August 2020


EyeWorld Journal Club
Review of “Excisional goniotomy versus trabecular micro-bypass stent implantation:
A prospective randomized clinical trial in eyes with mild to moderate open-angle glaucoma”

by Charles Medert, MD, Ann Quan, MD, Anne Kunkler, MD, Humberto Salazar, MD, Jesse Sengillo, MD, and Steven Gedde, MD

Steven Gedde, MD
Residency program director Bascom Palmer Eye Institute
Miami, Florida

Which of the many MIGS options works best as an adjunct to cataract surgery? This month, the Bascom Palmer residents reviewed this important randomized controlled trial that is published in the August issue of JCRS.

—David F. Chang, MD EyeWorld Journal
Club Editor

Bascom Palmer Eye Institute residents
Source: Bascom Palmer Eye Institute

Cataract and glaucoma frequently coexist in the elderly population. It has been estimated that 20% of patients who undergo cataract surgery in the United States have comorbid glaucoma or ocular hypertension.1 Historically, phacoemulsification (phaco) combined with trabeculectomy has been the preferred surgical approach for simultaneously managing cataract and glaucoma.1 However, a growing concern about intraoperative and postoperative complications associated with trabeculectomy has encouraged many surgeons to explore alternative techniques. Recent studies have evaluated the safety and efficacy of microinvasive glaucoma surgery (MIGS) combined with phaco.2 MIGS procedures designed to bypass the diseased trabecular meshwork (TM) via an ab interno approach are becoming increasingly popular due to their shorter recovery period and better safety profile compared with traditional filtering procedures.2,3
The iStent (Glaukos) was the first device approved by the Food and Drug Administration to circumvent aqueous outflow resistance at the level of the TM. Similarly, the Kahook Dual Blade (KDB, New World Medical) is designed to bypass the TM by excising a segment of diseased TM and inner wall of Schlemm’s canal. Few studies have compared the efficacy of these MIGS procedures head-to-head.4–6 Falkenberry et al. report the first prospective randomized clinical trial comparing KDB-phaco with iStent-phaco in eyes with mild to moderate open angle glaucoma.


This was a multicenter randomized clinical trial involving nine centers across the United States that enrolled patients from June 2016 to January 2019. Patients eligible for the study were those scheduled for elective phaco of a visually significant cataract and a concurrent history of mild to moderate open angle glaucoma treated with one to three topical therapies. Additional inclusion criteria included an age range of 18–90 years and a preintervention intraocular pressure (IOP) between 14 and 28 mm Hg. Patients were excluded if they had occludable angles, a history of incisional glaucoma surgery, a history of corticosteroid-induced IOP elevation, recent glaucoma laser therapy, and/or oral IOP-lowering agents. Topical IOP-lowering therapies were discontinued on the day of surgery, but investigators were allowed to restart them postoperatively at their discretion. Follow-up visits were scheduled 1 day, 1 week, 1 month, 3 months, 6 months, and 12 months postoperatively. The primary outcome measure was the proportion of eyes with an IOP reduction ≥20% or reduction of IOP-lowering medications by ≥1 compared to baseline during the study period.
Of the 166 eyes of 166 patients enrolled, 164 eyes were analyzed (82 in each group). Demographic characteristics were comparable between the groups with a Caucasian predominance and an average age of about 70 years. Most patients had a diagnosis of primary open angle glaucoma (152/164) and “mild” disease (127/164). The average baseline IOP was 18.5 mm Hg in both groups (p=0.97), and there was a similar baseline mean number of topical IOP-lowering medications in both groups (1.3 in KDB-phaco vs. 1.4 in iStent-phaco, p=0.69). Mean IOP was similar between treatment groups at all time points, except at 1 day and 1 month postoperatively in which the KDB-phaco group had a lower IOP (p=0.019 and p=0.029, respectively). There were no significant differences in mean number of postoperative medications between the two groups. The KDB-phaco group had a significantly higher proportion of eyes that achieved the primary outcome compared to the iStent-phaco group (93.7% vs. 83.3%, p=0.04). The proportion of eyes that achieved both conditions specified in the primary outcome (i.e., IOP reduction and drop reduction), however, was similar in both groups (36.7% in the KDB-phaco group vs. 35.9% in the iStent-phaco group, p=0.92). Importantly, both groups had comparable VA throughout the study and experienced a similar number of adverse events, all of which resolved spontaneously or with medical management. Approximately one-third of patients in both treatment groups experienced an IOP increase of 10 mm Hg or more postoperatively.


