A debate on MIGS: Can MIGS reach treatment goals?

Consensus not universal on the net benefit of MIGS in terms of safety, efficacy and expense

Roibeard O’hEineachain

Posted: Friday, February 1, 2019

The InnFocus device in place in the anterior chamber (l); Bleb 12 months postoperatively

The rationale behind the use of minimally invasive glaucoma surgery (MIGS) is to provide IOP reduction with reduced requirement for medication with a quick recovery time and few complications. The question of whether MIGS actually achieves those goals was the topic of a debate held in a Glaucoma Day session at the 36th Congress of the Vienna, Austria.

Julian Garcia Feijoo MD, PhD

Opening the debate, Julian Garcia Feijoo MD, PhD, argued that MIGS does achieve its desired goals when the treatment is tailored to the patient’s needs. For example, ab interno MIGS devices that improve drainage via Schlemm’s canal can achieve satisfactory results in eyes with target IOP in the mid-teens, suprachoroidal devices could add 1-2 extra mmHg decrease, whereas ab interno and ab externo devices that direct aqueous into the subconjunctival space can provide IOP reductions nearly on a par with trabeculectomy.

“The decision to treat and how aggressively to treat depends not just on the diagnosis and IOP level, but also on the stage of disease at diagnosis, the rate of progression, the age and life expectancy of the patient and additional risk factors,” said Prof Feijoo, Hospital Clinico San Carlos, Universidad Complutense Madrid, Madrid, Spain.

Numerous studies have demonstrated that ab interno MIGS, whether involving a subconjunctival bleb or enhanced drainage through Schlemm’s canal, can reduce glaucoma patients’ medication requirements.

For example, in a randomised study involving 100 eyes of 100 patients with glaucoma and cataract, 73% of eyes were using no hypotensive medications at 24 months after undergoing implantation of the Hydrus (Ivantis) Schlemm’s canal micro-stent combined with cataract surgery, compared to a medication-free rate of 38% among eyes in the cataract surgery group (p=0.0008).

For patients whose target IOP is in the mid-to-low teens, ab interno or ab externo devices that direct aqueous outflow through a subconjunctival bleb have a high rate of success. In a recent study involving patients undergoing Xen® gel stent (Allergan) implantation there was a mean reduction in mean IOP from 21.4 to 13.8mmHg (p< 0.0001) and a reduction in mean number of topical medications from 2.6 to 0.6 (p<0.0001). There are also minimally penetrating ab externo subconjunctival drainage devices (Innfocus, SANTEN) that involve considerably less tissue dissection than filtration procedures.
Summarising, Prof Feijoo maintained that MIGS and minimally penetrating glaucoma surgery techniques are a useful addition to the continuum of glaucoma treatments from the least invasive to the most invasive.

Chelvin Sng, MBBChir (Cantab), FRCSEd

Assigned the task of presenting the opposing view, Chelvin Sng, MBBChir (Cantab), FRCSEd, pointed out that the current MIGS implants are not yet achieving the original treatment goals determined at the conceptualisation of MIGS. When MIGS was first introduced several years ago, the treatment goals included: at least moderate efficacy, high safety profile, ease of use and minimal invasiveness. With the current repertoire of MIGS devices, these treatment goals are only partially but not completely achieved. However, with continual innovation and improvements, Dr Sng is optimistic that MIGS will eventually reach all its treatment targets.

Efficacy: In the FDA iStent® (Glaukos) Inject study, the mean reduction in unmedicated IOP at 24 months was 6.9mmHg in the iStent group compared to 5.4mmHg in those undergoing cataract surgery alone. The reduction in medications at 24 months was -1.4 vs -1.0 in the phaco alone group. Although the differences were statistically significant, it is debatable whether they were clinically significant in terms of slowing progression and preserving vision. In addition, the cost of an iStent Inject in Singapore is €1,250, which is equivalent to the cost of an eight-year supply of latanoprost (100 bottles).

Safety: Although subconjunctival MIGS implants are more effective than trabecular bypass procedures and are potentially capable of achieving IOP comparable with trabeculectomy, they are inevitably associated with bleb-related complications. For instance, there have been reports in the literature of bleb-related infections associated with the XEN implant, albeit at a lower incidence compared with trabeculectomy. Meanwhile, Alcon has announced the voluntary global market withdrawal of the suprachoroidal CyPass micro-stent because of increased endothelial cell loss detected among those with the implant compared with those who underwent cataract surgery alone. This was of particular concern because the CyPass micro-stent was indicated for patients with mild-to-moderate glaucoma, in whom safety was of paramount importance.

Ease of Use: The iStent Inject and other trabecular bypass MIGS devices may appear easy to use, but it is challenging to implant them precisely in the Schlemm’s canal. Similarly, XEN implantation appears much easier to perform than trabeculectomy, but there are nuances in the surgical technique and postoperative management that are essential for achieving optimal outcomes, and these may be difficult to master.

Minimal Invasiveness: While sparing of the conjunctiva was initially considered a cardinal feature of MIGS, it is now recognised that subconjunctival MIGS devices (eg. InnFocus microshunt, XEN bleb revision) require conjunctival peritomy to attain good outcomes with low IOP.

From the above examples, it appears that MIGS is not yet able to achieve all its original treatment goals determined at its conceptualisation. Nevertheless, even in their current iterations, Dr Sng believes that the current MIGS devices are still useful tools in our glaucoma surgical armamentarium. With appropriate patient selection, MIGS still constitutes a large part of her clinical practice. As MIGS comes of age, the treatment goals will also evolve with time.

Chelvin Sng: