A Novel Schlemm’s Canal Scaffold

Effectiveness and biocompatibility of a novel Schlemm's canal microstent for glaucoma management

To evaluate the effectiveness and biocompatibility of Wistend, a novel Schlemm's canal (SC) microstent made of Nitinol designed to improve aqueous humor outflow. New Zealand white (NZW) rabbits were divided into blank, sham-operated and Wistend groups. ICare® Tonovet Plus®, swept-source optical coherence tomography (SS-OCT), slit lamp biomicroscopy, retinal camera and scanning electron microscopy (SEM) were used for preoperative and postoperative observations. Hematoxylin and Eosin (H&E) tissue staining was adopted for biocompatibility. A significant difference in intraocular pressure (IOP) between the Wistend group and the control groups was observed during the six-month follow-up. SS-OCT identified arc line internal reflections within the SC in the anterior chamber angle. Conjunctival congestion and edema gradually diminished in the early stages. No corneal vascularization, no anterior chamber inflammatory response and no significant tissue reactions were noted in any groups. SEM showed the Wistend's windows and orifices remained clear, encircled by minimal incidental ocular tissue and free from blockage. Histopathological examination revealed no discernible differences between the Wistend-implanted and sham-operated eyes. These in vivo studies demonstrate the effectiveness and biocompatibility of the microstent. Our findings suggest a promising potential for Wistend in significantly reducing IOP and effectively facilitating the outflow of aqueous humor.

[Real-world outcomes of glaucoma surgical procedures for open-angle glaucoma]

This article provides an overview of real-world outcomes in glaucoma surgical procedures. While randomized clinical trials provide valuable insights, they do not fully reflect real-world clinical practice. Real-world studies enable the evaluation of outcomes in uncontrolled settings and play a crucial role in counselling and decision-making for glaucoma treatment. By examining real-world data the article aims to identify rare adverse events that may go unnoticed in controlled clinical trials. The focus is on assessing the effectiveness and safety of glaucoma surgical procedures beyond the controlled trial setting.

Hydrus microstent for the treatment of primary open-angle glaucoma: overview of its safety and efficacy

INTRODUCTION

Minimally invasive glaucoma surgeries (MIGS) are now a consolidated reality in many surgical units. The Hydrus Microstent is one of several MIGS devices bypassing trabecular outflow and had excellent results over the years. This article aims to review the key features of the Hydrus Microstent in terms of design, efficacy, and safety.

AREAS COVERED

The present review analyses the main characteristics of the device by evaluating the technical and physical details of its functioning. The evidence that supports a clinical decision summarizes the most influential clinical trials and the most accurate systematic reviews.

EXPERT OPINION

The Hydrus device has been extensively studied regarding biocompatibility and outflow potential. The subsequent clinical studies have been well-built and proved that the device effectively reduces intraocular pressure (IOP) and the eyedrop load. The device covers almost a quarter of Schlemm's canal circumference, offering at least two advantages: cannulating the Schlemm's canal provides evidence that the device has been implanted correctly; covering a larger area potentially allows to target multiple collector channels or at least areas of active outflow. This scaffold may prove more effective in naïve patients or subjects who used antiglaucoma eyedrops for a limited period, as the prolonged use of hypotonic medications has been associated with the surgical failure of ab interno microhook trabeculotomy.

Comparison of Safety and Efficacy of Hydrus and iStent Combined with Phacoemulsyfication in Open Angle Glaucoma Patients: 24-Month Follow-Up

