Current and future ophthalmic drug delivery systems. A shift to the posterior segment

Topical eye drop administration is useful only for the treatment of anterior segment diseases. The posterior eye segment is an important therapeutic target with unmet medical needs. The leading causes of visual impairment in the industrial countries are related to the disorders in the posterior eye tissues. New drugs for the medication of the posterior ocular segment have emerged, but most drugs are delivered by repeated intravitreal injections. Effective, safe, and comfortable methods of drug delivery are needed. The emerging methods include polymeric-controlled release injections and implants, nanoparticulates, microencapsulated cells, iontophoresis, and gene medicines. The biggest drug delivery challenge is to develop effective methods for posterior segment therapies that would also be applicable for the out-patient use.