Morphological and Dimensional Comparison of Functioning Blebs Following PRESERFLO-Microshunt and XEN-Gel-Stent, a Study Using Anterior Segment OCT

Abstract

Background: Evaluation of bleb morphology is a vital part of successful filtration glaucoma surgery. The PRESERFLO-MicroShunt (PRESERFLO) and the XEN-Gel-Stent (XEN) are drainage devices which are implanted through different surgical approaches (ab-externo versus ab-interno, respectively). This might result in different bleb morphology. Studying these morphological differences is important in leading post-operative care. Methods: Functioning blebs following implantation of PRESERFLO and XEN were retrospectively included and examined using high resolution anterior segment OCT. A qualitative assessment using the Jenaer Bleb Grading System and quantitative assessment by measuring 12 parameters representing bleb dimensions were performed. Results were compared between both groups. Results: Included were 80 eyes of 80 patients (41 after PRESERFLO, 39 after XEN). Functioning blebs following PRESERFLO showed higher frequency of hyperreflective tenon changes compared to XEN (31.7% VS 10.3% respectively, p = 0.02) and lower frequency of cavernous changes (17.1%VS 35.9%, p = 0.05) along with higher frequency of visible episcleral lake (92.7% VS 30.8%, p < 0.001). Blebs after PRESERFLO showed larger height (2.13 ± 0.5 VS 1.85 ± 0.6mm, p = 0.03), width (10.31 ± 2.3 VS 9.1 ± 2.3mm, p = 0.02), length (9.13 ± 1.8 VS 8.24 ± 1.9mm, p = 0.04), were located more posterior to limbus (6.21 ± 1.2 VS 5.21 ± 1.8mm, p = 0.005) and showed a thicker bleb wall (1.60 ± 0.5 VS 1.1 ± 0.4mm, p = 0.004). Conclusions: Functioning blebs after PRESERFLO and XEN are morphologically different. Main reasons might be the different surgical techniques (ab-externo versus ab-interno) and different dimensions of stents. These morphological differences should be considered when evaluating blebs as this might affect judgement of bleb functionality and thus on the decision when and how to intervene in the post-operative phase.