ABSTRACT
Transscleral delivery is a nondestructive and minimally invasive method that achieves targeted delivery of high molecular weight compounds to the posterior segment. A long-term transscleral delivery device may be clinically feasible because the human eye is remarkably tolerant of foreign bodies overlying the sclera, such as scleral buckles used in treating retinal detachment, even for years. The clinically used anesthetic benzalkonium chloride was found to enhance transscleral penetration of molecules as large as 20 kDa dextran into the retina and choroid. The delivery of drug to the retina may be somewhat surprising in the face of the classical belief that the retinal pigment epithelium forms a strict barrier to drug penetration; however, a study has shown that even molecules as large as 80 kDa dextrans can diffuse through this tissue. Drug characteristics such as its ionization and molecular shape also affect the rate of transscleral diffusion.
