Toxicity of the photosensitizer NPe6 following intravitreal injection

Background and objective: To determine the retinal toxicity of mono-l-aspar tyl 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 mug 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 expos ure. Fundus photography and electroretinograms were performed before treatm ent and 2 days, 1 week, and 2 weeks after injection. Animals were euthanize d and the eyes enucleated for histopathologic analysis. Results: After 1 week, 4 uncovered eyes given 50 and 100 mug had central re tinal vein occlusion and varying degrees of retinal hemorrhage. RPE prolife ration was seen in the covered eyes given 50 or 100 mug. Electroretinograms revealed absent retinal response at 100 mug and mild toxicity at 50 mug, b ut no change from normal at doses of less than or equal to 25 mug of NPe6, Conclusions: Intravitreal doses of less than or equal to 25 mug NPe6 caused little or no apparent toxicity; however, toxicity was significant at doses of 50 mug and 100 mug.