Retinal drug delivery system: challenges and approaches

The scientists have faced major challenges in Ocular drug delivery system because of the unique anatomy and physiology of eye. In treating anterior segment diseases topical eye drop is the most convenient and patient compliant route of drug administration. There are two types of barriers in ocular drug delivery system: static and dynamic barrier. Static barrier includes cornea, sclera, retina and blood- retinal barriers while dynamic barrier includes choroidal and conjunctival blood flow, tear dilution and lymphatic clearance. These barriers influence the bioavailability of drugs. Current article reviews the manacles in conventional ocular therapy, indispensable factors in ocular pharmacokinetics. It also describes a variety of approaches such as eye ointments, gel, prodrug, intravitreal injections, viscosity enhancers, penetration enhancers, liposomes, microparticles, niosomes, ocular inserts, implants, nanoparticles, nanosuspension, microemulsion, in situ-forming gel, iontophoresis, and periocular injections to increase the ocular bioavailability of drug and provide controlled and continous release of the drug to the anterior and posterior chamber of the eye.