New Surgical Procedures
Chat Highlights
July 5, 2006

On Wednesday, July 5, 2006, Dr. Rick Wilson, a glaucoma specialist at Wills, and the glaucoma chat group discussed "New Surgical Procedures."

Moderator:  Welcome back to chat, Dr. Wilson. Tonight the topic is about new surgical procedures for glaucoma.

Dr. Rick Wilson:    Since the early 1970’s, we have been trying to improve on the trabeculectomy with only gradual success. Since the late 1970's, we have been trying to improve on the aqueous shunt.  The improvement has been minimal since Tony Molteno introduced the first shunt in South Africa.

Now there has been a flurry of new procedures that aim, not to make a through-and-through hole in the wall of the eye for the aqueous humor to drain through, but to make a partial opening that will work.

[Aqueous humor is the fluid normally present in the front and rear chambers of the eye.]

P:    What are the advantages to a partial opening?

Dr. Rick Wilson:   If the eyeball is only opened half way, aqueous has to take natural channels out the rest of the way. Although a large amount of the resistance to outflow is eliminated, enough remains to maintain a normal IOP.  Therefore, the too-low pressures are avoided, as can be seen after trabeculectomy, and post-operative activity can be relatively normal.

P:   Aren't there some new techniques involving Schlemm's canal?

Dr. Rick Wilson:   Reay Brown and Mary Lynch were the first to implant a tiny double tube that went from the anterior chamber of the eye into Schlemm's canal.  The route bypasses the resistance of the trabecular meshwork, the sieve covering the outflow canal of the eye.  Their shunt was called the EyePass implant.  Although it has been approved, it is not being marketed or produced as it was not as effective as expected.

Another bypass of the trabecular meshwork into Schlemm's canal (also known as the canal of the sclero-corneal junction) is the Glaukos iStent.  It's a tiny titanium tube placed into the canal from the inside of the eye, and is still being tested.

P:   What about the Trabectome?

Dr. Rick Wilson:   That procedure seems like it has the most utility.  The Trabectome is a new device that uses cautery on a small hand piece to remove the trabecular meshwork, opening up the canal from inside the eye.  The success rate after three years' experience is 80%.

P:   Does "cautery" mean burning of tissue?

Dr. Rick Wilson:   Cautery is using heat to seal blood vessels.

P:   How does the Trabectome procedure improve on trabeculectomy?

Dr. Rick Wilson:   Since there's no bleb, there's no long-term risk of leaks and infection.  There's no risk of having an IOP (intraocular pressure) so low that the vision is blurred.  Normal activity can be resumed earlier after the procedure.  Further, in skilled hands, the Trabectome is a short procedure taking about 10 minutes versus 40 to 50 minutes for a trabeculectomy.

P:   What is a bleb?

Dr. Rick Wilson:   When the flap valve of a trabeculectomy is created, it is done under the conjunctiva, the clear layer of the eye.  The fluid that leaks through the man-made bypass drain accumulates under the conjunctiva, creating a bulge that is called a bleb.

P:   Is there anything else new?

Dr. Rick Wilson:   Yes, there's the iScience canaloplasty. In that procedure, a fine cannula (tube) is used that can express a viscous substance to expand the canal and allow a suture to be threaded around the 360 degrees of the canal. The suture is then tied tightly and pulls the trabecular meshwork in toward the center of the eye, opening up the spaces in the trabecular meshwork.

P:   Have you tried any of those new methods?

Dr. Rick Wilson:   I have done all of them except the Glaukos iStent.  The upside is few complications.  The downside is not as low an IOP as is achieved with trabeculectomy, but there is no bleb to thin and later be subject to leaks or infections.

P:   Having done all of those procedures except the Glaukos iStent, how effective did you find them to be and how successful were they?

Dr. Rick Wilson:   The EyePass was disappointing in that although the next morning the patient didn't even feel as if she had had surgery, the IOP never went lower than 18 mm Hg and gradually rose to 23 mm Hg, when a second trabeculectomy was needed.  The iScience procedures are working well, with an IOP usually of between 16 to 18 mm Hg.  The Trabectome has been disappointing in young patients with inflammatory glaucoma, but with good pressures in older POAG (primary open-angle glaucoma) patients, for which it was meant.

P:   Who would be the best subjects to receive any or all of those new procedures?

Dr. Rick Wilson:   Patients who have minimal to moderate damage, so that a target IOP of 16 to 19 mm Hg would be adequate, and who have a deep enough anterior chamber to facilitate whichever procedure was chosen.  The patients would need to have POAG, not a secondary glaucoma like inflammatory or traumatic glaucoma.

P:   Which of the new procedures can be performed on someone who has already had ALT (argon laser trabeculoplasty), SLT (selective laser trabeculoplasty), trabeculectomy, or a shunt implant?

