Nano and microtechnologies for ophthalmic administration, an overview

Ocular drug delivery is one of the most challenging fields of pharmaceutical research. It is generally employed to overcome the static (different layers of cornea, sclera, and retina, including blood aqueous and blood-retinal barriers) and dynamic barriers (choroidal and conjunctival blood flow, lymphatic clearance, and tear dilution) of the eye. Ophthalmic formulations must be sterile, and the biomaterials used in the preparation of pharmaceutical systems completely compatible and extremely well tolerated by ocular tissues. The location of the target tissue in the eye will determine the route of administration. Ophthalmic administration systems are intended for topical, intraocular and periocular administration. In this review, we describe the main pharmaceutical nano- and microsystems currently under study to administer drugs to the eye, covering microparticles, nanoparticles, liposomes, microemulsions, niosomes and dendrimers. Herein is also the corresponding revision of the published scientific literature, which has always emphasized the technological aspects. The review also discusses the biomaterials used in the preparation of nano- and microsystems of ophthalmic drug delivery, fabrication techniques, therapeutic significances, and future possibilities in the field.