Subconjunctival MIGS vs Trabeculectomy

Less invasive approaches promising, but more data needed to guide evidence-based decisions. Cheryl Guttman Krader reports

Subconjunctival minimally invasive glaucoma surgery (MIGS) procedures aim to provide a safer alternative to trabeculectomy, but more evidence is needed to understand how the subconjunctival MIGS procedures compare and where they fit into the algorithm for glaucoma surgical care, Henny J Beckers MD, PhD told delegates.

“Trabeculectomy remains the gold standard, but we look forward to results from randomised controlled trials of the subconjunctival MIGS procedures that are underway,” Dr Beckers said.

Currently, there are two options in the subconjunctival MIGS category—the XEN® Gel Stent (Allergan) and the PRESERFLO™ MicroShunt (Santen). Dr Beckers first reviewed five studies of the XEN stent. Those studies reported data from two-to-three years of follow-up for patients undergoing the MIGS procedure alone or combined with phacoemulsification. Mean IOP across the studies ranged from approximately 20 to 23 mmHg at baseline and reduced to between approximately 13 and 15 mmHg at last follow-up. However, needling rates were high (43% to 62%), and the reoperation rate in the three studies ranged from 12% to 26%.

Dr Beckers then reviewed findings from five published studies reporting outcomes from follow-up periods of up to five years after MicroShunt surgery. In these trials, mean IOP ranged from approximately 20 to 25 mmHg at baseline, reduced to approximately 11 to 14.5 mmHg after one year, and sustained over time in the studies with longer follow-up. Needling rates ranged from 5% to 18%, and the reoperation rate ranged up to 13.5%.

HEAD-TO-HEAD TRIALS Dr Beckers and colleagues compared the two subconjunctival MIGS procedures and reported their results in a retrospective study.i Summarising the results, she said the XEN and PRESERFLO showed similar efficacy.

“Although IOP was lower in the MicroShunt group at all timepoints, the difference between groups was not statistically significant for most comparisons,” she said.

For both procedures, complications were mostly mild and selflimiting, consisting of early hypotony and early microhyphaema. Stent curling was only reported in the XEN group and is a feature of the device’s material, Dr Beckers explained.

The XEN group had a higher rate of bleb needling than the MicroShunt group and a lower rate of glaucoma filtration surgery, but the differences were not statistically significant. Transscleral cyclophotocoagulation was performed significantly more often after the XEN procedure.

COMPARISONS WITH TRABECULECTOMY The ongoing Gold-Standard Pathway Study is a US-based multicentre trial comparing XEN implantation and trabeculectomy. Recruitment was just completed with 162 participants enrolled.

Data from one year of follow-up are available from a twoyear study that randomised 527 patients 3:1 to surgery with the MicroShunt or trabeculectomy.ii Mean IOP at baseline was 21.1 mmHg in both groups. At one year, mean IOP was 11.1 mmHg in the trabeculectomy group and 14.3 mmHg in the MicroShunt group.

“The MicroShunt result is inferior to trabeculectomy, but the trabeculectomy results are very good in this study. The 58 participating investigators in the study perhaps were very skilled with trabeculectomy, whereas many had no experience with the MicroShunt procedure. There may be a learning curve effect for the MicroShunt outcomes, and we will see if that is true in further studies,” Dr Beckers said.

As another potentially confounding issue, the MicroShunt group included a significantly higher proportion of Black patients, a demographic at increased risk for failure after blebforming surgery. In addition, both surgeries were performed using mitomycin-C (MMC) 0.2 mg/mL for two minutes.

“Now there is debate over whether a higher dose of MMC may improve the results of the MicroShunt surgery. Recently published studies found a trend to better IOP reduction using a concentration of 0.4 mg/mL. However, the reduction in medication use in the head-to-head comparison of the MicroShunt and trabeculectomy was also significantly better in the trabeculectomy group,” Dr Beckers said.

There were more postoperative interventions in the trabeculectomy group, although laser suture lysis procedures account for most of the difference. After excluding those procedures, the postoperative intervention rates were similar in the two groups.

Adverse events related to IOP were more common in the trabeculectomy group that had higher rates of hypotony and increased IOP requiring treatment in the early postoperative phase. After three months of follow-up, IOP was slightly higher in the MicroShunt group.

“The more predictable postoperative course (however, with fewer possibilities of early intervention) with the MicroShunt may also help explain why it was associated with higher IOPs than trabeculectomy over the later follow-up period,” Dr Beckers noted.

There was no statistically significant difference between groups in endothelial cell loss after one year.

“Overall, the first results indicate the MicroShunt appears to be slightly less effective than trabeculectomy. However, it is a more controlled procedure—with proper case selection it can provide an IOP in the low teens, and it usually shows excellent visual rehabilitation.”

This presentation was made at the 39th Congress of the ESCRS in Amsterdam.

i Acta Ophthalmologica. 2021, 99: e433–e440. ii Baker ND, et al. Ophthalmology. 2021 May 27: S0161-6420 (21) 00384-5.

Henny J Beckers MD, PhD, is a glaucoma specialist and cataract and glaucoma surgeon at the University Eye Clinic Maastricht, the Netherlands. henny.beckers@mumc.nl