Shunts
Chat Highlights
November 15, 2006

On Wednesday, November 15, 2006, Dr. Michael James Pro, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Shunts."

Moderator:  Good evening, Dr. Pro. Thanks for joining us.  Tonight we’d like to discuss shunts again.

P:  What is a glaucoma shunt?

Dr. Pro:   A shunt consists of a silicone tube attached to an equatorial explant (plate).  Glaucoma shunts are devices used in refractory glaucoma to lower the pressure.

P:  When are shunts used in treating glaucoma?

Dr. Pro:  They are frequently used after a trabeculectomy has failed, or when patients have complicated forms of glaucoma, such as inflammatory or neovascular.

P:  Are shunts ever used before trabeculectomies?

Dr. Pro:  They are usually not used before trabeculectomies, except in cases such as inflammatory glaucoma.

P:  Is shunt surgery more painful than a trabeculectomy?

Dr. Pro:  The eye is usually redder due to the need to cut more tissue.  Sometimes there is more pain because there is more manipulation.

P:  Are the risks of shunt surgery the same as for other eye surgery?

Dr. Pro:  The risks are similar to other types of glaucoma surgery.  But the failure rate is higher than in primary trabeculectomy because often there is more scar tissue from previous surgery.

P:  Can IOPs (intraocular pressure) below 16 mm Hg be achieved using a shunt?

Dr. Pro:  Shunts typically do not decrease the pressure past the mid-teens.  I tell all my patients this and warn them they may still need drops.  Also, unlike a trabeculectomy, shunts have a period of high pressure.

P:  I am 36-years old, and have had three trabeculectomies (one in the right eye, two in the left).  Vision loss is 40% in my right eye and 90% in my left eye.  Two weeks ago the IOP in my right eye was 18 mm Hg and 16 mm Hg in my left eye. In the past six months I have lost a significant amount of vision.  Would a shunt be a good idea for me now?

Dr. Pro:  I can't comment on each specific case.  Naturally, I need to review visual field tests and know more about a patient's history.  Your situation, however, is one that many patients have who later need a shunt.

P:  I had a shunt installed last May and still have some blurry vision.  I read in the archives of the chat highlights that if the IOP gets too low, a choroidal detachment could occur.  If my IOP increases, will the blurry vision go away? I have no blurry vision in my other eye when I close the eye with the shunt.

Dr. Pro:  After shunt surgery there is often a period of low pressure (hypotony).  That’s because the fluid leaves the eye faster than it is produced.

P:  Are there different types of shunts?

Dr. Pro:  There are two basic types.  The valved tube is supposed to prevent hypotony by having a stop valve that blocks flow at a certain low pressure.  The non-valved type has no restriction to outflow.  The surgeon has to tie the tube off with a dissolvable suture and wait about a month for the suture to release for the shunt to work.  During that time, a "capsule" develops around the plate, and outflow of aqueous is controlled.

P:  What happens when the IOP gets too low?

Dr. Pro:  At the time the dissolvable suture releases on the non-valved tubes, the outflow may still be too high and the pressure in the eye may go too low.  When that happens, the eye is soft and distorted, thus affecting the vision.  There can also be swelling in the space behind the retina.  That accumulation of fluid is called a choroidal effusion and it also affects the vision.

P:  When do these periods of high and low IOP occur after shunt surgery?

Dr. Pro:  With a non-valved shunt, the first period is high pressure, because the tube is tied off. At three to six weeks, as the tube opens, the pressure may be low.  Then the pressure usually stabilizes.  There is also a known "hypertensive" phase that occurs after one month, especially in the valved tubes when the glaucoma medications have "washed-out" and the pressure goes up again.  Drops are often started again, and the pressure usually drifts down over time.

Moderator:  Will you please explain a little more about how the capsule controls the pressure during the first month after a shunt is installed?

Dr. Pro:  Okay.  The back end of the tube shunt is basically a plastic plate that is sewn onto the sclera at the middle of the eye.  (This position is actually under the eyelid and can't be seen by the patient when looking in the mirror.)  The eye grows a protective scar tissue around the plate as part of the normal healing response.  It is this ring of scar tissue that we call the capsule, where the fluid accumulates and is passively drained from the eye.

P:  What is the purpose of the plate?

Dr. Pro:  The plate is to increase the outflow area.  This causes a larger lake of fluid to be present and theoretically reduces outflow resistance.

P:  Approximately how long after shunt surgery is vision restored?

Dr. Pro:  Generally a month or so, usually sooner.

P:  How long can a shunt last?  Do they all eventually scar over?

Dr. Pro:  The studies on the long-term success of the shunts are not encouraging.  The five-year success rate on some of the early shunt devices was around 25-40%. With the new devices, the success rate may be higher.  The three-year success rate with the Baerveldt is about 70%. (There are various studies.)

P:  How many shunt surgeries can a patient have in one eye?

Dr. Pro:  Three is usually the most any eye could have, as there is just no more room for the plates.

P:  Does the number of previous trabeculectomies affect the number of shunts possible in the eye?

Dr. Pro:  No.

P:  What are the restrictions after shunt surgery?  Are there any permanent precautions?

Dr. Pro:  I tell my patients to take it easy immediately after the surgery.  No weight lifting or vigorous exercise.  The only permanent precaution is to know that infection may occur.  So if the eye gets red, painful, or loss of vision occurs, the patient needs to see the doctor.

P:  How common is double vision after a shunt?

Dr. Pro:  The meaning of “double vision” needs to be clarified.  Double vision that is cleared by closing one eye is due to misalignment of the two eyes (one eye is looking the wrong way).  That is caused by the shunt surgery affecting the extra-ocular muscles, because the location of the muscle insertion is where the shunts are placed.  That is uncommon, but it’s a known complication.

P:  Can a shunt be rejected by the body?  Is anyone allergic to shunts?

Dr. Pro:  Infection of a tube shunt is a reason for the body to "reject" it, but the material of the shunt is non-allergenic.

P:  It seems that a trabeculectomy has a longer life than a shunt.

Dr. Pro:  Yes, but maybe that is because of the type of patients who gets shunts; that is, a patient with glaucoma that’s difficult to treat or a patient that has already had failed surgery.

P:  A few years ago, there was a lot of publicity about the Ex-Press mini-shunt.  Are the results in?

Dr. Pro:  The Express is a little different. It acts a bit like a tool in trabeculectomy surgery.  It is not a tube-shunt.  Anyway, the results are still early.  We have patients who have received it and are doing well, but all the data are still not in.

P:  My 34-month-old daughter has had a total of five Ahmed valves put in her eyes.  They were revised, removed and replaced.  She now has two in her right eye and one in her left eye. Is it true that babies with pediatric glaucoma require many surgeries and then the eyes 'quiet down' and then don't need as many?

Dr. Pro:  Unfortunately, the need for multiple surgeries is often true in pediatric glaucoma.  The shunts can move more than in the adult eye.

P:  My 34-month-old daughter says she sees two moons when we look at the full moon.  Could she have double vision?  Should I mention this to her specialist?

Dr. Pro:  About the two moons: any patient with pediatric glaucoma needs a pediatric ophthalmologist to assess vision and strabismus (alignment) issues.

Moderator:  Dr. Pro, thank you.  Your answers have been very thorough and informative. I'm sure everyone learned a lot.

Dr. Pro:  Thank you.

On December 6, Dr. Wilson discussed "Glaucoma, What's New?" in the Chat room. Click here for highlights of that meeting.

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