Outcomes after combined phacoemulsification and trabecular microbypass stent implantation in controlled open-angle glaucoma

ARTICLE

Outcomes after combined phacoemulsification and trabecular microbypass stent implantation in controlled open-angle glaucoma Leonard K. Seibold, MD, Kevin M. Gamett, MD, Jeffrey B. Kennedy, MD, Matthew J. Mulvahill, MS, Miranda E. Kroehl, PhD, Jeffrey R. SooHoo, MD, Mina B. Pantcheva, MD, Malik Y. Kahook, MD

PURPOSE: To study the effect of combined phacoemulsification cataract surgery and iStent (trabecular microbypass stent) implantation on intraocular pressure (IOP) and medication use in openangle glaucoma (OAG) patients with a low mean preoperative IOP. SETTING: University of Colorado Health Eye Center, Aurora, Colorado, USA. DESIGN: Retrospective case series. METHODS: Treatment outcomes analyzed included IOP, medication use, and corrected distance visual acuity (CDVA). Treatment success was defined as a 20% or more IOP reduction or discontinuation of at least 1 medication. RESULTS: Sixty-four eyes of 45 patients were included in the analysis. At 1 year, the mean IOP was significantly reduced from 14.7 G 3.2 mm Hg (SD) to 13.2 G 2.8 mm Hg (P < .01) and the mean medication use decreased from 1.81 G 1.13 to 1.41 G 1.48 (P Z .0001). The estimated IOP reduction at 1, 3, 6, and 12 months was 3.5% (P Z .23), 7.9% (P Z .04), 9.7% (P Z .01), and 12.2% (P Z .002), respectively. Treatment success at 1 year was achieved in 76.1% of patients, and 41% of patients were medication free at 1 year. The CDVA was significantly improved from 0.4 G 0.38 logMAR at baseline to 0.17 G 0.35 at 1 year (P < .0001). CONCLUSIONS: Combined cataract surgery and trabecular microbypass stent implantation was statistically effective in reducing IOP and/or medication burden in OAG patients with a low preoperative IOP. During the informed surgical consent process, the physician and patient should consider the clinical benefit of modest IOP lowering and/or a decrease in medication use. Financial Disclosure: Drs. Seibold, SooHoo, Pantcheva, and Kahook have received grant support from Glaukos Corp. No other author has a financial or proprietary interest in any material or method mentioned. J Cataract Refract Surg 2016; 42:1332–1338 Q 2016 ASCRS and ESCRS

The surgical treatment of glaucoma has traditionally involved the creation of a drainage fistula to facilitate aqueous drainage and reduce intraocular pressure (IOP).1 Although effective, filtration surgeries such as trabeculectomy or glaucoma drainage device implantation carry the risk for serious complications.2 In recent years, several new procedures have emerged for the reduction in IOP in a safer less-invasive manner by augmenting aqueous egress from natural outflow pathways.3,4 The iStent (Glaukos Corp.), a trabecular 1332

Q 2016 ASCRS and ESCRS Published by Elsevier Inc.

microbypass stent, is the first implant approved by the U.S. Food and Drug Administration (FDA) in this class of microinvasive glaucoma surgeries. The titanium device is designed to augment physiologic outflow through the conventional outflow pathway by establishing a bypass tract from the anterior chamber directly into the canal of Schlemm. The microbypass stent is labeled for single-device implantation in conjunction with cataract surgery in patients with mild to moderate open-angle glaucoma (OAG). http://dx.doi.org/10.1016/j.jcrs.2016.07.023 0886-3350

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A growing body of literature supports the efficacy and safety of the iStent device implanted at the time of cataract surgery.5–8 A multicenter randomized controlled trial comparing combined phacoemulsification and implantation of this microbypass stent with phacoemulsification alone found that eyes receiving the microbypass stent were more likely than the control group to achieve an IOP of less than 21 mm Hg without medication use.9 A previous randomized controlled trial by Fea8 found that combined surgery with the iStent microbypass device achieved a significantly lower IOP at 15 months compared with cataract surgery alone. Subsequent studies of the outcomes of this microbypass stent have shown IOP reductions in the range of 16% to 33% with a decrease of 0.5 to 2.0 glaucoma medications.10 Most medical and laser glaucoma treatments have an IOP-lowering efficacy that is directly correlated to the level of preoperative IOP. All previous reports to date assessing the effects of combined cataract surgery and microbypass stent placement focused on eyes with a mean medicated IOP over 18 mm Hg. The IOP-lowering efficacy of the microbypass stent placement in low-pressure glaucoma patients is largely unknown. Furthermore, in this population, the device is often used as a means of reducing the medication burden in patients who might not necessarily need a further significant reduction in IOP. In this study, we analyzed the outcomes of combined cataract surgery and iStent implantation in a population with a low mean preoperative IOP.

