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MIGS and the shifting paradigm in glaucoma treatment
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Glaucoma treatment is a life-long burden for patients and their health care system. IOP lowering is still the most consistent and recognized disease-modifying risk factor.
For years, the paradigm of glaucoma treatment included the initial use of IOP-lowering eye drops, followed by laser trabeculoplasty, trabeculectomy, glaucoma drainage device and lastly destructive cyclophotocoagulation. For more than a decade, laser trabeculoplasty has straddled the gap between anti-glaucoma medications and trabeculectomy, deferring this gold standard surgery that has substantial IOP-lowering efficacy but also a spectrum of potential sight-threatening complications including hypotony maculopathy, suprachoroidal hemorrhage, endophthalmitis and wipe-out. While newer laser trabeculoplasties have been demonstrated to be non-inferior to medications in terms of IOP lowering and having almost no long-term complications, the major drawback of laser is the percentage of non-responders. Hence, as quality of life, faster treatment recovery time, as well as visual and conjunctival preservation become more important for glaucoma patients and surgeons, the evolution of microincision glaucoma surgery has rattled the treatment paradigm in glaucoma. Where does MIGS ultimately belong in the treatment spectrum, and are we there yet?
Who is most likely to benefit from MIGS?
As with all surgeries, there is a learning curve with MIGS. However, once the procedure is familiarized, MIGS is generally more straightforward than trabeculectomy, with fewer postoperative enhancement procedures (suture lysis, wound repair, compression sutures and anterior chamber reformation) and fewer complications, making it a more accessible IOP-lowering tool even for surgeons who do not perform glaucoma procedures on a regular basis.
Patient selection is more critical than with trabeculectomy not only in terms of preoperative expectation alignment in regards to the more modest amount of IOP or medication reduction with MIGS compared with a trabeculectomy, but more importantly, recipients for MIGS are much more selective. MIGS is usually targeted for patients with primary open-angle or pseudoexofoliation/pigment dispersion glaucoma. It is more suited for those with mild to moderate disease rather than severe disease. The preoperative IOP should be suboptimal despite maximally tolerated anti-glaucoma medications and yet must not be exceedingly high. Furthermore, having some degree of cataract is a plus, as concomitant cataract extraction is preferred to synergize the IOP-lowering effect of MIGS. The performance of MIGS in pediatric, angle closure and secondary glaucoma populations has yet to be explored.
Are we there yet?
Because most MIGS procedures are blebless, needling and revisions are not viable options when their IOP-lowering effect wears off. While there is data on IOP-lowering efficacy up to years after MIGS, the long-term effects of leaving a non-functional foreign body implant inside the eye is only supported by our theoretical understanding about the materials used in these devices and not by actual long-term clinical data. When the Ex-Press shunt (Alcon) was first introduced, subconjunctival implant without a sclera flap resulted in shunt erosions, leading to subsequent modification of a subscleral implant.
Currently, the position of MIGS, in the treatment spectrum of mild to moderate open-angle glaucoma, is somewhere between medications/laser trabeculoplasty and trabeculectomy. This is determined by its higher safety profile in return for less IOP reduction compared with trabeculectomy. More often than not, MIGS is used for the purpose of medication reduction rather than significant IOP lowering. For MIGS to advance as a potential first-line treatment in naïve glaucomatous eyes, more head-to-head randomized control trials are warranted to compare among the different types of MIGS and their performance vs. medications (particularly preservative-free options) and laser trabeculoplasty. In addition, cost-effective analysis would provide justification on the financial validly of these commercial gadgets.
References:
Francis BA, et al. Ophthalmology. 2011;doi:10.1016/j.ophtha.2011.03.028.
Hoeh H, et al. J Cataract Refract Surg. 2013;doi:10.1016/j.jcrs.2012.10.040.
Lee JW, et al. Medicine (Baltimore). 2016;doi:10.1097/MD.0000000000003212.
Stewart RM, et al. Am J Ophthalmol. 2005;doi:10.1016/j.ajo.2005.02.033.
Tsang S, et al. Br J Ophthalmol. 2016;doi:10.1136/bjophthalmol-2015-307515.
For more information:
Dennis S.C. Lam, MD, FRCOphth, can be reached at State Key Laboratory in Ophthalmology, Sun Yat-Yen University, 54 South Xianlie Road, Guangzhou 510060, People’s Republic of China; email: dennislam.gm@gmail.com.
Disclosure: The authors report no relevant financial disclosures.