New directions in the optimization of ocular drug delivery.

The main effort in ocular drug delivery during the past two decades has been on the design of systems to prolong the residence time of topically applied drugs in the conjunctival sac. Four recent developments promise to chart a new course in ocular drug delivery research: collagen shield as a topical ocular drug delivery system, in-situ activated gel-forming systems, noncorneal route of ocular drug penetration, and need for minimizing the systemic absorption of topically applied drugs.