CASE REPORT Midterm failure of combined phacoemulsification with trabecular microbypass stenting: Clinicopathological analysis Manjool Shah, MD, Xavier Campos-M€ oller, MD, Liliana Werner, MD, PhD, Nick Mamalis, MD, Iqbal Ike K. Ahmed, MD, FRCSC A propagation of microinvasive glaucoma surgery (MIGS) tech- niques and devices has resulted in the availability of multiple new modalities for surgical intervention for open-angle glau- coma. As MIGS devices and methods approach a new phase in maturity, midterm failures will inevitably be reported. Although MIGS techniques prioritize safety, an understanding of the potential mechanisms of failure is paramount. In this case of a midterm failure of a trabecular microbypass, clinical findings and pathological correlates allow for a comprehensive understanding of the means by which MIGS devices might fail and offer the opportunity for intervention and potential prevention. J Cataract Refract Surg 2018; 44:654–657 Q 2018 ASCRS and ESCRS O pen-angle glaucoma (OAG) has traditionally been treated with the use of topical medications, lasers, and filtration surgery, such as trabeculectomy or tube shunt implantation. However, a relatively new class of glaucoma surgical modalities has emerged in recent years, allowing a microinvasive surgical approach with the use of implants that target the Schlemm canal and the collector channel system. 1 The iStent trabecular micro- bypass stent (Glaukos, Inc.) is the first U.S. Food and Drug Administration–approved microinvasive glaucoma sur- gery (MIGS) device in the United States. In combination with cataract extraction, this microbypass stent has shown greater efficacy in intraocular pressure (IOP) reduction than cataract extraction alone, with minimal adverse events or patient safety concerns. 2,3 Mechanistically, the goal of microbypass stent implanta- tion is to allow a more direct route of access for aqueous hu- mor from the anterior chamber to the distal outflow pathway, thus bypassing the high-resistance juxtacanalicu- lar trabecular meshwork and inner wall of Schlemm canal. Successful stent implantation requires cannulation of Schlemm canal, a circumferential structure approximately 190 to 370 mm in diameter. 4 Flow through Schlemm canal is not thought to be circumferential but rather somewhat radial and asymmetric, with some areas of the canal contributing to greater outflow than others. Increased flow is often observed in areas where Schlemm canal con- nects more directly with aqueous veins. 5 As described by Asher, 6 2 to 3 such veins are typically observable in a hu- man eye, and successful targeting of these regions might allow access of aqueous humor to a low-resistance outflow pathway with flow rates theoretically approaching 1 mL per minute per vein. 7 When correct targeting of a microbypass stent is achieved, the intraoperative finding of blood reflux through the lumen of the stent is often observed. This finding suggests patency of the distal outflow system. Although the mechanism of the effect of the iStent micro- bypass device has a clear anatomic and physiologic basis, there is limited understanding of the mechanisms of trabec- ular microbypass failure. An early inadequate effect may be Submitted: February 8, 2018 | Accepted: March 6, 2018 From the Department of Ophthalmology and Visual Sciences (Shah), W.K. Kellogg Eye Center, University of Michigan, Ann Arbor, Michigan, and the Department of Ophthalmology and Visual Sciences (Werner, Mamalis), John A. Moran Eye Center, University of Utah, Salt Lake City, Utah, USA; Western Health Eye Care Center (Campos-M€ oller), Corner Brook, Newfoundland, the Department of Ophthalmology and Vision Sciences (Ahmed), University of Toronto, Toronto, Prism Eye Institute (Ahmed), Mississauga, and Trillium Health Partners (Ahmed), Mississauga, Ontario, Canada. Supported in part by an unrestricted grant from Research to Prevent Blindness, Inc., New York, New York, to the Department of Ophthalmology and Visual Sciences, University of Utah, Salt Lake City, Utah, USA. Randy C. Polson, senior optical engineer, Utah Nanofab Laboratory, University of Utah, assisted with the scanning electron microscopy and energy-dispersive x-ray spectroscopy analyses. Corresponding author: Manjool Shah, MD, 1000 Wall Street, Ann Arbor, Michigan 48105, USA. Email: manjool@med.umich.edu. Q 2018 ASCRS and ESCRS Published by Elsevier Inc. 0886-3350/$ - see frontmatter https://doi.org/10.1016/j.jcrs.2018.03.030 654