Ocular drug delivery systems: A comprehensive review of innovative formulations, challenges and opportunities

The human eye's complex anatomy and physiology pose significant challenges to effective ocular drug delivery. This comprehensive review explores the eye's structure, ocular disorders such as cataracts, conjunctivitis, glaucoma, and fungal keratitis, and various ocular drug delivery systems. The review discusses the advantages and disadvantages of ocular drug delivery systems, including topical administration, intravitreal injection, subconjunctival routes, and implantable devices. Novel formulations such as nanosuspensions, microemulsions, liposomes, and niosomes are examined for their potential to overcome anatomical limitations and enhance bioavailability. The mechanisms of drug release, including diffusion, osmosis, and bio-erosion, are also discussed. Furthermore, the review highlights the importance of targeting specific ocular tissues and overcoming defensive mechanisms to achieve optimal therapeutic efficacy.