Emulsion and Emulgel-Based Ophthalmic Drug Delivery Systems

Ophthalmic drug delivery encounters unique challenges due to the anatomical and physiological ocular barriers, necessitating the development of novel drug delivery systems (NDDSs). This review focuses on emerging therapeutic platforms, including nanoemulsions (NEs), microemulsions (MEs), self-emulsifying drug delivery systems (SEDDSs) such as self-nano emulsifying drug delivery systems (SNEDDSs) and self-micro emulsifying drug delivery systems (SMEDDSs), emulgels, and in situ-forming emulgels, as novel strategies for enhancing ocular drug delivery. NEs and MEs, due to their small globule size, excellent drug solubility, stability, and bioavailability, offer promising solutions for effective ocular therapy. SEDDSs further enhance the stability and bioavailability of hydrophobic drugs through self-emulsification in aqueous environments. Emulgels, combining the benefits of emulsions and gels, provide sustained and controlled release of therapeutic agents, improving the ocular retention time and therapeutic efficacy. Additionally, in situ-forming emulgels offer the advantage of liquid-to-gel transition upon contact with ocular surfaces, optimizing drug delivery. The review discusses various ocular diseases, challenges for ocular delivery of conventional formulations, updates on emulsion-based novel drug delivery systems for ophthalmic drug delivery, mechanisms of enhanced ocular permeation, formulation strategies, advantages, and challenges, design-of-experiment considerations for optimization, characterizations, and recent advancements in these systems including patents and clinical trials, highlighting their potential for improving the treatment of various ocular diseases. Furthermore, this review explores marketed ophthalmic emulsions and future prospects for integrating these NDDSs into clinical ophthalmology, emphasizing their ability to overcome ocular barriers and enhance therapeutic efficacy.