Chronic inflammation plays a prominent role in many retinal diseases, highlighted by increased vascular permeability, neovascularization, leukocyte infiltration and an increase in the expression of inflammatory mediators such as cytokines and chemokines (Antonetti 2006). Corticosteroids are frequently used to treat chronic inflammatory conditions due to their well-characterized suppressive effect on the inflammatory cascade. Corticosteroids are commonly used treatments for inflammatory diseases of the posterior segment of the eye like macular edema following uveitis and retinal vein occlusion and the wet form of macular degeneration.
Pharmaceutical agents have been developed for use in the treatment of retinal disease; however, agents that are applied topically to the ocular surface may not reach the retina in sufficient quantities to provide a therapeutic effect. Intravitreal (IVT) injections, or the implantation of sustained delivery devices, have the potential to surmount this limitation, and can be used to administer therapeutic agents directly to the posterior segment (Ghate 2007). While the IVT route of administration enables direct deposition of drug to the posterior segment, the procedure leads to significant exposure of anterior segment ocular structures via diffusion. Limitations to these methods of administration can also include a requirement for a relatively frequent treatment regimen (monthly injections) as well as a side effect profile that may include cataract formation and elevated intraocular pressure (IOP). The field has primarily been focused on drug delivery via penetration into the globe, which is complicated and cumbersome. Thus, there is a significant need for targeting distinct tissues with a simple procedure that may improve safety and duration.
There are a variety of ways to locally deliver drugs to the back of the eye. Some of these approaches are highlighted below: (a, b) topical, (c, j) injections, (d, g, h, i) implants, and (e, f) microneedles. (Edelhauser et al 2010)