Managing MIGS: An optometrist’s practical comanagement guide

Like it or not, innovation in the surgical treatment of glaucoma has outpaced medical advancement in recent decades. The development of minimally invasive (or microinvasive) glaucoma surgery (MIGS) techniques has resulted in patients with glaucoma increasingly undergoing this type of surgery earlier in their treatment course due to an improved safety profile and shorter recovery period compared with traditional glaucoma surgeries. Consequently, this has shifted more of the postoperative care into comanagement. Despite the favorable safety and recovery profile of MIGS, complications may still occur. Optometrists should know what is expected, what is concerning, and when to contact the surgeon.

Case report

A 76-year-old woman with a history of pseudoexfoliative glaucoma OU, pseudophakia OD, and cataract OS presented 7 months post OMNI canaloplasty and goniotomy with travoprost intracameral implant (iDose TR) OD and reported pain and decreased vision in the operative eye. She was taking dorzolamide hydrochloride and timolol maleate (Cosopt) twice daily OU. Visual acuity was 20/70 OD with no improvement on pinhole and 20/20– OS. Pupils were both round and reactive, with an afferent pupillary defect OD. The IOP was 15 mm Hg OD and 10 mm Hg OS. Slit lamp examination revealed 3+ cell and flare OD. The left anterior chamber was deep and quiet. The posterior chamber intraocular lens OD appeared well positioned and clear. The patient had 2+ nuclear sclerosis OS. Gonioscopy revealed angles open to scleral spur OU, with a microhyphema inferiorly OD. The travoprost intracameral implant appeared to be well positioned superior temporally. Dilated fundus examination revealed a cup to disc ratio of 0.9 OD, with neuroretinal rim thinning of 360°, and 0.5 OS, with thinning inferiorly. The retina was unremarkable OU.

Background

Historically, topical medication has been the hallmark of initial glaucoma treatment, with surgical intervention generally reserved for severe and refractory cases. However, since the early 2000s, glaucoma providers have seen a rapid development of new MIGS techniques, with the number of procedures performed increasing 426% from 2012 to 2016.¹ MIGS is designed to lower IOP by enhancing the natural outflow of aqueous fluid and is often performed in conjunction with cataract surgery; however, some techniques are approved for standalone use. MIGS is defined by an ab interno approach, minimal disruption of the ocular anatomy, modest efficacy, a favorable safety profile, and rapid surgical recovery.^2,3 MIGS procedures can be further classified as 1) trabecular bypass procedures, 2) trabecular excisional/incisional procedures, or 3) Schlemm canal–based procedures. Subconjunctival procedures, such as the Xen Gel Stent, are often discussed with MIGS. However, based on their bleb-forming nature, these procedures share many potential complications with traditional glaucoma surgery and are therefore beyond the scope of this article.³

The first step to preventing postsurgical complications is to ensure that the patient is a good candidate for MIGS preoperatively. Ideal patients have mild to moderate glaucoma, open anterior chamber angles, and a target IOP no less than mid-teens. Patients with visually significant cataracts are particularly strong candidates. Prior to referring a patient for a potential MIGS procedure, careful gonioscopic examination is essential to determine that the patient’s anterior chamber angle anatomy is adequate for MIGS. Lastly, setting proper patient expectations and defining the goals of the procedure (IOP reduction vs decreased medication burden) are also paramount.

Expected findings vs complications

As with any surgical procedure, certain postoperative findings are expected following MIGS (Table 1). The optometrist’s role in postoperative care is to differentiate expected findings from complications, treat those complications that are within their scope, and communicate effectively with the glaucoma surgeon. By far, the most common complications following MIGS are IOP spikes and hyphema.^3-6 Elevated IOP following MIGS can happen secondary to retained viscoelastic, steroid response, hyphema, inflammation, or device obstruction. Older patients and those with severe glaucoma may be more at risk for postoperative IOP spikes due to weakened aqueous drainage pathways.⁴ Most cases of elevated IOP following MIGS are self-limited and can be treated medically. Hyphema is common after MIGS due to reflux bleeding, especially in goniotomy or trabeculotomy procedures. The hyphema should self-resolve in 1 to 2 weeks. Serious complications, such as endophthalmitis, secondary to MIGS have been shown to be extremely rare, occurring at rates similar to those seen with phacoemulsification alone.^4-6

Trabecular bypass procedures

The iStent (Glaukos Corporation) is one of the earliest and most commonly used MIGS devices.⁴ This first-generation device is a single heparin-coated, snorkel-shaped titanium implant that is inserted in the Schlemm canal. The second-generation iStent inject has a modified conical design. Up to 3 stents are approved for placement as a stand-alone procedure with the iStent infinite system. Postoperative IOP spikes (1%-33%) and hyphema (weighted mean of 2.21%-6.22%) are the most common complications.^3,4,6 However, both are significantly less frequent with the iStent inject compared with the first-generation iStent.⁴ Corneal injury (3.1%), peripheral anterior synechiae (PAS; 0.2%-1.8%), stent obstruction (up to 13.2%), and malposition (3%-18%) are other less frequent complications.³

