Surgeons seek appropriate niche for microincision glaucoma surgery

Microincision surgery for cataract promises to raise the bar in terms of safety, visual results and refractive outcomes. A similar trend is gradually taking root in glaucoma surgery.

Some surgeons are adopting microincision techniques to implant a growing array of devices designed to facilitate aqueous outflow and reduce IOP.

One microincision glaucoma surgery technique, trabeculectomy ab interno with the Trabectome (NeoMedix), has been approved by the U.S. Food and Drug Administration. Canaloplasty, a more involved ab externo procedure, is also approved in the U.S.

Some surgeons combine microincision cataract surgery (MICS) and microincision glaucoma surgery (MIGS) in select cases, while others think phacoemulsification alone is sufficient to reduce IOP.

In glaucoma, many surgeons have embraced microincisions and ab interno filtering and bypass devices because they reduce complications, E. Randy Craven, MD, said.

“Minimally invasive glaucoma surgeries evolved because we were trying to get away from problems associated with full-thickness filtering procedures that we have seen for years, which are hypotony, choroidal hemorrhage, bleb problems and things such as that,” he said. “We are seeing that these are newer ways of trying to avoid problems we’ve had with trabeculectomies in the past.”

A new MIGS device, the iStent micro-bypass implant (Glaukos), is currently under review by the FDA. An FDA panel recommended approval of a first-generation iStent in July 2010, Thomas W. Samuelson, MD, OSN Glaucoma Section Editor, said.

There are trade-offs to consider when choosing between ab externo microincision techniques and ab interno, according to Thomas W. Samuelson, MD. Image: Fleming S

Three versions of the iStent, as well as several other devices, are in various stages of the FDA review cycle.

“We’re going on a year and a half now waiting for approval from the FDA following the favorable panel recommendation,” Dr. Samuelson said. “Once that becomes available, then we’ll have another ab interno approach.”

MIGS an evolving concept

Steven D. Vold, MD, said there is some disagreement among clinicians regarding the definition of MIGS. For example, canaloplasty probably should not be classified as a microincision procedure because it is more akin to trabeculectomy than to MIGS, he said.

“There’s a big debate as to what the definition of microincisional glaucoma surgery is, exactly,” Dr. Vold said. “Some people say it’s canaloplasty; other people say it’s lasers and micro-stent technologies. We have to be careful because I suspect that terminology is going to change.”

Ike K. Ahmed, MD, FRCSC, OSN Glaucoma Board Member, said that MIGS involves far less tissue dissection than canaloplasty or trabeculectomy.

“It’s an ab interno microincisional procedure, meaning that we’re working through the clear cornea,” Dr. Ahmed said. “There’s no conjunctival incisions. It’s minimally traumatic to the target tissue, so that whatever we’re doing creates minimal reaction in and to the eye. The safety is extremely high. It is adaptable. It’s something that can be done quickly, and the recovery is very quick. And it has at least modest efficacy.”

Ike K. Ahmed

Even though it is more invasive and requires more tissue dissection than other microincision procedures, canaloplasty may be more effective than some microincision approaches and more desirable in terms of safety than trabeculectomy and tube shunt implantation. Canaloplasty fits into a clinical niche somewhere between trabeculectomy and MIGS, Dr. Ahmed said.

“Canaloplasty has some benefit,” he said. “I look at it as a safer procedure than trabeculectomy, in a category I call ‘BAGS’ — blebless ab externo glaucoma surgery. I look at it as having a bit more effectiveness than MIGS. So, it kind of fits in between, but it’s not really MIGS because it’s much more involved from an external point of view. … In terms of IOP reduction, I’d give a bit of an edge to canaloplasty over MIGS. It may not be as effective as trabeculectomy, although it’s close, but it’s better than MIGS.”

Safety and efficacy

Treatment with the Trabectome is an alternative to trabeculectomy, the gold standard for cases in which IOP in the mid-teens is an acceptable goal, Dr. Vold and colleagues said in a study published in Ophthalmic Surgery Lasers & Imaging in 2010.

The procedure involves insertion of the Trabectome through a clear corneal incision.

Dr. Samuelson said that while Trabectome surgery is easier to perform, it is less efficacious.

