Are There Limits to MIGS?

Although minimally invasive glaucoma surgery (MIGS) has expanded the options for primary open-angle glaucoma (POAG), its indications and benefits in primary angle-closure glaucoma (PACG) are less clear and should be approached with caution, according to Panayiota Founti MD, PhD.

“The evidence at this point for surgical treatment of angle closure supports the use of laser peripheral iridotomy (LPI), lens extraction, and incisional surgery,” she said. “There is no high-quality evidence to support the use of MIGS devices or newer bleb-forming procedures in angle closure disease.”

Compared to POAG, the field of angle closure has been somewhat neglected in recent decades.

“When it comes to landmark trials, if you look at the studies that have considerably changed clinical practice, up until 2016, there was no study on angle closure,” she said. “We had to wait until the Effectiveness of Early Lens Extraction for the Treatment of Primary Angle-closure Glaucoma study (EAGLE study) and the Zhongshan Angle Closure Prevention trial (ZAP trial) to change the way we think about angle closure in general and how we approach that in a hospital setting.”

Based on the EAGLE and ZAP trials, the PACG guidelines were updated to reflect the current thinking.

“There is broad agreement that, beyond LPI and lens extraction, incisional filtration surgery is the appropriate course of action for uncontrolled PACG—although the technique should be modified, compared to what we do in POAG, to minimise the risk of complications,” she said.

Turning to MIGS, Dr Founti cited the new guidance on surgical innovation by the European Glaucoma Society, which defines it as only the ab interno non-bleb-forming procedures rather than newer sub-conjunctival bleb-forming techniques, such as Xen Gel Stent and PreserFlo MicroShunt.

Regarding MIGS, while it may be possible to use some of these devices in angle-closure disease, Dr Founti advised it is perhaps wiser to err on the side of caution.

“If you have a patient in front of you with PACG and you want to be open with them about the potential benefits and risks of a MIGS procedure, you need to let them know there is no evidence to support this intervention for the type of glaucoma they have,” she said.

In terms of newer bleb-forming techniques—such as the Xen Gel Stent and PreserFlo MicroShunt—a lot more clinical evidence is needed to properly assess their safety and efficacy in angle-closure glaucoma.

She noted the randomised trials comparing the Xen Gel Stent and PreserFlo MicroShunt versus trabeculectomy have shown substantial rates of hypotony using both approaches (23% and 26%, respectively).

“Of course, not all that hypotony will necessarily lead to devastating complications, but it occurs in about one in four patients, and we need to be aware of that,” she said. “While this hypotony may not cause problems to most patients with POAG, it may lead to severe complications in patients with PACG.”

With a trabeculectomy, Dr Founti said such hypotony can be avoided with appropriate modifications intra- and postoperatively, to bypass low eye pressure in the early postoperative period.

“Trabeculectomy is the most commonly performed procedure in China for PACG and is usually combined with phacoemulsification,” she noted. “According to published data, when using the appropriate technique, the complication rate is not that different from POAG. This busts the myth trabeculectomy in primary angle-closure glaucoma is associated with high rates of aqueous misdirection.”

Dr Founti presented at Glaucoma Day at the 2023 ESCRS Congress in Vienna.

Panayiota Founti MD, PhD is a Consultant Ophthalmic Surgeon at Moorfields Eye Hospital, London, United Kingdom.

pfounti@gmail.com