substance you mention, if it is in a position where it could block the shunt tube.  Usually this is done in patients who have had the lens in an eye removed without having an intraocular lens inserted.  An intraocular lens would block the vitreous, which is located in the back of the eye, from getting to the front, where the tube is usually located.

P:  How does a doctor decide which kind of shunt to use, and are all shunts the same?

Dr. Rick Wilson:  No, they are not the same; in fact, they are quite different.  Usually, doctors choose the shunt they are most comfortable with because of training or experience with it.  The Molteno is a good choice in patients with iritis, because the second plate can be tied off or removed if hypotony develops.

P:  How does the success of the laser cyclo-destructive procedure of the ciliary body compare with shunt surgery?

Dr. Rick Wilson:  The laser cyclo-destructive procedure at Wills (cyclophotocoagulation) has about a five percent chance of ending up with too low an IOP and reduced vision.  It causes a lot of inflammation and is usually used if surgery that could help the fluid leave the eye has failed or the eye has too little vision to justify cutting surgery.  The shunt is usually a safer surgery. (See: Nd: YAG Cyclophotocoagulation for Difficult Glaucoma, http://www.willsglaucoma.org/yag.htm).

P:  Why would shunt surgery be performed instead of filtering surgery?

Dr. Rick Wilson:  Usually because the conjunctiva has too much scarring to establish a bleb where the aqueous goes to be absorbed.  However, a shunt, rather than a trabeculectomy, could be the first procedure in cases like neovascular and severe inflammatory glaucoma.

P:  How well do shunts compare with a second trab after cataract surgery?  Which is preferable?  I have had a trab in each eye and a trab revision and mitomycin and 4-FU, so my cornea may not be in good shape.

Dr. Rick Wilson:  If you may need a cornea graft in the future, a trabeculectomy may not give as good a result as a shunt as far as IOP is concerned, but it has a lower rate of graft rejection.  For that reason, I do a trabeculectomy in patients who have or may need a corneal graft.

P:  How long do shunts last?

Dr. Rick Wilson:  I have shunts that have been working for 18 years and others that have failed quite promptly, so it is not a question I can answer readily.

P:  If a shunt fails, what, if anything, can be done?

Dr. Rick Wilson:  The shunt can be revised, another plate (shunt) can be added, or laser cyclophotocoagulation can be performed.

P:  How many shunts can one eye safely hold?

Dr. Rick Wilson:  Three plates and two tubes are about the most I have ever put in, and then usually only in one-eyed patients.  If both eyes are working, all that hardware may interfere with the natural movement of the eye and cause double vision.

P:  I'll be having shunt surgery, lensectomy, vitrectomy, and sclera re-enforcement -- all in the same operation.  Are there any risks I should be aware of?

Dr. Rick Wilson:  Your surgeon should have gone over all those with you.  The risks include infection, hemorrhage, tube erosion, tube against the cornea with damage to the cornea, retinal detachment, swelling in the retina or between the layers of the eye.

P:  Does a shunt increase sensitivity to light?

Dr. Rick Wilson:  Usually not, but if there is any rubbing of the tube on the iris, or irritation to the cornea, or inflammation in the eye, there can be light sensitivity.

P:  Is it common for a doctor to use an anti-scarring drug in the form of an injection several days or weeks postoperatively if the scar tissue shows signs of building up too much?  If not, then what is done for those patients who tend to build up scar tissue quickly?

Dr. Rick Wilson:  Now that we have mitomycin, 5-FU is not given as often as it used to be.  But 5-FU can be used for several weeks postoperatively.

P:  Is laser cyclo-destruction the same as a laser trabeculoplasty?  My ophthalmologist is recommending the laser surgery if my latest prescription doesn't work for me.

Dr. Rick Wilson:  No, they are very different.  The laser trabeculoplasty is not nearly as harmful to the eye and can even be repeated if a selective laser is used.

P:  How many shunts can one eye safely hold?

Dr. Rick Wilson:  Three plates, two tubes.

P:  Are there risks of infection with a shunt after the scar tissue has formed?

Dr. Rick Wilson:  Not unless the tube erodes through the overlying conjunctiva.

P:  I had a vitrectomy during my shunt surgery.  Would that be a complete vitrectomy or just partial?

Dr. Rick Wilson:  Nearly complete if performed by a retina specialist; probably not if performed by a glaucoma specialist or general ophthalmologist.

P:  I have aniridia.  When there is no iris, will tubes be less likely to last?

Dr. Rick Wilson:  Not less likely to last, but harder to insert to avoid contact between the tube and the lens in the eye that is not covered by a protective iris or the inside of the cornea.

P:  I have had a shunt, and aniridia has not caused a scarring problem.  Can I assume my IOP will remain stable?

Dr. Rick Wilson:  Your control may decline gradually with time, but I have older patients who have shown no sign of worsening IOP over years and years.

P:  What is a hypo-reactive intraocular lens? I am having vitrectomy/pupilloplasty/cataract and shunt surgery next week.  One doctors says leave the lens out; the other doctor says put one in.

Dr. Rick Wilson:  An Acrysoft lens or a heparin-coated polymethylmethacrylate lens is usually considered hypo-reactive.  Let us know how you do, and please share your experience with the group.

End of highlights for July 10, 2002.

On July 17, Dr. Wilson discussed "Unconventional Treatments" in the Chat room. Click here for highlights of that meeting.

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