Ocular Drug Delivery - New Strategies for Targeting Anterior and Posterior Segments of the Eye

The ocular delivery of drugs encounters several limitations because of the dynamic and static barriers of the human's eye anatomy and physiology. The poor bioavailability of drugs are mainly related to the topical administration, i.e. eye drops which is the most common drug dosage form for the treatment of eye pathologies. Precorneal factors and drug limitations related to its solubility and susceptibility for physicochemical degradation could be the main reasons for the poor permeation and uptake in the ocular mucosa. Pathologies affecting the anterior and posterior segment of the eye are thereafter difficult to be treated and, given the chronic and degenerative nature of some of these injuries, it is crucial to improve drugs therapeutic effect. Nanotechnology-based delivery systems could be a suitable approach to overcome these limitations. Some of the most important colloidal systems are highlighted in this review, such as the use of mucoadhesive polymers, prodrugs, nanogels, liposomes, microemulsions, lipid and polymeric nanoparticles, cyclodextrins, dendrimers and nanocrystals, along with their clinical and therapeutic relevance for the administration of drugs for ocular delivery.