Elsevier

Survey of Ophthalmology

Volume 66, Issue 5, September–October 2021, Pages 714-742
Survey of Ophthalmology

Review article
Microinvasive glaucoma surgery: A review of 3476 eyes

https://doi.org/10.1016/j.survophthal.2020.09.005Get rights and content

Abstract

Microinvasive glaucoma surgery (MIGS) is a potentially safer and more efficacious method studied in patients with mild-to-moderate open-angle glaucoma requiring less invasive treatment goals; however, the literature on MIGS must be thoroughly evaluated. We conducted a review of MIGS by searching MEDLINE, EMBASE, and Cochrane CENTRAL. Primary efficacy indicators were reductions in intraocular pressure and topical medication use postoperatively. While all comparative randomized controlled trials assessing MIGS in English peer-reviewed journals were included, only observational studies with a target follow-up of at least one year and a high priority score were analyzed, resulting in a total of 3476 eyes across 20 trials. The mean age was 69.5 ± 2.9 years, 53.7% were female, and 77.4% were Caucasian. One study had last follow-up at less than one year, fifteen studies had follow-up extending 1-2 years, and four had longer than two years of follow-up. A pattern of more significant intraocular pressure and medication reduction was observed in patients who underwent MIGS (n = 2170) relative to control (n = 1306) interventions. iStent had the most literature supporting its efficacy, followed by Hydrus. The most common adverse events after MIGS implantation included stent obstruction, inflammation, and subsequent surgical intervention. Surgical complication rates and efficacy are favorable after MIGS. This review helps to consolidate the high-quality evidence that exists for various MIGS procedures and to identify gaps where further research is needed.

Introduction

Glaucoma is an irreversible, progressive optic neuropathy affecting approximately 76 million people worldwide in 2020.111 It is the second most diagnosed eye disorder and third leading cause of blindness.12,19 In 2010, glaucoma was estimated to cause blindness in 2.1 million individuals, which represents an increase of 62% since 1990.12

Glaucoma can progress to irreversible blindness without treatment. Intraocular pressure (IOP) is the major modifiable risk factor for the development and progression of glaucoma.18,103 Aqueous outflow can be impaired, raising IOP and causing axonal loss.117,118 The lack of symptoms until the disease is advanced makes diagnosis and treatment adherence difficult. Medications to lower IOP include prostaglandins, α-blockers, β-blockers, carbonic anhydrase inhibitors, osmotic agents, cholinergic agonists, rho-kinase inhibitors, and fixed combination agents which can be associated with an IOP reduction of up to 35%.32,110,117,118 Local discomfort, difficulty with drop instillation, systemic side effects, and cost have been found to reduce adherence to, and therefore the overall effectiveness of, topical medications.78,88 Chronic use of topical medications, specifically those that contain preservatives, can cause distressing side effects, affect compliance, and impact glaucoma surgery success rates through conjunctival inflammatory change, fibrosis, and cytotoxicity.9,14,73,119 While topical medication options have continued to evolve, such as the recently introduced preservative-free drops to reduce preservative toxicity, patients sometimes exhibit nonadherence to topical therapy, thus necessitating the consideration of other interventions.76,85,90

Laser trabeculoplasty is another option to improve aqueous drainage and decrease IOP.20,42,120 Selective laser trabeculoplasty (SLT) is the most commonly used approach and involves a laser that is focused on pigmented trabecular cells, leading to improved drainage of aqueous humor by allowing for these cells to be repopulated by endothelial cells.77,101 SLT has been reported to lower IOP by 10-20% after one treatment, although there may be variability between patients with respect to response.62,100,124 In addition to evidence on the cost-effectiveness of laser trabeculoplasty,16,63,106 the recently published Laser in Glaucoma and ocular HyperTension trial highlighted the potential advantages of SLT over topical medications, suggesting that SLT should be considered as a first-line treatment for open-angle glaucoma (OAG).37

For patients with progressing OAG despite maximal medical and laser intervention, incisional filtering or drainage devices such as trabeculectomy and tube shunts have traditionally been used. While these fistulating approaches can effectively reduce IOP, they are invasive, can result in more serious complications and higher morbidity, and have failure rates of up to 33% within three years.38,39,57 In certain cases, patients may need additional topical medications and/or secondary surgical intervention despite incisional surgery.39,59 Complications of traditional glaucoma surgery include a loss of visual acuity, inflammation, subconjunctival fibrosis, subchoroidal hemorrhage, hypotony, hyphema, blebitis, and endophthalmitis, even many years after a purportedly successful operation.17,39,59

