Minimally invasive glaucoma surgery (MIGS) arrived in the United States with the approval of the iStent trabecular micro-bypass device (Glaukos) in 2012.^1,2 Since its approval, the surgical treatment algorithm of glaucoma has undergone considerable change, and the advent of MIGS has stimulated a more proactive, interventional approach. MIGS procedures offer moderate IOP-lowering efficacy, carry an excellent safety profile and preserve the option for more aggressive future treatments.^3,4 Further, the MIGS category has seen continual growth with devices targeting different anatomical regions for IOP reduction, which has allowed for more individualized patient care.⁴

MIGS procedures primarily target four pathways for pressure reduction: increased trabecular outflow, increased uveoscleral outflow, increased subconjunctival outflow and decreased production of aqueous humor from the ciliary body. In this article, we review the MIGS category and provide insights to our clinical practice patterns.

Pathways and approaches

• Trabecular meshwork (TM)

MIGS procedures targeting the trabecular meshwork to bypass the conventional outflow pathway primarily achieve enhanced outflow via microstenting or micro-incisional approaches. For microstenting strategies, the space continues to grow.

The iStent device pipeline recently evolved with the approval of the iStent infinite (Glaukos). This device offers the capability of implanting three stents across multiple clock hours and has primarily been studied as a standalone procedure.⁵ The iStent infinite could be another favorable alternative for patients who are pseudophakic or have previously failed surgical intervention. A recent study evaluating the iStent infinite reported a favorable IOP reduction along with an excellent safety profile in a large number of patients with prior failed surgery.⁵

The Hydrus microstent (Alcon) is another trabecular micro-bypass device with similar indications to the first- and second-generation iStent devices for mild-to-moderate glaucoma.⁶ The HORIZON trial, the largest MIGS pivotal trial to date, published impressive 5-year findings demonstrating a sustained reduction in IOP with a long-term safety profile. In addition, about 73% of patients who were on one topical medication at baseline were medication-free at 5 years.⁷

The superior safety profile and tissue-sparing approach offered by trabecular micro-bypass stent devices make them a favorable first-line option in patients presenting with concomitant cataracts and glaucoma. Of the MIGS procedures, the trabecular micro-bypass devices carry the lowest risk of hyphema as they are not excising the TM.^8,9 In our practice, the iStent inject is the most common MIGS device employed as a first-line option given the favorable safety profile. With a microstenting procedure, most patients can expect to remove at least one medication from their regimen based on prior studies performed at our site^10,11 and in the literature.⁷

• Micro-incisional procedures

In addition to microstenting approaches, goniotomy and other micro-incisional procedures are popular options for IOP reduction.

A multitude of devices for achieving a goniotomy are available such as the Kahook Dual Blade (KDB, New World Medical), a device designed to excise trabecular tissue in a controlled fashion.¹² The KDB also has the advantage of being offered as a standalone procedure and thus can be performed independent of cataract surgery.¹³

Another popular goniotomy option is gonioscopy-assisted transluminal trabeculotomy (GATT), a procedure that utilizes a microcatheter or suture to perform a circumferential trabeculotomy via mechanical cleavage of the trabecular meshwork.¹⁴ GATT treats all 360 degrees of the angle as opposed to a limited goniotomy with a device such as a KDB, but it also carries a higher risk of hyphema.¹⁴

• Combined mechanism procedures

The OMNI surgical system (Sight Sciences) is another angle-based procedure with the advantage of offering a multiple-mechanism approach to IOP reduction.¹⁵ The device uses a microcatheter that facilitates 180 or close to 360 degrees of canaloplasty via viscodilation (viscocanaloplasty) followed by trabeculotomy with a single device. Theoretically, this approach targets multiple points of outflow resistance in the conventional outflow pathway. Multiple studies have been published supporting the OMNI device in combination with cataract surgery and as a standalone device.^15,16

For angle-based approaches that excise the TM, such as the KDB and/or OMNI devices, each of these procedures carry a higher risk of hyphema and this may persist for days-weeks following the surgery.^8,9,15 Thus, vision can be reduced in the postoperative period or worse than anticipated following a combined cataract/MIGS procedure.

