Microshunts promising future option in glaucoma management

Devices could present surgery as an earlier treatment option and an alternative to medications.

Microshunts are playing an increasingly important role in glaucoma management, with research showing they are potential noninvasive alternatives to trabeculectomy, thus avoiding the burden of multiple medications.

Elie Dahan

“Trabeculectomy has been with us for 40 years, but we have never stopped looking for an easier, safer and more reproducible alternative. This is because trabeculectomy works, but we are hesitant to use it more often. If we weren’t so worried about complications, we would use it more often and would not prescribe ‘cocktails’ of medications just to postpone it as long as we can,” Elie Dahan, MD, Ocular Surgery News Europe Edition Editorial Board Member, said in an interview with the Primary Care Optometry News sister publication.

In the past decade, several micro-shunts have been proposed, and three of them are currently in use. One of them, the Ex-Press glaucoma filtration device (Alcon), is now a well-established method used worldwide, with more than 60,000 procedures performed to date. The other two devices, the CyPass micro-stent system (Transcend Medical) and the iStent micro-bypass device (Glaukos), are newer technologies, used so far in a few small cohort studies.

Ex-Press

The Ex-Press is a miniature nail-shaped tube, 3 mm long, 400 µm wide, with a lumen of 50 µm or 200 µm through which the aqueous is filtered from the anterior chamber to the subscleral and subconjunctival spaces. Dr. Dahan views the Ex-Press technique as a compromise between trabeculectomy and non-penetrating surgery. It combines the advantages of both techniques while minimizing their drawback characteristics, he said, and is at least as easy as trabeculectomy because it is penetrating but has the safety advantage of a nonpenetrating procedure because it restricts the aqueous flow by its miniature design.

“After a few attempts to implant the device under the conjunctiva, a technique that was soon abandoned, I performed my first implantation of an Ex-Press under a scleral flap in September 2000,” Dr. Dahan said. “Since then I have implanted more than 600 Ex-Press devices, with a lot of satisfaction.”

He implants the device under a large 5-mm 3 5-mm scleral flap to obtain a shallow, diffused bleb.

“In my clinical practice, it has totally replaced trabeculectomy, and I have no doubt that it is a better technique. It is more straightforward, and we don’t have to excise tissue. The device is inserted like a nail, through a small slit in the sclera,” he said.

A complete success rate (i.e., IOP of 18 mm Hg without the use of medications) is the only reliable parameter to measure and compare the efficacy of glaucoma procedures, according to Dr. Dahan. Qualified success rates that involve using medications, with their significant compliance issues and wide individual variability, are a confounding factor in the analysis of surgical procedure results.

Dr. Dahan’s overall complete success rate with the Ex-Press implant at 1 year is more than 90%, dropping to around 80% at 2 years to 3 years and subsequently to 65% or 70% after 5 years.

“It is a more reproducible, safer procedure with fewer complications, and in the long run I have seen significant difference in complete success rate between Ex-Press implantation and trabeculectomy,” he said.

When pressure rises at 2 to 3 years, Dr. Dahan prefers to intervene surgically rather than return to medication use to prolong the complete success rate status. This might involve needling, revising the site of filtration by lifting the conjunctiva and the scleral flap, applying mitomycin C and then suturing the conjunctiva and scleral flap back in place. The filtration site can be revised so the implant can function for several more years, if not for the rest of the patient’s life.

In a randomized, prospective study that is currently awaiting publication, 15 patients had trabeculectomy in one eye and Ex-Press implantation in the other eye. After 30 months of follow-up, a difference in complete success rate is emerging in favor of Ex-Press.

iStent, CyPass

With the iStent and CyPass, experience is limited. The iStent has received a CE mark and is commercially available in select countries in Europe. It was also recently approved for use in Canada. A few small clinical studies reviewing the device have been published in the literature in the last 3 years.

The CyPass also has a CE mark but is only available in controlled clinical trials in Europe and the United States.

Marco Nardi

Large prospective, controlled studies are necessary to confirm the efficacy of both procedures before they can be used extensively by a greater number of surgeons, according to Marco Nardi, MD, OSN Europe Edition Editorial Board Member.

“Potentially, they have the characteristics to be used as an alternative to laser or medications at the early stages of glaucoma. But this cannot be done before they go through a proper validation process,” he said.

As part of the growing area of minimally invasive glaucoma surgery, micro-shunts are worth pursuing, Dr. Nardi said.

“They are a gentle approach, so minimally traumatic that the eye seems untouched the day after surgery,” he said. “There are few and minor complications and nothing like the fear of the unexpected that all surgeons who perform trabeculectomy are familiar with. Patients accept this surgery very well and without anxiety.”

The iStent is a trabecular bypass that increases the trabecular outflow. It is inserted ab interno through a small temporal incision in clear cornea.

The iStent could be competition for laser procedures and those that ablate the inner wall of Schlemm’s canal, but its role is not yet clear, he said.

“We have no comparative studies, nor [ultrasound biomicroscopy] studies, showing whether the distal end of the device maintains the Schlemm’s canal open to a certain extent,” Dr. Nardi said.

The CyPass device consists of a 6-mm tube of synthetic material that connects the anterior chamber to the supraciliary space. It is implanted ab interno in the angle under the scleral spur with a special inserter. A clear corneal incision, which can be the primary phacoemulsification incision in combined procedures, is used.

There is a strong rationale for using this device, reinforced by the low complication rate and the procedure’s repeatability, according to Dr. Nardi. If necessary, filtering surgery can be performed at a later stage.

Dr. Nardi is using both the CyPass and iStent devices in select patients, with encouraging results.

“I only have small numbers,” he said. “In the 12 patients with refractory glaucoma implanted with the CyPass, I had better than a 50% success rate, which is a good rate if we take into account that for the time being, I am only using this device in severe cases where everything else has failed. With the iStent, I have implanted six patients, five of whom [were] only a few weeks ago. The one patient with a longer follow-up is maintaining without medications the same IOP he had preoperatively with three medications.”

After extensive evaluation, official validation and perhaps further refinement, these devices may play a more prominent role in the glaucoma specialist’s armamentarium. – by Michela Cimberle

• Elie Dahan, MD, can be reached at Ein Tal Eye Center, 17 Brandeis St., Tel Aviv 62001, Israel; elie.dahan@gmail.com.
• Marco Nardi, MD, can be reached at Università di Pisa, Dipartimento di Neuroscienze, Via Roma 67, 56126 Pisa, Italy; 39-050-553431; marco.nardi@med.unipi.it.
• Disclosures: Dr. Dahan is a consultant for Alcon. Dr. Nardi is a consultant for Alcon and Transcend Medical.