Contact Lens Based Drug Delivery to the Posterior Segment Via Iontophoresis in Cadaver Rabbit Eyes

A drug loaded contact lens combined with electrodes positioned diametrically opposite and beyond the limbus can potentially deliver ionic drugs directly to the vitreous.

Commercial lenses are loaded with nile blue or fluorescein as the drug analogs and placed on cadaver rabbit eyes. Electrodes (19.6 mm²) are placed atop at opposite sides of the sclera to apply a constant current (0.125-0.250 mA) for 1-2 h. COMSOL simulations are conducted to determine the field distribution and the potential drop across various tissue layers and equivalent circuit model is developed to calculate the electrophoretic velocity and estimate the drug flux.

The device delivered both hydrophobic and hydrophilic dyes to the tissue. The amount of fluorescein delivered to the vitreous directly correlated with the applied current and time duration. The electrophoretic mobility from the experimental data agreed with the model estimates. Confocal microscopy showed that nile blue penetrated through the conjunctiva-sclera barrier to reach the retina showing that the electric field can transport molecules through the ocular tissue and into the vitreous. The ex vivo model neglects transport into flowing capillaries in the choroid. However, the time scale for electrophoretic transport across the choroid was found to be 550-1300 fold shorter than that for uptake into the choroidal capillaries.

Incorporation of an electric field with multiple electrodes on a single lens can effectively deliver ionic drugs to the posterior region at levels comparable to current methods with the benefits of being safer and less invasive.