Drug delivery to treat ocular diseases is one of the most challenging fields, due to complex anatomy of eye and its physiological barriers like precorneal loss and the presence of biological barriers, especially in the posterior segment of the eye. Although topical eye drop administration is usually preferred to treat disorders of the eye, the biological protecting factors lead to low ocular absorption and poor bioavailability (1– 10%). An efficient ocular drug delivery system, which can provide maximum precorneal residence time, overcome ocular barriers and sustain delivery of drugs following topical administration is desirable. Nanotechnology is an emerging field in drug delivery and considerable research is taking place towards the development of nanotechnology-based ocular drug delivery systems. Because of their ability to avoid various biological barriers and providing targeted and sustained drug delivery to various ocular tissues, nanotechnology-based formulations paved the approaches for efficient ophthalmic drug delivery for both the anterior and posterior segments of eye. This review discusses a variety of nanocarriers, such as nanoparticles, nanosuspension, liposomes, niosomes, discomes, micelles, dendrimers and microemulsion developed for the ocular delivery of many drugs. Some of them have shown promising results for improving ocular bioavailability. This review also attempts to extend the information on recently issued and filed patents on nanotechnology-based ocular drug delivery systems in the last few years.