Intraocular dexamethasone penetration via subconjunctival or retrobulbar injections in rabbits

Using high-performance liquid chromatography, we compared tissue levels of dexamethasone in the aqueous, vitreous, retina, and choroid of rabbits, 1 and 4 hours following subconjunctival or retrobulbar injection. One hour following injection, dexamethasone levels in all of these tissues were similar in both the subconjunctival and retrobulbar groups. Four hours following injection, the concentrations in the two groups also were similar, except in the choroid, in which the subconjunctival injection yielded significantly lower dexamethasone levels than the retrobulbar injection. Tissue steroid levels were comparable ipsilateral and contralateral to the injected eyes in both treatment groups after 4 hours, except in the retina, in which the levels were lower in the contralateral eye after subconjunctival injection. These data suggest that dexamethasone absorption and delivery is predominantly hematogenous following both subconjunctival and retrobulbar injection, especially in highly vascular tissues, such as the choroid. Hematogenous delivery of dexamethasone appears to peak earlier in the choroid and presumably in other intraocular tissues following subconjunctival injections, while retrobulbar injections provide more steady, long-term delivery.