Ocular Drug Delivery: Present Innovations and Future Challenges

Ocular drug delivery has always been a challenge for ophthalmologists and drug-delivery scientists due to the presence of various anatomic and physiologic barriers. Inimitable static and dynamic ocular barriers not only exclude the entry of xenobiotics but also discourage the active absorption of therapeutic agents. Designing an ideal delivery scheme should include enhanced drug bioavailability and controlled release of drug at the site of action, which can overcome various ocular barriers. Conventional ophthalmic medications include the use of topical eye drops and intravitreal injections of anti-vascular endothelial growth factor agent for treatment of anterior and posterior segment disorders, respectively. Current inventions for anterior ocular segment disorders such as punctum plugs, ocular implants, drug-eluting contact lenses, and ocular iontophoresis represent state-of-the-art inventions for sustained and controlled drug release. Parallel efforts for ocular drug delivery technologies for back of the eye disorders have resulted in the approval of various intravitreal implants. Novel drug-delivery technologies, including nanoparticles, nanomicelles, dendrimers, micro-needles, liposomes, and nanowafers, are increasingly studied for anterior and posterior disorders. To achieve patient compliance for back of the eye disorders, novel approaches for noninvasive delivery of potent therapeutic agents are on the rise. In this review article, we discuss past successes, present inventions, and future challenges in ocular drug-delivery technologies. This expert opinion also discusses the future challenges for ocular drug-delivery systems and the clinical translatable potential of nanotechnology from benchtop to bedside.