In the United States, drainage stents are fast becoming an important part of the glaucoma surgeon’s armamentarium. Both the EX-PRESS Glaucoma Filtration Device (Alcon, Fort Worth, Texas) and the iStent Trabecular Micro-Bypass (Glaukos, Laguna Hills, Calif.) are coming onto practitioners’ radars as potential options for their glaucoma patients—if not now then for the near future.

While both of these are drainage devices, they are very distinct, shunting fluid into different areas, according to Richard A. Lewis, M.D., Sacramento, Calif. “The iStent drains fluid into the canal,” Dr. Lewis said. “That is pending FDA approval—although it has the panel recommendation, the FDA hasn’t acted on that as of yet.” He described the device as very small and fairly straightforward to insert, with less trauma to the eye than with other stents. “There’s some good there,” Dr. Lewis said. “The bad is that we don’t get quite the pressure reduction that we do with subconjunctival shunts.”

By contrast, the EX-PRESS device drains fluid into the subconjunctival space. “It’s really a variant of a trabeculectomy that standardizes the hole,” Dr. Lewis said. “With a trabeculectomy we’re making a punch with a little hole puncher. With the EX-PRESS, we’re still using a hole punch, but we’re putting a stent in there, which drains into the subconjunctival space.” He finds this brings with it many of the same problems as trabeculectomy, including wound healing difficulties, hypotony, scarring, and fibrosis.
He sees the patient population for these two drainage stents as likely to be distinct. “The EX-PRESS could be used in any patient who needs a trabeculectomy, open or closed angle,” Dr. Lewis said. “The iStent could only be used in open [angle] glaucoma and will most likely be combined with cataract surgery.”

Thomas W. Samuelson, M.D., director, glaucoma service, and instructor, ophthalmic pharmacology, Regions Hospital, St. Paul, Minn., and attending surgeon, Minnesota Eye Consultants, Minneapolis, agreed that there is likely to be overlap between the two. “I think the iStent is going to be used earlier in the treatment scheme because it’s going to be used for early to moderate disease, at least in my opinion,” he said. “Although in the FDA clinical trial the iStent was used in conjunction with cataract surgery, and that’s probably going to be its biggest market, I perceive the possibility of using it outside of cataract surgery as well.”

Eyeing The iStent

A key benefit of the iStent is its minimally invasive nature. “The procedure has very low risk,” Dr. Samuelson said. “Indeed I think that the biggest risk will be that it doesn’t adequately control glaucoma so the disease will progress.”

Dr. Samuelson described the iStent as a titanium device that is 1 mm in length. “Contrary to what a lot of people believe, it’s not a tube, it’s more like a half-pipe,” Dr. Samuelson said. The device is designed with an open back so that none of the collector channels or drainage channels are blocked. “Aqueous goes through the opening and then it should have complete access to all of the collector channels,” Dr. Samuelson said. “It’s bi-directional, so once aqueous passes into the canal it can go either left or right circumferentially within the canal.”

Dr. Samuelson sees the design as very unique. “Other procedures such as the canaloplasty stent the canal open 360 degrees but don’t provide that direct pathway for aqueous to flow into the canal.”
The device is placed through a very small clear corneal incision. “You can usually do it through a 1.5-mm incision or less—maybe even through a needle tract incision,” Dr. Samuelson said. “It’s placed in Schlemm’s canal so it produces an open conduit from the anterior chamber into Schlemm’s canal.” Dr. Samuelson said one differentiating feature of the iStent is that it does not stent open the canal but rather provides a window through which aqueous flows into the canal. “Its circumferential extension is only 1 mm into the canal,” he said. “Keep in mind that the canal itself is about 36 mm long.”

One natural area of use for the iStent is likely to be in those glaucoma patients who are slated to undergo cataract surgery. “One of the things that makes it particularly appealing is that in the FDA trial there was no measurable reduction in the safety of the procedure when comparing the patients receiving cataract surgery plus iStent versus cataract surgery alone,” Dr. Samuelson said. “So we take one of the most successful and safest procedures with the most favorable risk benefit ratio and find that we do not adversely affect it by adding an iStent in any measurable way.” If adding the iStent to the mix during cataract surgery can make the patient’s glaucoma easier to manage, Dr. Samuelson sees it as beneficial to do so.