“I don’t have head-to-head data to support that statement, but I think if you look at the data that have been published on both procedures, canaloplasty trumps Trabectome in terms of efficacy,” Dr. Samuelson said. “There’s a price to pay for the efficacy, and that’s the fact that it’s a much more labor-intensive procedure, at least intraoperatively. It is certainly a much longer procedure by several-fold. It requires conjunctival and scleral dissections. And it is a more nuanced procedure and very surgeon- and technique-dependent. But it can be learned, and it’s a really good operation to have available for select patients.”

Canaloplasty, which involves the use of a suture to stretch the trabecular meshwork and promote the outflow of aqueous fluid, is more suited for patients with advanced glaucoma short of end-stage disease, Dr. Samuelson said. It is also preferable for patients with extreme axial length, high myopia and severe ocular surface disease, which entails an elevated risk of bleb infection, he said.

“I would say canaloplasty is minimally invasive in a different sort of way,” Dr. Samuelson said. “It’s certainly not minimally invasive in terms of how much dissecting you do. In fact, you do a lot of dissecting. But it is minimally invasive in that it’s putting the patient at less risk and it’s basically a nonpenetrating procedure. So, it’s minimally invasive in that sense.”

Indications and contraindications

Typically, the primary indication for MIGS is early to moderate open-angle glaucoma, Dr. Craven said.

“Most of these MIGS procedures have to have open angles,” he said. “Whether or not it has exfoliation or is pigmentary, I don’t know if we have that sorted out yet. But open angle is the main indication.”

MIGS devices are typically contraindicated in patients with advanced glaucomatous damage, previous trabeculectomy or tube implantation, Dr. Craven said.

Candidates for MIGS tend to be active adults with high expectations, according to Dr. Craven.

“I see a lot of people in Colorado who love to be up in the mountains, and if they have blebs, their eyes bug them. So, they want to have something else done,” he said.

Good candidates also include high myopes, patients on anticoagulant medication and cataract patients with IOP well-controlled by medications, Dr. Craven said.

A patient with a bleb in one eye who has to undergo glaucoma surgery in the fellow eye but does not want another bleb is also a suitable candidate for MIGS.

“If you can try a less invasive procedure that doesn’t leave them with a bleb, I think the patients really are interested in something like that. It kind of fits into that category that we’re looking for,” Dr. Craven said.

The main indication for the Trabectome is significant cataract with concomitant glaucoma that is not severe enough to warrant trabeculectomy, tube shunt implantation or canaloplasty, Dr. Samuelson said.

Cataract extraction alone is a viable alternative to the Trabectome, as is laser endocyclophotocoagulation (ECP), Dr. Samuelson said.

“I guess one comparator you might make to Trabectome is ECP,” he said. “Some people are ECP enthusiasts. Some people use ECP in that same fashion that others use Trabectome.”

Contraindications for the Trabectome include significant peripheral anterior synechiae resulting from angle closure, Dr. Samuelson said.

“Although typically Trabectome is performed before phacoemulsification, in someone with a shallow anterior chamber, you would probably do it after the cataract is removed just to open the angle up a bit more,” he said. “But it can’t really be effectively done in a patient who has significant synechial closure to the angle. You might not want to do it in patients with elevated episcleral venous pressure, but those cases are pretty infrequent.”

Dr. Vold reiterated that MIGS procedures such as Trabectome and iStent are best suited to patients with mild to moderate open-angle glaucoma.

“I think the predominant patient group tends to be the more mild to moderate open-angle glaucoma,” he said. “Now, can you use them in more advanced glaucoma? I think that’s probably true, but I think the target population is generally mild to moderate open-angle glaucoma.”

Canaloplasty is generally indicated for patients with moderate open-angle glaucoma, according to Dr. Vold.

“When I use canaloplasty, it is generally for people with moderate open-angle glaucoma who tend to be on one to three medications,” he said.

It is possible to use canaloplasty in patient who are on up to four medications, but it is not ideal for patients with blebs, Dr. Vold said, adding that canaloplasty combines nicely with cataract surgery.

Other microincision devices

In addition to the iStent, several other filtering and bypass devices designed to facilitate the egress of aqueous fluid are in the development pipeline, such as the AquaFlow drainage device (STAAR Surgical), the CyPass Micro-Stent (Transcend Medical) and the Hydrus intracanalicular implant (Ivantis).

