Chat Highlights
Aqueous Shunts for Glaucoma
July 12, 2000

Norma Devine, Editor

On Wednesday, July 12, 2000, Dr. Rick Wilson, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Aqueous Shunts for Glaucoma." 

Moderator:  Good evening,  Dr. Wilson.  Welcome back from your trip.  Shunts are on the agenda tonight.

Dr. Wilson:   Forgive me tonight if  I'm a bit addled.  It is 2:36 A.M. my time,  and I've been up since 2:00 A.M. your time.

P:  What is a shunt?

Dr. Wilson:  A shunt is a tiny silicone tube attached to a plate that is placed back half way around the eye. The tube leads the eye fluid out to the plate, where it is absorbed through the scar tissue surrounding it.

P:   What are shunts used for?

Dr. Wilson:  Shunts are our second- or third-line defense for glaucoma requiring surgery and are being used increasingly.  Shunts don't result in thin blebs that can leak or get infected, but they don't give as low a pressure as trabeculectomies.   

P:  Was there any particular reason I wasn't given a shunt?

Dr. Wilson:   Trabeculectomy is still our first-line procedure,  unless the patient has inflammatory or neovascular glaucoma or has conjunctiva so scarred that a trabeculectomy cannot be done.

P:  Are shunts longer lasting than trabs?  Are they more trouble-free?  

Dr. Wilson:  My impression is that shunts often last longer. However, a recent study revealed that shunts have a slow loss of effectiveness similar to that  exhibited by trabeculectomies.  It used to be said the average trab lasted seven years before it had to be redone. With 5-FU and Mitomycin, they are definitely lasting longer.  So it may be a toss-up between shunts and trabs.

P:  Is the surgery tricky?

Dr. Wilson:  Not too bad,  but the procedure takes about 10 minutes longer than a trab.

Moderator:   I was told my eyes are too small for a shunt.  Can that be?

Dr. Wilson:  No.  Shunts are certainly more hazardous in cramped, small eyes (as are trabs), but they can be done.

P:  Are these shunts the same basic idea as those used by neurosurgeons to relieve pressure from intra-cranial bleeds?

Dr. Wilson:  Yes. 

P:  Dr. Wilson,  are shunts used for children?

Dr. Wilson:   Yes, even infants, if need be.

Moderator:  What about nanophthalmic eyes?

Dr. Wilson:   The same.  Shunts may be safer than trabs for nanophthalmic eyes.  

P:  Do shunts make later trabs impossible? Or vice versa?

Dr. Wilson:  The latter is the most common.

P:  How much do shunts lower pressure?

Dr. Wilson:  Eyes with shunts usually end up with an IOP on average of  from 15 to 25.  It is common to have to use at least one medicine with the shunt to get the IOP to an acceptable level.

P:  Do you mean 15 to 25 with or without the additional medicine?

Dr. Wilson:  I mean 15 to 25 without medication.

P:  Perhaps you could tell us the risks of shunts, or the side effects, other than the pressure not being very low.  I had double vision and great discomfort with one brand,  but am happy after replacing it with the Baerveldt.  I'm not promoting the product, but the difference was considerable.  I don't know why any other kind would be used and would like to know if there are reasons I had to suffer with another kind. 

Dr. Wilson:  Actually, I recently had to remove a Baerveldt, which had caused double vision.  Other complications are rubbing of the tube on the iris causing inflammation or on the cornea causing corneal swelling and loss of clarity.  The conjunctiva covering the shunt can wear through, exposing the shunt to outside infection.  The drop in  IOP caused by the tube opening up can cause swelling or hemorrhage.

P:  Is Baerveldt a brand name or a style of shunt?

P:  A brand name.  But also, there are different designs.

P:  I have two Baerveldt implants.  The first ended up being a very miserable experience and scarred up.  The second Baerveldt has gone incredibly smoothly.  I don't know why. 

