Trabecular microbypass stent combined with phacoemulsification in patients with open-angle glaucoma, 1-year outcome in a Taiwanese population Su WW,

ORIGINAL ARTICLE

Ahead of print publication

Trabecular microbypass stent combined with phacoemulsification in patients with open-angle glaucoma, 1-year outcome in a Taiwanese population

Wei-Wen Su
Department of Ophthalmology, Chang Gung Memorial Hospital; Chang Gung University College of Medicine, Taoyuan, Taiwan

Date of Submission	30-Aug-2022
Date of Acceptance	31-Oct-2022
Date of Web Publication	21-Dec-2022

Correspondence Address:
Wei-Wen Su,
5 Fuhsin Street, Kweishan, Taoyuan 333
Taiwan

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/2211-5056.364567

Abstract

PURPOSE: The purpose of this study was to evaluate the safety and efficacy of one trabecular microbypass stent (first generation iStent) combined with phacoemulsification cataract surgery (phaco) in eyes with open-angle glaucoma (OAG) in a Taiwanese population.
MATERIALS AND METHODS: One trabecular microbypass stent was implanted after phacoemulsification cataract surgery by one surgeon. Intraocular pressure (IOP), medications, corrected distance visual acuity, complications, and adverse events were evaluated.
RESULTS: This case series included 28 eyes of 25 patients with OAG (19 primary open-angle glaucoma [POAG] and 9 normal tension glaucoma [NTG]). None had previous trabeculectomy or laser trabeculoplasty. At 1 year, the mean IOP decreased from 19.34 ± 3.92 mmHg to 15.84 ± 3.05 mmHg, and the mean number of glaucoma medications decreased from 1.82 ± 1.12 to 0.79 ± 1.17 (both P < 0.001). Longer survival was observed in the NTG eyes (NTG: 11.67 ± 1.00 months, POAG: 9.53 ± 3.78 months, P = 0.031). iStent reposition was performed in one eye, and four eyes received laser treatment for stent occlusion. None had secondary glaucoma surgery.
CONCLUSION: Combined phacoemulsification and iStent implantations are a safe and effective way in reducing IOP and medication burden in patients with OAG, especially NTG.

Keywords: iStent, open-angle glaucoma, Taiwanese, trabecular microbypass

How to cite this URL:
Su WW. Trabecular microbypass stent combined with phacoemulsification in patients with open-angle glaucoma, 1-year outcome in a Taiwanese population. Taiwan J Ophthalmol [Epub ahead of print] [cited 2023 Jan 28]. Available from: https://www.e-tjo.org/preprintarticle.asp?id=364567

Introduction

Glaucoma is the leading cause of irreversible blindness worldwide.^[1],[2],[3] Intraocular pressure (IOP) reduction remains the principal treatment for glaucoma, which includes medical treatment, laser procedures, and incisional glaucoma surgery. Traditionally, surgical treatment for glaucoma involves the creation of a drainage fistula to facilitate aqueous humor drainage, which, while effective, carries the risk of serious complications.^[4] In recent years, several new procedures have emerged for the reduction of IOP in a safer way by augmenting aqueous egress from natural outflow pathways.^[5],[6] The iStent (Glaukos Corporation, Laguna Hills, CA, USA), a trabecular microbypass stent, is the first implant approved by the U.S. Food and Drug Administration (FDA) in the class of microinvasive glaucoma surgeries (MIGSs).^[7],[8] This heparin-coated titanium device is implanted directly into the Schlemm's canal (SC) creating a bypass that augments physiologic outflow through the conventional outflow pathway.

Literature supported the efficacy and safety of the iStent device implanted at the time of cataract surgery.^{[7],[9],[10],[11],[12]} Eyes receiving iStent combined with phacoemulsification were more likely to achieve an IOP of <21 mmHg without medication than those received phacoemulsification alone.^[7],[10] iStent had been approved by Taiwan FDA since 2014 and was introduced to Chang Gung Memorial Hospital in 2018. In this study, we evaluate the 1-year outcome of combined phacoemulsification and one iStent implantation in eyes with open-angle glaucoma (OAG).

Materials and Methods

This was a single-center, retrospective case series conducted at the Chang Gung Memorial Hospital Linkou branch. This study was approved by the Chang Gung Medical Foundation Institutional Review Board and was conducted in accordance with the tenets set forth in the Declaration of Helsinki (IRB No.: 202200593B0).

Subject population

A retrospective chart review was performed for patients who received combined phacoemulsification cataract surgery with intraocular lens implantation (phaco/IOL) and one iStent implantation at Chang Gung Memorial Hospital Linkou branch from January 2018 to May 2021. The included eyes were those with visually significant cataracts, defined as clinically significant cataracts with a best-corrected visual acuity of 20/40 or worse, and the presence of primary OAG (POAG) or normal tension glaucoma (NTG). The diagnosis criteria for POAG or NTG were identical, including open anterior chamber angles on gonioscopy, glaucomatous optic disc cupping (cup-to-disc ratio, >0.7 with thinning or notching of the neural rim), and characteristic optic nerve-related visual field loss on Humphrey perimetry, except that in POAG, the untreated IOP exceeded 22 mmHg and in NTG, the IOP never exceeded 22 mmHg measuring at various time intervals of the day. Eyes with previous ocular surgery, a history of ocular trauma, or ocular manifestations other than glaucoma were excluded from the study. Medication washout before surgery was not performed.

