Photodynamic therapy and digital angiography of experimental iris neovascularization using liposomal benzoporphyrin derivative

Purpose: To study the efficacy of liposomal benzoporphyrin derivative (BPD) (Verteporfin) for the angiographic visualization and photodynamic therapy (PDT) of experimental iris neovascularization. Methods: Experimental iris neovascularization was induced in eight cynomolgus monkey eyes by occluding all the branch retinal veins with a dye-yellow (577-nm) laser, Iris angiography was done with sodium fluorescein, indocyanine green (ICG), and liposomal BPD to compare the visualization of normal and neovascular vessels by these three dyes. PDT was performed using an intravenous infusion of liposomal BPD (0.375-0.75 mg/kg), followed by irradiation with 689-nm light from a diode laser/slit-lamp delivery system using 600 mW/cm(2) irradiance and 150 J/cm(2) fluence. The effect of treatment was followed by iris photography and angiography, and the findings were confirmed by histopathology using light and electron microscopy. Results: Iris fluorescein angiography (FA) showed superficial tortuous and leaky new vessels. Liposomal BPD and ICG angiography of the same eye demonstrated deeper dilated and tortuous iris vessels, with minimal dye leakage. PDT of the iris with irradiation, performed within 20 minutes of the start of dye infusion (0.75 mg/kg), resulted in angiographic and histologic occlusion of iris vessels examined at 24 hours. Three to nine days after PDT, histopathologic examination showed regression of the iris neovascular membrane, with some open vessels, Conclusions: Liposomal BPD and ICG provided angiographic visualization of deeper normal and neovascular iris vessels. PDT using liposomal BPD leads to effective early closure to experimental iris neovascularization.