Nanotechnology in ophthalmic drug delivery: a survey of recent developments and patenting activity

Controlled release of drugs to the eye tissues is still an important, though challenging topic of research in the area of pharmaceutical technology. The eye is an organ highly protected from extraneous compounds by anatomical, functional and biochemical mechanisms. Such defences often limit the time of contact of the formulation with the eye surface and lead to an insufficient bioavailability of the applied drugs, especially at the level of eye posterior segment. Many nanotechnology strategies have been exploited for the diagnosis and cure of ocular diseases. They range from medical application of nanomaterials, including controlled drug and gene delivery systems, to nanoelectronic biosensors, to nanodevices for in vivo imaging and diagnosis, to implantable biomaterials for tissue regeneration and prolonged targeted therapy. Nanosized ocular drug delivery systems have shown important results in ocular drug delivery in the last years, both as topical applications on the eye surface or after intraocular administration. These colloidal carriers can be suitably engineered to overcome corneal and retinal barriers to drug penetration, protect the encapsulated drug, and prolong its activity by a controlled and/or prolonged site-specific release profile. Although the basic research on ophthalmic delivery systems supplies many technological approaches, very few of them have been able to reach a clinical relevance or to be translated into pre-industrial or industrial applications. The main reason lies in the complexity and specificity of the formulation parameters that ophthalmic products always require to tackle the high sensitivity of ocular tissues. This review surveys some of the more recent patents regarding nanotechnology applications to ophthalmic controlled and targeted drug delivery.