Submitted: January 10, 2016. Final revision submitted: June 21, 2016. Accepted: July 4, 2016. From the University of Colorado Health Eye Center (Seibold, Gamett, Kennedy, SooHoo, Pantcheva, Kahook), Department of Ophthalmology, and the Department of Biostatistics and Informatics (Mulvahill, Kroehl), University of Colorado at Denver, Aurora, Colorado, USA. Supported by National Institutes of Health/National Center for Advancing Translational Services, Bethesda, Maryland USA, Colorado Clinical and Translational Science Institute (grant UL1 TR001082). Presented at the annual meeting of the American Glaucoma Society, San Diego, California, USA, February 2015. Corresponding author: Leonard K. Seibold, MD, University of Colorado Eye Institute, 1675 Aurora Court, Mail Stop F-731, PO Box 6510, Aurora, Colorado 80045, USA. E-mail: leonard.seibold@ ucdenver.edu.

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PATIENTS AND METHODS Approval was obtained from the Colorado Multiple Institutional Review Board, and the study followed the tenets of the Declaration of Helsinki. A retrospective chart review was performed for all patients who had combined phacoemulsification cataract removal with intraocular lens (IOL) placement and iStent implantation at the University of Colorado from November 2012 through August 2014. Inclusion criteria were eyes with visually significant cataract and coexisting mild to moderate OAG. Exclusion criteria included eyes with less than 1 month of follow-up or those in which another glaucoma procedure was performed at the same time as phacoemulsification and microbypass stent implantation. The preoperative IOP or medication count was not used in the inclusion or exclusion criteria. Surgery was performed by 1 of 3 glaucoma fellowshiptrained, board-certified ophthalmologists who completed a wet-lab training program before device insertion. The preoperative medications included 1 drop each of moxifloxacin 0.5%, cyclopentolate 1.0%, phenylephrine 10.0%, tropicamide 1.0%, and flurbiprofen every 10 minutes for a total of 3 drops each. Anesthesia was achieved with topical tetracaine 0.5% eyedrops, lidocaine jelly 2.0%, and preservativefree lidocaine 1.0% injected intracamerally. Before microbypass stent implantation, phacoemulsification cataract removal was completed through a temporal clear corneal incision (CCI) with implantation of an IOL in the bag. The microbypass stent was then placed in accordance with the manufacturer's guidelines as described previously.9 Briefly, after IOL insertion, an additional ophthalmic viscosurgical device (OVD) was placed in the anterior chamber to deepen the angle and allow adequate visualization of the trabecular meshwork. The patient's head was then rotated away from the surgeon, and the microscope was tilted toward the surgeon. An additional OVD was placed on the surface of the cornea, and a Swan Jacob gonioprism was used to directly visualize the nasal angle. A single preloaded microbypass stent was then inserted through the same CCI into the canal of Schlemm nasally. When possible, the stent was implanted in areas of greater pigmentation, possibly indicating the location of more collector channels distally. Surgeon preference was used to determine whether a right- or left-facing stent was used. The OVD removal was then completed, and the eye was filled with a balanced salt solution to achieve physiologic pressure. Depending on surgeon preference, intracameral carbachol (Miostat) was instilled at the end of some cases to limit postoperative IOP spikes. Postoperative care included follow-up at 1 day, 1 week, and 1 month. A fluoroquinolone antibiotic was used 4 times daily for 1 week. A combination of prednisolone acetate 1.0% and ketorolac 0.5% was prescribed 4 times daily for 1 week and then tapered according to resolution of inflammation. Postoperatively, glaucoma medications were restarted at the surgeon's discretion based on the disease severity and IOP target. In accordance with the World Glaucoma Association's guidelines,11 each patient's visual acuity, IOP, glaucoma medication use, and complications were recorded for 1 day, 1 week, 1 month, 3 months, 6 months, and 1 year postoperatively. Patients with less than 1 month of follow-up after surgery were excluded from analysis. Surgical success was defined as an IOP reduction of 20% or more or a discontinuation of at least 1 glaucoma medication. Failure was further defined by an IOP higher than