The Hydrus Microstent (Alcon) is an 8-mm nitinol implant that is inserted in the Schlemm canal during cataract extraction, bypassing the trabecular meshwork and stenting the Schlemm canal over 90º (3 clock hours). Hyphema and IOP spikes are common complications, occurring in 0.5% to 36% and 0.5% to 20% of patients, respectively.³ PAS is another adverse event that may be of particular interest with Hydrus. PAS occurs in 8.7% to 20% of patients, with the incidence increasing longitudinally, possibly due to chronic low-grade inflammation secondary to prolonged mechanical tension.^3,4,6 Although this could theoretically lead to aqueous obstruction and increased IOP, findings from studies have not yet shown this to be a clinically significant complication.⁴ Corneal edema (1.4%-28%), device obstruction (1.1%-12.2%), and malposition (1.1%-7.9%) are additional potential complications.^3,7

Trabecular excisional/incisional procedures

This category of MIGS includes Trabectome (MicroSurgical Technology), Kahook Dual Blade (New World Medical), gonioscopy-assisted transluminal trabeculotomy (GATT), and the OMNI Surgical System (Sight Sciences). These devices unroof the Schlemm canal to varying degrees with or without prior cannulation. Understandably, hyphema is a common complication of these procedures, occurring in up to 100% of cases.^3,6 In fact, hyphema is often considered an indication of treatment success, as it denotes that the collector channels have been exposed. Delayed hyphema, up to 31 months after the procedure, has been reported in 4.6% of patients undergoing Trabectome.^3,6,8 IOP spikes are another common complication, occurring as frequently as 36% of the time with stand-alone GATT.^3,5,6 PAS, hypotony, and corneal injury are other less common concerns.^3-6 Interestingly, ciliochoroidal detachments have been detected in 41% to 92% of patients using anterior segment optic coherence tomography (OCT). However, these patients are typically asymptomatic and the condition is self-limiting.

Schlemm canal–based procedures

Ab interno canaloplasty (ABiC), performed using several different commercially available devices, is a stand-alone treatment that dilates the Schlemm canal and collector channels using viscoelastic material. Hyphema (up to 100%), IOP spikes (up to 44%), and supraciliary effusion (71%) are the most common complications.^4,6,9 Another potential complication that is relatively unique to ABiC is Descemet membrane detachment (3.7%).⁴ This is thought to occur secondary to excessive pressure used during viscoelastic injection (Table 2).

Red flags

Causes for concern warranting same-day referral to the treating surgeon include high IOP associated with pain, nausea, or significant corneal edema; large hyphema; severe inflammation; device malposition; sudden or significantly reduced vision; hypotony; or shallow anterior chamber (Table 3). The threshold for urgency in IOP elevation depends on the extent of IOP elevation, glaucoma severity, target IOP, symptoms, fellow eye status, and duration. Persistent or layered hyphema, recurrent bleeding, reduced vision, corneal blood staining, or hyphema associated with elevated IOP should also prompt communication with the surgeon. Prolonged postoperative hyphema may necessitate an extended steroid taper, as blood is proinflammatory. If inflammation is excessive, consider steroid nonadherence, device malposition causing iris chafing, or endophthalmitis. Red flags include fibrin, hypopyon, severe photophobia, worsening anterior chamber reaction, or reduced vision. Uveitis-glaucoma-hyphema syndrome, due to device malpositioning or migration, should be suspected any time a patient has prolonged inflammation or recurrent hyphema. Gonioscopy is necessary at 1 week post procedure to ensure proper device positioning and to rule out obstruction by iris tissue, blood, or fibrin.

Long-term considerations

Although some MIGS procedures have been shown to be durable treatment for open-angle glaucoma, others require more longitudinal data. Therefore, it is clinically necessary to continue close long-term follow-up for these patients postoperatively. Following the 90-day global period, it is important to reestablish a subjective and objective baseline using the visual field and OCT. Additionally, as with any intraocular surgery, endothelial cell loss is a concern, particularly with the Hydrus Microstent,^10,11 and lifelong monitoring for corneal decompensation is crucial.

Case revisited

Due to the anterior chamber reaction and delayed onset hyphema, our patient was started on prednisolone acetate 1% OD 4 times daily, and her surgeon was notified of the findings. Although her IOP remained stable on weekly follow-up, the hyphema and intraocular inflammation persisted. Ultimately, the travoprost intracameral implant was removed due to suspected uveitis-glaucoma-hyphema syndrome and a trabeculectomy was performed.

Conclusion

MIGS procedures have shifted the glaucoma treatment landscape toward earlier surgical intervention thanks to their enhanced safety parameters and relatively rapid recovery. However, adverse events still occur, including discomfort, anterior chamber inflammation, elevated IOP, decreased vision, and hyphema. All should be mild and self-limited. Adequate understanding of the procedure performed, the goals of treatment, and the potential complications, along with clear communication, is paramount to success. Despite the shift in glaucoma management, optometrists are still well positioned to continue to care for these patients both in the postoperative period and long term.

References

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10. Ahmed IIK, Sheybani A, De Francesco T, Samuelson TW. Corneal endothelial safety profile in minimally invasive glaucoma surgery. J Cataract Refract Surg. 2024;50(4):369-377. doi:10.1097/j.jcrs.0000000000001365

11. Ahmed IIK, De Francesco T, Rhee D, et al; HORIZON Investigators. 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