MIGS Wisdom

With Ike Ahmed, Earl Randy Craven, Marlene Moster, Constance Okeke, I. Paul Singh, and Robert N. Weinreb

MIGS are broadly accepted to provide fast post-surgical recovery while sparing the conjunctiva for later, more conventional procedures, if required. But, as Randy Craven points out, the sheer breadth of MIGS procedures on offer can be confusing: “People are often unsure as to whether they should peel off the trabecular meshwork, bypass it or go into the suprachoroidal space.” Fortunately, our AGT Expert Panel has shared its wisdom regarding the best approach to selecting procedures from the wide range of available MIGS.

Identify constraints

We operate in the real world, not an ideal world. Paul Singh reminds us that we cannot ignore the approved indications per device: “The iStent and the Hydrus are only approved for use with cataract surgery – so they are not options for stand-alone pseudophakic surgery.” In those cases, Singh opts for viscodilation or stripping procedures. Constance Okeke raises financial considerations: “The reality is that not everybody can pay for the procedure that the surgeon would recommend – you have to consider the insurance situation.” And this could turn out to be a moving target given that the insurance environment may change; studies that assess MIGS benefits in terms of assisting compliance, reducing medication costs, and reducing severe glaucoma incidence may allow better quantification of their cost-effectiveness.

Ike Ahmed is clear: “Development of new treatment-based quality of life tools, such as we’ve seen for dry eye products, could give us the data to support extended insurance coverage for these new procedures.”

Take care

Robert N. Weinreb recommends careful analysis of existing evidence. “It is true that the MIGS field needs more studies,” he says. “But those studies that have been done suggest that placing a single microbypass stent in the trabecular meshwork is generally not effective.” His view is that the most successful procedures will be those that access the greatest number of functional collector channels; “For example, I speculate that two or more microbypass stents would be more effective than a single microbypass stent.” Similarly, Weinreb suggests that stripping trabecular meshwork over a large area, perhaps using the dual blade or trabectome, could also provide better pressure lowering.

Ahmed points out that surgical choices might also take into account aspects of the outcome: “Most MIGS procedures give very similar results in terms of pressure – but there are interprocedural differences in terms of recovery, hyphema rates, tissue remodeling and healing.” And Singh emphasizes that the definition of a successful outcome should include medication reduction: “If a previously-medicated patient can maintain the same pressure as before the procedure, but without medication, that is a good result.”

Craven’s default position is to access the conventional outflow system with a bypass: “I like to use a couple of iStents – a good first step for many patients – or perhaps a longer stent, such as the Hydrus.” Singh agrees that the ideal may be to support natural, conventional outflow. “My aim is to cause as little damage as possible, so I opt for stents or viscodilation, if I can,” he says, but notes that disease stage and severity may dictate other strategies: “In advanced disease, where the patient is on multiple medications and has posterior resistance, a stent approach may not be sufficient.” In those cases, Singh recommends goniotomy or trabeculotomy approaches with viscodilation. Weinreb agrees: “In advanced disease, you accept a bit more risk to obtain lower pressure by completely bypassing the outflow pathways.” In the past, he says, that meant trabeculotomy, but today it could mean opting for, as an example, a Xen device.

Don’t forget blebs

In this context, how does the panel perceive the challenges and benefits of ab interno and ab externo bleb creation procedures? Craven says that moving from ab interno to ab externo has been an evolution driven by issues with the ab interno technique: “After having problems with encapsulations and excessive needlings, I found that opening the conjunctiva a little via ab externo made a big difference.” He suggests that ab externo-derived blebs are more manageable, and placement more reliable because the opening is smaller than that made by a trabeculectomy. Singh expands on this: “Correctly positioned ab externo blebs are different from trabeculectomy blebs – they’re lower and less vascular, and when you get fibrosis the needling is different from that required for traditional blebs.” His view is that, although Xen bypasses the natural drainage systems, it offers a higher quality of life: “Better comfort, and a return to pre-operative visual acuity within a week of the procedure.”

Marlene Moster asserts that inter-patient differences can be significant: “The Tenon’s in some patients is just not meant for a Xen – there’s too much of it.” In those cases, Moster avoids Xen because it scars faster, even with mitomycin. Instead, she opts for an ab interno approach. Singh reiterates that the final choice of procedure is likely to be influenced by type and age of patient, number of medications, disease severity and target pressure; “For example, the Xen is a great choice for pseudophakic patients on three or four medications complaining of cost and side-effects, whose target pressure is in the mid-teens.” Ahmed concurs: “I love the safety of MIGS canal-based procedures, but when I see a relatively young patient with severe disease on multiple medications, with a target of 12mmHg pressure and no medications, I turn to the bleb.”

Indeed, the advent of devices such as the Xen has made it possible to opt for a bleb approach earlier in the disease state than would be usual with trabeculectomies. Singh states that he now uses Xen – and would consider Infocus – in moderate patients where the target is to be medication-free: “These devices have a better safety profile and give more predictable outcomes – and spare the conjunctiva for other procedures if necessary.” Moster adds that Infocus provides a more predictable bleb than trabeculectomy, and suspects it will become regularly used for cases where a significant reduction in IOP is required.

Weinreb concludes that blebs will continue to be with us for at least several years: “Many of our patients need pressures below 12 mmHg – and at present the only way to achieve pressures below episcleral venous pressure is to bypass the outflow pathway, as one can do with trabeculectomy and Xen implants, and presumably will do in the future with other microshunts.” Craven advises that the patient should be involved in this decision: “It’s right that they should know about the longer-term risk of bleb-related problems.” Singh adds: “It’s also important to let them know about the sequence of various options – namely, commencing with MIGS and proceeding to bleb strategies, if necessary.”

Remember your options

Final word: what do we do when the above modalities fail? Moster suggests MicroPulse cycloablation therapy: “We’ve had good results from using low amounts of energy and repeating as necessary.” She suggests cycloablation is best used late in the treatment paradigm. “MicroPulse decreases inflow – but my preference is to maximize outflow, if possible.”

Okeke agrees: “I prefer to use it for refractive disease, where I don’t want to go back into the eye – often in cases where I am less concerned about the visual outcome because the vision is already compromised.” Craven adds that MicroPulse has the advantage of being applicable in the clinic, thereby freeing up the operating room.

In conclusion, surgeons contemplating MIGS procedures need not feel overwhelmed by the options; the advice summarized here provides welcome guidance when navigating the complexity of this field.

The Advanced Glaucoma Technologies Forum was hosted by The Ophthalmologist and supported by Ellex, Santen, Heidelberg Engineering, Reichert Ametek and Aerie Pharmaceuticals Inc.

Ike Ahmed is Assistant Professor at the University of Toronto, Canada.

Earl Randy Craven is Associate Professor of Ophthalmology at Johns Hopkins University, Maryland, USA.

Marlene Moster is Professor of Ophthalmology, Wills Eye Hospital, Philadelphia, USA.

Constance Okeke is a glaucoma and cataract surgery specialist at Virginia Eye Consultants, and also an

Assistant Professor of Ophthalmology at Eastern Virginia Medical School, Virginia, USA.

I. Paul Singh is an ophthalmic surgeon at Eye Centers of Racine and Kenosha, Wisconsin, USA.

Robert N. Weinreb is Distinguished Professor and Chair, Ophthalmology, University of California, USA.