Functional assessment of the XEN® Gel Stent relative to the implant position using non-invasive stress testing and automated gonioscopy

PURPOSE: Gel Stent position within the anterior chamber angle influences aqueous humor outflow and complication rates during the early postoperative period. METHODS: -63 Gel Stent implantation between 09/2024 and 07/2025 at Charité - Universitätsmedizin Berlin, Germany were included in this single-center, prospective cohort study. Eyes were categorized postoperatively according to stent position within the anterior chamber angle (Grades 0-4). Stent position was evaluated 12 weeks postoperatively through automated gonioscopy (GS-1, Nidek). Aqueous humor outflow was assessed using a standardized non-invasive stress test. Primary outcome was the intraocular pressure (IOP) reduction during stress test. Secondary outcomes included IOP reduction from baseline to 12 weeks postoperatively, number of glaucoma medications, complications and need for additional interventions. RESULTS: Gel Stent implantation from 22.2 ± 7.5 mmHg to 12.1 ± 5.1 mmHg 12 weeks postoperatively measured with Goldmann applanation tonometry (p < 0.001, Z -5.6). Stress test induced IOP reduction increased from 14.8 ± 13.3% pre-implantation to 32.7 ± 19.7% at 12 weeks (p < 0.001, CI -24.1 to -11.8). Eyes with stent placement within the scleral spur or ciliary body band (Grading 3 + 4, n = 34) had greater aqueous humor outflow improvement compared with eyes graded 0-2 (stent above scleral spur, n = 12) (p = 0.010, 95% CI -28.6 to -4.2). Postoperative transient hypotony occurred in 85.3% vs. 61.5% of eyes in Grading group 3 + 4 vs. 0-2 (p = 0.08). 4 eyes were considered non-functional due to malposition (Grading x). Mean number of glaucoma medications decreased from 2.8 ± 1.3 preoperatively to 0.2 ± 0.9 postoperatively. CONCLUSION: Gel Stent within the scleral spur or ciliary body band (Grade 3 + 4) was associated with greater pressure reduction during stress testing, suggesting an increased aqueous humor outflow in this study cohort. Such placement was associated with high treatment success and no increase in major complications, except the risk of misplacement, while transient hypotony was common.