Efficacy and safety of combined cataract surgery with 2 trabecular microbypass stents versus ab interno trabeculotomy

ARTICLE

Efficacy and safety of combined cataract surgery with 2 trabecular microbypass stents versus ab interno trabeculotomy Michelle Khan, MD, Hady Saheb, MD, MPH, Arvind Neelakantan, MD, Ronald Fellman, MD, Zachary Vest, MD, Paul Harasymowycz, MD, Iqbal Ike K. Ahmed, MD

PURPOSE: To compare the outcomes of combined cataract surgery with trabecular microbypass stents and ab interno trabeculotomy in patients with open-angle glaucoma. SETTING: University of Toronto, Toronto, Ontario, and University of Montreal, Montreal, Quebec, Canada, and Glaucoma Associates of Texas, Dallas, Texas, USA. DESIGN: Retrospective case series. METHODS: Patients with primary open-angle, pseudoexfoliative, or pigmentary dispersion glaucoma were included. Primary outcome measures were intraocular pressure (IOP), postoperative medications, success (IOP %18 mm Hg, no glaucoma medications or reoperations), and postoperative adverse events. RESULTS: The average patient age was 76.5 years G 12 [SD]. Forty-nine eyes had phacoemulsification and 2 had stent implantations; 52 eyes had phacoemulsification and trabeculotomy surgery with a 12-month postoperative follow-up. The analysis of variance indicated a significant reduction in mean IOP from baseline to 12 months for stent (19.6 G 5.3 mm Hg to 14.3 G 3.1 mm Hg; P < .001) and trabeculotomy (20.6 G 6.8 mm Hg to 17.3 G 6.5 mm Hg; P < .001) and lower mean IOP at 12 months in the stent group (P Z .01). The median number of glaucoma medications decreased from baseline to 12 months in both groups and was lower in the stent group at 3, 6, and 12 months. Thirty-nine percent (19 eyes) in the stent group and 14% (7 eyes) in the trabeculotomy group achieved success at 12 months (P Z .006). The incidence of hyphema was lower in the stent group (P Z .008). CONCLUSIONS: Both types of surgery achieved a significant reduction in IOP and medication use at 12 months, with the stent group achieving higher success and a reduced incidence of postoperative hyphema. Financial Disclosure: Dr. Ahmed is a consultant to and investigator for Glaukos Corp., Ivantis, Inc., Transcend Medical, Inc., and Aquesys, Inc., and has received speaker honoraria from Neomedix, Inc. Dr. Saheb has received travel funding from Glaukos Corp., Ivantis, Inc., and Transcend Medical, Inc., and a research grant from Ivantis, Inc. Dr. Harasymowycz has received a research grant from Ivantis, Inc. Dr. Fellman is a consultant to Endo Optiks, Inc., and has received honoraria from Optous and research funds from Ivantis, Inc., Glaukos Corp., and Transcend Medical, Inc. No other author has a financial or proprietary interest in any material or method mentioned. J Cataract Refract Surg 2015; 41:1716–1724 Q 2015 ASCRS and ESCRS

Microinvasive glaucoma surgery (MIGS) is playing an increasingly important role in the evolving glaucomatreatment algorithm. Microinvasive glaucoma surgery is defined as any procedure that shares the following qualities: ab interno microincision, minimum trauma, good efficacy, high safety profile, and rapid recovery.1 1716

Q 2015 ASCRS and ESCRS Published by Elsevier Inc.

