Novel surgical technique to manage iStent inject over-implantation

Introduction

The iStent inject (Glaukos Corporation, San Clemente, CA) is a form of minimally invasive glaucoma surgery (MIGS) that has grown in popularity in recent years. It comprises two trabecular micro-bypass titanium stents which are implanted ab internally to lower intraocular pressure (IOP), by creating a bypass channel between the anterior chamber and Schlemm's canal to improve the drainage of aqueous humour. It is 360 μm in height, with a rear flange of 230 μm width that resides in the anterior chamber, whilst the head resides in the Schlemm's canal and the thorax of the stent within the trabecular meshwork. ¹ Both stents are preloaded in a single delivery system. Having been FDA-approved for use in conjunction with cataract surgery for the treatment of mild to moderate primary open angle glaucoma, ² the iStent inject has demonstrated good efficacy and safety when performed in conjunction with ³ and without^4–6 cataract surgery.

The optimal in-situ position of the iStent inject has been shown to correlate with post-operative IOP-lowering outcomes ⁷ and the flange of the iStent inject should remain visible in the anterior chamber after implantation. ¹ However, stent malpositioning in the form of under- or over-implantation may occur intra-operatively. ⁷ The management of under-implantation has been described – the under-implanted iStent may be rethreaded back onto the trocar and then redeployed with less pressure against the trabecular meshwork, with the second stent remaining in the delivery system pushing the first stent through upon delivery.^1,8 However, the management of over-implantation remains a challenge. Unlike in under-implantation where the iStent inject remains easily accessible for rescue manoeuvres, in over-implantation, the device is not accessible as it is too deeply embedded within the trabecular meshwork.

We describe a novel surgical technique to manage over-implantation – requiring the use of only the iStent inject delivery system to perform both device extraction and reimplantation, without the need for additional instruments.

Methods

Institutional review board approval was not required because the intent was to employ an innovative technique to enhance the care of individual patients and no patient demographic information was collected. The intra-operative images and surgical video clips are of the angle of the eye and no patient-identifiable characteristics are present. The following describes the surgical technique used (Supplementary Video 1).

Firstly, following over-implantation of the device (Figure 1(a)), the fine, sharp trochar of the delivery system is applied to the approximate location of the implant and used to circle around the implant circumference, with the aim to expose the metallic reflective flange of the iStent inject device (Figure 1(b)).

OPEN IN VIEWER

Figure 1.

(a) Over-implanted iStent inject embedded in trabecular meshwork. (b) The trochar of the iStent inject delivery system is used to circle around the circumference of the over-implanted device, exposing the flange of the stent. (c) The trabecular meshwork tissue is pulled away from the implant in as many directions as possible using the trochar. (d) The needle of the iStent inject delivery system is snuggled along the side of the still-buried device. (e) The iStent inject device is successfully tumbled out and lies free in the anterior chamber. (f) The iStent inject device is re-implanted successfully in the trabecular meshwork.

Secondly, once the edges of the implant are visualised, still using the trochar, the trabecular meshwork tissue is pulled away from the implant in all directions (Figure 1(c)) to maximise visualization of the flange and to create space for application of the delivery system needle in the next step.

Thirdly, once there is sufficient view of the device flange, the needle of the delivery system is extended out and snuggled along one of the sides of the implant (Figure 1(d)).

Fourthly, with gentle outward nudging movements against the device flange, the delivery system needle is used to tumble the iStent inject device out of the trabecular meshwork (Figure 1(e)).

Finally, after the iStent inject device is extracted and free in the anterior chamber, the device is reoriented to align its lumen along the axis of the approaching trochar, which is used to rethread the device. The device is then gently manoeuvred posteriorly into the hub of the injector through a forward motion of the injector and then reimplanted at a suitable alternate location in the trabecular meshwork (Figure 1(f)).

Figure 2(a) to (d) similarly shows how the technique is used to successfully reimplant another over-implanted iStent inject device with the above steps.

OPEN IN VIEWER

Figure 2.

(a) The trochar of the iStent inject delivery system is used to circle around the circumference of the over-implanted iStent inject to expose the flange of the stent. (b) Trabecular meshwork tissue is pulled away from the implant and the needle of the iStent inject delivery system is snuggled along the side of the still-buried device with a small amount of inadvertent bleeding. (c) The iStent inject device is successfully tumbled out, rethreaded and reloaded in the anterior chamber. (d) The iStent inject device is re-implanted successfully in the trabecular meshwork.

At times, bleeding may occur due to trauma to the trabecular meshwork occurring during the initial implantation attempt. Significant bleeding may obscure visualisation and hinder further manipulation to the over-implanted iStent inject device. In this scenario, viscoelastic should first be injected, also under intra-operative gonioscopic guidance, towards the site of bleeding in the angle. Viscoelastic will displace blood away from the area of interest, improving visualization of the trabecular meshwork and the over-implanted iStent inject. Our suggested technique may then be employed to rectify stent over-implantation.

Results

With the above surgical technique, over-implantation of the iStent inject device can be successfully managed to ensure ideal positioning to optimise post-operative outcomes. This method demonstrates how this may be achieved simply by using only the iStent inject delivery system itself for both device extraction and reimplantation, without the need for additional instrumentation.

Discussion

Stent malpositioning is one of the most common post-operative adverse events following iStent inject implantation. ⁹ . Voskanyan et al. ⁴ reported an incidence of 1% of stent malpositioning and another 13.1% where the stent was not visible on gonioscopy, none of which received additional treatment.

The intra-operative management of iStent inject over-implantation has been rarely discussed in literature. Anecdoctal reports suggest that some surgeons do not opt to retrieve the over-implanted stent if it can no longer be visualised. ⁸ However, studies have proven that both under- and over-implantation of the device are correlated with reduced IOP-lowering efficacy and reduced dilatation of the Schlemm's canal post-operatively. ⁷ One technique that has been described in the management of over-implanted iStent inject devices that remain visible involves the use of a microforceps to grasp and retrieve the over-implanted iStent inject and rethreading it on the trocar for further re-implantation. ¹⁰ However, this requires the use of additional instrumentation which may not be easily accessible to the surgeon and may incur additional cost to the patient. Furthermore, this method applies more easily to over-implanted devices that remain visible in the angle. Our method of retrieval and re-implantation requires only the use of the iStent inject delivery system and may be used with devices that are entirely embedded within the trabecular meshwork. Separately, post-operative use of the Nd:YAG laser has been previously described ⁵ to relieve stent occlusion from iris or overgrowth of the surrounding trabecular meshwork. However, laser treatment is unlikely to change the position of the stent nor fundamentally address stent malposition, which has been previously shown to result in suboptimal post-operative surgical outcomes. ⁷ Rectification of stent malposition is likely to be most effectively performed intra-operatively.

Conclusion

Over-implantation of the iStent inject should be managed intra-operatively to ensure optimal post-operative outcomes. This novel technique provides a cost-effective, feasible and effective means to manage over-implantation, utilizing only the iStent inject delivery system itself to perform both device extraction and reimplantation, without the need for additional instrumentation.

Supplemental Material