A Prospective Analysis of iStent Inject Microstent Positioning: Schlemm's Canal Dilatation and Intraocular Pressure Correlations.

PRéCIS:: A larger proportion of iStent inject microstents than suggested by gonioscopic examination could be entirely burrowed within the trabeculum (45.7%). The length of device protrusion within the anterior chamber is linked to post-operative intraocular pressure.

INTRODUCTION: The iStent inject® (Glaukos Corporation, CA, USA) is a relatively new device designed to be implanted ab-interno through the trabecular meshwork. While some preliminary studies have shown intraocular pressure (IOP) lowering potential, the full extent of the mechanisms through which IOP is reduced remains unconfirmed. The aim of this study is to use in vivo optical coherence tomography (OCT) analysis of the anatomic and physiological effects of iStent inject® device positioning on the structures of the iridocorneal angle and IOP.

METHODS: In total, 25 eyes of 19 subjects (mean age 75.5±10.5▒y) with mild-to-moderate open-angle glaucoma were enrolled in this prospective study. All patients underwent implantation of 2 iStent inject® devices combined with cataract surgery. In the post-operative period, after IOP stabilized, anterior segment OCT (AS-OCT) was performed and several measurements were made of Schlemm's canal (SC) and devices positions. Thirteen unoperated fellow eyes served as control eyes.

RESULTS: Ninety-two percent of devices were visible on AS-OCT versus 88% visible on gonioscopic examination. Of all visible devices, 54.3% had a protruding portion into the anterior chamber with a mean protruding length of 88.5▒µm, and 72% of devices heads were not positioned within SC with a mean shortest distance of 109.4▒µm. In operated eyes, the average major diameter of SC was 308.7±197.4▒µm (median 303.8▒µm) versus 126.9±60.3▒µm in control eyes. Device protrusion and larger SC diameters were associated with lower postoperative IOP (rs=-0.54; P=0.005 and rs=-0.43; P=0.04 respectively), while distance between devices heads and SC was inversely associated with SC dilatation (rs=-0.41; P=0.04).

CONCLUSIONS: This study highlights the value of AS-OCT in exploring positioning of trabecular bypass devices such as the iStent inject ®. Our study shows that more microstents than suggested by gonioscopy could be completely burrowed within the trabeculum. It also suggests that surgical outcomes of cataract surgery combined with iStent inject® implantation may be connected to the amplitude of device protrusion within the anterior chamber as well as the post-operative dimensions of Schlemm's canal.