The first 2 MIGS procedures to become widely commercially available were the trabecular microbypass stent (iStent, Glaukos Corp.) and the ab interno trabeculotomy (Trabectome, Neomedix, Inc.). The trabecular microbypass stent is a heparin-coated titanium stent implanted ab interno in Schlemm canal. http://dx.doi.org/10.1016/j.jcrs.2014.12.061 0886-3350

CATARACT SURGERY WITH 2 TRABECULAR MICROBYPASS STENTS VS AB INTERNO TRABECULOTOMY

The ab interno trabeculotomy procedure uses a highfrequency electrocautery device that creates a goniotomy by removing a strip of the trabecular meshwork and the inner wall of Schlemm canal.1 The trabecular microbypass stent has been most extensively studied in randomized controlled trials comparing combined surgery with phacoemulsification with phacoemulsification alone.2–4 Ab interno trabeculotomy outcomes have been reported in several case series5–7 with and without simultaneous phacoemulsification. These 2 MIGS procedures have not yet been compared. The present study compared the safety and efficacy of stent implantation and ab interno trabeculotomy surgery in combination with phacoemulsification during a 1-year postoperative follow-up in patients with concurrent cataract and open-angle glaucoma (OAG). PATIENTS AND METHODS This retrospective interventional comparative case series received institutional review board approval. Medical records of patients with concurrent cataract and OAG who had either combined phacoemulsification and 2 stent implantations or combined phacoemulsification and ab interno trabeculotomy surgery and 12-month follow-ups were reviewed. Included were patients with primary OAG (POAG), pseudoexfoliation (PXF), and pigmentary dispersion glaucoma. Excluded were patients with adjunctive surgery such as endocyclophotocoagulation, endocycloplasty, or goniosynechialysis. Also excluded were patients with angle-closure glaucoma, previous incisional conjunctival surgery, or postoperative follow-ups of less than 12 months. Patient data collected were age, race, sex, visual field mean deviation at baseline, type of glaucoma, past or concurrent surgeries, preoperative and postoperative

Submitted: August 31, 2014. Final revision submitted: December 9, 2014. Accepted: December 11, 2014. From the University of Toronto (Khan), Toronto, Ontario, McGill University Health Centre (Saheb), University of Montreal (Harasymowycz), Montreal, Quebec, and Credit Valley EyeCare (Ahmed), Mississauga, Ontario, Canada; the Glaucoma Center of Texas (Neelakantan) and Glaucoma Associates of Texas (Fellman, Vest), Dallas, Texas, USA. Presented at the annual conference of the Canadian Ophthalmological Society, Montreal, Quebec, Canada, June 2013, the annual meeting of the American Academy of Ophthalmology, New Orleans, Louisiana, November 2013, and the ASCRS Symposium on Cataract, IOL and Refractive Surgery, Boston, Massachusetts, USA, April 2014. Corresponding author: Iqbal Ike K. Ahmed, MD, Credit Valley EyeCare, 3200 Erin Mills Parkway, Mississauga, Ontario, AL5L 1W8 Canada. E-mail: [email protected].

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intraocular pressure (IOP) and number of glaucoma medications, and postoperative adverse events, including hyphema, peripheral anterior synechia (PAS) formation, postoperative hypotony (IOP !5 mm Hg), IOP spikes (defined as an increase in IOP of greater than 10 mm Hg from the previous visit), endophthalmitis, suprachoroidal hemorrhage, and reoperations. Postoperative information was collected at 1 day, 1 week, and 1, 3, 6, and 12 months. Severity of glaucomatous disease was not a consideration in selecting patients for this study.

