The most critical decision that surgeons make is choosing the right treatment path for patients. In minimally invasive glaucoma surgery (MIGS), that path has many options. As the number of available MIGS procedures has increased, so has the amount of conflicting information, leading many physicians to hold back.

The foremost feature of MIGS is safety, and for the group of procedures available today this has been proven true.¹ However, the withdrawal of the CyPass microstent (Alcon) due to accelerated endothelial cell loss left physicians asking valid questions about the use of implants in MIGS.² Yet there remain many other options with a demonstrated safety record.

Choosing Which Procedure to Perform

Treatment decisions go back to the beginning of medicine. Physicians are always in search of the best answer in terms of which procedure to perform and when to perform it. Choosing when to use a stent in MIGS, when to use a cutting procedure and/or viscodilation, or when to use microinvasive bleb surgery should be a multifaceted process based on a sound level of evidence. That means looking at efficacy, safety, long-term data, comparative data, quality-of-life data, and what works best for the individual surgeon. There is also a surgeon’s personal experience with a procedure to consider, and, of course, the patient’s anatomy and disease severity.

Healing from and potential failure of any glaucoma procedure has always been a challenge. Debates continue on whether cutting or removing tissue cause more scarring than implanting a stent which can protect a patent trabecular bypass. This is countered by the concern for stent blockage and limited area of outflow. Without more preclinical models, better postoperative imaging and studies, or high-quality, comparative long-term trials, the answers remain unclear.

In my practice, I use all approaches in treating glaucoma and believe there is no strict dogma as to what makes one procedure a “go-to” approach over another. Ultimately, it comes down to weighing all these factors and choosing what is best for each individual patient.

Combination vs Standalone

In looking at patients on a case-by-case basis, we can also divide these procedures into 2 categories: combination procedures performed with cataract surgery, and standalone procedures. There is a considerable amount of high-quality published evidence on stenting combined with phacoemulsification. When the priority is cataract surgery, it has been an advantage to use stenting because there is minimal impact in terms of inflammation, bleeding, pressure spikes, or postoperative recovery. Cutting procedures also have a role in combination procedures for many surgeons who feel they can access more collector channels and achieve greater efficacy, although this may be at the expense of safety. High-quality comparative data are still needed to elucidate this.

There are data for cutting techniques in standalone procedures, albeit not necessarily the highest quality. When performing MIGS outside of cataract surgery, most surgeons have historically chosen cutting with or without viscodilation procedures based on trends, efficacy, and labeling.

Until recently, in the United States there was not a standalone option for stenting. That changed in 2022 with the clearance of a trabecular meshwork stent for patients with primary open-angle glaucoma in whom previous medical and surgical treatment has failed. The pivotal study data are positive, and it will be helpful to see more data as they are collected over time.³

For patients with more advanced disease, I cautiously evaluate each case before selecting a standalone MIGS procedure. The outflow system in these patients is likely not as intact as it would be in a patient with mild or moderate glaucoma, and these patients require low intraocular pressures. However, standalone MIGS has a place, particularly in addressing the shortcoming of drops in earlier glaucoma, and I’m excited to review future data on such procedures.

Cutting, Dilating, and Stenting

Cutting, dilating, and stenting all have a role to play in MIGS. Each has its own set of advantages and disadvantages, including efficacy, safety, and function. Furthermore, consistency, reproducibility, and impact on future surgery are also important considerations. When looking at these approaches in the domain of surgeons, the choice is nuanced — and more technical.

Cutting approaches allow surgeons to cut or remove diseased trabecular meshwork and can provide a large area of access to collector channels. These approaches don’t rely on the technical placement of stents, but they do cause more tissue disruption, bleeding, and postoperative variability. It is still unclear how much of the trabecular meshwork should be removed, as well as which techniques are most effective (eg, laser vs blade/hook vs catheter vs suture). Surgeons also need to avoid trauma to the cornea, angle, iris, or suprachoroidal space. Canal dilatation alone reduces the risk of bleeding but surgeons still need to circumnavigate the canal, and most combine some form of cutting when performing canaloplasty. More prospective comparative data are needed here as well.

While there have been some conflicting messages about leaving a device in the eye, investigators have been exploring this and the results are reassuring. Looking at high-quality randomized clinical trial evidence, canal stenting has exhibited an extremely high degree of long-term safety.^4,5 Although the suprachoroidal implant CyPass caused endothelial cell loss, trabecular meshwork and canal stenting data show excellent tolerability of the implants, including endothelial safety^4,5 — and well-placed implants have been shown to be well tolerated over the last 20 years. However, stents must be placed well, and surgeons should be trained in doing so. The stent should not be overimplanted or underimplanted, and it must be in the right place to achieve sufficient IOP and medication lowering. Manufacturers have moved toward developing multiple stents or larger stents to provide a greater access to collector channels.

Conclusion

The bottom line is that it benefits surgeons and patients to have many approaches to MIGS. Knowledge and training are critical for all surgeons and procedures. Each MIGS has its benefits and drawbacks for a specific patient, but there is little to be concerned about with today’s MIGS — implant or no implant. GP

Iqbal Ike K. Ahmed, MD, FRCSC, is the John R. and Hazel M. Robertson Presidential Endowed Chair, a professor in the department of ophthalmology and visual sciences, and the director of the Alan S. Crandall Center for Glaucoma Innovation at the John A. Moran Eye Center of the University of Utah in Salt Lake City, Utah. He is also the chief innovation officer at Prism Eye Institute and faculty at the University of Toronto in Toronto, Canada. He reports consultancy and trial investigation for Alcon, AbbVie, Glaukos, Iantrek, iStar Medical, MST Surgical, New World Medical, Nova Eye Medical, Sight Sciences, and Santen. Reach him at ikeahmed@mac.com.

References

1. Saheb H, Ahmed II. Micro-invasive glaucoma surgery: current perspectives and future directions. Curr Opin Ophthalmol. 2012;23(2):96-104. doi:10.1097/ICU.0b013e32834ff1e7
2. Lass JH, Benetz BA, He J, et al. Corneal endothelial cell loss and morphometric changes 5 years after phacoemulsification with or without CyPass Micro-Stent. Am J Ophthalmol. 2019;208:211-218. doi:10.1016/j.ajo.2019.07.016
3. Sarkisian SR Jr, Grover DS, Gallardo MJ, et al. Effectiveness and safety of iStent Infinite trabecular micro-bypass for uncontrolled glaucoma. J Glaucoma. 2023;32(1):9-18. doi:10.1097/IJG.0000000000002141
4. Ahmed IIK, Sheybani A, De Francesco T, et al. Long-term endothelial safety profile with iStent inject in patients with open-angle glaucoma. Am J Ophthalmol. 2023;252:17-25. doi:10.1016/j.ajo.2023.02.014
5. Ahmed IIK, De Francesco T, Rhee D, et al. Long-term outcomes from the HORIZON randomized trial for a Schlemm’s canal microstent in combination cataract and glaucoma surgery. Ophthalmology. 2022;129(7):742-751. doi:10.1016/j.ophtha.2022.02.021