Nanostructure colloids in ocular drug delivery: advances and challenges

The eye is one of the most important and sensitive organs of the human body that is naturally protected by the membrane and vascular barriers. Although these barriers protect the eye effectively, different types of diseases such as age-related macular degeneration (AMD), diabetic macular edema (DME), cataract, proliferative vitreoretinopathy (PVR), uveitis, cytomegalovirus (CMV), and glaucoma and other physiological factors affect the posterior and anterior portions of the eye. Effective ocular drug delivery is still a major and serious challenge in the medical field. Conventional methods are not efficient due to many limitations including low ocular bioavailability of drugs, low levels of drugs in the ocular tissue and washed-off drugs from the eye in a very short period of time. The use of nanotechnology to design drug delivery systems to achieve controlled release as well as penetration of protective barriers has been promising. In the past decades, different types of nano-scaled ocular drug delivery systems have been developed. Some of these nano-systems are effective for drug delivery to the anterior and some of them to the posterior segment. In this article, the authors reviewed and discussed the efficiency and effectiveness of different types of nanoscale ocular drug deliveries with their advances and challenges.