Surgically Induced Astigmatism After PRESERFLO MicroShunt Ab-Externo Implantation in Microinvasive Bleb Surgery

PURPOSE: To investigate surgically induced astigmatism (SIA) after stand-alone PRESERFLO MicroShunt (Santen Pharmaceutical Co Ltd) ab-externo implantation. METHODS: This retrospective study included eyes that had mandatory preoperative and 3-month subjective refraction available, with 12-month data collected when available. Tomography measurements, when available, were obtained using Scheimpflug imaging. Refractive and anterior (ASA) and posterior (PSA) surface astigmatism were evaluated using vector analysis. From baseline to 3 months, the centroid SIA was 0.47 D at 78.00°. When restricting to the 57 eyes with 12-month follow-up data, this gave a centroid SIA of 0.61 D at 76.22° from baseline to 3 months and 0.38 D at 82.57° from 3 to 12 months. In 25 eyes with preoperative and 3-month tomography data, centroid SIA was 0.17 D at 43.06° for the ASA and 0.35 D at 92.29° for the PSA. CONCLUSIONS: PRESERFLO MicroShunt implantation induces a small but significant refractive astigmatism vector directed toward the vertical meridian, sustained over 12 months. PSA changes demonstrated a measurable vectorial shift but were small in magnitude, ultimately appearing unlikely to fully explain the refractive SIA, suggesting that non-corneal mechanisms related to intraocular pressure reduction might be critical contributors.