Implantation of Glaucoma Drainage Devices
Chat Highlights
April 30, 2003

Norma Devine, Editor

On Wednesday, April 30, 2003, Dr. Elliot Werner, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Implantation of Glaucoma Drainage Devices."

Moderator:  Welcome, Dr. Werner.  Tonight our topic is Implantation of Glaucoma Drainage Devices (shunts).  When would a shunt need to be implanted?

Dr. Elliot Werner:  In general, shunts are used in patients who have a failed trabeculectomy.  Shunts are also used for those who have had previous eye surgery with scarring of the conjunctiva on the surface of the eye so that a standard trabeculectomy would not work.

P:  How many different types of shunts are there?

Dr. Elliot Werner:  I know of four that are used in the United States.  They are named after their inventors:  Baerveldt, Krupin, Molteno, and Ahmed.  These standard devices have a long track record of success.  There's also a new device, called the Ex-PRESS, that is controversial.   

P:  What is the Ex-PRESS?

Dr. Elliot Werner:  The Ex-PRESS is a tiny steel tube that is placed in the eye and is much smaller than the others, but does not have a track record.

P:  Why is the Ex-PRESS controversial?

Dr. Elliot Werner:  Because there are no published studies of it in the USA.  It was pushed through the FDA (Food and Drug Administration) with some less-than-truthful information.  It has been heavily marketed without much in the way of actual data.

P:  Do you think that once the Ex-PRESS has a track record, it will be a good device?

Dr. Elliot Werner:  That's hard to say.  Devices in the past, based on the same principle, have generally not worked out. 

P:  Do you ever need to implant a shunt device in a child or infant?

Dr. Elliot Werner:  Yes, shunts are used in children, because trabeculectomy has a very poor success rate in small children.

P:  Is an Aqua Flow considered a shunt? 

Dr. Elliot Werner:  No.  An Aqua Flow is a piece of collagen that is placed in the bed of an operation called a deep sclerectomy, a procedure similar to a trabeculectomy.

P:  I was diagnosed with Chandler's syndrome* in February and had an Ahmed tube shunt installed on March 17th.  I am really just starting to see somewhat clearly, but still cannot read anything because of blurred vision.  My pressures remain at 16 mm Hg.  When, if ever, would you expect my vision to improve? (*Progressive loss of iris stroma, with hole formation and pupil distortion, accompanied by severe glaucoma.) 

Dr. Elliot Werner:  It is not unusual for the vision to take three to six months to settle down after shunt surgery.

P:  I have ICE (irido-corneal syndrome) and a trabeculectomy.  If the trabeculectomy fails, and I need a shunt, where would it be positioned? 

Dr. Elliot Werner:  Most shunts are placed in the upper outer quadrant, or as we say, the superior temporal quadrant.

P:  Are valves and tube shunts the same thing?

Dr. Elliot Werner:  Yes, in the sense that valves are a type of tube shunt.  Some shunts, however, have valves, some do not.  

P:  What are most of the drainage devices made of?  

Dr. Elliot Werner:  Most are made of a plastic called silastic, and also silicone.

P:  Is the silicone material used in some valves thought to be harmful in any way over time?

Dr. Elliot Werner:  Not as far as we know.  It is not liquid silicone.  Solid silicone is tolerated very well by the body.

P:  How long do drainage devices, such as the Ahmed, last? 

Dr. Elliot Werner:  They last a lifetime, if they continue to work and do not cause complications.

P:  Will you please give us a general description of the other four devices you named and also explain where they drain to?  I'm trying to get some kind of mental picture of what these things are.

Dr. Elliot Werner:  The devices are similar in design.  Each consists of a small hollow tube attached to a plate that is about the size of a dime, so they look a little like a lollipop.  The tube is inserted into the anterior chamber.  The plate is sutured to the surface of the eyeball about 10 millimeters behind the cornea. The fluid drains into a space between the plate and the conjunctiva.