Statistical Analysis The IOP data are summarized by mean values and the medication data by medians and interquartile ranges. Median numbers of medications were used in statistical analyses instead of means because the Kolmogorov-Smirnov goodness-of-fit test showed that the medication data did not conform to a normal Gaussian distribution. Mean values with SDs are also included. Sex, race, type of glaucoma, and incidence of postoperative adverse events were compared between the stent and ab interno trabeculotomy groups using the Fisher exact test. The Student t test was used to assess age differences between the groups, and the Mann-Whitney U test was used to compare the median number of medications. Changes from baseline in median number of medications were evaluated using the nonparametric Wilcoxon signed-rank test. Changes in IOP from preoperative baseline to the 12-month follow-up were assessed using 2-way analysis of variance (ANOVA) to compare groups and to determine time-related changes within each group. At 12 months, surgical success was assessed using an IOP of 18 mm Hg or lower, no medications, and no glaucoma reoperations as the composite criteria, and rates were compared between the 2 groups using the Fisher exact test. These rates were also compared with success criteria in former major surgical glaucoma studies. To control for possible confounding factors, multivariate logistic regression was also applied to determine the odds of success between the 2 groups, adjusting for patient age, sex, race, and type of glaucoma (POAG versus other). Two-tailed P values less than 0.05 were considered statistically significant to examine the effects of both surgeries on IOP and number of medications over the 12-month period. Statistical analysis was performed using SPSS software (version 21.0, International Business Machines Corp.).

RESULTS The study included 49 eyes (49 patients) with 2 stent implantations and 52 eyes (52 patients) having ab interno trabeculotomy surgery performed by 1 of 3 surgeons (I.I.K.A., A.N., P.H.) from August 15, 2007, to September 6, 2012. All patients were followed for a 12-month period postoperatively. No statistically significant differences were found in age (P Z .55), race (P Z .34), or sex (P Z .84) between the 2 study groups. The stent group contained a statistically significant higher proportion of patients with PXF (P Z .007) (Table 1). Baseline IOP was comparable between the 2 study groups (P Z .37). A statistically significant decrease in IOP from baseline to 12 months was observed in

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CATARACT SURGERY WITH 2 TRABECULAR MICROBYPASS STENTS VS AB INTERNO TRABECULOTOMY

Table 1. Demographic characteristics in stent and ab interno trabeculotomy groups (101 eyes). Study Group

Variable

Stent (n Z 49)

Ab Interno Trabeculotomy (n Z 52) P Value

Mean age (y) G SD 77.5 G 11.9 Sex, n (%) Male 20 (41) Female 29 (59) Race, n (%) White 34 (69) Other 15 (31) Mean visual field 11.5 G 8.0 deviation (dB) G SD Type of glaucoma, n (%) Primary open angle 38 (78) Pigmentary dispersion 0 Pseudoexfoliation 11 (22)

76.1 G 12.1

.55 .84

23 (44) 29 (56) .34 36 (70) 16 (30) 8.6 G 9.7

50 (96) 1 (2) 1 (2)

.17

.47 1 .007*

*Statistically significant

the stent group, from 19.6 mm Hg G 5.3 (SD) to 14.3 G 3.1 mm Hg (ANOVA, F Z 8.05; P ! .001), and in the ab interno trabeculotomy group, from 20.6 G 6.8 mm Hg to 17.3 G 6.5 mm Hg (F Z 7.46, P ! .001) groups. The ANOVA indicated statistically significant lower IOP in the stent cohort during the 12-month follow-up period (F Z 6.76, P Z .011). The combined stent and cataract surgery group had a lower IOP than the combined ab interno trabeculotomy and cataract surgery group 1 week (P Z .035), 6 months (P Z .041), and 12 months (P Z .01)

postoperatively (Table 2). These results were calculated using last observation carried forward for patients with reoperations. There was no statistically significant difference in the median number of glaucoma medications between the stent and ab interno trabeculotomy groups at baseline (stent: median Z 3, range 1 to 6; ab interno trabeculotomy: median Z 3, range 0 to 5; P Z .53). The type of surgery had a statistically significant effect on the reduction in medication use, with a lower median number of medications in the stent group than in the ab interno trabeculotomy group at 3 months (2 versus 3, P Z .006), 6 months (1 versus 2, P Z .012), and 12 months (1 versus 2, P Z .001). A statistically significant decrease in medication use was seen in both study groups from baseline (P ! .001), and medication use at the 12-month period was statistically significantly lower in the stent group than in the ab interno trabeculotomy group (P Z .001) (Table 3). Table 4 shows the mean number of medications at each timepoint. In comparing IOP data after reoperations, similar results were observed. A statistically significant decrease in IOP was observed in the stent (F Z 8.01, P ! .001) and ab interno trabeculotomy (F Z 7.45, P ! .001) groups from baseline to 12 months. The ANOVA indicated a statistically significantly lower mean IOP in the stent cohort during the 12–month postoperative follow-up period (F Z 6.84, P Z .01) and 1 week (P Z .074), 6 months (P Z .039), and 12 months (P Z .022) postoperatively. Similarly, in comparing IOP data, surgery type had a statistically significant effect on the reduction in medication use, with a lower median number of medications in the stent group than in the ab interno trabeculotomy group at 1 month

