ABSTRACT
The topical route is the most commonly utilized method of administering a medication to the eye. Theoretically, it is adequate for the treatment of most external conditions of the eye and those of the anterior segment, which includes the iris and ciliary muscle. Introducing the drug directly to the conjunctival sac should in theory localize the drug effect, facilitate drug entry which is otherwise hard to achieve by systemic delivery and avoids first-pass metabolism. In practice, topical application frequently fails to establish a therapeutic drug level for a desired length of time within the target ocular tissues and fluids. Inefficient ocular treatment is a result of many factors, including the rapid precorneal clearance, the highly selective absorptive properties of the corneal barrier, the unproductive drug loss via the conjunctival route and the difficulty that many people, particularly the elderly, have in dosing eyedrops to the eye. Typically, less than 5% of the instilled dose reaches the aqueous humour (Jarvinen and Jarvinen, 1996).
