Targeting Ocular Drug Delivery: An Examination of Local Anatomy and Current Approaches

Abstract

Ocular drug delivery remains the focus of much modern research. Primary routes of administration include the surface, the intravitreal space, the subretinal space, and the subconjunctival space, each with its own series of unique challenges, limitations, and advantages. Each of these approaches requires careful consideration of the local anatomy, physical barriers, and key cells as well as the interface between the anatomy and the drug or drug system being delivered. While least invasive, the topical route poses a challenge with the many physical barriers that prevent drug penetration into the eye; while injection into the intravitreal, subretinal, and subconjunctival spaces are direct and targeted but limited due to the many internal clearance mechanisms and potential for damage to the eye. Polymeric-based, sustained-release drug delivery systems have been identified as a potential solution to many of these challenges; however, the design and successful implementation of a sustained-release system that is well-tolerated, bioactive, biocompatible, and degradable remains, in many cases, only in the early stages. The drugs and biomaterials in question also require special attention as small chemical changes could result in vastly different outcomes. This paper explores the anatomy and key cells of these four primary drug delivery routes as well as the interface between drug and drug delivery systems and the anatomy, reviewing the recent developments and current state of research in each area. Finally, this paper also examines the frequently used drugs and biomaterials found in ocular drug delivery and summarizes the primary interactions observed.

Nano-based ocular drug delivery systems: an insight into the preclinical/clinical studies and their potential in the treatment of posterior ocular diseases

“…Given that the openings in the conjunctival epithelium are larger than those in the cornea, it is possible that large-molecule drugs can also penetrate via this route. 84 Cell-penetrating peptides are common examples of modifications to nanocarriers to improve drug delivery to the retina from the ocular surface. These peptides often make in vivo uptake into the retina easier via the conjunctival-scleral pathway.…”

Studies on PVP-Based Hydrogel Polymers as Dressing Materials with Prolonged Anticancer Drug Delivery Function

“…This, in turn, reduces the amount of the dose reaching the desired place. Therefore, many investigations are currently being conducted to develop appropriate polymer carriers that provide target drug biodistribution [ 9 , 10 ].…”

Long‐Acting Ocular Injectables: Are We Looking In The Right Direction?

“…[ 25 ] With subconjunctival delivery, drugs target the ocular surface and potentially penetrate deeper tissues, including the scleral stroma and the ciliary body. [ 26 ] Similarly, sub‐tenon injections –, i.e., into the tenon capsule – are commonly used to manage conditions in the posterior eye segment, such as uveitis or macular edema, thereby achieving local effects. [ 27 ] While less frequent, retrobulbar injections are employed for conditions like optic neuritis, targeting the optic nerve and its surroundings.…”