Table 2. Intraocular pressure in stent and ab interno trabeculotomy groups. Study Group Stent Timepoint Preoperative Postoperative 1 day 1 week 1 month 3 month 6 month 12 month

Ab Interno Trabeculotomy

Mean IOP (mm Hg) G SD

Patients (n)

Mean IOP (mm Hg) G SD

Patients (n)

P Value

19.6 G 5.2

49

20.6 G 6.8

52

.37

14.5 G 7.8 17.2 G 8.8 14.9 G 5.8 14.4 G 4.0 13.8 G 2.9 14.3 G 3.1

49 49 44 39 41 49

16.8 G 6.6 19.7 G 7.7 15.8 G 3.6 15.5 G 3.6 16.5 G 4.9 17.3 G 6.5

48 49 51 38 47 52

.08 .035* .57 .39 .041* .01*

IOP Z intraocular pressure Following glaucoma reoperation, the IOP prior to reoperation was used for the rest of the follow-up period (i.e., last observation carried forward [LOCF]). *Statistically significant, repeated-measures ANOVA using LOCF.

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CATARACT SURGERY WITH 2 TRABECULAR MICROBYPASS STENTS VS AB INTERNO TRABECULOTOMY

Table 3. Median number of glaucoma medications in stent and ab interno trabeculotomy groups. Study Group Stent Timepoint Preoperative Postoperative 1 day 1 week 1 month 3 months 6 months 12 months

Ab Interno Trabeculotomy

Medications (n)*

Patients (n)

Medications (n)*

Patients (n)

P Value

3.0 (2.0, 3.0)

49

3.0 (2.0, 4.0)

52

.53

3.0 (2.0, 3.0) 2.0 (1.0, 3.0) 2.0 (1.0, 3.0) 2.0 (0.5, 3.0) 1.0 (0.0, 3.0) 1.0 (0.0, 2.0)

49 49 44 39 41 49

1.0 (0.0, 3.0) 3.0 (1.0, 3.0) 3.0 (2.0, 3.0) 3.0 (2.0, 4.0) 2.0 (2.0, 4.0) 2.0 (1.0, 3.0)

47 47 50 35 45 52

!.001† .53 .05 .006† .012† .001†

Following glaucoma reoperation, the IOP prior to reoperation was used for the rest of the follow-up period (i.e., last observation carried forward). *Data are median (interquartile range) † Statistically significant, Mann-Whitney U test

POAG subgroup (P Z .63). Type of surgery had a statistically significant effect on the reduction in medication use, with a lower median number of medications in the stent group than in the ab interno trabeculotomy group at 1 day (3.0 versus 1.0; P ! .001), 1 month (P Z .04), 3 months (2.0 versus 3.0; P Z .005), 6 months (1.0 versus 2.0; P Z .016), and 12 months (1.0 versus 2.0; P Z .001). Previous studies assessing the success of glaucoma surgeries have defined success criteria as an IOP of 21 mm Hg or less, an IOP reduction of 20% or more, no loss of light perception, and no need for glaucoma reoperations. Success in this study was defined as an IOP of 18 mm Hg or less, no medications, and no need for glaucoma reoperations (see Discussion). Nineteen of 49 eyes (39%) in the stent group and 7 of 52 eyes (14%) in the ab interno trabeculotomy group met this composite success criterion at 12 months (P Z .006). Multivariate logistic regression confirmed that the