Trabecular microbypass stent

The iStent (Glaukos Corporation, Laguna Hills, CA, USA) trabecular bypass stent is the first implant approved by the U.S. FDA in the class of MIGS. The first generation iStent is a heparin-coated, titanium, L-shaped, single-piece stent, 1.0 mm in length and 0.33 mm in height, with a snorkel length of 0.25 mm, and a nominal snorkel bore diameter of 120 μm. The stent was manufactured in both a right-and left-eye model (GTS100R and GTS100 L) to facilitate ease of implantation. The 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 stent is attached to the end of a disposable inserter designed to hold the implant and to release the implant once inserted nasally within SC.

Surgical technique

Surgery was performed by a single surgeon (Su WW). The surgical procedure was as follows: after topical or peribulbar anesthesia with Marcaine and lidocaine and sterilization, standard phacoemulsification was performed through a 2.65-mm temporal clear corneal incision, followed by IOLs implantation in the capsular bag. Then, the anterior chamber was filled with an additional ophthalmic viscosurgical device (OVD) and the patient's head was rotated away from the surgeon for 35° and the surgical microscope was tilted toward the surgeon for 35°. An additional OVD was placed on the surface of the cornea, and a surgical gonioprism was used to visualize the nasal angle directly. A single preloaded microbypass stent (model GTS100 L) was then inserted through the temporal clear corneal incision into the nasal SC. After stent implantation, the OVD was removed completely, and the clear corneal wound was sealed with intrastromal hydration. Postoperative medication included topical fluoroquinolone antibiotic four times a day and topical prednisolone acetate 1% four times a day for 1 month. After surgery, patients were followed-up at 1 day, 1 week, and 1, 3, 6, 9, and 12 months where their visual acuity, IOP, glaucoma medications, and complications were recorded.

Outcome measures

The main efficacy outcomes in the study were IOP and the number of ocular hypotensive medications. Additional efficacy measures included the proportion of eyes with surgical success, defined as postsurgical IOP <21 mmHg without medication or additional surgeries, or a ≥20% reduction in IOP from baseline without an increase in glaucoma medications. Eyes would be marked as a failure if they did not meet the above criteria at two consecutive visits. The Kaplan–Meier survival curve was plotted among POAG and NTG over 1 year of follow-up.

Statistical analyses

Descriptive statistics were used to summarize IOP and the number of medications in the postoperative visits. Proportional analyses were performed for the percent of eyes that met the surgical success criterion. Individual t-test was used to compare postoperative values. Kaplan–Meier survival analysis was used to estimate success rates along the postoperative follow-up period. Statistical analyses were performed using SPSS v23.0 for Windows (SPSS Inc., Chicago, IL, USA), and statistical significance was set at P < 0.05.

Results

Twenty-eight eyes of 25 patients (12 males and 13 females) received phaco-IOL + iStent and completed 12 months' follow-up during the study period. The mean age at surgery was 67.01 ± 6.61 years old. Most of the patients had mild-to-moderate glaucoma where the average mean deviation of the Humphrey visual field test was -6.76 ± 6.23 dB. The mean IOP at baseline was 19.34 ± 3.92 mmHg on a mean of 1.82 ± 1.12 glaucoma medications. Twenty eyes (71.43%) were using 1–2 medications. Prostaglandin analog was the most commonly prescribed glaucoma drug (22/28), followed by the β-adrenoceptor antagonist (15/28), carbonic anhydrase inhibitor (10/28), and α-adrenoceptor agonist (4/28). [Table 1] shows the baseline demographics of the enrolled eyes.

Table 1: Baseline demographic and ocular characteristics of the study subjects

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At 12 months after phaco/IOL + iStent, the mean IOP was 15.84 ± 3.05 mmHg (21.0% reduction) on a mean of 0.75 ± 1.17 medications (1.18 reduction in medication, both P = 0.01). Sixteen eyes (57.14%) had IOP lower than 21 mmHg without glaucoma medication. For the 20 eyes that were using 1–2 mediations before surgery, 15 (75%) were medication free with an IOP lower than 21 mmHg. Visual acuity improved significantly postoperatively from 0.71 ± 0.49 to 0.38 ± 0.59 (LogMAR, P < 0.001). [Table 2] shows the 12-month postoperative outcomes in NTG and POAG eyes. The postoperative changes in IOP and the number of glaucoma medications are shown in [Figure 1]. A significant reduction in IOP and the number of glaucoma medications was observed at each time point. Surgical success rate was 72.41% at 3 months, 82.14% at 6 months, 75.00% at 9 months, and 67.86% at 12 months of follow-up [Figure 2]. [Figure 3] shows the Kaplan–Meier survival analysis over 1 year of follow-up in patients with NTG and POAG.

