Threshold power levels for NPe6 photodynamic therapy

OBJECTIVE: To determine the threshold power levels for producing retinal an d choroidal vascular occlusion using mono-L-aspartyl chlorin e6 (NPe6) phot odynamic therapy; to evaluate its efficacy with longer intervals between ph otosensitizer injection and laser application; to determine the elapsed tim e between light application and appearance of angiographic changes. METHODS: Pigmented and nonpigmented rabbits were injected intravenously wit h 2 mg/kg of NPe6 before laser irradiation of the retina-choroid. Group 1 w as treated at increasing power levels; fluorescein angiograms were obtained at each fluence. Group 2 animals were exposed to laser irradiation at 5 mi nutes, and 1 and 3 hours postinjection to determine (by fluorescein angiogr aphy 24 hours post-treatment) if increasing the interval affected outcome. Group 3 animals underwent fluorescein angiography at 30 minutes, 1 hour, 2 hours, and 24 hours posttreatment to document the time between laser applic ation and subsequent vessel closure. RESULTS: Choroidal vessel occlusion was angiographically evident in all les ions at fluences of greater than or equal to 2.65 J/cm(2) in pigmented rabb its and at greater than or equal to 0.88 J/cm(2) in nonpigmented rabbits. L esion diameter decreased as the time between injection and treatment increa sed. Vessel occlusion was document-ed at least 2 hours after treatment. CONCLUSION: Choroidal vessel occlusion can occur at very low fluence.