(2.5 versus 3.0; P Z .046), 3 months (2.0 versus 3.0; P Z .008), 6 months (1.0 versus 3.0; P Z .011), and 12 months (1.0 versus 2.0; P Z .002). A statistically significant decrease in medication use from baseline was seen in both study groups (P ! .001). When isolating POAG patients in both study groups, the results were consistent. Baseline IOP was comparable between the 2 study groups (P Z .20). A significant decrease in IOP was observed in the stent (F Z 4.68, P ! .001) and ab interno trabeculotomy groups (F Z 6.90, P ! .001) from baseline to 12 months. The ANOVA indicated a statistically significant lower mean IOP in the stent group during the 12-month follow-up period (F Z 7.45, P Z.008) and at 1 week (P Z .01), 6 months (P Z .034), and 12 months (P Z .026). Similarly, there was no statistically significant difference in the median number of glaucoma medications in the stent and ab interno trabeculotomy groups at baseline in the

Table 4. Mean number of glaucoma medications in stent and ab interno trabeculotomy groups. Study Group Stent Timepoint Preoperative Postoperative 1 day 1 week 1 month 3 months 6 months 12 months

Ab Interno Trabeculotomy

Medications (n)*

Patients (n)

Medications (n)*

Patients (n)

2.86 G 0.91

49

2.90 G 1.10

52

2.47 G 1.10 2.22 G 1.18 2.14 G 1.30 1.77 G 1.23 1.63 G 1.40 1.22 G 1.28

49 49 44 39 41 49

1.30 G 1.53 2.40 G 1.30 2.68 G 1.24 2.54 G 1.22 2.42 G 1.36 2.15 G 1.35

47 47 50 35 45 52

*Data are mean G SD

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CATARACT SURGERY WITH 2 TRABECULAR MICROBYPASS STENTS VS AB INTERNO TRABECULOTOMY

Table 5. Postoperative adverse events in stent and ab interno trabeculotomy groups. Number (%)

Adverse Event Hyphema Peripheral anterior synechiae formation Early postoperative interventions† Intraocular pressure spike Transitory hypotony Glaucoma reoperation Suprachoroidal hemorrhage

Ab Interno Stent Trabeculotomy P (49 Patients) (52 Patients) Value 2 (4) 10 (20)

12 (23) 8 (15)

.008* .61

4 (8)

2 (4)

.43

8 (16)

17 (33)

.07

2 (4) 0 0

0 4 (8) 0

.24 .12 d

*Statistically significant, Fisher exact test † Defined as interventions within the first 3 months postoperatively

odds of success were more than 4 times greater with stent than with ab interno trabeculotomy (odds ratio, 4.1; 95% confidence interval, 1.5-11.6; P Z .004) controlling for age (P Z .27), sex (P Z .44), race (P Z .28), and type of glaucoma (P Z .26). When using the less stringent success criteria of an IOP of 21 mm Hg or less on no medications, no loss of light perception, and no glaucoma reoperations, there was a 10% increase in patients achieving success in the stent group (P Z .38). When using the composite success criteria of an IOP of 21 mm Hg or less with an IOP reduction of 20% or more, no loss of light perception, and no glaucoma reoperations, 29 patients (60%) in the stent group and 18 patients (35%) in the ab interno trabeculotomy group met these criteria (P Z .01). Table 5 shows the postoperative adverse events in the 2 study groups. The incidence of hyphema was higher in the ab interno trabeculotomy group (P Z .008). The hyphema resolved within 1 week postoperatively in both groups. A greater percentage of patients in the ab interno trabeculotomy group than in the stent group had IOP spikes, although the difference did not reach statistical significance (P Z .07). The 2 cases of transient hypotony presented 1 day postoperatively and resolved by the 1-week followup visit. Visual acuity in these patients was 20/25 and 20/70, respectively, and remained the same at the 1-week follow-up visit. There were no cases of choroidal effusion or endophthalmitis. In the stent group, postoperative interventions were cortex removal (n Z 1), pupilloplasty (n Z 1), iridoplasty (n Z 2), neodymium:YAG capsulotomy