Several studies have compared the KDB and iStent combined with cataract surgery in a retrospective fashion, but this is the first study to do so in a prospective randomized manner.4–6 As in the prior studies, the authors found that KDB-phaco outperformed iStent-phaco. Specifically, KDB-phaco was superior when looking at the primary outcome, which was the proportion of eyes with an IOP reduction ≥20% or reduction of IOP-lowering medications by ≥1 compared to baseline. Selecting this as the primary outcome reflects the general goal of MIGS procedures as stated by the authors, which is to alleviate “patient-specific” issues related to glaucoma medication burden and to achieve modest IOP reductions.7
While it is exciting to see another prospective randomized controlled trial added to the MIGS literature, there are several limitations to the study. As the authors point out, the sample size was relatively small. This limits the power of the study to identify significant differences between treatment groups, especially with events that have a low rate of occurrence like surgical complications. The study protocol did not include a washout measurement of IOP preoperatively and at 1 year, which would have been helpful in determining the efficacy of each treatment. There was also no algorithm for postoperative drop escalation. Instead, these decisions were left to the investigator’s discretion, which is potentially problematic as they were not blinded to the patient’s treatment group.
Open angle glaucoma is a slowly progressive disease that can take decades to evolve.8 Thus the longevity/durability of surgical interventions is important when determining the success of a procedure. While 12 months is a commonly used endpoint as seen in this study, differences in performance and safety may not manifest until several years after surgery as demonstrated by another MIGS procedure, the now defunct CyPass Micro-Stent (Alcon).9 It would have been interesting to follow the patients in this study over a longer period of time. Including disease-specific outcome measures such as visual field and retinal nerve fiber layer analysis would have also been helpful in judging the efficacy of the treatments.
Cataract surgery alone has been shown to reduce IOP and, in turn, the number of IOP-lowering medications.10 This means that each patient in this study, in effect, received two IOP-lowering procedures: phaco and either KDB or iStent. Including a separate phaco-only group for comparison would have been helpful for readers interested in the additive effects of angle-based procedures in phaco-MIGS. There are also newer techniques and technologies pertinent to the iStent such as the use of multiple implants and the iStent inject, which were not explored despite their place in current practice.
Despite these limitations, the study is an important contribution to the medical literature. The randomization technique appeared successful as demonstrated by the balanced baseline data/demographics. The use of intention-to-treat analysis was also a strength and further reduced bias when coupled with the aforementioned randomization. Finally, the utilization of a standardized surgical approach based on the manufacturer’s Directions for Use helped control for surgeon-specific differences in technique.


We applaud the authors for conducting the first prospective, randomized clinical trial comparing the KDB and iStent in combination with phaco in eyes with mild to moderate open angle glaucoma. Overall, KDB-phaco and iStent-phaco groups had comparable reductions in IOP and need for IOP-lowering medications with similar safety profiles. The authors report KDB-phaco significantly achieved “patient-specific” surgical success compared to the iStent-phaco group. However, statistical significance was not found when comparing IOP reduction or medication reduction alone, so it’s unclear to what extent these approaches differ. Additional randomized clinical trials are needed to better characterize the indications and outcomes of various MIGS procedures.


1. Budenz DL, Gedde SJ. New options for combined cataract and glaucoma surgery. Curr Opin Ophthalmol. 2014;25:141–147.
2. Lavia C, et al. Minimally-invasive glaucoma surgeries (MIGS) for open angle glaucoma: A systematic review and meta-analysis. PLoS One. 2017;12:e0183142.
3. Richter GM, Coleman AL. Minimally invasive glaucoma surgery: Current status and future prospects. Clin Ophthalmol. 2016;10:189–206.
4. Le C, et al. Surgical outcomes of phacoemulsification followed by iStent implantation versus goniotomy with the Kahook Dual Blade in patients with mild primary open-angle glaucoma with a minimum of 12-month follow-up. J Glaucoma. 2019;28:411–414.
5. Dorairaj SK, et al. A multicenter retrospective comparison of goniotomy versus trabecular bypass device implantation in glaucoma patients undergoing cataract extraction. Clin Ophthalmol. 2018;12:791–797.
6. ElMallah MK, et al. 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. Adv Ther. 2019;36:2515–2527.
7. Davis SA, et al. Drop instillation and glaucoma. Curr Opin Ophthalmol. 2018;29:171–177.
8. Heijl A, et al. Natural history of open-angle glaucoma. Ophthalmology. 2009;116:2271–2276.
9. Lass JH, et al. Corneal endothelial cell loss and morphometric changes 5 years after phacoemulsification with or without CyPass Micro-Stent. Am J Ophthalmol. 2019;208:211–218.
10. Slabaugh MA, et al. The effect of phacoemulsification on intraocular pressure in medically controlled open-angle glaucoma patients. Am J Ophthalmol. 2014;157:26–31.



Review of “Excisional goniotomy versus trabecular micro-bypass stent implantation: A prospective randomized clinical trial in eyes with mild to moderate open-angle glaucoma” Review of “Excisional goniotomy versus trabecular micro-bypass stent implantation: A prospective randomized
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