Dr. Rick Wilson:   The iScience may not be able to be done if there has been surgery or trauma that injured Schlemm's canal. The others usually can be done.

P:   Is the aftercare any simpler with these new procedures?  Is there less need for the use of steroids?

Dr. Rick Wilson:   Yes, because the risk of too low a pressure or a flat chamber is eliminated; the use of steroids is reduced. All the follow-up visits to cut sutures after a trabeculectomy are unnecessary, although a fair number of follow-up visits remain.

P:   Is there any decrease in the use of post-operative eyedrops to keep the IOP low?

Dr. Rick Wilson:   Often the pre-op glaucoma drops can be eliminated.  However, if a low normal IOP is needed, drops may be added to the surgery to achieve the target pressure.

P:   Is the need for mitomycin C or 5-FU eliminated with the new procedures?

Dr. Rick Wilson:   Yes. They are not used with these procedures at this time.

Moderator:  How are the new procedures tested?

Dr. Rick Wilson:   After the technique is tested on animals and eye bank eyes (eyes from deceased donors), a protocol is developed to test the procedure in human beings.  Strict testing is done pre- and post-operatively, with close follow-up to judge the effectiveness of the procedure.  The results are usually written up and published in medical journals.

P:   How do the eyes of mice differ from those of human beings?

Dr. Rick Wilson:   The eyes are small, so they are difficult to work on and hard to compare to the human eye.  Rabbits are often used, but they heal very quickly, so medicines to prevent scarring are usually necessary for procedures like trabeculectomy.

P:   Locally, there have been advertisements about laser surgery, avoiding the many risks and costs associated with cutting surgery.  Do you see that in the future for glaucoma?

Dr. Rick Wilson:   An Excimer laser, which makes small holes in the trabecular meshwork and into Schlemm's Canal from the inside of the eye, shows some promise.  Those who are advertising are just promoting themselves and the use of the SLT that is no more effective than the ALT that we have been using since the early 1980’s.  The SLT is more benign than the ALT, but no more effective.

P:   Tonight, as previously, you don't sound enthusiastic about SLT.  Have there been any studies about whether SLT is more effective in pigmentary glaucoma, say in a patient with a grade 3 or 4 pigment in the trabecular meshwork, than in a patient with primary open-angle glaucoma?

Dr. Rick Wilson:   The experience at Duke University was that the SLT was less effective in pigmentary glaucoma than in patients with less pigment.  That seems counter-intuitive, but real.

P:   When a new procedure is approved, how do glaucoma surgeons learn how to do it?

Dr. Rick Wilson:   Through videos, journals, presentations at meetings, training sessions at meetings, often with "wet labs" that use animal, or occasionally, human eyes. Many doctors travel to watch a surgeon who performs the procedures and teaches others.

P:   Who approves these new procedures?

Dr. Rick Wilson:   The Trabectome is approved by the FDA (Food and Drug Administration). The Glaukos has an investigational approval, as does the iScience.

P:   Do any of these new procedures avoid the need to cut a big flap in the conjunctiva?

Dr. Rick Wilson:   The Trabectome and Glaukos procedures do.  The EyePass and the iScience procedures still require a fair-sized scleral flap.

P:   If a bleb should fail, could a patient then have a Trabectome?

Dr. Rick Wilson:   Yes, although it may not work quite as well when the flow around the canal has been disrupted in one place.

P:   What is deep sclerectomy?

Dr. Rick Wilson:   A deep sclerectomy is like a trabeculectomy, except instead of removing the inner piece of the eye wall under the half-thickness scleral flap, the wall of the eye under the flap is thinned so that fluid leaks right through it.  The rate of leakage is not so much that the pressure drops too low, but enough to control the IOP, we hope, without drops.

P:   When you discussed the partial-thickness opening in the eye wall, you were not referring to the scleral flap?

Dr. Rick Wilson:   Not if the scleral flap is over a hole into the eye.  Then the fluid leaks out under the scleral flap and is really a full-wall-thickness procedure.  A partial- thickness procedure would leave the outer layer of the sclera or the trabecular meshwork intact.

P:   How long does a trabeculectomy last?

Dr. Rick Wilson:   It used to be said that trabeculectomies lasted seven years, on average. I think we are doing better than that now with the use of mitomycin and 5-FU.

P:   What happens to a patient with closed-angle glaucoma when iridotomy and drops are not adequate to keep pressure down?

Dr. Rick Wilson:   The procedures we have been talking about are not used in angle-closure glaucoma, so a trabeculectomy would probably be the next step after laser surgery and drops.

Moderator:  Dr. Wilson, you covered a lot of new information tonight.  Thank you.

Dr. Rick Wilson:   You're welcome.  Goodnight, everyone.  Hope you all had a good 4th of July.  See you next week.

On July 12, Dr. Wilson discussed "An Overview of Glaucoma" in the Chat room. Click here for highlights of that meeting.

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