Chat Highlights
Glaucoma Shunts
July 18, 2001

Norma Devine, Editor

On Wednesday, July 18, 2001, Dr. Rick Wilson, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Glaucoma Shunts."

Moderator:  Tonight we will be discussing glaucoma shunts with Dr. Rick Wilson.  

P:  Doctor, what is the difference between a shunt and a trabeculectomy?

Dr. Rick Wilson:  A trabeculectomy is a flap valve fashioned out of the white scleral wall of the eye.  No foreign material is used.  A shunt is a plastic tube leading fluid from the eye to a plate (reservoir) on the top of the eye, way back under the upper lid.

P:  Are shunts sometimes used before a trabeculectomy?  

Dr. Rick Wilson:  The indications for using a shunt first are patients with inflammatory glaucoma, patients with neovascular glaucoma, patients with anterior chamber intraocular lenses after cataract extraction, patients with so much conjunctival scarring that a trabeculectomy would not be possible, and patients who need to wear contact lenses.

P:  Why would you do one or the other?

Dr. Rick Wilson:  Trabeculectomies let fluid filter out through the flap underneath the conjunctiva.  If the conjunctiva is so scarred that it cannot be raised from the sclera (white wall of the eye), then a trabeculectomy would be impossible.

Moderator:  Are there any risks involved in a shunt surgery?

Dr. Rick Wilson:  There are risks in all of these procedures.  With a shunt, there is little chance of late infection or leakage from a bleb or too low an intraocular pressure long term.  However, there are risks of too low an intraocular pressure shortly after the surgery and, to a much lesser extent, double vision.  Shunts also usually result in IOPs (intraocular pressures) over 15 even with medication, a level that is too high for patients with advanced glaucoma.

P:  Does the patient feel the presence of a shunt? 

Dr. Rick Wilson:  Usually, patients don't feel the shunt.   

P:  I've had a shunt for three months and don't feel a thing.  Perhaps I am just lucky. 

P:  Once the aqueous fluid is in the reservoir, what happens next?  Does the reservoir  just lower the pressure by increasing the volume of the anterior chamber or is the aqueous disposed of somehow?

Dr. Rick Wilson:  Good question.  The aqueous filters slowly through the scar tissue surrounding the plate into the tissue in the orbit, where it is picked up by the lymphatic and blood vessels and carried away similarly to a trabeculectomy.

P:  It sounds as if you would normally do a trabeculectomy first and reserve the shunt for the special cases you described.  Is that right?

Dr. Rick Wilson:  That's right.  

P:  Where does the tube enter the eye and what holds it in place?  

Dr. Rick Wilson:  The tube goes through the wall of the eye, which aims it in the right direction. The reservoir and the tube are sutured to the sclera to hold them in place.

P:  I recently had an Ahmed valve placed at the bottom of my right eye.  Are there advantages and disadvantages to a shunt there?  

Dr. Rick Wilson:  The disadvantage of a shunt in the bottom of the orbit is there is not as much room there.  The bleb (pocket of fluid over the reservoir) may push the eye up so far that double vision is the result.

P:  Are the tubes usually placed in the front of the eye? 

Dr. Rick Wilson:  Yes, in most cases.  In patients who have had their vitreous (the jelly-like substance that fills the back of the eye) removed, the tube can then be put into the posterior chamber behind the iris.

P:  Is the plate made of a different, more permeable material than the tube, or are both made of silicone?

Dr. Rick Wilson:  The plate is made of polymethylmethacrylate or silicone.  It is not at all permeable, but keeps the scar tissue from closing the end of the tube.  The tube creates a pocket for the fluid to flow to before it seeps into the tissue surrounding the plate.

Moderator:  Why would a shunt be placed at the bottom of the eye?

Dr. Rick Wilson:  Usually a shunt is placed at the bottom of the eye when the top two quadrants of the eye are scarred or already have another tube and plate there.  Unless a patient has only one eye, I don't put shunts inferiorly because of the threat of double vision. 

Moderator:  What do you mean by " unless the patient has one eye?"

Dr. Rick Wilson:  If the patient is one-eyed, there can't be any double vision, even if scar tissue prevented the eye from moving at all.

P:  What determines the choice of a shunt with or without a valve?  

Dr. Rick Wilson:  The experience of the surgeon and how low an IOP is required.  The valves that we have now are only partially successful.  They may not prevent too low an IOP,  and if there is inflammation in the eye, the valve may get clogged up . Valved shunts are usually smaller than the non-valved shunts and result in a higher average IOP than the non-valved shunts.  Because they are smaller, valved shunts can be put in much more easily  than the non-valved shunts.  That makes them popular now.  

P:  The double vision problem I had been warned about has been very minor.  I only have double vision when I first wake up and look down. Three months after the implant, my eye is still quite red, especially when I wake up.  Switching recently from Ophtho Tate to Acular has made no difference.  There's no discomfort, but will the redness eventually subside?

Dr. Rick Wilson:  The eye may always be a little red if there is a lot of scarring.  Most times the eye gradually becomes quiet. 

Moderator:  How long is the postoperative care for a shunt, compared to a trabeculectomy?  What are the restrictions?

Dr. Rick Wilson:  The postoperative care is about the same length of time for both operations.  The early postoperative course is not nearly  as restrictive for shunt patients, because they have just a small needle hole into the eye that is filled with the tube.  If the IOP is low, however, the restrictions against bending over and lifting are in effect.

P:  What replaces vitreous that has been removed? 

Dr. Rick Wilson:  Usually the vitreous is removed and replaced with salt water, which is then replaced by the body with the same fluid filling the anterior chamber.  In some patients, the back cavity of the eye is filled with gas, which is gradually absorbed, or by silicone oil, which isn't absorbed.  

P:   What is the life span of a shunt?

Dr. Rick Wilson:  A shunt will be there long after the patient is dust. 

P:  I know a shunt may outlast my bones, but for how long will the shunt remain effective?   

Dr. Rick Wilson:  I have shunts that have been working for 16 years.  Others gradually lose effectiveness, as the scar tissue around the shunts thickens with time. 

P:  What is the life span of a trabeculectomy? 

Dr. Rick Wilson:  The life span of a trabeculectomy is quite variable.  I have seen trabeculectomies working for more than 20 years.  It used to be said that the average trabeculectomy lasted seven years.  Now, with the use of anti-scarring agents, I think that estimate is too conservative.  

Moderator:  Can you replace a shunt that scar tissue made ineffective?

Dr. Rick Wilson:  Scar tissue can be removed to restore the effectiveness of the shunt. 

P:  Is the removal of scar tissue common?  

Dr. Rick Wilson:   Yes.  

P:  Is scar tissue more of a problem with the young or old, male or female?  

Dr. Rick Wilson:  Scar tissue is more of a problem in young patients, those with darkly pigmented skin, those with inflammation, and those with previous surgery.

P:  If a patient does not have medical insurance and needs a trabeculectomy or a shunt, what can he or she do?  

Dr. Rick Wilson:  Most university hospitals have resident clinics that will provide the service at little or no cost.  Many Lions clubs also help indigent patients obtain eye care.

P:  The Knights of Templar used to help pay for eye surgeries, but I don't know if they still do.  They helped me pay for cataract surgery.

End of highlights for July 18, 2001.

On July 2, Dr. Henderer met with the Monday night support group.  Click here for highlights of that meeting.

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