If minimally invasive glaucoma surgery (MIGS) targets the eye’s natural aqueous outflow pathway¹ and is not broadly indicated for advanced glaucoma, could it find utility in patients who have already undergone incisional glaucoma procedures? The short answer is yes. Let’s consider a case where it worked and dig into the literature on the subject.

Case Study

A 73-year-old female was referred by her primary eye care optometrist for evaluation of advancing glaucoma in the left eye. Her ocular history was significant for severe open-angle glaucoma in both eyes, with left eye Tmax of 41 mmHg, and she had already undergone selective laser trabeculoplasty, cataract surgery, and a filtering bleb in years prior. She had listed several allergies and intolerances to a variety of topical glaucoma medications and had moderate symptoms of ocular surface disease (OSD). On evaluation, her intraocular pressure (IOP) was 26 mmHg on 4 medications. Examination showed mild OSD in both eyes and small, low bleb on the left. Minimal change to IOP or bleb size was noted after digital palpation. Optic nerve exam and retinal nerve fiber layer (RNFL) optical coherence tomography were consistent with visual field loss confirmed on automated perimetry (Figure 1). Her structural and functional losses from glaucoma in the left eye had advanced compared to testing performed 4 months earlier.

What are the options for this patient? Pressure control is a priority, and we considered 3 potential options: (1) additional medical therapy; (2) additional incisional glaucoma surgery (most likely a tube shunt, or possibly a bleb revision); and (3) a MIGS or cilioablative procedure.

By loose definition, considering her prior incisional glaucoma surgery and subsequent rise in IOP to levels higher than goal, our patient has refractory glaucoma in her left eye. This is a medically and surgically challenging situation. Escalation of medical therapy may be an increasingly available option thanks to newer generation medications such as latanoprostene bunod (Vyzulta; Bausch + Lomb), netarsudil (Rhopressa; Aerie Pharmaceuticals), and netarsudil/latanoprost (Rocklatan; Aerie Pharmaceuticals). However, it is also important to take current drop burden and compliance (or possible lack thereof) into account and be careful not to create a more onerous drop regimen that is not sustainable for the patient. Additional incisional glaucoma surgery is at the other end of the spectrum. In the Primary Tube Versus Trabeculectomy (TVT) study, patients undergoing trabeculectomy had a cumulative probability of failure of 28%.² Similarly, in the original Tube Versus Trabeculectomy study of patients with previous cataract or incisional glaucoma surgery, the cumulative probability of reoperation in patients having had trabeculectomy was 29%.³

The odds of success with additional incisional glaucoma surgery generally are not in our favor. When investigators in the TVT study group analyzed trabeculectomy patients requiring a second incisional glaucoma surgery (predominantly a tube shunt), they found the cumulative probability of failure to be 47% at 4 years and noted a total of 15 complications in 8 patients having undergone repeat operations.⁴

Our patient desired to find a balance in safety and effectiveness for the management of her refractory glaucoma. We discussed all options, including addition of a new medication or a tube shunt, neither of which she felt good about. She was concerned about her ocular dryness and admitted to difficulties with her current drop schedule. While she acknowledged an understanding of the severity of her condition, she sought a “Goldilocks” solution: one that provided IOP impact with a better risk profile than additional bleb-based procedures. This is where MIGS entered the discussion.

MIGS encompasses a variety of surgical procedures, and the most standard definition describes the procedures as those that create minimal disruption to the natural outflow of the eye, have a modest effect, and have demonstrated an excellent safety profile.⁵ Examples of such procedures include trabecular bypass with varying degrees of Schlemm’s canal scaffolding (iStent and iStent inject by Glaukos and Hydrus by Ivantis), trabecular meshwork removal (Kahook Dual Blade; New World Medical), and viscocanaloplasty with or without trabeculotomy (OMNI; SightSciences). Ciliodestructive procedures and angle-based bleb procedures (Xen; Allergan) were excluded from the discussion for the purpose of attempting to answer our question from before: can we revert to angle-based MIGS after a failed bleb-based surgery, as we have noted in our patient’s case?

