Canaloplasty procedure shows promise for open-angle glaucoma in European study

Combining catheterization of Schlemm’s canal with suture tension lowered IOP in open-angle glaucoma more than viscocanalostomy.

Issue: March 1, 2007

ByJared Schultz

Canaloplasty is showing better IOP-lowering efficacy in early clinical experience than viscocanalostomy for open-angle glaucoma, according to two surgeons.

In canaloplasty, a microcatheter manufactured by iScience is passed into and around Schlemm’s canal. Viscoelastic is then injected through the microcatheter while it is advanced to dilate the canal. A suture is attached to the catheter and retracted through the canal, and the two ends are tied together, leaving slight tension on the canal.

Manfred Tetz, MD, presented interim results from an ongoing multicenter clinical study of the procedure at the European Society of Cataract and Refractive Surgeons meeting. The trial is taking place at four European and six U.S. outpatient surgical centers, he said.

According to Dr. Tetz, 244 patients were enrolled in the study. The patients’ mean age was 68 years, and most of the patients were women, he said.

Of those patients, 188 eyes had no previous glaucoma surgery, and 89% underwent a successful 360° catheterization, he said.

There were five serious complications, including two unrelated to the procedure, two cases of increased IOP that were medically treated and one case of continued high IOP that is being investigated, according to Dr. Tetz.

European results

Early European study data included 65 patients taking an average of two medications with a mean preoperative IOP of 21.9 mm Hg. At 6 months’ follow-up, mean IOP decreased 37% to 13.8 mm Hg, and the average number of medications per patient was 0.2, Dr. Tetz said.

Dr. Tetz also reviewed his own results from his first 20 patients, nine of whom underwent canaloplasty in combination with cataract surgery. At 6 months’ postop, patients had a mean IOP of 13.7 mm Hg, he said. Compared to his previous viscocanalostomy data, the results were an improvement, he said.

“Comparing this to our previous viscocanalostomy data, we were about 3 mm Hg on average lower” with canaloplasty, he said. “There is a success rate that is higher than viscocanalostomy, and we seem to have an improved pressure lowering effect than visco alone.”

Cannulation of Schlemm's canal with ophthalmic microcatheter

Images: Koerber N

Increasing suture tension

Norbert Koerber, MD, also discussed his interim results from the multicenter trial, with a focus on the role of suture tension.

According to Dr. Koerber, his results showed a strong correlation between increasing suture tension and lower IOP. At 12 months’ follow-up, Dr. Koerber showed that if the tension was less than grade 0.5, the mean IOP was 17.3 mm Hg, but if the tension rose above 0.5, the mean IOP fell to 12.5 mm Hg.

This difference was even more pronounced when the tension was either higher or lower than grade 1, he said. At 12 months, the mean IOP was 14.4 mm Hg when the tension was less than 1, but when the tension was more than 1, the IOP dropped significantly to 8.7 mm Hg.

“The tension force is absolutely a strong factor for the pressure-lowering effect, and the process is still going on,” he said.

Pathophysiological processes

Although the mechanism behind the pressure-lowering effects of suture tension are not entirely known, the researchers are learning more as the study continues, Dr. Tetz told Ocular Surgery News in a telephone interview.

“We have found that if we do not see a tension toward the anterior chamber, the postoperative pressure is higher, so we have had some indentation toward the anterior chamber of Schlemm’s canal or some inward pulling to get better results,” Dr. Tetz said.

During his presentation, Dr. Koerber said doctors should look for a “ledge” as a signal of good tension. He described the importance of this ledge in an e-mail interview with OSN.

“The ledge to look for is the prominence of the trabecular meshwork visible in ultrasound imaging,” he wrote. “It is a measure for the tension of the canalicular located suture.”

Dr. Tetz told OSN that there may be more at play in the pressure-lowering mechanism of the suture tension. Although stretching of the walls of Schlemm’s canal is one of the theories, he said the IOP-lowering effect could be a matter of preventing collapse of the canal.

“I think a secondary collapse of Schlemm’s canal is a major influence factor of open-angle glaucoma,” he said. “I think we will be rewriting the book on understanding of glaucoma disease and the pathophysiological process quite soon.”

For more information:

Manfred Tetz, MD, can be reached at the Berlin Eye Research Institute, Alt-Moabit 98/99, D-10559 Berlin, Germany; 49-030-398-098-50; fax: 49-030-398-098-44. He has no financial interest in the iScience microcatheter.

Norbert Koerber, MD, can be reached at Augen-OP-Centrum Porz, Ernst-Mühlendyck-Str. 1, 51143 Köln, Germany; 49-02203-591725. He has no financial interest in the iScience microcatheter and he is not a consultant for iScience.

iScience, maker of the iCath ASAT, can be reached at 4055 Campbell Ave., Menlo Park, CA 94025; 650-421-2700; fax: 650-362-1841; Web site: www.isciencesurgical.com.

Jared Schultz is an OSN Staff Writer who covers all aspects of ophthalmology. He focuses geographically on Europe and the Asia-Pacific region.