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Table 1. Descriptive statistics of eye demographics and baseline characteristics by surgical success or failure. Eyes with insufficient follow-up were classified as lost to follow-up. Overall Parameter Sex (n Z 64) Female Male Age (n Z 64) Ethnicity (n Z 64) White African American Other Hispanic Asian Prior surgery (n Z 63) None SLT Canaloplasty Diagnosis (n Z 64) POAG Other Meds baseline (n Z 64) CDVA baseline (n Z 63) IOP baseline (n Z 64)

Success

Failure

LTF

Count or Mean

% or SD

Count or Mean

% or SD

Count or Mean

% or SD

Count or Mean

% or SD

P Value

41 23 73.92

64.1 35.9 8.77

23 21 73.82

52.3 47.7 9.34

12 1 72.46

92.3 7.7 7.81

6 1 77.29

85.7 14.3 6.58

.0088

34 12 12 4 2

53.1 18.8 18.8 6.2 3.1

28 5 8 2 1

63.6 11.4 18.2 4.5 2.3

4 7 1 1 0

30.8 53.8 7.7 7.7 0.0

2 0 3 1 1

28.6 0.0 42.9 14.3 14.3

.0047

48 14 1

76.2 22.2 1.6

34 8 1

79.1 18.6 2.3

8 5 0

61.5 38.5 0.0

6 1 0

85.7 14.3 0.0

.5501

55 9 1.81 0.40 14.68

85.9 14.1 1.13 0.38 3.19

36 8 1.98 0.42 15.05

81.8 18.2 1.05 0.43 3.43

85.7 14.3 0.95 0.36 2.51

.2544

13 0 1.54 0.26 14.12

100.0 0.0 1.39 0.15 2.50

6 1 1.29 0.54 13.43

.5048

.1989 .2499 .3616

CDVA Z corrected distance visual acuity; IOP Z intraocular pressure; LTF Z lost to follow-up; Meds Z medications; POAG Z primary open-angle glaucoma; SLT Z selective laser trabeculoplasty

21 mm Hg or lower than 5 mm Hg, reoperation for glaucoma within 1 year of surgery, or loss of light perception (LP) acuity. Eyes could not be marked as failure by IOP or medication reduction criteria until 1 month after surgery and had to meet failure criteria at 2 consecutive visits. The patient baseline characteristics were assessed by treatment failure using paired t tests or analysis of variance and chi-square tests; failure categories were expanded to include known success/failure as well as those with unknown/ undefined status. The hazard ratios of patient variables for failure were estimated using univariate Cox proportionalhazards regression models, and a Kaplan-Meier survival curve of the cohort was constructed. The corrected distance visual acuity (CDVA) was defined as CDVA when present and pinhole visual acuity when CDVA was missing. To assess the change from baseline in the number of medications and in visual acuity, Wilcoxon signed-rank tests were used because of notable non-normality. A secondary sensitivity analysis using paired t tests and reliance on the central limit theorem to provide robustness against incorrect model assumptions was performed to evaluate changes in the mean values. The congruent results between the 2 tests were used to support the hypothesis of a significant change from baseline. Linear mixed models were used to assess the longitudinal trajectory of log-transformed IOP from baseline to the 12-month visit, adjusting for medication count. A P value of 0.05 was considered statistically significant. Statistical analyses were performed with the R software environmentA (version 3.2.2) and SAS/STAT software (version 9.4 of the SAS System for Unix, SAS Institute, Inc.)

