Vascular Targeting in Photodynamic Occlusion of Subretinal Vessels

Purpose: To evaluate the potential of photodynamic therapy (PDT) using benzoporphyrin derivative (BPD) for occlusion of subretinal neovascular membranes, the authors studied efficiency and collateral damage of PDT-induced photothrombosis in the rabbit choriocapillary layer. Method: Benzoporphyrin derivative, a new photosensitizer, currently in clinical trials for tumor therapy, was used. Low-density lipoprotein served as a carrier to enhance selective targeting of vascular endothelial cells. Results: Complete choriocapillary occlusion was achieved at a BPD dose of 2 mg/ kg and a radiant exposure as low as 10 J/cm 2 . When PDT was performed 3 hours after BPD application, damage to the neural retina was minimal. Only inner photoreceptor segments showed mitochondrial swelling probably secondary to choroidal ischemia. Bruch's membrane remained intact. Retinal pigment epithelium was invariably damaged as seen with other photosensitizers. Conclusion: Compared with photocoagulation BPD-PDT allows endothelial-bound intraluminal photothrombosis, sparing important structures such as neural retina and Bruch's membrane. It may thus provide a more selective treatment of juxtafoveal and subfoveal neovascular membranes.