Safer Glaucoma Surgeries Find Favor

Bleb-less procedures reduce complications, hypotony and infection risk.

By Jerry Helzner, Senior Editor

For decades, trabeculectomy stood as the “gold standard” for treating advanced and refractory glaucoma. Despite its invasive nature and potential for complications, bleb-related problems, need for additional surgeries and even endophthalmitis, trabeculectomy is the surgical procedure for glaucoma most taught in ophthalmology residency programs.

The foundation underpinning the pre-eminence of trabeculectomy in glaucoma surgery has been somewhat shaken in the past several years with the release of the large-scale Tube vs. Trabeculectomy (TVT) study that showed traditional glaucoma shunts overall to be a somewhat safer and more effective treatment for some glaucomas than trabeculectomy. Good news for sure, but traditional shunts are best implanted by experienced and skilled glaucoma specialists who can avoid the danger of sudden and disastrous hypotony, which is an ever-present risk with shunts.

However, even well before the TVT study began, several innovative companies and a number of elite glaucoma specialists were collaborating on advanced concepts that promised safer and minimally invasive bleb-less surgeries for open-angle glaucoma. The primary goal of these new procedures was to largely eliminate complications, hypotony and infections while also reducing the number of medications needed by patients. These innovators were also interested in developing attractive options for combined cataract/glaucoma surgery. They would accomplish these aims (in different ways) by tapping into Schlemm's canal, the conventional pathway for aqueous outflow.

Here, I will discuss three minimally invasive, bleb-less procedures performed in the OR that are in the vanguard of the next wave of safer glaucoma surgeries. Of the three, canaloplasty (iScience) and Trabectome (NeoMedix) have been FDA-approved for several years, while the iStent (Glaukos, Inc.) is in regular use internationally and has been recommended for approval by the FDA's Ophthalmic Devices Advisory Panel.

Three Different Concepts

Though the three procedures all have the same goals — and appear to be meeting these objectives in studies and in practice — the basic approaches are different.

► Canaloplasty uses an illuminated, beacon-tipped microcatheter to facilitate a 360-degree viscodilation of Schlemm's canal. Once this is achieved, an intracanalicular suture is placed that cinches the trabecular meshwork inward while permanently opening Schlemm's canal.

► Trabectome surgery uses the Trabectome System, which does require a significant capital investment to purchase and a per-procedure cost. The Trabectome procedure itself is very minimally invasive, involving a small clear-corneal incision, gonio lens placement to obtain an accurate view of the angle and an electrical ablation to remove a small strip of trabecular meshwork and access Schlemm's canal.

In canaloplasty, Schlemm's canal is exposed and an illuminated microcatheter is passed a full 360 degrees through the canal.

► The iStent also employs a clear-corneal incision and gonioprism to view the angle. Aqueous outflow is re-established by the ab interno placement of a stent into Schlemm's canal. Surgeons can titrate patients to lower desired target pressures by implanting two or more stents directly into the canal in a single procedure. The iStent procedure bypasses the trabecular meshwork, which has been shown to be a major source of resistance to aqueous outflow.

The Trabectome procedure ablates a small slice of the trabecular meshwork to facilitate aqueous outflow.

According to Chris Calcaterra, chief commercial officer for Glaukos, the company is the first to have conducted a prospective, randomized, controlled multi-center US clinical trial for PMA approval of a glaucoma drainage device. The company also pioneered the concept of using micro-stents in combination with cataract surgery to treat co-morbid cataract/OAG patients.

Respected glaucoma specialist Thomas W. Samuelson, MD, of Minneapolis, has reported that in the 29-site, 240-eye US pivotal trial of patients with cataract and mild-to-moderate open-angle glaucoma, the iStent group produced outcomes that were significantly superior to cataract surgery alone in reducing drug burden, while both lowering IOP and demonstrating a reduced need for medications. The trial indicated an iStent safety profile that was comparable to cataract surgery alone. The iStent PMA submission is currently under FDA review for implantation in combination with cataract surgery.

In addition to its flagship iStent technology, Glaukos has developed a complete franchise of ab interno micro-stents for treating the full range of glaucoma disease stage severity and has additional stents that are under evaluation in FDA registration trials.

The iStent, which has been recommended for approval by an FDA advisory committee, allows aqueous to flow directly into Schlemm's canal, bypassing the trabecular meshwork. One or more iStents can be used in this procedure.

One Surgeon's Assessment

Brian Francis, MD, a glaucoma specialist at the Doheny Eye Institute at the University of Southern California, views Trabectome and iStent as somewhat similar procedures because they both employ a clear-corneal incision and a gonio lens to obtain an accurate view of the angle and perform the procedure.

“Though the procedures do differ in the method for accessing Schlemm's canal and re-establishing the aqueous outflow, there is some overlap between Trabectome and iStent,” he says. “Canaloplasty doesn't have as much overlap with the other two procedures. I tend to use canaloplasty in more advanced cases.”

