Ocular implants and inserts: revolutionizing drug delivery in ophthalmology

The ophthalmic route for drug administration remains a significant constraint in ophthalmology due to the unique anatomy and several protective barriers in the eyes, which limit absorption and therapeutic efficacy. Conventionally, drugs are delivered to the eye through various types of formulations, including eye drops (solutions, suspensions, and emulsions), ointments and gels, in-situ gels, and periocular injections. While effective, they suffer from various drawbacks, including poor bioavailability (<5%), reflex blinking, tear turnover, nasolacrimal drainage, and frequent dosing requirements. A key challenge remains: ensuring sufficient drug reaches the target area for the desired effect. This necessitates developing sophisticated drug delivery systems capable of site-specific controlled release within the ocular tissue, including implantable and insertable devices. In 2024, the global ocular implant market reached a valuation of USD 15.72 billion and is projected to expand at a compound annual growth rate of approximately 5.8 % from 2025 to 2030, fuelled by increasing demand for minimally invasive and long-acting treatment options. These devices are not only used for sustained and controlled drug delivery but also play an important role in correcting refractive error through intraocular lenses. Recent advancements, including artificial intelligence, IoTconnected devices, smart stimuli-responsive materials, and precision 3D printing, are significantly enhancing the diagnostic, monitoring, and management purposes of ocular conditions in modern ophthalmic care. This review provides a detailed analysis of various implantable and insertable technologies, ranging from Intacs rings, ocular ring inserts, and drug-eluting contact lenses to intracameral implants, conjunctival inserts, intraocular lenses/inlays, injected micro- and nanoparticles, intravitreal implants, and microneedles. For each category, we examine the working mechanisms, clinical applications, technological innovations, and design considerations, with a focus on segmented drug delivery for the anterior and posterior regions. The review also highlights clinical applications, provides an overview of marketed, patented, and FDA-approved devices in the U.S., and outlines ongoing clinical trials. Additionally, it addresses the difficulties in translating research into clinical practice, recent technological advancements, and future directions for navigating regulatory barriers in the development of these devices. Through highlighting critical research gaps, this review intends to influence the advancement of ocular implants and inserts. This article aims to guide future developments in the domain of ocular therapeutics through implantable and insertable drug delivery devices.