RESULTS Seventy eyes with visually significant cataract and mild or moderate OAG had phacoemulsification cataract extraction with microbypass stent implantation during the study period. Six eyes were excluded because of inadequate follow-up beyond the 1-week postoperative appointment, leaving 64 eyes of 45 patients included in the analysis. Table 1 shows the patients' baseline demographics and variables in the 64 eyes for the overall study population as well as separated by success and failure. The only significant differences between success and failure among patient demographics or baseline variables were ethnicity and sex, with a larger percentage of white patients and men achieving success than nonwhite patients and women, respectively. Surgical success rates were 87.7% (95% confidence interval [CI], 76.0-94.0) at 3 months, 82.1% (95% CI, 69.3-90.0) at 6 months, and 76.1% (95% CI, 62.4-90.0) at 12 months of follow-up. Figure 1 shows the Kaplan-Meier survival analysis over 1 year of followup. Seven eyes completed 1 month of follow-up but did not have a subsequent visit. Therefore, they were excluded from the survival analysis because failure criteria had to be met on 2 consecutive visits after

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Table 2. Univariate Cox proportional hazards regression results of failure for each patient variable. Variable

HR

Lower CI

Upper CI

P Value

Age Sex White ethnicity Previous surgery Baseline IOP Baseline med count

0.98 8.79 0.29 2.13 0.93 0.66

0.93 1.21 0.06 0.66 0.78 0.31

1.04 64.02 1.29 6.89 1.10 1.42

.59 .03 .10 .21 .39 .29

CI Z 95% confidence interval; HR Z hazard ratio, IOP Z intraocular pressure; med Z medication

Figure 1. Kaplan-Meier plot of treatment success/failure by time. The point size represents the count of censored observations.

1 month to be considered a failure. Table 2 shows the univariate Cox regression analysis results of the effect of certain patient variables on the likelihood of failure. Women had a significantly greater risk for failure than men (hazard ratio 8.79; 95% CI, 1.21-64.02; P Z .03). All other variables failed to have a significant effect on failure. Most failures were the result of an IOP reduction of less than 20% and no decrease in medication use (12 of 13). One failure was the result of an IOP higher than 21 mm Hg on 2 consecutive postoperative visits after 1 month. No patient required reoperation for glaucoma or had loss of LP acuity in the first postoperative year. The observed mean IOP at baseline was 14.7 G 3.2 mm Hg (range 10 to 25 mm Hg) with a mean use of 1.8 G 1.1 topical glaucoma medications. One year postoperatively, the mean IOP was reduced to

Figure 2. Observed mean IOP change after surgery. Error bars represent 95% CIs (IOP Z intraocular pressure).

13.2 G 2.8 mm Hg on 1.4 G 1.5 topical medications. After adjusting for the use of topical medications, the mean IOP reduction at 12 months was estimated at 87.8% of baseline IOP (ie, a 12% reduction) (12.9 mm Hg versus 14.7 mm Hg; P Z .002). The estimated IOP reduction at 1, 3, and 6 months was 3.5% (P Z .23), 7.9% (P Z .04), and 9.7% (P Z .01), respectively. The number of IOP-lowering medications was also significantly associated with the follow-up IOP. For an increase in use of 1 medication, the mean IOP was reduced by 5% (P Z .0003). Figure 2 shows the observed mean IOP over the course of follow-up. The mean medication use was significantly reduced from baseline at each postoperative visit (P ! .001), including the 1-year timepoint (Table 3). Figure 3 shows the shift toward lower medication requirements and the increase in patients who achieved medication independence. Twenty (40.8%) of 49 eyes were medication free at 1 year compared with 6 (9.4%) of 64 eyes at baseline. The mean number of preoperative medications for eyes achieving medication independence was 1.45 (range 0 to 3), with 2 of them on no preoperative drops. Figure 4 shows the range of medication change after surgery and the median medication counts at each follow-up. The CDVA was significantly improved from baseline at all follow-up timepoints (Table 3) (P ! .0001). DISCUSSION Since FDA approval of the iStent trabecular microbypass implant, use of the device has continued to increase in the United States for patients with coexisting cataracts and mild to moderate OAG. As use of the device expands, more data should become available to determine outcomes in different populations and clinical scenarios. In this retrospective review, we assessed the 1-year outcomes of combined cataract surgery and implantation of the microbypass stent in patients with low IOP at baseline and compared the results with those in previously published reports.

