Tube Shunt Surgery in Glaucoma Patients
Chat Highlights
June 8, 2005

On Wednesday, June 8, 2005, Dr. Geoff Schwartz a glaucoma specialist at Wills, and the glaucoma chat group discussed "Tube Shunt Surgery in Glaucoma Patients. "

Moderator:  Welcome, Dr. Schwartz.

Dr. Geoff Schwartz:  Hello, everyone.

Moderator:  Thank you for joining us. Will you please tell us a little about yourself before we start to discuss tube shunts?

Dr. Geoff Schwartz:  I am a glaucoma specialist.  I did my residency at Wills Eye Hospital and a fellowship in glaucoma at Bascom Palmer Eye Institute.  I am currently on the glaucoma service at Wills Eye Hospital and am in private practice in the Lansdale and Fort Washington, Pennsylvania, area.

Moderator:  Dr. Schwartz, do you specialize in tube-shunt surgery?

Dr. Geoff Schwartz:  Yes, that is one of my special interests.

P:  When is a tube shunt recommended for glaucoma patients?

Dr. Geoff Schwartz:  Generally, tube shunts are reserved for difficult glaucoma cases for which conventional filtering surgery has failed or is likely to fail.  Examples include failed trabeculectomy, active uveitis, neovascular glaucoma, and inadequate conjunctiva.  Those are just a few of the major ones.

P:  What does the word "shunt" mean in the context of tube shunt?

Dr. Geoff Schwartz:  Shunt literally means "shunting" or "moving fluid" from the internal part of the eye to an external area where the venous and lymphatic systems take away the fluid.  By doing that, we are able to lower the pressure inside the eye.

P:  Where is the shunt implanted in the eye?

Dr. Geoff Schwartz:  The shunts, or drainage devices, in current use generally have a tube placed in the anterior chamber that flows to an extraocular reservoir, or plate.  It is typically placed under the extraocular muscles superiorly, approximately 8 mm from the anterior chamber.

P:  What types of shunts are available, and what determines which one you select?

Dr. Geoff Schwartz:  There are four currently used tube shunts:  Krupin, Baerveldt, Ahmed, and the double- and single-plate Molteno.  The Krupin and Ahmed are valved implants.  The Baerveldt and Molteno are non-valved.  Typically, Baerveldt and Molteno obtain lower pressures; however, it is the surgeon's choice, depending upon what he is most comfortable using.

P:  So the shunt drains fluid from the anterior chamber, not to the posterior chamber but to the outer part of the eye?

Dr. Geoff Schwartz:  Correct, it drains to an external portion of the eye, which is under the conjunctiva (the skin of the eye).  That is where our body absorbs the fluid naturally.  Shunts are used because the natural drain in the anterior chamber of the eye is not working correctly.  When the natural drain of our eye is not working correctly, fluid builds up, causing the intraocular pressure to rise, which can lead to damage to the optic nerve.

P:  How many shunts can be placed in an eye?

Dr. Geoff Schwartz:  Multiple shunts can be placed in an eye.  The most I have seen is three; however, typically, if two fail, other procedures should be considered.

P:  If a shunt fails, is it removed before another one is implanted?

Dr. Geoff Schwartz:  Typically, if a second or third shunt is placed, the previous shunts are left in place, unless they are causing a problem.

P:  Does postoperative hypotony occur more often with a trab (trabeculectomy) or a shunt procedure?

Dr. Geoff Schwartz:  In my experience, postoperative hypotony occurs just slightly more often with a shunt than with a trab.  However, some studies have shown a much higher hypotony rate with tube shunts than with a trab.  Currently, there is a prospective study comparing tube shunts with trabs which may clarify this issue.

P:  Is the recovery time longer for a shunt than for a trab?

Dr. Geoff Schwartz:  Typically, my recovery times are equivalent; however, that is very surgeon-dependent.  Tube shunts do have higher complication rates in general, which is why they are reserved for more difficult glaucoma cases and ones that have failed previous surgery.

P:  Why does the doctor typically start with a trab, and if it fails go to a shunt?

