Retreatment effect of Npe6 photodynamic therapy on the normal primate macula

Purpose: To evaluate the safety and efficacy of repeated photodynamic thera py (PDT) with mono-L-aspartyl chlorin e6 (NPe6) on normal primate fovea and choroid. Methods: Macaca fuscata monkeys were used as experimental subjects. Mono-L- aspartyl chlorin e6 at a dose of 2 mg/kg was administered by intravenous in fusion. Laser irradiation was applied within 5 minutes using a 664-nm diode laser at a power output of 5.9 mW (750 MW/cm(2)), spot size of 1,000 mum, and time of 10 seconds. This resulted in a fluence of 7.5 J/cm(2). Three co nsecutive PDT treatments at 2-week intervals were applied over the center o f the fovea and posterior fundus near the arcade vessels of each eye. The a nimals were killed and the eyes were enucleated for histologic study 2 week s after the last treatment. Results: Limited changes could be observed in the sensory retina under ligh t microscopy. Photoreceptor cells and outer segments were not damaged, even after repeated PDT. Proliferation and duplication of the retinal pigment e pithelial cells were common findings. A plaque of fibrous tissue was presen t, interwoven with retinal pigment epithelial cells in eyes that received r epeated PDT. The retinal vessels remained patent even after three sessions of PDT. However, occlusion of the choriocapillaris and the large choroidal vessels was observed after repeated PDT treatment. Conclusion: Repeated PDT of healthy nonhuman primate fundi using a hydrophi lic photosensitizer (NPe6) shows preservation of the neurosensory retina co mponents and architecture with damage confined to the retinal pigment epith elium and choriocapillaris.