The paper presents the results of a 24-month-long observation comparing the effectiveness and safety of two micro-invasive glaucoma surgery (MIGS) devices: Hydrus Microstent and iStent Trabecular Bypass in combination with cataract phacoemulsification in the treatment of open-angle glaucoma. We also analyzed the impact of preoperative factors on achieving surgical success in both surgical methods. The prospective, comparative, non-randomized study included 65 glaucoma surgeries. In 35 patients (53.8%), an iStent implant procedure was performed, while 30 patients (46.2%) underwent a Hydrus implant procedure. The demographic data was similar in both treatment groups. At 24 months after surgery, the mean IOP in the iStent group was 15.9 ± 3.0 mmHg and in the Hydrus group 16.2 ± 1.8 mmHg. The difference between the mean iStent vs Hydrus after two years of treatment was -0.3 (p = 0.683). At the 24 month follow-up, the average change in the number of antiglaucoma medications used was 71.7% in the iStent group and 79.6% in the Hydrus group. The difference in mean percentage change between groups was 7.9% in favor of Hydrus. Patients under the age of 70 may benefit from a greater risk reduction in the Hydrus group (HR = 0.81), while those over the age of 70 may benefit from a risk reduction in the iStent group (HR = 1.33). IOP cases with >18 mmHg before the surgery have a better chance of surgical success with the Hydrus method (HR = 0.28), and with IOP < 18 mmHg in the iStent group (HR = 1.93). Cases with more drugs (≥3 drugs) are more favorable in the Hydrus group (HR = 0.23), while those with a maximum of two drugs have a better prognosis in the iStent group (HR = 2.23). The most common postoperative complication was the presence of erythrocytes in the anterior chamber (AC), found in 40.0% of operated eyes in the Hydrus group. The profile of observed complications and significant improvement in visual acuity allows us to consider both implants as a safe way of treating patients with early or moderate glaucoma and co-existing cataracts.

Ocular Biocompatibility of a Nitinol Capsular Tension Ring (CTR)

Introduction: The biocompatibility of nitinol in the human body has extensively been demonstrated. Although nitinol is already being used for intraocular surgeries such as lens fragmentation and foreign body extraction, little is known about its intracapsular, long-term behavior. The purpose of this study is to evaluate the long-term uveal and capsular biocompatibility of a nitinol CTR placed in the capsular bag after cataract surgery in an animal model.

Method: After approval of the study by the Institutional Animal Care and the Ethics Committee, bilateral phacoemulsification was performed in 6 rabbits; 1 eye received a nitinol CTR and the other a control polymethylmethacrylate (PMMA) open-ended ring. Ophthalmic evaluation for the presence of infections in all 12 eyes was performed after 7 days, 4 weeks, 3 months, and 6 months follow-up period. After a follow-up period of 6 months, the eyes were enucleated, and a histopathologic evaluation was performed.

Results: Neither of the groups showed any clinical signs of posterior capsule opacification (PCO) or inflammation. The nitinol group showed slightly less inflammation during histopathologic examination compared to the PMMA group.

No biocompatibility issues have been observed in this animal study.

Conclusions: There were no histological differences between eyes implanted with nitinol and eyes implanted with PMMA rings. Nitinol has proven to show high biocompatibility when implanted in the capsular bag of the rabbit eye.

Microinvasive glaucoma surgery: a review and classification of implant-dependent procedures and techniques

The aim of this article is to discuss how physiology and anatomical background affect the effectiveness of implant‐dependent microinvasive glaucoma surgery (MIGS). First, we provide a micro view of aqueous outflow and tissue behaviour. Second, we review studies exploring the mechanisms of the pressure‐lowering effect of MIGS, as well as tissue behaviour during aqueous flow and tissue motion. We also describe and classify microinvasive surgical procedures and the most important types of implants, as well as their mechanisms of action, implantation techniques and efficacy. Further, we summarize the indications and surgical results presented in recent studies, providing an evidence‐based update on novel and emerging MIGS techniques for the treatment of open‐angle glaucoma. These data can help surgeons to personalize the management of glaucoma and to choose the best MIGS option for individual glaucoma patients.