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Table 3. Mean and median medication use and CDVA over time. P Value

Percentile Parameter Medication use Baseline Postop 1 month 3 months 6 months 12 months CDVA Baseline Postop 1 month 3 months 6 months 12 months

Wilcoxon

t Test

3

d

d

1 0 1 1

2 2 3 3

!.0001 !.0001 !.0001 .0003

!.0001 !.0001 !.0001 .0001

0.18

0.3

0.48

d

d

0 0 0 0

0.1 0.1 0.1 0.1

0.18 0.18 0.18 0.18

!.0001 !.0001 !.0001 !.0001

!.0001 !.0001 !.0001 !.0001

Mean G SD

25th

1.81 G 1.13

1

2

1.19 G 1.22 1.00 G 1.24 1.15 G 1.4 1.41 G 1.48

0 0 0 0

0.4 G 0.38 0.17 G 0.27 0.1 G 0.11 0.17 G 0.28 0.17 G 0.35

Median

75th

CDVA Z corrected distance visual acuity

The combined procedure was generally effective in lowering IOP by at least 20% or reducing dependence on IOP-lowering medications. Using these success criteria, the procedure was successful in the majority (w76%) of patients 12 months after surgery. Despite our relatively high success rate, the observed reduction in mean IOP was rather modest (w1.5 mm Hg), although it was statistically significant at 1 year of follow-up. Similarly, although the mean medication use reduced initially after surgery, it increased starting 3 months postoperatively. This increase in medication use likely contributed to the overall decline in IOP at 1 year. However, it is encouraging that 41% of patients who completed 1 year of follow-up remained medication free. Several clinical studies have evaluated the efficacy of implanting a single microbypass iStent device at the time of cataract surgery. The first published report of its clinical use was in 2008 by Spiegel et al.,12 who performed combined procedures in 47 patients with

primary OAG at 4 centers in Europe. At 6 months, the mean IOP was lowered by 25.4% from a baseline of 21.5 mm Hg and medication use was decreased by a mean of 1.0 agent. A majority of patients (w68%) had discontinued all medications by 6 months. In the first randomized controlled trial by Fea in 2010,8 36 patients with an IOP higher than 18 mm Hg on at least 1 medication were randomized to phacoemulsification alone or combined with implantation of a single iStent device. The mean IOP reduction was greater in the microbypass stent group (17%) than in the control group 15 months postoperatively. The mean medication use was lower in the microbypass stent group than in the control group (0.4 versus 1.3), and 67% in the microbypass stent group were medication free compared with 24% in the control group. A relatively large prospective case series of cataract

Figure 3. Proportion of eyes using each number of medications preoperatively (above x-axis) and postoperatively (below x-axis) (meds Z medications).

Figure 4. Median change in medication count from baseline at each follow-up visit. Error bars represent the 95% nonparametric CIs. Gray dots represent individual data points.

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surgery combined with iStent implantation from the United Kingdom7 found a significant reduction in mean IOP from 21.1 mm Hg to 16.7 mm Hg (21% decrease) and medication use from 2.3 to 0.6 agents at 6 months. Approximately two thirds of patients were medication free after surgery. In the largest study to date, Samuelson et al.9 published evidence of the efficacy and safety of the iStent device when used in conjunction with cataract surgery. In this randomized controlled multicenter trial, 240 eyes were randomized to cataract surgery alone or with the microbypass stent. Patients all had mild to moderate OAG with a medicated IOP of 24 mm Hg or lower. At 1 year, patients receiving the microbypass stent were significantly more likely to achieve the primary outcome measure (IOP %21 mm Hg without medication) than cataract surgery alone (72% versus 50%). Furthermore, patients in the stent group were more likely to achieve at least a 20% IOP reduction than those in the control group (66% versus 48%; P Z .003). After 2 years of follow-up, the microbypass stent group continued to achieve the primary outcome measure significantly more often than the control group, although to a lesser degree (71% versus 61%).5 The mean IOP after medication washout was reduced by 8.4 mm Hg from baseline in the microbypass stent group at 12 months and 24 months. The mean medication use was significantly lower in the microbypass stent group at 1 year but was similar to that in the control group by 2 years. The efficacy of the iStent device in our study was comparatively lower than in previous studies. Our patient population had a significant cohort with a relatively low IOP at baseline with a treated IOP of 18 mm Hg or lower in 60 of 64 eyes. The mean preoperative IOP of patients in this study was only 14.7 mm Hg on a mean of 1.8 medications. The main driver for implantation of the microbypass stent was to reduce dependence on medication. In contrast, the pivotal Investigational Device Exemption (IDE) trial9 used strict enrollment criteria of an unmedicated IOP of 22 to 36 mm Hg. Although the mean IOP reduction was 33% in that trial, the mean unmedicated IOP was 25.3 G 1.8 mm Hg and the mean medicated IOP was 22.2 G 2.0 mm Hg preoperatively. In addition, the aforementioned studies showed a higher percentage of IOP reduction in all glaucoma patients evaluated, with a mean medicated IOP of 18 mm Hg or higher. This suggests that although the iStent device can lead to a significant reduction in IOP, its absolute effect on IOP could become blunted in patients with lower preoperative IOP levels. The IOP-lowering effect of phacoemulsification cataract surgery alone has been well described. In the Ocular Hypertension Treatment Study (OHTS),13

