Challenges and solutions in topical ocular drug-delivery systems

Vision significantly affects quality of life and the treatment of ocular disease poses a number of unique challenges. This review presents the major challenges faced during topical ocular drug administration and highlights strategies used to overcome the natural transport barriers of the eye. The circulation of tear fluid and aqueous humor decrease the residence time of topically delivered drugs, while ocular barriers in the corneal and conjuctival epithelia and the retinal pigment epithelium limit transport. Successful treatment strategies increase the residence time of drugs in the eye and/or enhance the ability of the drug to penetrate the ocular barriers and reach the target tissue. In this review, we discuss several drug-delivery strategies that have achieved clinical success or demonstrate high potential. We also draw attention to a number of excellent reviews that explore various ocular drug-delivery techniques in depth. Finally, we highlight cutting-edge drug-delivery technologies that improve the efficacy of current drug-delivery methods or use proven techniques to deliver novel therapeutics.