Animal models and drug candidates for use in glaucoma filtration surgery: A systematic review

Glaucoma, a degenerative disease of the optic nerve, is the leading cause of irreversible blindness worldwide. Currently, there is no curative treatment. The only proven treatment is lowering intraocular pressure (IOP), the most important risk factor. Glaucoma filtration surgery (GFS) can effectively lower IOP. However, approximately 10% of all surgeries fail yearly due to excessive wound healing, leading to fibrosis. GFS animal models are commonly used for the development of novel treatment modalities. The aim of the present review was to provide an overview of available animal models and anti-fibrotic drug candidates. MEDLINE and Embase were systematically searched. Manuscripts until September 1st^, 2021 were included. Studies that used animal models of GFS were included in this review. Additionally, the snowball method was used to identify other publications which had not been identified through the systematic search. Two hundred articles were included in this manuscript. Small rodents (e.g. mice and rats) are often used to study the fibrotic response after GFS and to test drug candidates. Due to their larger eyes, rabbits are better suited to develop medical devices. Novel drugs aim to inhibit specific pathways, e.g. through the use of modulators, monoclonal antibodies, aqueous suppressants or gene therapy. Although most newly studied drugs offer a higher safety profile compared to antimetabolites, their efficacy is in most cases lower when compared to MMC. Current literature on animal models and potential drug candidates for GFS were summarized in this review. Future research should focus on refining current animal models (for example through the induction of glaucoma prior to undertaking GFS) and standardizing animal research to ensure a higher reproducibility and reliability across different research groups. Lastly, novel therapies need to be further optimized, e.g. by conducting more research on the dosage, administration route, application frequency, the option of creating combination therapies, or the development of drug delivery systems for sustained release of anti-fibrotic medication.

Modeling the effects of glaucoma surgery on intraocular pressure

Minimally invasive glaucoma surgeries (MIGS) offer an effective way to lower intraocular pressure without inducing extensive trauma to the anterior segment. In order to predict their efficacy, an analytical model of the conventional aqueous humor outflow pathway is developed using a resistor network. The model describes outflow through the normal eye and allows for the effects of geometric changes in the outflow pathway as IOP changes. By selectively removing these resistors, the model can be used to examine and predict the outcomes of several surgical procedures currently used to treat glaucoma. Treatments examined include traditional trabeculectomy, several ab interno methods for trabeculotomy and trabeculectomy, as well as recently developed trabecular stents that bypass the trabecular meshwork and dilate Schlemm canal. The model's predictions for the efficacy of these procedures generally matched well with the efficacy determined in experimental studies, although it tended to somewhat overestimate the efficacy of these procedures. Matching the model to experimental data indicated that a partial trabeculotomy substantially increases flow to collector channels within that region and approximately 1.5 clock hours past the ends of the trabeculotomized region. Similarly, trabecular bypass stents substantially increase flow to collector channels up to 1.5 clock hours past the open ends of the stent. The resistor model we have developed can be used to predict the efficacy of a variety of MIGS procedures. Circumferential flow in Schlemm canal extends the efficacy of MIGS, but this effect is limited to a few clock hours.

Corrosion resistance of a Nitinol ocular microstent: Implications on biocompatibility

Nitinol is commonly used in medical implants due to its unique thermomechanical properties of shape memory and superelasticity. Free nickel has the potential to induce biological responses that may be a concern for permanent implants manufactured from nickel-containing alloys. Although there are extensive reports on the effects of surface treatments on corrosion behavior in cardiovascular Nitinol implants, there is a lack of data on corrosion resistance and impact on biocompatibility for ocular implants. Therefore, the objective of this study was to determine localized corrosion and nickel elution resistance of an electropolished Nitinol-based ocular device (Hydrus Microstent, Ivantis, Inc.) intended for patients with primary open angle glaucoma. Pitting corrosion susceptibility was characterized by potentiodynamic polarization testing per ASTM F2129. In addition, nickel ion release was quantified with immersion testing to 63 days. The results indicated high localized corrosion resistance as all samples reached polarization potentials of 800 mV without pitting initiation. Maximum nickel elution rates per device were less than approximately 1.1 ng/device/day after the first day of immersion and reduced to less than 0.1 ng/device/day after 7 days. For a patient with bilateral microstents, these nickel concentrations are ×10,000 lower than previously published tolerable intake levels for systemic toxicity. Overall, these corrosion results are in good agreement with literature values of well processed and biocompatible Nitinol devices indicating adverse systemic biological responses are not expected in vivo.

