ABSTRACT
Current ocular drug delivery methods include such methods as topical drops, ointments, and therapeutic lenses, soluble ocular drug inserts, collagen shields, liposomes, and transcorneal iontophoresis (reviewed in Refs. 1, 2, 3, 4, and 5, respectively). Topically applied drugs, such as suspensions, ointments, and gels, are seldom maintained at the necessary therapeutic concentration in the target tissues due to rapid tear turnover and drainage, tear dilution, and/or an impermeable corneal surface epithelium. Topical drops, currently the most common form of ocular drug delivery, quickly lose their effectiveness and cannot reach the back of the eye because of their rapid elimination. Reduced ocular bioavailability of the drug, in turn, could result in excessive systemic toxicity, causing unwanted side effects such as uncontrolled growth of nonsusceptible pathogens. Emulsifying the drug in an ointment or viscous solution such as polyvinyl alcohol or methylcellulose can decrease the clearance rate over solutions but decrease vision for a time (1). Other current ocular drug delivery methods are also not devoid of problems; for example, collagen shields reduce visual acuity due to the translucent nature of collagen (3,6). Although advancements have been made in these existing systems, efficient drug delivery to the eye remains problematic.
