Purpose: To investigate the theoretical hydrodynamic effects of a single or a double XEN 45 Gel Stent (XEN45) implant in glaucomatous eyes. Methods: A prospective non-randomized clinical study on 63 glaucomatous eyes of 63 patients. The preoperative intraocular pressure (IOP) values after 14 days of medical therapy washout was correlated to the postoperative IOP values 7 and 45 days after the implant of a XEN45. A mathematical model based on the Hagen-Poiseuille law was designed to assess the residual aqueous humor outflow (AHO) facility in glaucomatous eyes in function of the postoperative IOP reduction. Using XEN45 as unit of measurement, we transformed through equations the residual preoperative AHO in XEN45 equivalent in order to establish theoretical number of stents needed to reach the target IOP. Results: The mean preoperative washout IOP was 28.9 ± 5.4 mmHg, after 7 and 45 days the mean postoperative IOP was 12.6 ± 4.3 and 15.3 ± 4.4 mmHg, respectively (p < 0.001). A significant positive correlation was found between preoperative and postoperative IOP values. We obtained a mathematical relationship to estimate the theoretical number of XEN45 stents needed to reach the target IOP. Conclusion: The basal IOP (after medical therapy washout) is a predictive factor for the surgical success after a XEN45 implant. Establishing the residual preoperative AHO it is possible to predict the theoretical number of stents to implant. A double XEN45 implant could be considered a possible further tool to reach the target IOP in patients with severe AHO deficiency.
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