Dr. Francis says both Trabectome and the iStent are well-suited for combination phaco/glaucoma surgery.

“You are using the same incision for both the phaco and glaucoma procedures,” he says. “There is no extra dissection and reduced extra OR time. These are ease-of-use factors that make these combination procedures appealing to surgeons.”

Efficacy of Minimally Invasive Procedure

Though some view the newer, minimally invasive procedures as being consigned to patients with mild-to-moderate open-angle glaucoma, some recent studies indicate that they may be even more effective than initially believed.

In one 90-patient study presented at ARVO in 2009, the results of canaloplasty compared favorably with trabeculectomy and Alcon's Ex-Press mini-shunt. In another 2009 ARVO presentation, the iStent performed well in patients with refractory glaucoma who had failed at least one prior glaucoma surgery. And in a 2010 ARVO paper, a 427-patient study deemed Trabectome surgery a success when used on patients who had significantly higher baseline IOP due to exfoliative glaucoma. A larger-scale study presented at the 2009 ARVO meeting also found Trabectome effective over a broad cross-section of glaucoma patients.

“I think glaucoma specialists believe that trabeculectomy is generally more effective in lowering pressure,” says Dr. Francis. “However, if you exclude hypotonous eyes with very low pressures from the comparative studies, you may find that the newer procedures are achieving IOP results similar to trabeculectomy, especially if medications can be used. I am certainly doing fewer trabs than I used to and I think that is the trend. Trabeculectomy isn't going to go away. These are all useful procedures, including the Ex-Press mini-shunt, and we should be deciding which procedure to use on a patient-by-patient basis.”

Safety Drives Innovation

Richard A. Lewis, MD, of Sacramento, Calif., who has been involved with canaloplasty since its inception, offers a simple reason for his advocacy of the procedure.

“In my case, it was a safety issue,” says Dr. Lewis. “It bothered me that patients were getting endophthalmitis infections after trabeculectomy.”

The results of canaloplasty speak for themselves — studies show a lowering of IOP and fewer complications with an end to bleb-related issues, hypotony and infections.

“We now have three-year data and the good results are being sustained,” asserts Dr. Lewis. “There has definitely been an upturn in the adoption of the procedure. One goal is to get more cataract surgeons to do it.”

Dr. Lewis believes that certain types of patients with open-angle disease are excellent candidates for canaloplasty.

They include contact lens wearers, eyes with significant ocular surface disease, patients with failed trabeculectomy in the fellow eye, those with corneal implants, individuals who don't heal well where a bleb might get infected and those whose eyes are prone to scarring, such as people of African heritage.

“Canaloplasty has an important place in glaucoma practice because it is safe and effective for some difficult patient cases,” asserts Dr. Lewis.

If there has been a negative associated with canaloplasty, it is that the procedure has a reputation for requiring a steep learning curve that takes time to master. The rebuttal to that argument is that most patients who undergo canaloplasty have far fewer postop problems than patients who have trabeculectomy.

“It's definitely a more patient-friendly procedure than trabeculectomy,” says Dr. Lewis. “In terms of the learning curve, iScience offers an excellent instruction program for teaching canaloplasty. With experience, an ophthalmologist can perform the procedure in the OR in about 30 to 35 minutes.”

Adoption by Residency Programs

As mentioned at the beginning of this article, general ophthalmologists are trained to perform trabeculectomy and implant traditional glaucoma shunts in their residency programs. The companies behind Trabectome, iStent and canaloplasty are eager to have their procedures taught in residency programs as a way to drive adoption in the next generation of glaucoma specialists and cataract surgeons.

Dr. Lewis says that such training is already happening.

“Some residency programs have already incorporated these newer procedures, but it depends on who's teaching,” he says. “Getting these procedures into training programs will certainly drive future adoption.”

“I think the path to wider adoption for these procedures is to first gain acceptance in the glaucoma community and then in general ophthalmology,” says Dr. Francis. “We are now seeing these newer procedures getting into some residency programs, with residents being exposed to these procedures and learning how and when to use them.”

And this from Nathan Radcliffe, MD, a glaucoma specialist at Weill-Cornell Medical College in New York City.

“Adoption by teaching programs might be slow and sporadic until a particular surgery gains consensus approval, as residency programs typically have multiple glaucoma instructors. Minimally invasive surgeries such as Trabectome and iStent should be excellent resident cases because safer surgeries are also safer to teach, will have broader indications and should also have more forgiving learning curves for the residents.”

One question that must be asked is if there is actually a need for three new, and in some ways similar, minimally invasive IOP-lowering procedures that have come along at about the same time. Despite the proven effectiveness and safety of all three procedures, can each one find its niche?

“I look at these procedures as constituting a new class of glaucoma surgery that together represent a big advancement,” says Dr. Francis. “I believe there is room for all three.” OM