Minimally Invasive Glaucoma Surgery: A New Era in Glaucoma Treatment

Glaucoma stands as the foremost cause of irreversible blindness globally.1 As of 2020, around 76 million people across the world were afflicted with this condition, a number that continues to rise annually, paralleling the expansion and aging of the population. It is projected that by 2040, over 111.8 million individuals will be grappling with glaucoma.2 Despite the long-standing recognition of trabeculectomy as the “gold standard” in glaucoma filtration surgeries,3,4 it presents notable challenges. These include complications such as shallow anterior chamber, malignant glaucoma, hypotony, and bleb-related complications, along with extensive and complex postoperative management.5,6 These challenges have fueled ongoing modifications and innovations in clinical approaches to glaucoma treatment, notably the advent of minimally invasive glaucoma surgery (MIGS).7 MIGS, in contrast to traditional methods, is distinguished by its precision in reducing intraocular pressure (IOP), microincision technique, minimal trauma, fewer complications, a shorter learning curve, and quicker patient recovery.8,9 Over the last decade, there has been a significant evolution and refinement of MIGS surgical techniques and instruments, solidifying its critical role in glaucoma treatment. Notably, the frequency of MIGS procedures soared by 426% between 2012 and 2016. In 2017, out of 175,000 glaucoma surgeries performed in the United States, MIGS represented the majority (75.5%), surpassing trabeculectomy (13.1%), and aqueous humor drainage valve implantation (11.4%). As published in this issue of the Asia-Pacific Journal of Ophthalmology, Chan et al10 endeavor to comprehensively review recent advancements and practical applications of MIGS. It methodically outlines various MIGS procedures, offering crucial insights encompassing surgical indications, operative techniques, and clinical trial outcomes, possessing significant practical and academic value. Presently, MIGS surgeries are categorized into 4 groups based on their operative sites and distinct mechanisms of IOP reduction: enhancing aqueous outflow through trabecular meshwork/Schlemm’s canal, through suprachoroidal space, through subconjunctival space, and reducing aqueous production via ciliary procedures. For enhancing aqueous outflow through trabecular/Schlemm canal surgery, Chan et al10 are bifurcated into bypassing trabecular meshwork by tissue excision and bypassing trabecular meshwork by implantable devices. The tissue excision focuses on surgical techniques such as Kahook Dual Blade goniotomy, Trabectome, gonioscopy-assisted transluminal trabeculotomy, TRAB 360/OMNI, and excimer laser trabeculotomy. Implantable devices scrutinize the principles, surgical techniques, effectiveness, and safety of contemporary clinical devices such as iStent, iStent inject, iStent inject W, and Hydrus Microstent implantation, offering vital guidance to clinicians in surgical choices. It is pertinent to mention that the extent of Schlemm canal incisions can range from 120 to 360 degrees. However, studies have confirmed that a 120 degrees incision is sufficient for treating primary open-angle glaucoma.11,12 Moreover, devices facilitating these incisions extend beyond the Kahook Dual Blade, with instruments like Tanito Microhook and even bended 25 to 26 G syringe needle offering more refined functionalities and granting superior visibility during canal incisions.13–15 Currently, MIGS surgical devices accessing the suprachoroidal space that have received certification include the CyPass and iStent Supra. Unfortunately, CyPass has been removed from the market owing to the escalated corneal endothelial cell loss experienced by certain patients postoperatively.16,17 The article by Chan et al10 principally examines the iStent Supra, expressing optimism for the future introduction of more such devices into clinical practice. Subconjunctival MIGS devices encompass the XEN gel stent and the PRESERFLO MicroShunt. Chan et al10 focuses on comparing the effectiveness and safety between XEN gel stent implantation and ab interno, as well as the differences between implantation in the subconjunctival space and sub-Tenon space. Moreover, it considers the necessity of incorporating mitomycin C into the surgical procedure to mitigate subconjunctival fibrosis, thereby reducing conjunctival fibrosis, alongside highlighting the frequency of postoperative bleb needling rate.10 Targeting the ciliary body—the aqueous humor production site—surgeries to dampen its secretory activity can alleviate IOP through methods like ultrasonic coagulation or direct photocoagulation of the ciliary processes.18–20 Chan et al10 revisit the pros and cons of conventional cyclophotocoagulation, comparing it to innovative approaches like MicroPulse transscleral laser therapy, ultrasonic cycloplasty, and endoscopic cyclophotocoagulation, affirming the MIGS attributes of safety, effectiveness, fewer complications, repeatability, and precision.10 It is critical to note that while MIGS was initially deemed suitable mainly for primary open-angle glaucoma, the necessity to enhance treatment strategies for primary angle-closure glaucoma (PACG)—a prevalent glaucoma type and a significant cause of blindness, especially in the Asia-Pacific region—has gained urgency.2,21 Encouragingly, a growing number of clinical studies are investigating PACG, with early findings indicating the efficacy of MIGS and combination surgeries with cataract procedures in treating PACG.13,14,22–25 Combined phacoemulsification and goniosynechialysis, as well as interventions such as Schlemm canal incisions (ab interno trabeculotomy or goniotomy),13,14,22–26 Trabectome,27 iStent,28 XEN,29 etc., have demonstrated excellent therapeutic outcomes for PACG with cataract. We expect that these studies will revolutionize PACG treatment, bringing substantial benefits to patients. Emerging technologies, such as trabeculotome tunneling trabeculoplasty and minimally invasive microsclerostomy, conceptually carry some promise. However, all new technologies need adequate evidence, especially from randomized control trials, before full endorsement can be given. In conclusion, MIGS has introduced revolutionary options for glaucoma patients, characterized by less invasive techniques, diminished complications, effective outcomes, simplified postoperative care, and a short learning curve. Chan et al10 by summarizing the recent developments in various MIGS procedures, serve as a pivotal reference for clinicians in making surgical choices. Looking ahead, we fervently hope that as our understanding deepens regarding the pathophysiological mechanisms of aqueous humor outflow pathways and as technological and clinical research progresses, we will witness the emergence of novel minimally invasive surgical tools and methods, enhancing the quality of life for glaucoma patients globally.