CHOROIDAL CONCENTRATION OF INTERFERON AFTER RETROBULBAR INJECTION

Purpose, To determine whether recombinant human interferon alpha-2a (I FN alpha 9a) would diffuse into the choroid in significant amounts fro m a retrobulbar depot. Methods, One million international units of IFN alpha-2a were injected into the retrobulbar space of the eyes of 17 r abbits, and choroidal and serum concentrations were measured at 1, 2, 4, 8, 12, and 24 hours. The same dose of IFN alpha-2a was injected sub cutaneously into 10 rabbits, and choroidal and serum concentrations we re measured at the same intervals for comparison. Parabulbar and ocula r tissues were studied by light microscopy for evidence of local toxic ity. Results, Peak concentration IFN alpha-2a in the choroid after ret robulbar injection occurred at 2 hours and averaged 32,000 IU/mg. Peak concentration in the serum occurred at 4 ho;rs and averaged 227 IU/ml . Concentrations in choroid and serum fell rapidly, and IFN alpha-2a w as not detectible at 24 hours. No IFN alpha-2a was detected in the cho roid of the paired eye, and only a trace (<50 IU/mg) tvas found in eit her eye after subcutaneous injection. Light microscopy revealed some l ymphocytes in the fat adjacent to the retrobulbar depot after six dail y injections of IFN alpha-2a or saline. Sclera, choroid, and retina ap peared unaffected. Conclusions. IFN alpha-2a diffuses into the choroid from a retrobulbar depot in significant amounts. The serum concentrat ion from a retrobulbar injection is <1% of the choroidal concentration . The retrobulbar route to the choroid may be optimal for testing the effect of IFN alpha-Pa on choroidal neovascularization.