Toxicity of the Photosensitizer NPe6 Following Intravitreal Injection

■ BACKGROUND AND OBJECTIVE: To determine the retinal toxicity of mono-L-aspartyl chlorin e6 (NPe6) following intravitreal injection. ■ METHODS: Twelve Dutch-belted rabbits divided into 5 experimental groups (n=2 each) were injected intravitreally with 6.25, 12.5, 25, 50, or 100 μg of NPe6; one control group (n=2) was injected with intravitreal normal saline. One eye in each rabbit was sutured shut to test the effect of light exposure. Fundus photography and electroretinograms were performed before treatment and 2 days, 1 week, and 2 weeks after injection. Animals were euthanized and the eyes enucleated for histopathologic analysis. ■ RESULTS: After 1 week, 4 uncovered eyes given 50 and 100 μg had central retinal vein occlusion and varying degrees of retinal hemorrhage. RPE proliferation was seen in the covered eyes given 50 or 100 μg. Electroretinograms revealed absent retinal response at 100 μg and mild toxicity at 50 μg, but no change from normal at doses of ≤ 25 μg of NPe6. ■ CONCLUSIONS: Intravitreal doses of ≤ 25 μg NPe6 caused little or no apparent toxicity; however, toxicity was significant at doses of 50 pg and 100 pg.