Dr. Wilson:  Baerveldts and Ahmeds are the shunts most likely to cause double vision.  Ahmeds and Krupins are more likely to result in a higher IOP.  My favorite is the double-plate Molteno or the Baerveldt.

P:  Doctor, I was told that the large-sized Baerveldt did not offer enough extra benefit to justify using it, and the medium was used.  What do you think?

Dr. Wilson:  That has been well shown in studies.  The Baerveldt 500 has been taken off the market because of the studies.

P:  I can't really feel the implants themselves, but they affect my eyes in weird ways.  Directly after surgery and for up to six months, I had a hard time getting my eyes to work together.  The right eye felt swollen and looked buggy, waking up was difficult because it took a while to feel normal.  I have two very white patches of sclera over my tubes, but all in all I feel better after a month from the second surgery than I felt six months after the first.

P:  Are shunts used for individuals with normal tension glaucome (NTG)?

Dr. Wilson:  Shunts are not great for patients with NTG (normal-tension glaucoma) since shunts have a hard time lowering IOP into the less than 15 mm Hg  range.

Moderator:  How quickly is the pressure lowered?

Dr. Wilson:   Shunts that are not equipped with a one-way flow valve are tied off at the time of surgery with a dissolvable tie.  The tie dissolves at about one month.  Then there is a sudden drop in pressure as the eye fluid runs out the tube and fills up the reservoirs.  If the eye is healthy and continues  making fluid, the IOP is again raised to normal.  If the eye cannot make fluid fast enough and the pressure becomes too low, there can be complications of fluid build-up between the layers of the eye or there can be bleeding.

P:  Is the drop in pressure with a shunt the reason shunts aren't made to produce lower pressures?

Dr. Wilson:  No, it is the thickness of the scar tissue that builds up around the shunt reservoir that determines the final IOP.  Once the shunt is big enough, most seem the same.

Moderator:  Can you give us a number as to the percentage of patients that have complications?

Dr. Wilson:  The number varies dramatically, depending upon how sick the eye is and what kind of glaucoma it has.  Fewer than 25% have some kind of complication, and most of those are not sight- or life-threatening. 

P:  How does the under 25% complication rate compare with the rate of complications with trabs?

Dr. Wilson:  There are more complications,  but the success rate is higher with shunts in recalcitrant glaucoma.

P:  What is recalcitrant glaucoma?

Dr. Wilson:  Glaucoma that's very hard to control.

P:  Do you have to know that certain drops will lower your pressure before you can have a shunt?

Dr. Wilson:  It is helpful to know that ahead of time. 

P:  Then shunts wouldn't work for me, because no eye drops lower my pressure.  I guess I will never be able to have shunts. 

Dr. Wilson:  Hopefully, shunts and other surgeries will be better by the time you need anything else.  New medicines are coming out more commonly now.

P:  Do you have any information about fatigue that will help me?

Dr. Wilson:  Alphagan commonly causes fatigue.  Beta blockers may also cause fatigue. Xalatan can cause joint pain.

P:  How about Ocupress?  

Dr. Wilson:   Ocupress is a mild beta blocker.

P:  I wish a doctor had taken me off beta blockers as an experiment, to see if I felt any different.  I think its the only way for patients to know, unless the effects are felt as extreme.

P:  I make sure to occlude my tear duct, now that I am on Betoptic in both eyes.

P:  Are kids who have had trabs at  increased risk for infection in ocean water vs. chlorinated pool water?

Dr. Wilson:  The more contaminated the water,  the greater the risk.  However, the risk depends entirely upon the appearance of the bleb.  If the bleb is thin and there are no vessels over it, there is real risk.  If the bleb is thin and well vascularized, then the risk from swimming is minimal.  Night all.  My head just missed the keys.  Have a great week and summer.

End of highlights for July 12th chat.

Click here to read more about Aqueous Shunts.

On July 19th, Dr. Rick Wilson discussed "Testing in Glaucoma" in the Chat room. Click here for highlights of that meeting.

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