INTRODUCTION
Eye drops have been the most popular and best accepted dosage form for ocular delivery of drugs. However, conventional eye drops have well known disadvantages such as low ocular availability due to defence mechanisms of the eye. Frequent instillation is recommended or even required in order to reach therapeutic levels of the drug at the site of action. Many attempts have been made over several decades to increase the ocular availability and hence improve the efficacy of topically applied drugs. This has led to the emergence of new drug delivery devices with common ambitions, including decreasing the instillation frequency, prolonging the residence time of the drug applied and thus improving patient compliance.