Moderator:  I recall seeing a demonstration model of a human eye with a shunt in Dr. Wilson's office. 

Dr. Elliot Werner:  We all have one of those to show to patients.

P:  How does a valved shunt work?

Dr. Elliot Werner:  They all work the same way.  The valve just slows the outflow of aqueous to avoid very low pressures right after the operation.  The valved devices, however, do not have as high a long-term success rate as the non-valved, or open tube, design.

P:  What are the possible complications?  

Dr. Elliot Werner:  The usual surgical complications:  hemorrhage, infection, inflammation, swelling of the cornea or other eye tissues.

P:  What are some reasons they cease to work?  Scar tissue?

Dr. Elliot Werner:  If they fail, it is usually for one of two reasons.  Either there is scarring of the conjunctiva around the plate, or the internal opening of the tube becomes blocked.

P:  My iris changed color from brown to green after the surgery.  Is that normal and will the color return to brown?

Dr. Elliot Werner:  I haven't heard that before. It might be that you have some edema of the cornea that makes your eye look a different color.

P:  What are the options if the shunt fails or becomes blocked?  Can you try to unclog it?

Dr. Elliot Werner:  You can try to unblock it or remove the scar tissue.  That sometimes works.  Or you can put a second shunt in another location of the same eye.  That also sometimes works.  Another option is a procedure called cyclophotocoagulation, in which a laser is used to destroy part of the ciliary body to reduce the amount of aqueous the eye produces.

P:  How many shunts can one eye hold?  

Dr. Elliot Werner:  I have heard of doctors doing four shunts in one eye, one in each quadrant.  I, personally, have never seen more than two.  A recent study from the University of Miami found that 5% of their shunt patients got a second one over a ten-year period.

P:  Is surgical implantation of shunts ever used for NTG (normal-tension glaucoma)?

Dr. Elliot Werner:  Occasionally, but not often, since they rarely get the pressures low enough to make a difference in NTG.

P:  How much do shunts lower intraocular pressure?  Do patients still need medication?

Dr. Elliot Werner:  About half of shunt patients continue to need medication.  It is unusual to get a long-term pressure below 12 mm Hg with a shunt.

P:  Roughly what percentage of patients eventually have shunts?  Are shunts not used in certain types of glaucoma or under certain special circumstances?

Dr. Elliot Werner:  I don't know of any data, but far more trabeculectomies are performed than shunts, so it is a relatively small number.  Those of us who deal with difficult glaucoma, however, do a lot of them.

P:  Can a shunt be placed in the same place where there is a failed trabeculectomy? 

Dr. Elliot Werner:  Yes, you can put a shunt in the same location as a failed trabeculectomy.

P:  I can see my shunt.  Will I always be able to?  Or will it disappear with time?

Dr. Elliot Werner:  If you can see it, you will probably always see it.  Shunts  don't become less apparent with time, but the redness and swelling will go away.

P:  Are there any other drainage devices being developed?  Say, something to replace the trabecular meshwork, for example.

Dr. Elliot Werner:  Not that I know of.  Nothing in clinical trials or close to clinical trials.

P:  Do you have a favorite shunt, a brand you would use over the others, all other selective criteria being equal?

Dr. Elliot Werner:  I almost always use a Baerveldt.  My experience and the medical literature suggest it has the best combination of safety and results.

P:  I have a Baerveldt that was  implanted in 1999.  The pressure edged up soon afterwards to 16 mm Hg and has remained there.  So far, I like it better than the former shunt that was removed.  I wish more people had Baerveldt shunts.  

P:  Well, shunts are commonly used after trabeculectomies fail.  Trabeculectomies fail because of scarring.  If that is so, why would shunts scar over more slowly than trabeculectomies? 

Dr. Elliot Werner:  Because the conjunctiva is in a different place.  The conjunctiva over a trabeculectomy is right at the edge of the cornea.  The conjunctiva over the plate of a shunt is 10 or 12 millimeters back and sometimes is less prone to scarring.

