MIGS Maxing: Canaloplasty or Trabecular Micro-Bypass Surgery?

Both canaloplasty and trabecular micro-bypass surgery (TMBS) are proven techniques for carrying out minimally invasive glaucoma surgery (MIGS), but when it comes to primary open-angle glaucoma (POAG), are they equals in efficacy, or is one technique better than the other?

Both target the eye’s conventional outflow pathway, but they diverge significantly in implementation. Canaloplasty involves cleaning the eye’s natural drainage canal without requiring implants, whereas TMBS procedures require the surgeon to insert stents to bypass local blockages.

Keith Barton MD and his colleagues—based at hospitals in London, Quebec, Melbourne, and Chicago, among others—wanted to ascertain which was best for POAG. They started by examining the International Glaucoma Surgery Registry (IGSR).

“We set up an ambispective study using data from the IGSR to evaluate mild-to-moderate POAG patients who underwent iTrack ab interno canaloplasty or iStent trabecular micro-bypass implantation. The former group formed a prospective group, the latter group was retrospective,” said Dr Barton, who presented his results in a poster.

“Patients were included in the study with or without concomitant phacoemulsification, and underwent follow-up at 12 months or afterwards. Our primary outcomes were intraocular pressure (IOP), medication usage, and surgical success.”

After setting these parameters, Dr Barton and his colleagues studied 339 eyes, of which ≥94% underwent concomitant phacoemulsification. Of these eyes, 224 underwent iTrack canaloplasty and 115 underwent iStent TMBS.

Dr Barton said that differences in baseline IOP (P = 0.417) and medications (P = 0.741) between the two groups at the start of the study were ‘non-significant’. At the study’s last follow-up, mean IOP and medication usage decreased from 17.3±4.2 and 2.0±1.1 at baseline to 14.2±3.5 and 1.3±1.1 in the iStent group, and from 16.9±5.0 and 2.0±1.1 at baseline to 14.3±3.4 and 1.1±1.3 in the iTrack group.

“We found that there were no significant differences in reduction of IOP and medications in either of the two groups. At the study’s conclusions, we found P = 0.422 for IOP and P = 0.211 for medications,” Dr Barton said.

“Success was achieved in 61% of eyes in both groups, and more eyes were medication free in the iTrack group (at 42% vs. 29%). Postoperatively, both groups demonstrated infrequent and self-limited complications, no sight-threatening events, and low reoperation rates.”

According to Dr Barton, both canaloplasty and TMBS therefore possess favourable safety profiles with limited additional glaucoma surgeries. Furthermore, canaloplasty may offer an advantage to some patients as more eyes in this group were medication-free compared with the TMBS group.

Keith Barton MD is a professor of ophthalmology at University College London and a consultant ophthalmic surgeon in the glaucoma service at Moorfields Eye Hospital, UK.