Little is known about effecting meaningful change in IOP by optimizing the natural outflow after filtering or drainage device surgery. One mathematical model suggests aqueous outflow drops to about 10% of normal after trabeculectomy but does not account for physiologic changes that may occur over time, such as with a nonfunctional bleb.⁶ Clinical data that do exist on the matter are scarce. Limited studies evaluating MIGS in refractory glaucoma have demonstrated cautiously promising results. One such study evaluated iStent Inject in 22 eyes after failed trabeculectomy, demonstrating significant decrease in IOP (22.5 mmHg preoperatively to 15.5 mmHg postoperatively), with no significant decrease in number of medications.⁷ Other investigators evaluated combining multiple MIGS devices with planned topical therapy in refractory glaucoma patients and found mean medicated IOP was reduced by more than 37% compared to preoperative evaluation.⁸ A highlight of yet another study was the safety of a MIGS device in severe and refractory glaucoma, finding the Kahook Dual Blade produced a reduction in IOP of 24% and no sight-threating threatening complications.⁹ While the results of these studies are indeed positive, they are all retrospective in design and recommend careful consideration of patient characteristics and IOP targets.

Case Conclusion

After thorough discussion and education about possible need for additional surgery in the future, we elected to proceed with a standalone pseudophakic MIGS procedure using the OMNI device for 360° with viscodilation and 180° of the inferior trabeculotomy. Postoperative IOP after 4 months was 16 mmHg on her same preoperative medication regimen due to the severity of her glaucoma. This represented a 38% decrease in IOP and a successful intervention.

Summary

For uncontrolled IOP after incisional glaucoma surgery, glaucoma surgeons have an expanding multitude of options to avoid additional incisional surgery, including newer medications and minimally invasive procedures. While clinical data remain limited on the efficacy of MIGS in refractory glaucoma, early returns suggest reason to be cautiously optimistic. MIGS may just be the “Goldilocks” option some patients are looking for. GP

Brandon Baartman, MD, is an anterior-segment and glaucoma specialist at Vance Thompson Vision in Omaha, Nebraska. Dr. Baartman reports that he is a consultant to and investigator for SightSciences, and an investigator for Glaukos. Reach him at brandon.baartman@vancethompsonvision.com.

References

1. Kerr NM, Wang J, Barton K. Minimally invasive glaucoma surgery as primary stand-alone surgery for glaucoma. Clin Exp Ophthalmol. 2017;45(4):393-400.
2. Gedde SJ, Feuer WJ, Lim KS, et al. Treatment outcomes in the Primary Tube Versus Trabeculectomy study after 3 years of follow-up. Ophthalmology. 2020;127(3):333-345.
3. Gedde SJ, Schiffman JC, Feuer WJ, et al. Treatment outcomes in the Tube Versus Trabeculectomy (TVT) study after five years of follow-up. Am J Ophthalmol. 2012;153(5):789-803.e2.
4. Saheb H, Gedde SJ, Schiffman JC, Feuer WJ; Tube Versus Trabeculectomy Study Group. Outcomes of glaucoma reoperations in the Tube Versus Trabeculectomy (TVT) study. Am J Ophthalmol. 2014;157(6):1179-1189.e2.
5. Saheb H, Ahmed IK. Micro-invasive glaucoma surgery: current perspectives and future directions. Curr Opin Ophthalmol. 2012;23(2):96-104.
6. Kotliar KE, Kozlova TV, Lanzl IM. Postoperative aqueous outflow in the human eye after glaucoma filtration surgery: biofluidmechanical considerations. Biomed Tech (Berl). 2009;54(1):14-22.
7. Davids AM, Pahlitzsch M, Boeker A, et al. iStent inject as a reasonable alternative procedure following failed trabeculectomy?. Eur J Ophthalmol. 2018;28(6):735-740.
8. Myers JS, Masood I, Hornbeak DM, et al. Prospective evaluation of two iStent trabecular stents, one iStent Supra suprachoroidal stent, and postoperative prostaglandin in refractory glaucoma: 4-year outcomes. Adv Ther. 2018;35(3):395-407.
9. Salinas L, Chaudhary A, Berdahl JP, et al. Goniotomy using the Kahook Dual Blade in severe and refractory glaucoma: 6-month outcomes. J Glaucoma. 2018;27(10):849-855.