Advances in the understanding of retinal drug disposition and the role of blood-ocular barrier transporters.

INTRODUCTION: The blood-retinal barrier (BRB) is required for proper vision and controls exchange of nutrients with the choroidal vessels. This barrier serves as a selective partition between the retina and the circulation, and to maintain the specialized environment of the neural retina with a high degree of control of solute and fluid permeability. AREAS COVERED: The authors review the understanding of retinal drug disposition. The article highlights the routes of ocular drug delivery, and discusses the newest pharmaceutical ophthalmic formulations. Furthermore, the article focuses on drug transporters that are expressed in the corneal epithelium and BRB (ATP-binding cassette and solute carrier superfamilies). These transporters play essential roles in mediating the biodisponibility of drugs in the anterior and posterior chambers of the eye. Finally, the article reviews the ocular complications that are caused by intravitreal injections. EXPERT OPINION: Intraocular drug delivery is the only mode that currently directly broaches the BRB and thereby attains the highest peak intravitreal or intraretinal drug concentration. There is an urgent need for the development of optimal and efficient drug delivery systems.