The Ex-PRESS glaucoma filtration device (Alcon) received FDA clearance in 2002.

The Ex-PRESS device, canaloplasty, Trabectome and the iStent are approved in Canada, Dr. Ahmed said.

The iStent, the first ab interno micro-bypass implant for glaucoma, is designed to fit into Schlemm’s canal.

Dr. Vold said the iStent provides rapid postoperative visual recovery and IOP reduction. It is not uncommon in his hands for patients to have 20/20 vision and an IOP of 10 mm Hg on the first day postoperatively, he said.

“These eyes look remarkably quiet. There’s hardly any tissue trauma. If you use multiple stents, a lot of times you get pressures in the mid-teens or better. I really think that there are some real possibilities with this procedure,” Dr. Vold said.

The Ex-PRESS, a mini-shunt implanted between the inner and outer regions of the eye, is designed to bypass the eye’s natural drainage structures.

In an article published in OSN in 2008, Dr. Samuelson characterized the Ex-PRESS mini-shunt as a safe and standardized sclerostomy procedure with a short learning curve.

The AquaFlow, a collagen implant, is inserted during a nonpenetrating deep sclerectomy procedure. It is designed to channel excess aqueous fluid from the eye.

The Hydrus is inserted through a microincision and designed to create an opening through the trabecular meshwork and dilate Schlemm’s canal to facilitate the exit of aqueous fluid.

The CyPass is inserted into the eye during routine cataract surgery, after the IOL has been implanted.

Dr. Vold said there is a lack of long-term data on the CyPass, which has been implanted in about 200 cases in the U.S. The CyPass entered the first phase of its pivotal FDA clinical trial in October 2009 and began phase 2 of this trial in August 2011.

The Hydrus and the iStent show promise but need to undergo more scrutiny as well, Dr. Vold said.

“We don’t have a lot of long-term follow-up. I’ve got more than 2 years of follow-up on some of these patients, but I think it’s just too early to make a final call on the exact clinical role of these devices yet,” Dr. Vold said. “I think both the Hydrus and iStent devices have a lot of potential. There’s just a lot of research that still needs to be done on these devices, in my view.”

Dr. Craven has been involved with FDA clinical trials for the Hydrus, iStent and CyPass. He implanted the first iStent in the U.S. as part of the clinical trial. He was also the first U.S. surgeon to implant the CyPass outside the U.S. before the FDA trial began.

“It’s a learning curve with these ab interno techniques, because if you’re not used to working with some sort of gonioscope in the OR to visualize the angle and working in there, it’s a transitional change,” Dr. Craven said. “I think for a lot of people that’s probably their biggest apprehension to get into it. But once you overcome that kind of curve, for me, it has opened up a lot more considerations for most of my patients who are approaching cataract surgery with glaucoma.”

The Hydrus implant covers 8 mm of Schlemm’s canal, while the iStent covers 1 mm of the canal, Dr. Samuelson said. Consequently, more than one iStent may be required to achieve more than modest IOP reduction, he said.

“The first Hydrus that I put in [was] 15 mm in length,” Dr. Samuelson said. “So, you get some sense of how much longer that is. The added length adds complexity to the procedure, and 15 mm was too long; 8 mm (the length of the current Hydrus device) seems to be just about right.”

The CyPass and third-generation iStent are inserted into the suprachoroidal space, Dr. Samuelson said.

Combined procedures

Dr. Vold said that the Trabectome and iStent procedures can be performed concurrently with cataract surgery.

“Sometimes it’s the cataract that really drives the procedure,” Dr. Vold said. “And [patients are on] medications for glaucoma. … If they need a cataract removed, sometimes that’s the ideal time to get them off their medications.”

Dr. Vold said he prefers a 1.7- or 1.8-mm incision for a combined cataract and glaucoma procedure.

“The one that’s going to need the largest incision is the cataract surgery,” Dr. Vold said. “The Trabectome procedure requires a 1.7-mm to 1.8-mm incision. That’s about ideal for the cataract and the glaucoma procedure. For these little micro-stents, we may be able to do it with even smaller incisions.”

Dr. Vold said he typically performs the cataract surgery first, then moves on to the glaucoma procedure.

