Chlorin e6 as a Photosensitizer for Inducing Targeted Effects in Transscleral Photodynamic Therapy

Introduction: This study aimed to evaluate the role of chlorin e6 in mediating targeted vascular injury during transscleral photodynamic therapy (TS-PDT) under controlled thermal conditions. Methods: Twenty eyes of ten rabbits were randomized into two groups. The TS-PDT group received intravenous chlorin e6 (2.5 mg/kg) followed by transscleral laser irradiation (660 nm, 0.17 W, 10 min.). The control group (TSLT) underwent identical laser exposure without a photosensitizer. Scleral temperature was monitored in real time using a thermal probe. On day 14, histological analysis assessed choroidal vascular thrombosis and stromal fibrosis using a semiquantitative scoring system. Retinal and scleral tissue damage was also evaluated. Results: The analysis accounting for inter-animal clustering revealed a significant association between chlorin e6 administration and choroidal vascular thrombosis (90% vs. 50%; adjusted OR=9.8, 95% CI: 1.4-68.9; P=0.021) and fibrosis (80% vs. 40%; adjusted OR=6.2, 95% CI: 1.1-35.0; P=0.039). Severity scores for thrombosis and fibrosis were also significantly higher in the TS-PDT group (P<0.001 for both). No significant differences in scleral temperature (P≥0.45) orretinal/scleral damage were observed. Conclusion: Vascular damage during TS-PDT is primarily photochemical, mediated by chlorin e6. No significant intergroupdifferences were observed in monitored scleral surface temperaturesunder these parameters, arguing against a major contribution from differential surface heating. The method demonstrates short-term structuralpreservation of surrounding ocular tissues, supporting itspotential as an organ-preserving treatment for intraocular tumors.