Position of the ISTENT Inject® Trabecular Micro-Bypass System Visualized with the NIDEK GS-1 Gonioscope-A Postoperative Analysis

Abstract

Glaucoma is one of the leading causes of irreversible blindness globally and is characterized by the gradual loss of retinal ganglion cells. The primary risk factor for the development and progression of glaucoma is increased intraocular pressure (IOP). Numerous surgical interventions exist to lower IOP should conservative therapy fail. One trend in recent years has been minimally invasive glaucoma surgery (MIGS) as an alternative to traditional methods. The ISTENT inject^® is an ab interno trabecular micro-bypass implant designed to be implanted through the trabecular meshwork into the Schlemm's canal to lower IOP. The aim of the study was the postoperative visualization and description of the positioning of the ISTENT inject^® using automated circumferential goniophotography. Patients with symptomatic cataracts and mild to moderate primary open-angle glaucoma (POAG), pseudoexfoliation glaucoma (PEX), and pigment-dispersion glaucoma were included who underwent combined cataract surgery with the ISTENT inject^® and received postoperative automated gonioscopy with the NIDEK Gonioscope GS-1 to visualize the location of the implant. Twenty-four implants of 14 eyes in 11 patients could be visualized. Out of the implants, 14.3% were in the trabecular meshwork, 46.4% were at the border between the trabecular meshwork and scleral spur, 25% were below the trabecular meshwork, and 14.3% of the implants were not detectable in the gonioscopy. In the overall cohort, a statistically significant IOP reduction was found over the 12-month postoperative observation period. Even in three eyes, in each of which both stents were located below the trabecular meshwork, an IOP reduction over 12 months was observed compared to the baseline IOP. In this study, vertical two-dimensional positioning of the ISTENT inject^® was performed for the first time using NIDKE GS-1 automated 360° goniophotography. The method is suitable for postoperative visualization, control, and documentation of positioning after ISTENT inject^® implantation. Further studies are needed to analyze the correlation between positioning of the ISTENT inject^® in the chamber angle and postoperative IOP reduction.

Keywords: MIGS; glaucoma; gonioscopy.

Figure 1

Position of the ISTENT inject^® in the chamber angle. Grade 1 refers to the central positioning of the implant in the nonpigmented and pigmented trabecular meshwork. Grade 2 is inferior: the lumen of the stent is at the level of the pigmented trabecular meshwork. In grade 3, the lumen of the stent lies in the transition zone between the pigmented trabecular meshwork and the scleral spur. Below the scleral spur, the stent lies at the level of the ciliary body band (grade 4). (SL, Schwalbe’s line; np-TM, nonpigmented trabecular meshwork; p-TM, pigmented trabecular meshwork; SS, scleral spur; CBB, ciliary body band; ROI, root of iris).

Figure 2

Position of the ISTENT inject^® in the chamber angle (n = 28).

Figure 3

(a): 360° gonioscopy with the ISTENT inject^®. (b,c): Position of ISTENT inject^® in the chamber angle (1 Schwalbe’s line; 2 nonpigmented and pigmented trabecular meshwork; 3 scleral spur; 4 ciliary body band; 5 root of iris).