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69 EW RESIDENTS the paper reports a 2-way ANOVA analysis was used, which if true, would not appropriately adjust for repeated IOP measurements of the same patient. The median number of glaucoma medications in both groups was 3 and decreased to 1 and 2 in the iStent and Trabectome groups, respectively. This decrease was statistically significant when compared to baseline medication usage (p<0.001 for both) and between groups (p=0.001). The authors reported similar statistically significant decreases in IOP and medication reliance when comparing results after censoring IOP data post reoperations and in a subgroup analysis only looking at patients with POAG. There were 4 reoperations in the Trabectome group and none in the stent group. However, no actual IOP values were reported for the analysis following the censoring of IOP data post reop- erations and in the POAG subgroup, which limits the ability to discern the clinical significance of the au- thor's findings in this population. Using the definition of success of IOP <18 mm Hg on no medica- tions and no glaucoma reoperations, 39% of eyes in the stent group and 14% in the ab interno trabeculot- omy group achieved success at 12 months (p=0.006). The paper does not specify if these criteria were specified a priori or as part of a post-hoc analysis, which can lead to bias, especially in a retrospective study. It is also not clear whether the multivariable logistic regression analysis was adjusted, such as with a generalized estimating equation or a general linear model, to account for clustered longitudinal measure- ments. The only statistically signif- icant greater complication risk was hyphema in the ab interno trabecu- lotomy group compared with stents (p=0.008). There was no statistical difference in the number of early (within 3 months) postop proce- dures (p=0.43) or overall reoperation (0 in iStent group, 4 in ab interno trabeculotomy; p=0.12). This paper compares 2 similar trabecular meshwork-based MIGS procedures. Such a head-to-head comparison is important in clinical decision-making. In agreement with prior studies, 3–6 Khan et al demon- strated that both iStent and ab interno trabeculotomy are effective in a matched cohort population. It is unclear if these were consecutive patients. All patients underwent concurrent cataract extraction with either MIGS procedure. Patients with primary open angle (POAG), pseudoexfoliation (PXG) and pig- ment dispersion (PDG) glaucoma were included. Patients with any adjunctive eye surgery other than cataract extraction were excluded along with any patients with angle closure glaucoma or postop follow- up less than 12 months. Surgical success was defined as an IOP <18 mm Hg on no medications and no glaucoma reoperations. The analysis was also carried out with "standard" glaucoma surgical study success cri- teria of IOP <21 mm Hg with an IOP reduction of >20%, no loss of light perception, and no glaucoma reoper- ations. Data was collected at day 1, week 1, and month 1, 3, 6, and 12. Statistical analysis of age was con- ducted with a student t test; gender, race, type of glaucoma, and adverse postop events with a Fisher's exact test; a Mann-Whitney U-test was used to compare median number of medications; and analysis of vari- ance (ANOVA) to compare changes in IOP preop and at every postop visit. Median change in medication was used since the data did not fit a normal distribution. Although not randomly as- signed given the retrospective nature of the study, the 2 arms of the study were similar in demographics including age and preop IOP and number of medications; however, there was a significantly higher pro- portion of patients with PXG in the iStent group, which may respond differently to MIGS. This possible bias was addressed by the authors via a post-hoc subgroup analysis on POAG patients in both study arms. When comparing the entire cohort from preop to 1 year postop, within treatment arms there was a statisti- cally significant decrease in IOP in the iStent arm and the Trabectome arm: 19.6+5.3 to 14.3+3.1 mm Hg (P<0.001) and 20.6+6.8 to 17.3+6.5 mm Hg (P<0.001), respectively. This analysis only compared the final 1-year IOP to preop IOP. According to the tables, repeated measures of ANOVA also revealed that the iStent arm had a significantly lower IOP than the Trabectome arm at 1 year. However, the methods section of placed with cataract extraction against cataract extraction with Trabectome as a cost effectiveness longitudinal study would be benefi- cial to the field. For now, the analy- sis by Khan et al serves as a starting basis to discuss MIGS options with patients. EW Acknowledgements The authors would like to thank Robert Chang, MD, and Douglas Fredrick, MD, for their time and assistance in preparing this article. References 1. Quigley HA, Broman AT. The number of people with glaucoma worldwide in 2010 and 2020. Br J Ophthalmol 2006;90(3):262–7. 