(n Z 2), and anterior chamber paracentesis (n Z 1). In the ab interno trabeculotomy group, postoperative interventions were goniopuncture (n Z 2) and YAG capsulotomy (n Z 1) 3 months postoperatively. The number of postoperative interventions was not significantly different between groups (P Z .43). Additional glaucoma surgery was performed in 4 patients in the ab interno trabeculotomy group compared with 0 patients in the stent group during the 12-month follow-up period (P Z .12). Three patients had trabeculectomy surgery 6 days, 3.5 months, and 9 months postoperatively. One patient had ab interno trabeculotomy revision and a first-stage glaucoma drainage device 11 months postoperatively due to continued elevation in IOP and subsequently had the tube inserted into the anterior chamber 13 months postoperatively. Prior to reoperation, their IOP and number of medications were 16, 24, 30, and 38 mm Hg and 2, 4, 4, and 4, respectively. DISCUSSION Trabeculectomy remains the most commonly performed surgery in the management of OAG. However, the difficulty in predictability, rate of complications, and risk for rare but devastating adverse events in both the short and long term8,9 has led to an interest in alternative surgical options. Microinvasive glaucoma surgery procedures have an increasingly important role in the glaucoma treatment algorithm. The present study is the first to compare 2 commercially available MIGS procedures in combination with phacoemulsification. Both trabecular microbypass stent implantation and ab interno trabeculotomy surgery in combination with phacoemulsification achieve a significant reduction in IOP and number of glaucoma medications 1 year postoperatively, with excellent safety profiles. The trabecular microbypass stent (iStent) is an L-shaped titanium device that creates a patent bypass through the trabecular meshwork to facilitate physiologic outflow and thus lower IOP. Studies have shown a significantly higher proportion of patients achieving reduced IOP without medications.3,4 These outcomes were reported in randomized clinical trials comparing combined phacoemulsification and single stent implantation with phacoemulsification alone.2–4 Furthermore, Belovay et al.10 found a benefit to implanting multiple stents. Fernandez-Barrientos et al.11 found that implantation of 2 stents resulted in reduced IOP and number of glaucoma medications when compared with phacoemulsification alone. The ab interno trabeculotomy removes a segment of the trabecular meshwork and inner wall of Schlemm

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Figure 1. Mean IOP results (with standard deviation bars) over the 12-month period in the stent and ab interno trabeculotomy study groups.

Figure 2. Median number of glaucoma medications over the 12-month period in both study groups.

canal through electrocautery, allowing direct access of aqueous to collector channels. The ab interno trabeculotomy also has been shown to be effective in lowering IOP and medication use.5–7 In contrast to studies of stent implantation, ab interno trabeculotomy outcomes were studied in a case series,12 underlining the importance of comparative studies between the 2 procedures. Results in this study showed the mean IOP reduction was greater in eyes having stent implantation than in those having ab interno trabeculotomy when combined with phacoemulsification, with a statistically significant difference between the 2 groups at the 1-week, 6month, and 12-month timepoints (Figure 1). Within each group and similar to previous studies,2,3 there was a statistically significant, sustained decrease in IOP over the 12-month follow-up. The median number of glaucoma medications was statistically significantly lower in the stent study group than in the ab interno trabeculotomy group at 3, 6, and 12 months (Figure 2). These results suggest that the stent provides further reduction in IOP and number of medications than the ab interno trabeculotomy. Delayed reduction in the number of glaucoma medications in both groups is explained by the postoperative regimen of the study surgeons. Some of the study surgeons maintained patients on the preoperative glaucoma medications until 3 months postoperatively, after which time the possibility of steroid response becomes negligible. Both groups saw a drop in the number of glaucoma medications after 3 months. Furthermore, the success rate was statistically significantly higher in the stent cohort than in the ab interno trabeculotomy cohort (39% versus 14%),