Hydrus microstent implantation for surgical management of glaucoma: a review of design, efficacy and safety

With the advent of microinvasive glaucoma surgery (MIGS), the spectrum of modalities available to manage patients with this chronic and heterogeneous condition has broadened. Despite its novelty however, there has been a rapid evolution in the development of a multitude of devices, each targeting a structure along the aqueous drainage pathway. A growing body of evidence has demonstrated IOP and medication burden reduction, and a more favorable safety profile with MIGS procedures in contrast to traditional incisional surgeries. Among the array of MIGS, the Hydrus® Microstent (Ivantis, Inc., Irvine, CA) is a recent FDA approved device, designed to bypass the trabecular meshwork and provide a scaffold for Schlemm’s canal. The objective of this article is to review the Hydrus from conception to clinical use, and present data on its efficacy and safety to date. The available literature has shown promise, however inherent to all novel devices, only long-term monitoring will ensure sustained IOP control and an acceptable safety profile. Surgical advancements in glaucoma have revolutionized the field, and continued research and development will establish these approaches in clinical treatment algorithms.

Combined phacoemulsification and microinvasive glaucoma surgery in comparison to phacoemulsification alone for open angle glaucoma

IMPORTANCE

Microinvasive glaucoma surgery (MIGS) combined with phacoemulsification is increasingly utilised in glaucoma management.

OBJECTIVE

To describe the postoperative outcomes of phacoemulsification alone compared to combined phacoemulsification and iStent (Glaukos, San Clemente, CA) or Hydrus (Ivantis, Irvine, CA) for open angle glaucoma.

METHODS

Retrospective single surgeon comparative case series in a private practice setting. A total of 297 eyes in 190 patients (M:F = 85:105) were included consecutively from March 2011 to June 2017 with the data analysed using linear mixed models. Main outcome measures were intraocular pressure (IOP) and number of medications.

RESULTS

By 6 months, all groups showed a reduction in IOP, with the combined iStent group by 4.2 mm Hg and the combined Hydrus group by 4.5 mm Hg, and this trend was sustained with follow-up to two years. All groups also showed a reduction in number of medications, with the phacoemulsification alone cases by 0.3, the combined iStent group by 0.7 and the combined Hydrus group by 1.1 medications. Both the combined surgeries had sustained reduction of number of medications with follow-up to 2 years. Postoperative complications from MIGS device insertion were uncommon and all resolved by one month.

CONCLUSIONS AND RELEVANCE

The combination of phacoemulsification and a MIGS device in open angle glaucoma patients reduced the intraocular pressure and the number of medications by the first postoperative month and had longer-term effects at 2 years follow-up. If the device is inserted without intraoperative complication, the rate of significant short-term risks are low.

Microinvasive Glaucoma Stent (MIGS) Surgery With Concomitant Phakoemulsification Cataract Extraction: Outcomes and the Learning Curve

PURPOSE

To evaluate learning effects with respect to outcomes of a microinvasive glaucoma stent (MIGS) inserted during cataract surgery in glaucoma patients.

PATIENTS AND METHODS

Single surgeon, observational cohort study of 25 consecutive Ivantis Hydrus microstent insertions, with a minimum follow-up of 12 months. A learning curve analysis was performed by assessing hypotensive effect, adverse effects, and surgical procedure duration, with respect to consecutive case number. Success was defined with respect to various intraocular pressure (IOP) targets (21, 18, 15 mm Hg) and reduction in required antiglaucoma medications. Complete success was defined as achieving target IOP without antiglaucoma therapy.

RESULTS

No clinically significant adverse events or learning effects were identified, although surgical time reduced with consecutive case number. Mean follow-up was 16.8 months. At final follow-up the mean IOP for all eyes was reduced from 18.1 (±3.6) mm Hg [and a simulated untreated value of 25.9 (±5.2) mm Hg] to 15.3 (±2.2) mm Hg (P=0.007; <0.0001) and the mean number of topical antiglaucoma medications was reduced from 1.96 (±0.96) to 0.04 (±0.20) (P<0.0001). Complete success (IOP<21 mm Hg, no medications) was 96% at final follow-up. Complete success (IOP<18 mm Hg, no medications) was 80% at final follow-up, but only 32% with a target IOP of <15 mm Hg (no medications).