2. Gedde SJ, Herndon LW, Brandt JD, Budenz DL, Feuer WJ, Schiffman JC. Postoperative complications in the Tube Versus Trabeculecto- my (TVT) study during five years of follow-up. Am J Ophthalmol 2012;153(5):804–814. 3. Wellik SR, Dale EA. A review of the iStent trabecular micro-bypass stent: safety and effi- cacy. Clin Ophthalmol. 2015 Apr 15;9:677–84. 4. Craven ER, Katz LJ, Wells JM, Giamporcaro JE; iStent Study Group. Cataract surgery with trabecular micro-bypass stent implantation in patients with mild-to-moderate open-angle glaucoma and cataract: two-year follow-up. J Cataract Refract Surg. 2012 Aug;38(8):1339– 45. 5. Belovay GW, Naqi A, Chan BJ, Rateb M, Ahmed II. Using multiple trabecular micro- bypass stents in cataract patients to treat open-angle glaucoma. J Cataract Refract Surg. 2012 Nov;38(11):1911–7. 6. Bahler CK, Smedley GT, Zhou J, Johnson DH. Trabecular bypass stents decrease intraocular pressure in cultured human anterior segments. Am J Ophthalmol. 2004 Dec;138(6):988–94. 7. Minckler DS, et al. Clinical results with the Trabectome for treatment of open-angle glau- coma. Ophthalmology. 2005 Jun;112(6):962–7. 8. Ahuja Y, et al. Clinical results of ab interno trabeculotomy using the Trabectome for open-angle glaucoma: the Mayo Clinic series in Rochester, Minnesota. Am J Ophthalmol. 2013 Nov;156(5):927–935. 9. Mansberger SL, Gordon MO, Jampel H, Bhorade A, Brandt JD, Wilson B, Kass MA; Ocular Hypertension Treatment Study Group. Reduction in intraocular pressure after cataract extraction: the Ocular Hypertension Treatment Study. Ophthalmology. 2012 Sep;119(9):1826–31. Contact information Fredrick: dfred@stanford.edu cataract surgery with interno trabeculotomy" at lowering IOP and reducing reli- ance on medication at 12 months. At least for these clinical practices, the implantation of 2 iStents with cataract extraction has statistically superior IOP lowering and reduction in median IOP medications com- pared to ab interno trabeculotomy with cataract extraction. While the authors discuss the inherent limita- tions in a retrospective case series design, they attempt to overcome these weaknesses through subgroup analysis of the POAG group and multivariate analysis. Nonetheless, as the authors appropriately highlight, it is import- ant to keep in mind the limitations of the study design. This was a retrospective design with a relatively small number of eyes, and therefore random assignment was not possi- ble, which is important in a hetero- geneous disorder such as glaucoma because response to the surgeries may depend on disease severity and type. Even though the mean deviation of the visual fields was similar, that may not correlate with the collector channel function, and suboptimal candidates may have been selected for the Trabectome arm. In addition to the severity of the glaucoma, the severity of the cataracts was not compared. One study using the OHTS data has demonstrated 16.5% IOP lowering with cataract extraction alone, with a higher percentage of IOP reduction with higher starting IOP as well as with pseudoexfoliation and pigmen- tary glaucomas. 9 Furthermore, it is unclear how many of each proce- dure was performed by each surgeon or practice, as the case selection by each surgeon could lead to selection or training bias. There was no mask- ing of the treatment groups for sub- sequent IOP measurements, risking observation bias. Lastly, there was a significant proportion of Caucasian patients in both groups and 2 of the 3 practices were in Canada, where such devices have been approved for a longer period of time, limiting the generalizability of the current findings to other countries or ethnic groups. As the popularity of MIGS pro- cedures increase as new, safer devices are approved, it is important to prospectively evaluate their relative efficacy and cost. Future prospective trials that compare 1 targeted iStent August 2015

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