• Subconjunctival

The most aggressive or least minimally invasive form of MIGS is currently owned by the Xen gel stent (Allergan), a subconjunctival gel stent and bleb-forming procedure that routes aqueous humor directly to the subconjunctival space in a fashion similar to traditional filtering procedures. The device is composed of a biocompatible material to minimize fibrosis/scarring and is designed to avoid postoperative hypotony.

As a subconjunctival procedure, the Xen is often reserved for patients with advanced glaucomatous disease or continued progression despite multiple MIGS procedures. The gel stent has been implanted with a variety of techniques including both ab-interno and ab-externo approaches. The optimal approach for achieving a satisfactory outcome remains unclear, but the Xen device has shown promise for providing IOP-lowering efficacy similar to a traditional incisional procedure.

An additional player in the subconjunctival space down the road could be the PreserFlo ab-externo microshunt (Santen, distributed by Glaukos), which is available for use internationally but has yet to receive FDA approval.¹⁷

Practice patterns

In our practice, multiple factors dictate our decision-making process in a patient with open-angle glaucoma. In the setting of concomitant cataract and glaucoma, disease stage, baseline IOP and number of medications guide our surgical treatment plan. For drop management, we typically keep patients on their existing glaucoma medication regimen until the 1-month time point and the patient has completed their postoperative steroid drops.

In patients with a higher baseline IOP and mild-moderate stage of disease, for example, we typically move forward with a tissue-sparing procedure such as the iStent inject trabecular microbypass system in combination with cataract surgery. In the setting of a patient with moderate-severe stage of disease on more than two medications with concomitant cataract and glaucoma, we may consider a more aggressive approach and treat with the OMNI surgical system or KDB combined with endocyclophotocoagulation.

As the most invasive option in the MIGS treatment algorithm, we typically reserve use of the Xen gel stent for patients who have failed prior MIGS procedures and continue to exhibit disease progression.

Special considerations

At our location in Sioux Falls, SD, we care for a significant number of patients with pseudoexfoliative glaucoma (PXG). In these patients, we nearly always start with a trabecular microbypass stent procedure in combination with cataract surgery. Patients with PXG have been found to respond favorably to trabecular microbypass procedures with a sustained reduction in IOP and medications.^1,2

In our study published in 2020,¹⁰ patients with PXG achieved a reduction in IOP of >5 mm Hg that was sustained out to 5 years postoperative. We believe the favorable results observed with the iStent in this population and other forms of secondary glaucoma^10,18 are due to the device bypassing the known region of obstruction (trabecular meshwork).

Conclusion

The MIGS space has grown considerably over the last decade, leading to an interventional approach to treatment of glaucoma. This expansion of options has allowed for an individualized approach to the surgical management of glaucoma. Both staff and providers should be aware of the differences of each MIGS category to address patient questions and manage expectations. OP

