Recent Advances in Topical Ocular Drug Delivery

Topical ocular drug delivery has been considered to be an ideal route of administration for treatment of ocular diseases related to the anterior segment of the eye. However, topical ocular delivery is a challenging task because of barriers such as nasolacrimal drainage, corneal epithelium, blood-ocular barriers, and metabolism in the eye. Approaches to improve ocular bioavailability include physical approaches such as formulations of drugs as solutions (Zymaxid(™)), suspensions (Zigran(®)), gels (Akten(®)) and chemical approaches such as prodrugs (Xalatan(™)), chemical delivery systems, and soft drugs. The purpose of this review article is to summarize recent advances in topical drug delivery to the anterior segment of the eye. Functional transporters in the corneal epithelium were also discussed as they provide prospects in topical ocular delivery. In addition to conventional delivery systems, novel delivery systems involving nanocarriers were also investigated for topical ocular delivery. Furthermore, due to increased interest, gene therapy applications of topical ocular delivery of genes to the anterior segment of the eye were also discussed. Research in topical ocular delivery is active for more than 50 years and proven to be advantageous for the treatment of many ocular diseases. However, there is scope for innovation in topical drug delivery to develop delivery systems with a high patient safety profile and compliance for effective clinical usefulness.