Drug delivery to the posterior segment of the eye: some insights on the penetration pathways after subconjunctival injection.

The aim of this study is to gain an understanding of the penetration pathways for a drug to enter the posterior segment of the eye after subconjunctival injection. 14C-mannitol was injected subconjunctivally, and 14C-mannitol and 14C-inulin were injected intracamerally. The aqueous and vitreous levels were determined at selected time points. The results of subconjunctival injection and intracameral injection were compared. The vitreous level of the dosed eye is much higher than that of the corresponding contralateral eye after subconjunctival injection so that the recirculation pathway is not a dominant penetration pathway. In addition, the results also showed that it is unlikely for significant amounts of drug to move from the aqueous to the vitreous chamber after subconjunctival injection. Therefore, direct penetration is the dominant pathway for a subconjunctivally injected compound to enter the vitreous chamber.