Fundamentals, challenges, and nanomedicine-based solutions for ocular diseases.

The eye consists of sensitive, compactly adjoined tissue structures which act as strong physical (static) and physiological (dynamic) barriers that prevent entry of foreign bodies into the eye. Together, these barriers reduce the bioavailability of topically and intraocularly administered medicaments thus demanding frequent drug administration for the treatment of chronic eye diseases. Hence, development of drug delivery systems (DDS) that can be retained in ocular tissues for longer durations can help to reduce the frequency of drug administration, whereas, delivery systems that traverse through ocular barriers may offer higher bioavailability of administered drugs to otherwise inaccessible ocular tissues. These objectives can be partially/fully achieved using nanoparticulate/colloidal DDS. Colloidal DDS, due to their nanodimensions, undergo internalization by cells which enables transport of drugs through ocular barriers. Furthermore, nanoparticles can prolong duration of drug release and can increase residence time of entrapped cargo molecules in ocular tissues. Together, these aspects facilitate a higher bioavailability, prolonged therapeutic effect and reduced frequency of drug administration for the effective treatment of chronic ocular diseases. Hence, nanocarriers have been widely explored for ophthalmic drug delivery applications. In this review, we discuss the anatomy of ocular tissues along with their barrier properties. We then discuss ocular diseases along with the various routes of drug administration and pathways of drug transport in the eye. The next section discusses the influence of physicochemical properties of therapeutic molecules on their ocular distribution and conventional and advanced (nanoparticulate/colloidal DDS) drug formulations that are used for the treatment of ocular diseases. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Neurological Disease Therapeutic Approaches and Drug Discovery > Emerging Technologies Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.