Ultrastructural analysis of explanted CyPass microstents and correlation with clinical findings

R Lämmer,Lisa Hübner,J M Weller,B Hohberger,U Schlötzer-Schrehardt,C Y Mardin

doi:10.1007/s00417-022-05620-x

Abstract

PurposeThe purpose of this study was to obtain insight into cellular processes after CyPass microstent implantation into the supraciliary space. With this knowledge, we expected to find some reason for surgical failure.MethodsNine CyPass microstents of 8 patients with primary open-angle glaucoma (n = 1), pseudoexfoliation glaucoma (n = 5), uveitic glaucoma (n = 1), and posttraumatic open-angle glaucoma (n = 1) were explanted due to recurrence of IOP elevation, corneal decompensation, or persistent hypotony. The explants were processed for light and transmission electron microscopy.ResultsFibrotic material, consisting of collagen fibrils, microfibrils, pseudoexfoliation fibrils produced by activated fibroblasts, was detected in the stent lumen of 4/5 pseudoexfoliation glaucoma patients and also in posttraumatic open-angle glaucoma. Fibrotic material was also present on the outer surface and within fenestrations of the majority of stents. Complete absence of fibrotic reaction was noticed in 3 of 9 microstents.ConclusionAlthough MIGS is known to be less invasive than conventional surgery, implants placed in the suprachoroidal space may be adversely affected by a fibrotic tissue reaction resulting in implant failure. Understanding mechanisms and risk factors leading to fibrotic scarring following antiglaucomatous surgery may help to develop novel strategies that improve surgical outcome.

Highlights

Glaucoma is a chronic, progressive optic neuropathy that represents the second leading cause of blindness globally [1]
Micro-invasive glaucoma surgery (MIGS) with implantation of stents has been developed to bridge the gap between medical therapy/laser treatment and conventional filtration surgery, which renders the best effect in intraocular pressure (IOP) reduction but carries a higher risk for complications [2–4]
Elevated IOP refractory to medical treatment was the reason for CyPass microstent explantation in 5 eyes, corneal decompensation in three eyes (PXG, uveitic glaucoma (UVG), POAG), and refractory hypotony in one eye (PXG)

Summary

Introduction

Progressive optic neuropathy that represents the second leading cause of blindness globally [1]. It is defined by an acquired loss of retinal ganglion cells and axons within the optic nerve, astrocyte loss, as well as a corresponding progressive visual field damage. Micro-invasive glaucoma surgery (MIGS) with implantation of stents has been developed to bridge the gap between medical therapy/laser treatment and conventional filtration surgery, which renders the best effect in intraocular pressure (IOP) reduction but carries a higher risk for complications [2–4]. Five criteria are known to describe MIGS: a micro-invasive approach, minimal tissue trauma, at least modest efficacy, rapid recovery, and a high safety profile [5]. Depending on type of stent, there are different approaches for IOP reduction: increasing trabecular outflow by bypassing the trabecular meshwork (iStent or Hydrus), increasing uveoscleral outflow via suprachoroidal pathways (CyPass microstent), or creating a subconjunctival drainage pathway (XEN gel stent) [6]

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