Dr. Geoff Schwartz:  Because there are higher complication rates associated with tube shunts.  The major complications are bleeding, double vision, retinal detachment, intraocular pressure too high or too low, and corneal decompensation.

P:  Is it easier to regulate the pressure with a shunt than with a trabeculectomy?

Dr. Geoff Schwartz:  No.

P:  Do all shunts have a valve? Are there moving parts?

Dr. Geoff Schwartz:  Some shunts have a valve and some do not.  There are no moving parts.  Theoretically, in shunts that have a valve mechanism, the valve is a one-way valve, which only opens when the pressure reaches a pre-determined level approximating 14 mm Hg.

P:  Is the Mini-Express shunt still being used?

Dr. Geoff Schwartz:  That type of shunt had major complications.  Loss of vision occurred in a high number of eyes.  They have tried to use it in a different manner by placing it under a trabeculectomy flap.  Most glaucoma specialists, however, consider it just a fancy trab with no added benefit.

P:  Is it true that glaucoma patients can stop using eyedrops and medication after successful shunt surgery?

Dr. Geoff Schwartz:  That depends on each patient's particular situation and what level intraocular pressure the doctor is trying to achieve.  Sometimes patients may not need any drops, and sometimes they do, in addition to the surgery.

P:  Why does the Ahmed valve scar over and clog?  My 16-month-old daughter has two of the valves in her right eye and one in her left eye.  Her intraocular pressures are 20 mm Hg, right eye, and 27 mm Hg, left eye.  Can't they make a better valve?

Dr. Geoff Schwartz:  This has more to do with babies as well as young adults in that they have a high propensity for healing too well (scarring).  Currently, we are investigating materials that will cause less scarring.

P:  Is a retinal detachment secondary to the vitreous being pulled away from the retina?  Is that complication not seen in patients who have had vitrectomies?

Dr. Geoff Schwartz:  The exact answer is not known.  Any surgery, however, whether it is a tube shunt, cataract, trab, etc., can have this complication, which is probably due to the wall of the eye being disturbed during the normal course of an operation.  Sometimes that can be related to the vitreous being pulled away from the retina. However, it still does not happen that often.

P:  I know a youngster with a shunt.  She had head trauma a couple months ago; now the eye pressure is elevated.  Could trauma to the head move or somehow hamper the function of the shunt?

Dr. Geoff Schwartz:  That is a difficult question to answer.  Unless the eye was specifically traumatized with visual signs of bleeding or other symptoms, it is unlikely.

P:  My mother had a Baerveldt shunt put in two years ago.  The doctor thought it was urgent as her pressure was 36 mm Hg at 5:00 p.m., and she had the surgery at 7:30 p.m.  Are pressures of 36 mm Hg urgent enough to implant a shunt right away?

Dr. Geoff Schwartz:  Again, that would depend on how advanced your mother's glaucoma was and what was causing the pressure to go up. The surgery may very well have been necessary.

P:  Are shunts more appropriate for particular age groups, for example, children?

Dr. Geoff Schwartz:  No, they are not restricted to a particular age group.  Whether tube shunts or trabeculectomies are better in babies or adults is controversial, because it is felt that trabs have a higher chance of having a late infection.

P:  How long can a shunt function?

Dr. Geoff Schwartz:  The longest I've seen is approximately 30 years, but it varies.  Tube shunts have been around since the 1970s; however, early on there were many more complications than we see today.  Even within the last five years, shunt surgery has been much improved by new techniques.

P:  Could someone with acute myopia get a tube shunt after a failed trab?

Dr. Geoff Schwartz:  Acute myopia typically has no bearing on glaucoma or glaucoma surgery.  Acute myopia just means suddenly nearsighted.

Moderator:  Dr. Schwartz, thank you so much for joining us.  It's been a pleasure and your answers were very informative.  We hope you can come again.

Dr. Geoff Schwartz:  Thank you and have a good evening.

On June 15, Dr. Wilson discussed "The Doctor-Patient Relationship and External Stresses" in the Chat room. Click here for highlights of that meeting.

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