MIGS devices greatly expand treatment armamentarium
The recent FDA approvals of the Glaukos iStent, Alcon CyPass and Allergan Xen surgical devices for the treatment of glaucoma have significantly expanded the options for the American ophthalmologist. We also have a new simple disposable Kahook Dual Blade from New World Medical for trabeculectomy, which is an intriguing and inexpensive alternative to the implantable microinvasive glaucoma surgery devices.
It is interesting and important that each of these MIGS procedures utilizes a different mechanism of action, suggesting that they may be used together or sequentially in more complex patients. In addition, none of them preclude resorting to a tube shunt or trabeculectomy in a refractory glaucoma patient.
The standard in the U.S. is still to treat initially with medical therapy. We have several excellent safe and effective drops, but the unfortunate fact is that most patients are not adherent to the physician-prescribed medical regimen. This has led many experts in the glaucoma field to suggest that glaucoma may be best treated with surgery.
We have had very effective surgical procedures for decades. In the landmark Tube Versus Trabeculectomy Study, both of these classic operations reduced IOP by approximately 13 mm Hg with a mean IOP outcome below 15 mm Hg. Unfortunately, intraoperative complications were a daunting 57% for trabeculectomy and 34% for tube shunt. In addition, reoperation rates were high at 27% and 17%, respectively. Medication burden was reduced, but long term most patients still required at least one topical antihypertensive drop. The results of this study have increased the utilization of tube shunts over trabeculectomy, but all surgeons are looking for an effective but safer surgical procedure to lower IOP. The recently approved MIGS procedures appear to be the answer.
While there are no prospective randomized clinical trials comparing the relative safety and efficacy of the MIGS procedures, a careful review of the clinical trial data leads me to the following conclusions. All of the MIGS procedures have a somewhat lower efficacy than a tube shunt or trabeculectomy. Whether in combination with cataract surgery or utilized alone, one can anticipate a reduction in IOP of 7 mm Hg to 10 mm Hg when starting with a washout pressure of 25 mm Hg to 26 mm Hg. Just more than 70% of patients will achieve a 20% or greater drop in IOP with all three approaches. Safety is greatly enhanced, with intraoperative complications as defined in the Tube Versus Trabeculectomy Study being reduced to less than 5%. Surgical reoperation is also much lower, and if YAG laser capsulotomy is eliminated, also less than 5%. As I review the FDA and outside of the U.S. clinical data, the lowest complication and reoperation rates are with the iStent. In particular, hypotony and encapsulated blebs are basically nonexistent. Medication burden is reduced with every procedure, but again over time many if not most glaucoma patients find themselves taking at least a single antihypertensive drop. Fortunately, efficacy is meaningful, and intraoperative and postoperative complication rates and loss of best corrected visual acuity are significantly reduced.
For me, as a cataract surgeon treating primarily mild to moderate glaucoma, I have the greatest experience with the iStent and prefer it as a first procedure because of the extraordinary safety profile. Also, I have enjoyed the opportunity to travel to Armenia and implant next-generation trabecular bypass devices, in which more than one could be implanted, increasing the efficacy of this very safe MIGS procedure. On this trip, I also had the opportunity to implant a supraciliary shunt similar to the CyPass and found it technically quite easy with good efficacy and a low morbidity. Early data from outside the U.S. suggest that trabecular bypass and supraciliary shunts can be safely and effectively combined, either same day or sequentially weeks to months apart. In addition, a Xen device, which to me is minimally invasive filtration surgery, can be anticipated to be additive as well. It makes sense that many surgeons will favor a glaucoma filtration procedure with a lower complication rate for most patients when filtration surgery is indicated, for example in patients when cataract surgery is not being done or who have refractory glaucoma. Finally, a classical tube shunt or trabeculectomy is always there if the MIGS procedures have failed to achieve an adequate reduction in IOP.
So, for now, in my patients with combined cataract and mild to moderate glaucoma, I will start with phaco/IOL and a trabecular bypass procedure. If IOP control is inadequate, further surgery with another class of MIGS procedure appropriate to disease severity can be anticipated to generate additional lowering of IOP. I anticipate the already evident steady reduction in the number of trabeculectomy procedures to continue, and tube shunt volume to decline as well. In the future, multiple implantable extended-release glaucoma drug devices can be anticipated, and there is no reason effective glaucoma medications cannot be imbedded in the MIGS devices themselves. All in all, we are entering a time of disruptive innovation in the treatment of glaucoma, much to the benefit of our patients.
Disclosure: Lindstrom reports he is a consultant for Glaukos, Alcon, Allergan, Johnson & Johnson Vision and Bausch + Lomb.