He points out that people have actually been moving away from the combined phacoemulsification trabeculectomy procedure for the opposite reason. “Adding a trabeculectomy to a phacoemulsification procedure adds considerable risk,” he said. “While it may lower pressure more, there’s definitely a subset of glaucoma patients, i.e., those with early to moderate disease, in which we don’t do them a favor by exposing them to that increased risk, unless they really need it.” By classifying the glaucoma as early to moderate as opposed to more advanced disease, he thinks that practitioners can effectively separate which patients can benefit from a combined iStent or a combined phaco trabeculectomy.
Outcomes with the iStent vary depending upon the patient and can be confounded by medication. However, in the recent FDA trial patients were required to be off of their glaucoma medication pre-op. “All of the patients went into the surgery with an average pressure of about 25 mm Hg on no medicines,” Dr. Samuelson said. “The average pressure post-operatively was around 18 mm Hg at 1 year on 0.4 medicines in the cataract only group and 0.2 medicines in the iStent group—a statistically significant difference.” As a rule, patients were less likely to need to return to medication on the iStent. “There were twice as many patients in the cataract alone group back on medicines compared to the group receiving the iStent,” Dr. Samuelson said.

Assuming the iStent nabs FDA approval, Dr. Samuelson envisions a possible way of expanding the device’s usefulness. “There may be other applications for the iStent such as use of multiple stents,” he said. “There is work in Canada by Iqbal (Ike) K. Ahmed, M.D., [assistant professor, University of Toronto, Toronto] that shows that using more than one stent may obtain lower pressures. I don’t think that we’re going to compromise safety by adding additional stents.” Dr. Samuelson thinks that if the use of multiple iStents proves to be safe and minimally invasive while further lowering pressure, that will expand indications to a higher percentage of patients with glaucoma.

Dr. Samuelson sees the EX-PRESS shunt as a more precise, less invasive, safer trabeculectomy. “At least initially I don’t see these two stents as competing for the same patient population,” he said. “I see the iStent being for early to moderate disease and the Ex-PRESS as a very useful adjunct to trabeculectomy for patients with more advanced disease.”

On The EX-PRESS Track

Robert D. Fechtner, M.D., professor of ophthalmology, Institute of Ophthalmology and Visual Science, New Jersey Medical School, University of Medicine & Dentistry of New Jersey, Newark, N.J., described the EX-PRESS as a small, stainless steel device that has a narrow aperture to provide some resistance to flow through the device. “It replaces one step of the trabeculectomy procedure,” he said.

With a full-fledged trabeculectomy, after the flap is created the surgeon enters the eye and removes partial thickness cornea 0.5 mm to 1 mm or more. “This essentially creates a zero resistance channel to outflow and allows the eye pressure to drop to near atmospheric pressure,” Dr. Fechtner said. “We then restore resistance by suturing the flap in place.”

Use of the EX-PRESS standardizes one part of the procedure. “Once the flap is created, we enter under the flap with a small needle, typically 25-27-gauge, and insert the EX-PRESS device, which functions as a very small aperture with some resistance,” Dr. Fechtner said. “We then provide additional resistance with the scleral flap, much as we do in trabeculectomy.”

Dr. Fechtner finds that the key differences for the surgeon and the patient are the relatively non-invasiveness of the paracentesis and the small needle entry. The rest of the surgery is extraocular. “When performing the EX-PRESS procedure, it is unnecessary and in fact not really technically possible to do an iridectomy,” Dr. Fechtner said. “This avoids many complications that might be associated with an iridectomy.”

It then becomes a question of determining for which patients the Ex-PRESS shunt may be preferable to a traditional trabeculectomy. Dr. Fechtner sees this issue of patient selection as a continuously evolving one for glaucoma surgeons. “We started out with Molteno tubes (IOP, Costa Mesa, Calif.) in our most complex eyes, and we now have a trab versus tube study suggesting that tubes might come very early in our surgical algorithm,” he said. “Similarly, I think that as we gain experience with the EX-PRESS and we accumulate knowledge about the results, we will have a better idea of where it fits and what the best match is.”

In Dr. Fechtner’s view there are a couple of types of patients for whom use of the EX-PRESS device is an excellent option. “The first obvious place where the EX-PRESS would be a good match would be in a patient who is at increased risk of bleeding,” he said. A second type of patient that he often selects for the EX-PRESS is one in which there may be concern of vitreous behind the iris and that an iridectomy would release this into the sclerostomy.

