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 lim iting factor in determining the useful life of a drug administered as a mic ro dispersion. Because microparticles can be lost from the vitreous by diff usion, a condensed depot of drug can give a greater lifetime. However, it n eeds to be anchored outside the visual pathway which requires an intraocula r operative procedure. Attaching a reservoir to the external sclera with a diffusion-controlled entry through a tube to the vitreous is suggested as h aving more flexibility than other systems.