CONCLUSIONS

No significant learning curve effects were observed for a trained surgeon with respect to MIGS microstent insertion performed at the time of cataract surgery. Adjunctive MIGS surgery was successful in lowering IOP to <18 mm Hg and reducing/abolishing the requirement for antiglaucoma medication in eyes with open-angle glaucoma, but less successful at achieving low IOP levels (<15 mm Hg).

Glaucoma treatment trends: a review

Glaucoma is one of the most common causes of blindness worldwide, and its prevalence is increasing. The aim of the present review is to describe the current medical and surgical treatment trends in the management of open-angle glaucoma. There has been an increase in the availability of glaucoma medications and the use of laser trabeculoplasty over the past decade, with a subsequent decrease in invasive incisional surgery. In addition, a new class of glaucoma procedures, termed microinvasive glaucoma surgery, has emerged, which aims to fill the gap between conservative medical management and more invasive surgery.

[Modern methods of minimally invasive glaucoma surgery]

Over the years, glaucoma surgery has improved from iridectomy by A. Graefe and traumatizing procedures performed without magnification tools or microsurgical instrument to high-technology interventions that are not only microscopic, but also pathogenetically oriented. Various modifications of trabeculectomy, initially introduced by J. Cairns back in 1968, had been the gold standard for several decades and were notable for pronounced and stable hypotensive effects. However, there was also a strong association with such complications as choroidal detachment and hyphema, thus, boosting the development of so called nonfistulizing surgeries. Of the latter, the most widely used are non-penetrating procedures, including deep sclerectomy and viscocanalostomy. Although very safe, they appear unable to produce a truly long-lasting hypotensive effect. Moreover, just as fistulizing trabeculectomy, non-penetrating procedures damage the limbus and adjacent conjunctiva reducing the possibility of a second intervention. This fact together with other drawbacks mentioned above, on the one hand, and technical progress, on the other, were essential prerequisites for the appearance of a new type of surgery - minimally invasive glaucoma surgery (MIGS). Parameters that should be met for a procedure to be considered minimally invasive are debated. The main requirement has, however, been established: ab interno approach through a corneal incision. As surgical tools are enhanced and new techniques arise, options for glaucoma treatment widen greatly, ensuring our future move to higher level standards in the field. This review contains all recent data on minimally invasive techniques currently in use in glaucoma surgery or those under investigation. The authors have also analyzed effectiveness reports and present their conclusions regarding the current state of MIGS worldwide.

Update on Schlemm's canal based procedures

Surgical options for glaucoma have expanded in recent years. This article provides an evidence-based update on the novel or emerging surgical techniques for the treatment of open-angle glaucoma that are based on the Schlemm's canal (SC). Canaloplasty is an ab externo approach and was developed as an alternative to traditional filtering surgeries. The Hydrus microstent (Ivantis Inc., Irvine, CA) is a so-called SC scaffold that directly bypasses the trabecular meshwork to drain aqueous humor into the SC, which it keeps dilated over approximately one quadrant. Canaloplasty has also been shown to lower intraocular pressure (IOP) by up to 40% and combined with cataract surgery. IOP was lowered 44% at 24 months while maintaining a favorable safety profile. The Hydrus device has been proposed as an adjunct to cataract extraction surgery. To date, no published evidence from clinical trials is available on its in vivo safety and efficacy. Schlemm's canal based glaucoma procedures show promise as alternative treatments to traditional glaucoma surgery. Surgeons must be comfortable with angle anatomy. A prerequisite for functionality of these techniques is the integrity of the distal outflow system. At present, however, it is not possible to conclude whether these novel procedures will be viable alternatives to standard filtering surgery over the long-term.