Microinvasive glaucoma surgery (MIGS) is a relatively new and innovative surgical method of addressing the treatment gap between medical therapy and more invasive filtering surgery in glaucoma.1,31 This method and related devices have been studied most commonly in patients with nonrefractory, mild-to-moderate glaucoma. Based on the Hodapp-Parrish Anderson criteria, an early/mild glaucomatous defect can be defined as a mean deviation (MD) less than −6 dB, with less than 25% of the points depressed below the 5% level and less than 10 points below the 1% level on a pattern deviation plot, and a sensitivity of at least 15 dB for all points in the central 5°. Moderate defects were defined as an MD between -6 and -12 dB with less than 50% of the points depressed below the 5% level and less than 20 points below the 1% level on a pattern deviation plot and no points in the central 5° with a sensitivity of 0 dB and up to only one hemifield having a central point within 5° of fixation with a sensitivity of less than 15 dB.45,94,107 To note, Canadian guidelines stipulate that the visual field defect should not be within 10 (vs. 5) degrees of fixation in both early and moderate glaucoma cases.15,21

In most instances, MIGS devices are placed ab interno via a clear corneal incision to create a conduit from the anterior chamber to enhance aqueous outflow. This prevents significant disruption of ocular anatomy, which is beneficial in case more invasive surgery is eventually required.93 Although not comprehensively studied in every instance, MIGS has the potential for a high safety profile, shortened surgical time, and lower complication rate relative to filtering or drainage device surgery, as well as high biocompatibility, shorter postoperative recovery, improved quality of life, and at least modest efficacy in lowering IOP and topical medication burden.10,93,105 Most trabecular bypass MIGS are adjunctive and performed with cataract surgery, and it is uncertain whether the safety profile of MIGS is significantly different from cataract surgery alone. MIGS devices have been found to effectively treat mild-to-moderate OAG in standalone procedures with an average reduction in IOP ranging from 1.0 to 11.0 mm Hg2,99 and a sustained reduction of IOP in glaucomatous eyes by up to 35% at 24 months.46, 47, 48 Multiple mechanisms to improve outflow are possible including trabecular bypass, suprachoroidal drainage, or subconjunctival outflow used to create a bleb.93 Despite these potentially advantageous benefits of MIGS devices and procedures in glaucoma management, they may only be approved in specific circumstances or patient populations. For example, in the United States, trabecular meshwork MIGS devices are only approved if implanted in conjunction with cataract surgery in patients with mild-to-moderate glaucomaF, G, H, I; however, there may be significant differences in other countries' approval processes of MIGS devices. For instance, trabecular bypass MIGS devices may be implanted in eyes as an isolated procedure (i.e., without cataract surgery). Furthermore, MIGS may also be used off label in patients with severe glaucoma.29

Despite a significant interest and research on MIGS, many published studies have been underpowered, retrospective, and associated with the traditional limitations of observational studies, such as selection bias and confounding by indication.13 The purpose of this selected review is to assess the efficacy and safety of various MIGS devices relative to control procedures such as cataract surgery and topical medications. We highlight comparative evidence as reported in major randomized controlled trials (RCTs) and well-powered and designed observational studies.

Section snippets

Search strategy

After registering this review with the International Prospective Register of Systematic Reviews database (CRD42019144855), we conducted our search in accordance with the guidelines and recommendations set out by the Preferred Reporting Items of Systematic Reviews (PRISMA) guidelines.74 Searches on Ovid MEDLINE and EMBASE (January 1, 2006, to July 26, 2019) in addition to Cochrane CENTRAL Library (to July 27, 2019) were performed using keywords and subject headings to identify relevant

Study inclusion and baseline characteristics

A total of 10,076 articles were identified in the literature search. After screening of study titles and abstracts and exclusion of duplicates, 9886 articles were excluded, and 90 articles remained eligible for full-text examination. Of these, 20 (22.2% of full-text screens) articles met all inclusion criteria2,4,7,22,25,27,28,30,35,54,61,82,94, 95, 96,98,99,113,115,116 (Fig. 1). The studies included a total of 3476 unique eyes at baseline and 3325 (95.7%) eyes at the last follow-up visit. Of

Summary of efficacy findings and implications

Our purpose is to summarize the evidence from RCTs reporting on MIGS procedures. While past systematic reviews and meta-analyses have been conducted, this is the first MIGS review to comprehensively aggregate the evidence from the MIGS devices with available data.

In general, the mean reduction in IOP was greater, and the number of postoperative medications was lower in the phaco-MIGS cohorts relative to control.28,30,82,94, 95, 96,115 In the first MIGS comparison study, the Hydrus stent

Conclusion

Overall, while the efficacy and safety profile of MIGS has been favorable, these results are not definitive. This review helps to consolidate the high-quality evidence that exists for various MIGS procedures and to identify gaps where further research is needed. Further prospective randomized masked trials and cost-effectiveness studies with endpoints sensitive to patient-reported outcome measures, IOP, topical medication reduction, and safety parameters are necessary to elucidate the role of

Statement of Disclosure

  • A)

    Any commercial or similar relationships of the authors or members of their families to products or companies mentioned in or related to the subject matter of the article being submitted.

    • P.N., M.P., and J.P. have no conflicts to disclose. M.B.S. received consultant/consulting fees from Light Matter Interaction and Santen. M.B.S. received speaker honoraria from Bausch Health, Johnson & Johnson Vision, and Théa-Labtician. M.B.S. received both from Alcon and Allergan. I.I.K.A. received

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