Ocular drug delivery is challenging due to the presence of anatomical and physiologicabarriers. These barriers can affect drug entry into the eye following multiple routes of administration (e.g., topical, systemic, and injectable). Topical administration in the form of eye drops is preferred for treating anterior segment diseases, as it is convenient and provides local delivery of drugsMajo concerns with topical delivery include poor drug absorption and low bioavailability. To improve the bioavailability of topically administered drugs, novel drug delivery systems are being investigatedNanocarrier delivery systems demonstrate enhanced drug permeation and prolonged drug releaseThis review provides an overview of ocular barriers to anterior segment delivery, along with ways to overcome these barriers using nanocarrier systems. The disposition of nanocarriers following topical administration, their safety, toxicity and clinical trials involving nanocarrier systems are also discussed. © 2018 by the authors. Licensee MDPI, Basel, Switzerland.