Clinicians seek appropriate niche for microincision glaucoma surgery

Issue: April 2012

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.

“As the population ages with a more active lifestyle, we look to glaucoma procedures to provide fewer long- and short-term complications, better intraocular pressure control and fewer patient compliance concerns than topically applied medications,” Brett G. Bence, OD, FAAO, told Primary Care Optometry News in an interview.

Dr. Bence practices with three glaucoma surgeons at Northwest Eye Surgeons with clinics in the greater Puget Sound area of western Washington State, where he provides postoperative care and recommends glaucoma filtering surgery consults when appropriate.

One microincision glaucoma surgery technique, trabeculectomy ab interno with the Trabectome (NeoMedix), has been approved by the U.S. Food and Drug Administration, the European Union and a number of other countries and is undergoing review in Latin America. 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 believe 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, of Specialty Eye Care, Parker, Colo., said in an interview.

Steven D. Vold

“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 include hypotony, choroidal hemorrhage and bleb problems,” he said.

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, of Minnesota Eye Consultants, Minneapolis, said in an interview.

MIGS an evolving concept

Steven D. Vold, MD, of Boozman-Hof Regional Eye Clinic, Rogers, Ark., 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. “We have to be careful because I suspect that the terminology will change,” he said in an interview.

Ike K. Ahmed, MD, FRCSC, of Credit Valley EyeCare, Mississauga, Ontario, said that MIGS involves far less tissue dissection than canaloplasty or trabeculectomy.

E. Randy Craven

“It’s an ab interno microincisional procedure, meaning that we’re working through the clear cornea,” Dr. Ahmed said in an interview. “There are 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 can be done quickly, and the recovery is very quick. And it has modest efficacy.”

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 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, canaloplasty is a bit more effective than MIGS but not as effective as trabeculectomy.”

Ike K. Ahmed

Indications and contraindications

Dr. Bence and his colleagues at Northwest Eye Surgeons agree that trabeculectomy and tube implants are reserved for more advanced glaucoma, but they see a role for microincision glaucoma surgery for mild to moderate glaucoma.

“These devices may be particularly useful if there is concurrent ocular surface disease and/or intolerance or allergic reaction to topical glaucoma medications,” Dr. Bence said.

The newer ab interno (no conjunctival incision) glaucoma devices are less invasive and are expected to have an improved safety profile, he said.

“Conversely, we feel that the risks associated with Trabectome – IOP spikes, hyphema and disappointing pressure control – appear to outweigh the short- and long-term benefits, although we respect that others may have a different experience,” Dr. Bence said.

The clinicians at Northwest Eye look forward to trying alternative ab interno shunts once they are FDA approved and their performance is demonstrated over time. “They show promise based on reviewers’ observations,” Dr. Bence said. “We also see a growing opportunity for their use with combined cataract and glaucoma surgery for this increasing segment of moderate glaucoma.”

Brett G. Bence

Dr. Bence said his practice’s general approach is to choose trabeculectomy or tube implants if the desired IOP is 12 mm Hg or less for severe glaucoma and canaloplasty or viscocanalostomy if the target is 13 mm Hg to 15 mm Hg for moderate glaucoma.

“Ex-Press (Optonol) shunts, if your glaucoma surgeon uses them, are essentially an ab externo modified trabeculectomy with some measure of less risk for hypotony than trabs,” Dr. Bence said. “We have implanted these with reasonable success. The disadvantage is cost, because, currently, this device is not covered by insurance except on a case-by-case basis.

“We have achieved a good level of IOP control with canaloplasty, often obtaining pressures 1 mm Hg to 2 mm Hg lower than with viscocanalostomies,” Dr. Bence continued. “Disadvantages include the added cost and more time for dissecting in the operating room; however, this remains a preferred option over viscocanalostomy if the patient has adequate insurance coverage.”

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

MIGS devices are usually contraindicated in patients with advanced glaucomatous damage, previous trabeculectomy or tube implantation, he said. Candidates for MIGS tend to be active adults with high expectations.

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 must undergo glaucoma surgery in the fellow eye but does not want another bleb is also a suitable candidate for MIGS.

The primary 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), he said.

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

Thomas W. Samuelson

“Although Trabectome is typically 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 be effectively performed in a patient with 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.

“The predominant patient group tends to be the more mild to moderate open-angle glaucoma,” Dr. Vold said, “although you may use them in more advanced glaucoma.

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

It is possible to use canaloplasty in patients 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. – by Matt Hasson and Nancy Hemphill, ELS

References:

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.

For more information:

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; ike.ahmed@utoronto.ca.

Brett G. Bence, OD, FAAO, is a partner and director of optometry at Northwest Eye Surgeons. He can be reached at 1306 Roosevelt Ave., Mount Vernon, WA 98273; (360) 428-2020; fax: (360) 428-6918; bbence@nweyes.com.

E. Randy Craven, MD, can be reached at Specialty Eye Care, 11960 Lioness Way, Suite 190, Parker, CO 80134; (303) 794-1111; 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; 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; svold@cox.net.

Disclosures: Dr. Ahmed is a consultant for Alcon, AquaSys, Glaukos, Ivantis and Transcend Medical. Dr. Bence has no financial interests to disclose. 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.