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patients who had cataract surgery sustained significant IOP reductions that were also correlated with preoperative IOP. The mean IOP reduction was 16.5% in this group of ocular hypertension patients with a mean preoperative IOP of 23.9 mm Hg. In the iStent IDE trial control group,5 the mean preoperative IOP of 17.9 mm Hg on 1.5 medications was reduced to 17.0 mm Hg on 0.4 medications at 1 year and 17.8 mm Hg on 0.5 medications at 2 years. Although the IOP and medication reductions in our study are similar to the data on phacoemulsification alone, it is difficult to directly compare results given the lower preoperative IOP in our cohort. The results in our study provide new insights for physicians and patients contemplating combined cataract surgery with microbypass stent implantation in patients with low medicated IOP levels. First, patients with relatively low medicated IOP levels preoperatively can still benefit from microbypass stent implantation; however, physician and patient expectations must be appropriate. It appears unlikely that eyes with a low baseline IOP will achieve the more than 30% reduction in IOP from combined cataract surgery and microbypass stent implantation that was found in the iStent IDE trial.5 Therefore, patients requiring a lower IOP might be unable to reach that target with this approach alone. Conversely, if the preoperative IOP is at goal and a reduction of medication burden is the impetus for performing microbypass stent implantation, the procedure would seem to be useful. Finally, in our study women were more likely to fail than men. The reason for this is unclear; however, it could be an artifact of our small cohort and the relatively few failures in men. The risk factors for failure after iStent implantation require further investigation because larger samples with a longer follow-up might yield different results. Our study has several limitations. First, its retrospective design precluded IOP measurements after washout of medications, standardized enrolment criteria, and uniform follow-up visit dates. Second, the lack of a control group prevented delineation of the IOP-lowering effect of the microbypass stent itself from that of phacoemulsification cataract surgery. As evidenced by the OHTS trial,13 phacoemulsification alone can produce a significant reduction in IOP. Also, our standard approach was to follow the instructions for use document that was provided with the iStent, which outlines the use of a single device and did not explore the use of 2 stents reported to be more effective at lowering IOP.14 Finally, our outcomes are limited to 1 year of follow-up, similar to the FDA-approval trial data. Longer-term follow-up data are needed to determine the durability of treatment effect in this patient population.

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In conclusion, combined cataract surgery with iStent implantation appears to be effective in reducing IOP and/or medication dependence in patients with coexisting cataracts and low-pressure OAG. A significant proportion of patients were medication free at the 1-year follow-up. The overall efficacy of IOP reduction in patients with low baseline IOP appears to be less than that reported in previous publications. The benefit of modest IOP lowering and/or decreasing the burden of therapy should be considered during the informed surgical consent process. WHAT WAS KNOWN  At the time of cataract surgery, implantation of the trabecular microbypass stent has been shown to lower IOP and reduce the medication burden in patients with mild to moderate OAG.  Previous studies of microbypass stent efficacy included patients with uncontrolled IOP or a mean medicated IOP higher than 18 mm Hg; however, use of the device in patients with lower medicated IOP has not been studied. WHAT THIS PAPER ADDS  Combined phacoemulsification and microbypass stent implantation can reduce IOP and medication burden in medically controlled OAG patients.  The IOP-lowering efficacy of the procedure in patients with a low preoperative IOP levels was modest and comparatively less than that in studies of patients with a higher mean preoperative IOP.

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