Intratympanic drug injection to the inner ear precludes systemic side effects and bypasses the blood-labyrinth barrier. Currently, the drug delivery via this route is limited by the permeability of the round window membrane (RWM), one of the two openings to the inner ear. In order to understand and improve the drug delivery into the inner ear, we aim to visualise the diffusion of tracer molecules across the RWM, and try to increase its penetration by applying reagents. The outcome from this study will provide proof-of-concept for a new drug delivery approaches through the RWM to the inner ear.