Review: practical issues in intravitreal drug delivery.

The delivery of drugs to the retina from solution or from prolonged release forms is considered in terms of pharmacokinetics, interference with vision, and toxicity and safety. It is concluded that visual loss will be the limiting factor in determining the useful life of a drug administered as a microdispersion. Because microparticles can be lost from the vitreous by diffusion, a condensed depot of drug can give a greater lifetime. However, it needs to be anchored outside the visual pathway which requires an intraocular operative procedure. Attaching a reservoir to the external sclera with a diffusion-controlled entry through a tube to the vitreous is suggested as having more flexibility than other systems.