From drops to devices: microneedle-mediated ocular drug delivery for improved therapeutic outcomes

Ocular diseases remain a major cause of visual impairment worldwide, however, effective treatment is hindered by multiple anatomical and physiological barriers that restrict drug penetration into ocular tissues. Conventional ocular drug delivery systems, including eye drops, systemic administration, and intravitreal injections, suffer from poor bioavailability, rapid precorneal clearance, frequent dosing, and invasive procedures, ultimately limiting therapeutic efficacy and patient compliance. Microneedle (MN)-mediated ocular drug delivery has emerged as a promising minimally invasive platform capable of overcoming these barriers by enabling localized, targeted, and sustained drug delivery to both anterior and posterior segments of the eye. This review comprehensively discusses ocular barriers, the limitations of conventional therapies, microneedle design principles, materials, fabrication techniques, and administration routes, including corneal, trans-scleral, subconjunctival, and suprachoroidal delivery. Unlike previous reviews, this article integrates administration routes with disease-specific applications, provides a comparative evaluation of conventional and microneedle-based ocular drug delivery systems, and critically discusses material selection according to target ocular tissues. Furthermore, recent advances in smart and stimuli-responsive microneedles, translational challenges, manufacturing considerations, sterilization, regulatory aspects, and future clinical perspectives are summarized. Overall, this review highlights the potential of ocular microneedles as next-generation drug delivery systems capable of improving ocular bioavailability, reducing treatment burden, enhancing patient compliance, and accelerating clinical translation for the management of diverse ocular disorders.