PDT of Corneal Neovessels Using a New Hydrosoluble Photosensitizer (WST11)

Abstract

Abstract: : Purpose:To evaluate the photodynamic treatment (PDT) potential and safety of a new hydrosoluble photosensitizer (WST11) on rabbit corneal neovessels (NV). Methods: Elvax 40 implants sequestering 75µg of LPS are implanted in the rabbit cornea at 3mm from the limbus. For PDT, WST11 in 5% glucose is infused IV during 3 minutes and a 3.5 mm laser beam (753nm, 600mW/cm²) is used. To screen for best occlusive parameters, 2 doses of WST11 (5 and 10mg/Kg), 2 laser fluences (70 and 140J/cm2) with 1’ or 5’ distance to light illumination (DLI) were evaluated (n=6/condition). The treated NV are examined clinically during the period of laser delivery. At 2 hours, 2 and 8 days after PDT, the eyes are enucleated, fixed and semi–thin sections prepared. Results:During PDT a bleaching of the laser illuminated zone surrounded by a ring of relative vasodilation is observed clinically. Immediately after the laser delivery, partial vascular occlusion of the treated area is clinically observed in 33% of the eyes receiving 70 J/cm2, WST11 5mg/Kg, DLI1min and only in 15% when the DLI is 5min. Eyes treated with 70 J/cm², WST11 10mg/Kg, DLI1min show partial vascular occlusion in 100%of the cases and only in 66%of the cases when the DLI is 5min. Total occlusion of the irradiated vascular bed occurred in 100% of the eyes treated with 140J/cm², WST11 10mg/Kg, DLI 1min and in 75% of the eyes with a DLI of 5 min. No signs of corneal or other ocular structure toxicity, inflammation or intraocular hemorrhages occurred following the delivery of the above PDT protocols. Histology analysis of the treated corneal areas demonstrate that two hours after PDT, vascular stasis associated with intracellular alterations of the endothelial cells but no vessel wall rupture takes place. On day 2 and 8 after treatment, NV occlusion persisted in the eyes treated with the highest parameters. However, on day 8 post treatment patent NV are observed within the previously treated (and occluded) vascular zone. No collateral lesions or damage of the adjacent corneal tissues is observed and the endothelial cell layer remains intact throughout. Conclusions:PDT effect of the new photosensitizer WST11 is closely associated with the DLI used and probably due to its rapid elimination from the circulation. Selective PDT parameters with WST11 result in an efficient, safe and continuous occlusion of corneal NV.

Keywords: neovascularization • photodynamic therapy • vascular cells