and this difference remained statistically significant after controlling for age, sex, race, and type of glaucoma. Multivariate analysis indicated that patients having stent implantation were approximately 4 times more likely to achieve a successful outcome based on IOP and medication criteria than those who had ab interno trabeculotomy surgery (Figure 3). Medicationfree status was chosen as 1 of 3 success criteria because MIGS procedures often include a postoperative goal of maintaining target IOP without glaucoma medications. The medication-free component of this study’s success criteria makes them more stringent than success criteria in other glaucoma studies.9,13,14 No patient in the stent group required additional surgery, whereas 4 eyes (8%) in the ab interno trabeculotomy group required further glaucoma surgery. Analysis using the less stringent success criteria consistent with previous literature showed similar differences in results.3,14 Previous literature has reported adverse events for combined ab interno trabeculotomy and phacoemulsification7,15–17 as well as for combined stent and phacoemulsification.3 In the present comparative study, the ab interno trabeculotomy group experienced a greater occurrence of hyphema formation (23%) than the stent group (4%). The majority of these occurred in the immediate postoperative period, and the higher frequency in the ab interno trabeculotomy group might be explained by the larger opening of Schlemm canal caused by a wide ablation of the trabecular meshwork in this procedure compared with the focal openings in the trabecular meshwork with stent implantation. This larger opening in the trabecular meshwork might

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Figure 3. Percentage of patients achieving success (IOP % 18 mm Hg, no medications, no loss of light perception, and no need for glaucoma reoperation) in both study groups over 12 months.

predispose the eye to more reflux of blood from the episcleral venous plexus through aqueous veins and collector channels into Schlemm canal. Both groups experienced a similar number of IOP spikes (O10 mm Hg higher than previous visit) within the first week postoperatively. Intraocular pressure spikes can be related to a number of factors in MIGS, including retained ophthalmic viscosurgical devices, steroid response, the effect of weaning from glaucoma medications, hyphema, and inflammation. Peripheral anterior synechia formation was seen in 10 patients in the stent group and 8 patients in the ab interno trabeculotomy group. These procedures might predispose the eye to PAS given the focally increased outflow through the bypass of the trabecular meshwork as well as a local inflammatory response. Patients in this study had a moderate level of glaucomatous disease, with mean deviations of 11.5 and 8.6 units in the stent and ab interno trabeculotomy groups, respectively. Both of these MIGS procedures were able to reach target IOP in the majority of patients without further glaucoma surgery (0 in the stent group, 4 in the ab interno trabeculotomy group). There was a significantly higher proportion of PXF patients in the stent group than in the ab interno trabeculotomy group. Patients with PXF have been shown to have a more pronounced hypotensive effect from cataract surgery.18 Further data analysis was performed to determine whether the additional IOP lowering in the stent group versus in the ab interno trabeculotomy group could be explained by the difference in proportion of PXF patients between