Malik Y. Kahook, M.D., associate professor, University of Colorado, Denver, agreed that the EX-PRESS device is suitable for the same group of patients who would otherwise undergo traditional trabeculectomy. However, he stressed that these are not the more extreme cases. “It’s not the patient population that has failed two trabeculectomies for whom you then go on to a glaucoma drainage device like an Ahmed (New World Medical, Rancho Cucamonga, Calif.) or a Baerveldt (Abbott Medical Optics, AMO, Santa Ana, Calif.). It’s also not the [early glaucoma] category, what we’re calling the ‘cataract plus,’ where we would use the iStent and potentially the CyPass (Transcend Medical, Menlo Park, Calif.),” Dr. Kahook said.

There are a few cases, however, in which Dr. Kahook finds the Ex-PRESS to be particularly helpful. “I use it for the monocular patient who needs quick visual recovery because in my hands, the EX-PRESS patient has quicker visual recovery than a traditional trabeculectomy patient,” he said. “I also use it when I’m combining a cataract plus a trabeculectomy.” He finds this to be a less traumatic procedure. “It’s a quieter eye because I’m not doing a peripheral iridectomy, I have more control of the anterior chamber, and I’m much less likely to get a shallow or flat anterior chamber post-operatively,” Dr. Kahook said. He also tends to use the EX-PRESS in those patients who are on anticoagulants. This way, he can avoid an iridectomy and is much less likely to have a hyphema.

Outcomes with the EX-PRESS are promising. Dr. Kahook recently conducted a study comparing the Ex-PRESS shunt to trabeculectomy, with results slated to come out in an upcoming issue of the American Journal of Ophthalmology. He found that the device offers similar pressure lowering to traditional trabeculectomy. “We compared trabeculectomy to the EX-PRESS with 2 years of follow-up and we found that the IOP lowering was roughly comparable to that of trabeculectomy,” he said. “They both essentially did the same and the pressure lowering was in the 11-13 mm Hg range for all patients.”

Dr. Kahook also found that the speed of visual recovery with the EX-PRESS outstrips traditional trabeculectomy. “We found that patients recover onto their baseline visual acuity at 1 week after EX-PRESS versus 1 month for trabeculectomy,” he said. Dr. Kahook attributes this more rapid healing response to a combination of things. “There is much less surgical manipulation with the EX-PRESS so you’re less likely to have corneal edema or uveitis post-operatively,” he said. “You’re also less likely to induce any astigmatism because it’s minimally invasive.” In addition, he pointed out that with the EX-PRESS the chances of complications such as hyphema are decreased, and patients are less likely to have very low intraocular pressure in the early post-op days.

Dr. Fechtner likewise has observed more rapid recovery with the EX-PRESS shunt, with pressure lowering equivalent to trabeculectomy. “I do think that vision is better early on, and my clinical impression has been that it’s easier to manage these post-operatively, as I have evolved into a better technique using the device,” Dr. Fechtner said.

Overall, Dr. Fechtner sees both the iStent and the EX-PRESS shunt as moving glaucoma surgery forward. “I think that we should be very grateful as glaucoma surgeons to see industry and fellow surgeons innovating,” he said. “We understand the problems with our current glaucoma procedures and yet we stick with them, waiting for something to offer advantages—any small advantage to me is a major step forward in glaucoma surgery.”

by Maxine Lipner
Senior EyeWorld Contributing Editor
eyeworld.org

Editors’ Note: Dr. Fechtner has financial interests with Alcon. Dr. Kahook has financial interests with Alcon and consults for the U.S. Food and Drug Administration. Dr. Lewis has financial interests with Alcon, Glaukos, iScience (Menlo Park, Calif.), and Sanofi-Avantis (Bridgewater, N.J.). Dr. Samuelson has financial interests with AMO, AcuMems (Menlo Park, Calif.), Alcon, Allergan (Irvine, Calif.), AqueSys (Irvine, Calif.), Endo Optiks (Little Silver, N.J.), Glaukos, iScience, Ivantis (Irvine, Calif.), Pfizer (New York), QLT (Menlo Park, Calif.), and Santen (Napa, Calif.).

Contact Information
Fechtner: 973-972-2030, fechtnrd@umdnj.edu
Kahook: 720-848-2500, malik.kahook@gmail.com
Lewis: 916-649-1515, rlewiseyemd@yahoo.com
Samuelson: twsamuelson@mneye.com