ABSTRACT
It is now generally accepted that topically applied drugs can enter the eye by both a corneal and a noncorneal pathway. Although the corneal pathway is the primary route of intraocular entry for most drugs, penetration through the conjunctiva and sclera can also be important (1-3) and, under some circumstances, could be more important than the corneal route (4-22). Ahmed and Patton (5,6), using blocking techniques, showed that the noncorneal pathway was the dominant route for intraocular entry of inulin, a molecule that is poorly absorbed across the cornea. This group was also the first to suggest that it might be possible to exploit the conjunctival/scleral absorption route to promote site-specific delivery of drugs to intraocular tissues in the back of the eye (23). The increasing interest in intraocular delivery of peptide and protein drugs, drug therapy targeting posterior segment eye disease, and the advent of new chemical entities and novel ophthalmic drug delivery systems necessitates a thorough understanding of the noncorneal pathway and approaches of exploiting this route in ocular therapy.