groups. A multivariate analysis did not show significance of PXF in IOP and medication reduction between the study groups. Furthermore, when isolating POAG patients in our study, we found the success rate and IOP-lowering differences to be maintained. A common challenge in MIGS studies is the confounding effect of phacoemulsification on IOP reduction with combined phacoemulsification and MIGS procedures. Multiple studies have shown that phacoemulsification alone reduces IOP.19–22 This IOP reduction following phacoemulsification typically confounds the results in case series, including any MIGS procedures combined with phacoemulsification. However, the present study compared 2 groups of patients that had phacoemulsification, thereby neutralizing this common confounding effect. This study design allows a more direct comparison of the effect of trabecular microbypass stents and ab interno trabeculotomy. In contrast to other MIGS studies,8,14 the inclusion criteria in this study did not include a baseline IOP requirement and IOP at baseline was well controlled in the majority of patients. This baseline IOP inclusion criterion in other studies predisposes results of the analysis to a regression to the mean that might play a role in the magnitude of IOP reduction. The lack of a baseline IOP requirement in this study reduces the extent of regression to the mean and its role in the IOP results in this study. Limitations of this study include the inherent weaknesses common to retrospective studies, specifically the inability to randomize our patients, selection bias, intersurgeon variability, and lack of standardization in quantifying complications. However, baseline IOP and medication use did not show statistically significant differences between groups. The low incidence of complications also limits the power of the study to detect statistically significant differences between the 2 study groups. The frequency and timing of interventions postoperatively was left to the discretion of the surgeons and could not be standardized across sites; however, the IOP and number of medications before glaucoma reoperation suggest that a reoperation bias is not a likely explanation for the higher number of glaucoma reoperations in the ab interno trabeculotomy group. In conclusion, both trabecular microbypass stent implantation and ab interno trabeculotomy surgery in combination with phacoemulsification achieved a statistically significant reduction in IOP and number of glaucoma medications over a 12-month period postoperatively with an excellent safety profile. Combined cataract surgery and stent

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implantation resulted in further reduction in IOP and the number of glaucoma medications as well as a lower incidence of hyphema. These findings are useful for improving our understanding of the comparative surgical outcomes of these 2 MIGS procedures. These results have to be confirmed in a randomized clinical trial. WHAT WAS KNOWN  Both trabecular microbypass stent implantation and ab interno trabeculotomy surgery in combination with phacoemulsification achieve a significant reduction in IOP and number of glaucoma medications 1 year postoperatively. Each procedure has an excellent safety profile. WHAT THIS PAPER ADDS  Microbypass stent implantation and ab interno trabeculotomy surgery combined with phacoemulsification led to a significant reduction in IOP and medication use, with the stent group achieving higher success and a lower rate of hypotony.

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REFERENCES 1. Saheb H, Ahmed IIK. Micro-invasive glaucoma surgery: current perspectives and future directions. Curr Opin Ophthalmol 2012; 23:96–104 2. Fea AM. Phacoemulsification versus phacoemulsification with micro-bypass stent implantation in primary open-angle glaucoma; randomized double- masked clinical trial. J Cataract Refract Surg 2010; 36:407–412 3. Samuelson TW, Katz LJ, Wells JM, Duh Y-J, Giamporcaro JE; for the US iStent Study Group. Randomized evaluation of the trabecular micro-bypass stent with phacoemulsification in patients with glaucoma and cataract. Ophthalmology 2011; 118:459–467 4. Craven ER, Katz LJ, Wells JM, Giamporcaro JE; for the 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 Surgery 2012; 38:1339–1345 5. Minckler DS, Baerveldt G, Alfaro MR, Francis BA. Clinical results with the Trabectome for treatment of open-angle glaucoma. Ophthalmology 2005; 112:962–967 6. Minckler D, Baerveldt G, Ramirez MA, Mosaed S, Wilson R, Shaarawy T, Zack B, Dustin L, Francis B. Clinical results with the Trabectome, a novel surgical device for treatment of openangle glaucoma. Trans Am Ophthalmol Soc 2006; 104:40–50. Available at: http://www.aosonline.org/xactions/2006/15456110_v104_p040.pdf. Accessed May 30, 2015 7. Minckler D, Mosaed S, Dustin L, Francis B; and the Trabectome Study Group. Trabectome (trabeculectomy-internal approach): additional experience and extended follow-up. Trans Am Ophthalmol Soc 2008; 106:149–159. peer discussion 159 160.

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First author: Michelle Khan, MD University of Toronto, Toronto, Ontario, Canada