Cell-based in vitro models for ocular permeability studies

Ocular drug delivery is one of the most challenging administration routes, due to the eye's unique anatomy and physiology. In general, drug absorption into the eye is limited and generally, less than 10% of the administered drug reaches the posterior segment of the eye. Ocular drug delivery studies in past decades have employed in vivo animal models, such as rabbits, and have been conducted in vitro by using isolated rabbit ocular tissues, which also implies the sacrifice of a huge number of animals.Therefore, a demand for improved cell culture that can replace animal experimentation with an adequate reproducibility is mandatory. Corneal epithelial cell culture models are the longer-considered strategy to study in vitro ocular drug delivery. From these, rabbit and human cell lines are the most frequently used. Primary cells have been employed that were transformed by using some chemicals or viruses to establish continuous/immortalized cells. Alternatively, original immortalized cells as a consequence of a tumor were also employed. Additionally, some attempts have been made to develop a tridimensional corneal structure.In this chapter, the general principles and models for the cell-based in vitro models for ocular permeability studies are presented.