References

1. Saheb H, Ahmed I. Micro-invasive glaucoma surgery: current perspectives and future directions. Current opinion in ophthalmology. Published online 2012. http://journals.lww.com/co-ophthalmology/Abstract/2012/03000/Micro_invasive_glaucoma_surgery___current.4.aspx . Accessed December 22, 2022.
2. Samuelson TW, Katz LJ, Wells JM, Duh YJ, Giamporcaro JE. Randomized Evaluation of the Trabecular Micro-Bypass Stent with Phacoemulsification in Patients with Glaucoma and Cataract. Ophthalmology. 2011;118(3):459-467.
3. Lavia C, Dallorto L, Maule M, Ceccarelli M, Fea AM. Minimally-invasive glaucoma surgeries (MIGS) for open angle glaucoma: A systematic review and meta-analysis. PloS one. 2017;12(8):e0183142.
4. Shah M. Micro-invasive glaucoma surgery – an interventional glaucoma revolution. Eye and vision (London, England). 2019;6(1):29. d
5. Sarkisian SR, Grover DS, Gallardo M, et al. Effectiveness and Safety of iStent infinite Trabecular Micro-Bypass For Uncontrolled Glaucoma. J Glaucoma. Published online October 20, 2022.
6. Samuelson TW, Chang DF, Marquis R, et al. A Schlemm canal microstent for intraocular pressure reduction in primary open-angle glaucoma and cataract: the HORIZON study. Ophthalmology. 2019;126(1):29-37.
7. 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.
8. Sarkisian SR, Mathews B, Ding K, Patel A, Nicek Z. 360° ab-interno trabeculotomy in refractory primary open-angle glaucoma. Clinical Ophthalmology (Auckland, NZ). 2019;13:161-168.
9. ElMallah MK, Seibold LK, Kahook MY, Williamson BK, Singh IP, Dorairaj SK. 12-month retrospective comparison of kahook dual blade excisional goniotomy with istent trabecular bypass device implantation in glaucomatous eyes at the time of cataract surgery. Advances in Therapy. 2019;36(9):2515-2527.
10. Ferguson TJ, Swan RJ, Bleeker A, et al. Trabecular microbypass stent implantation in pseudoexfoliative glaucoma: long-term results. J Cataract Refract Surg. 2020;46(9):1284-1289.
11. Ferguson TJ, Mechels KB, Dockter Z, et al. iStent trabecular microbypass stent implantation with phacoemulsification in patients with open-angle glaucoma: 6-year outcomes. Clinical Ophthalmology (Auckland, NZ). 2020;14:1859.
12. Greenwood MD, Seibold LK, Radcliffe NM, et al. Goniotomy with a single-use dual blade: Short-term results. Journal of Cataract & Refractive Surgery. 2017;43(9):1197-1201.
13. Sieck EG, Epstein RS, Kennedy JB, et al. Outcomes of Kahook Dual Blade goniotomy with and without phacoemulsification cataract extraction. Ophthalmology Glaucoma. 2018;1(1):75-81.
14. Grover DS, Smith O, Fellman RL, et al. Gonioscopy-assisted Transluminal Trabeculotomy: An Ab Interno Circumferential Trabeculotomy: 24 Months Follow-up. J Glaucoma. 2018;27(5):393-401.
15. Hirsch L, Cotliar J, Vold S, et al. Canaloplasty and trabeculotomy ab interno with the OMNI system combined with cataract surgery in open-angle glaucoma: 12-month outcomes from the ROMEO study. Journal of Cataract & Refractive Surgery. 2021;47(7):907-915.
16. Vold SD, Williamson BK, Hirsch L, et al. Canaloplasty and trabeculotomy with the OMNI system in pseudophakic patients with open-angle glaucoma: the ROMEO study. Ophthalmology Glaucoma. 2021;4(2):173-181.
17. Beckers HJ, Aptel F, Webers CA, et al. Safety and effectiveness of the PRESERFLO^® MicroShunt in primary open-angle glaucoma: results from a 2-year multicenter study. Ophthalmology Glaucoma. 2022;5(2):195-209.
18. Ferguson TJ, Ibach M, Schweitzer J, Karpuk KL, Stephens JD, Berdahl JP. Trabecular micro-bypass stent implantation with cataract extraction in pigmentary glaucoma. Clinical & Experimental Ophthalmology. 2019;2018(4):5926906.

Tanner J. Ferguson, MD is the current cataract, cornea, glaucoma and refractive surgery fellow at Vance Thompson Vision in Sioux Falls, SD. He completed his residency training at the Cole Eye Institute at the Cleveland Clinic.

Lawrence Nguyen, OD is the current resident optometrist at Vance Thompson Vision in Sioux Falls, SD. She received her degree and graduated summa cum laude from the University of Houston College of Optometry.