P:  Why would that tissue scar differently? 

Dr. Elliot Werner:  Because the conjunctiva there is less exposed to the air and various insults of the outside world.

P:  Forgive me for being dense, but a trabeculectomy makes an opening in only a small part of the trabecular meshwork?  

Dr. Elliot Werner:  Correct, the opening is only about 2 millimeters.

P:  I understand that in Europe, glaucoma specialists turn to surgery sooner than they do in the States.  Can you discuss this difference and provide the reasoning behind the American approach?

Dr. Elliot Werner:  I'm not sure that is true.  According to my contacts with  European doctors, they treat glaucoma about the same as we do.  Surgery is risky and glaucoma surgery has a high complication rate compared to other forms of eye surgery, so we don't like to rush into it.

P:  Do glaucoma patients suffer hypotony after shunt surgery? 

Dr. Elliot Werner:  Yes, but fortunately that is not common.  Sometimes you can go back and tie the tube to reduce the drainage.  Sometimes you have to remove the tube.

P:  What is the usual procedure to remove shunts?

Dr. Elliot Werner:  It's sort of the opposite of putting them in. You have to open up the conjunctiva, cut out all the sutures, and then remove the tube and plate.

P:  Is removing them difficult?  Or would you rather leave them in and add another?

Dr. Elliot Werner:  Removing them is not difficult, but if you're removing one, it usually means there is something dreadfully wrong, so it usually is not a good situation.

P:  How big is the trabecular meshwork?

Dr. Elliot Werner:  The trabecular meshwork is a circular structure around the limbus, about where the white of the eye and the cornea meet. It is about 12 millimeters in diameter and about 0.5 millimeter wide.

P:  Is the trabecular meshwork around the entire circumference of the cornea?

P:  Yes, it is a complete circle around the entire periphery of the cornea.

P:  Do I understand correctly that you said the trabecular meshwork is a circle around the circumference of the cornea?  Where is the angle then?  I'm a bit dense on the anatomy here.  I've never picked that up from diagrams I've seen. The trabecular meshwork is shown at the bottom.

Dr. Elliot Werner:  The trabecular meshwork is in the angle.  The angle is the space formed by the junction of the iris and the peripheral cornea.

Dr. Elliot Werner:  Now let me ask a question.  How many of you would prefer surgery if that meant no more eye drops, but carried a greater risk of serious complications from the surgery itself?

Moderator:  Tough question.  I say drops only because I had complications both times I had trabeculectomies.

P:  I would not prefer the surgery.   

P:  Nor I.  I am not keen about living with blebs the rest of my life.

P:  Eye drops, please!

P:  I won't lie.  I didn't think that surgery was a piece of cake.

P:  I will take the drops any day over surgery.

P:  I've been on a witches brew of drugs.  I'm completely off drugs after my trabeculectomy.  I'll take surgery.  The side effects of the meds were terrible.

P:  I'll take drops.  Actually, I'd prefer neither.

P:  Easy for me.  Surgery.  No drops!  But mitomycin C damage has to stop.

P:  I am suffering side effects from the drops and Diamox, but I also have had surgery and I am glad to take the meds.

P:  I would not complain if I had to go back on maximum medication if that would help avoid surgery.

P:  I've had many surgeries -- a good addiction.

Dr. Elliot Werner:  That helps answer the earlier question of why we treat patients the way we do in the United States. 

Moderator:  Dr. Werner,  next month your topic will be "Training a Glaucoma Specialist."

Dr. Elliot Werner:  Yes,  I'm looking forward to that. I will write a big note on my refrigerator so I don't forget.

P:  Thank you, Dr. Werner.  I always learn a lot from you.

End of highlights for April 30, 2003.

On May 7, Dr. Wilson discussed "Medications" in the Chat room. Click here for highlights of that meeting.

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