Figure 1: Change in IOP and number of glaucoma medication in eyes with NTG and POAG after phaco/iStent. IOP = intraocular pressure, M = months, Med = medication, NTG = normal tension glaucoma, POAG = primary open-angle glaucoma

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Figure 2: Proportion of eyes with IOP <21 mmHg without glaucoma medications, or a ≥20% reduction in IOP from baseline without an increase in glaucoma medications. IOP = intraocular pressure

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Figure 3: Kaplan–Meier survival curve showing survival of NTG and POAG eyes along the 12-month follow-up. NTG = normal tension glaucoma, POAG = primary open-angle glaucoma

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Table 2: The 12 months postoperative outcomes in normal tension glaucoma and primary open-angle glaucoma

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Complications

one eye developed total hyphema during surgery which resolved spontaneously within days. Three eyes developed transient IOP spikes (IOP >25 mmHg) shortly after surgery. iStent malposition occurred in one eye and a secondary surgical reposition was performed 6 months after the primary surgery. Four eyes developed stent occlusion by iris tissue ½ year after stent implantation and were opened with neodymium: YAG laser. The occlusion was not associated with intraoperative hyphema. [Table 3] lists the types of surgical complications.

Table 3: Surgical complications

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Discussion

The iStent trabecular microbypass implant had been approved in Taiwan since 2014 and has become increasingly popular in recent years. iStent has been shown to improve aqueous outflow by creating a patent channel through the trabecular meshwork (TM) into SC through ab interno placement of the device. To date, the safety and efficacy of the iStent trabecular microbypass have been established through numerous studies, including standalone implantation or in combination with cataract surgery, single or multiple stents, and in patients with various subtypes and severity of glaucoma.^{[7],[9],[10],[13],[14],[15],[16],[17]}

In the current study, the mean IOP decreased by 21% compared to preoperative medicated IOP, associated with a mean reduction in the number of glaucoma medications of 1.18. Near 70% of eyes were either medication free with an IOP lower than 21 mmHg or had a 20% or more IOP reduction without an increase in glaucoma medications at 1 year. This result was comparable to previous reports. While some might argue that cataract surgery itself lowers IOP, according to a previous report by the American Academy of Ophthalmology, for POAG, phacoemulsification reduced IOP by 13% and glaucoma medications by 12%.^[18] In the current study, phaco/iStent still showed an improved IOP control. Considering that our patients did not undergo medication washout before surgery, the substantial IOP reduction could be higher.

The safety profile was favorable in the current study. Except for one case of intraoperative total hyphema, there were no intraoperative complications and no serious postoperative adverse events. The hyphema was only temporary and resolved completely with no sequelae. Four eyes developed subsequent stent obstruction by iris tissue, which were successfully opened by YAG laser treatment.

The current study population included a subset of NTG patients (30%) and the baseline IOP was relatively lower than those previously reported, however, significant IOP reduction was still achieved. The mean medication burden decreased by 61% versus baseline. Our study showed that the 1-year survival was better in NTG than in POAG, suggesting that eyes with higher preoperative IOP (and hence higher number of medication) were more prone to surgical failure. The iStent trabecular microbypass stent was designed to create a patent bypass through the TM that allows for aqueous to bypass the TM with increased outflow resistance and provide a direct pathway into SC and the subsequent collector channels. A previous study using bovine eyes reported that increasing the IOP from 7 to 45 mmHg coincided with a twofold reduction in outflow facility.^[19] This finding suggested that elevated IOP might lead to the collapse of the aqueous plexus and blockage of the collector channel ostia, thereby reducing the effective filtration area, which in turn leads to increased outflow resistance. This may explain why eyes with higher preoperative IOP had lower surgical success rates in the current study. In NTG, the primary reason for patients receiving iStent implantation was to achieve medication independence and to improve their quality of life. Considering the high prevalence of NTG in East Asian countries, iStent trabecular microbypass can be a safe and effective alternative treatment for NTG.

There were several limitations of the current study. The sample size was small, and the retrospective design without wash-out periods might have introduced information bias. The 12 months' follow-up period was too short to reflect the long-term efficacy of iStent. In addition, phacoemulsification itself may have an IOP-lowering effect, enhancing the effect of iStent.^[18]

Conclusion

Combined phaco/iStent can be a safe and effective way in reducing IOP and medication burden in patients with OAG, especially NTG.

Acknowledgement

The authors thank Ping-Hsuan, Huang for the statistical assistance and wish to acknowledge the support of the Maintenance Project of the Center for Big Data Analytics and Statistics (Grant CLRPG3D0049) at Chang Gung Memorial Hospital for study design and monitor, data analysis, and interpretation.

Financial support and sponsorship

Nil.

Conflicts of interest

The authors declare that there are no conflicts of interests of this article.

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