“For phaco-trabs, I typically use a two-site approach,” he said. “I do the cataract surgery first. I don’t even move. I stay at the side of the table, and then I perform the incision superiorly. Filtration surgery utilizing the Ex-PRESS glaucoma filtration device performs favorably when compared to the trabeculectomy, so we use quite a few of these devices as well.”

However, when performing a Trabectome procedure, Dr. Vold sometimes performs the glaucoma procedure first because of superior visualization through the cornea.

Dr. Ahmed said data show that phacoemulsification alone reduces IOP.

MIGS is a solid alternative to phacoemulsification in mild cases in which patients’ IOP is well-controlled on medications. Conversely, trabeculectomy or phacotrabeculectomy are alternatives to MIGS in patients with higher preoperative IOP, even on medications, Dr. Ahmed said.

“We may see MIGS competing with phaco-trab for those that are more advanced with controlled IOPs or maybe in mild to moderate glaucoma patients who have a higher preoperative pressure even on medications, where the surgeon is perhaps going to be reluctant to go to MIGS because he is concerned whether it’s going to be efficacious enough,” Dr. Ahmed said. “But there may be a role for it, and that’s where the competition with phaco-trab would be.”

For now, while awaiting approval for iStent, Trabectome is the most physiological alternative to phacoemulsification alone for early to moderate disease, Dr. Samuelson said.

“Do I have a patient who can get by with cataract surgery alone, or do I have a patient who needs something in addition to cataract surgery? For the latter group, Trabectome is most efficient with modest efficacy, while canaloplasty has better efficacy but is more labor intensive of the currently available techniques,” he said. – by Matt Hasson

Should MIGS be considered for glaucoma patients before more invasive surgery such as trabeculectomy or tube shunts?

Lindstrom's Perspective
MIGS a promising opportunity for patients and physicians

References:

• Gedde SJ, Herndon LW, Brandt JD, Budenz DL, Feuer WJ, Schiffman JC. Surgical complications in the Tube Versus Trabeculectomy Study during the first year of follow-up. Am J Ophthalmol. 2007;143(1):23-31.
• Gedde SJ, Schiffman JC, Feuer WJ, Herndon LW, Brandt JD, Budenz DL. Treatment outcomes in the tube versus trabeculectomy study after one year of follow-up. Am J Ophthalmol. 2007;143(1):9-22.
• Shingleton, BJ, Wooler KB, Bourne CI, O’Donoghue MW. Combined cataract and trabeculectomy surgery in eyes with pseudoexfoliation glaucoma. J Cataract Refract Surg. 2011;37(11):1961-1970.
• Tham CC, Li FC, Leung DY, Kwong YY, Yick DW, Lam DS. Microincision bimanual phacotrabeculectomy in eyes with coexisting glaucoma and cataract. J Cataract Refract Surg. 2006;32(11):1917-1920.
• Vold S, Dustin L; Trabectome Study Group. Impact of laser trabeculoplasty on Trabectome outcomes. Ophthalmic Surg Lasers Imaging. 2010;41(4):443-451.

• Ike K. Ahmed, MD, FRCSC, can be reached at Credit Valley EyeCare, 3200 Erin Mills Parkway, Unit 1, Mississauga, Ontario L5L 1W8, Canada; 905-820-6789; email: ike.ahmed@utoronto.ca.
• E. Randy Craven, MD, can be reached at Specialty Eye Care, 11960 Lioness Way, Suite 190, Parker, CO 80134; 303-794-1111; email: ercraven@glaucdocs.com.
• Thomas W. Samuelson, MD, can be reached at Minnesota Eye Consultants, 701 E. 24th St., Suite 106, Minneapolis, MN 55404; 612-813-3628; email: twsamuelson@mneye.com.
• Steven D. Vold, MD, can be reached at Boozman-Hof Regional Eye Clinic, 3737 West Walnut, Rogers, AR 72756; 479-246-1700; email: svold@cox.net.
• Disclosures: Dr. Ahmed is a consultant for Alcon, AquaSys, Glaukos, Ivantis and Transcend Medical. Dr. Craven is a consultant for and receives research support from Glaukos, Ivantis and Transcend Medical. Dr. Samuelson is a consultant and investigator for Glaukos and Ivantis. Dr. Vold is a consultant for AquaSys, Glaukos, iScience and Transcend Medical.