Tracing of Suprachoroidally Microneedle Injected Labeled Drugs and Microbeads in Human, Pig and Rabbit Tissue Using Liquid Nitrogen Snap-Freeze Thaw and Lypholization Techniques

Abstract

Purpose: : To visualize drug delivery to the suprachoroidal space following a single microneedle injection.

Methods: : Human, pig and rabbit whole globe donor tissue was injected transsclerally using a single microneedle into the suprachoroidal space. The whole globe was snap frozen and dissected. Other snapfrozen whole globes were dissected after dry-freezing (lyophilization). Frozen or lyophilized tissue was fixed for confocal microscopy, TEM and light microscopy using PAS staining. Globes were injected transsclerally with microneedles into the suprachoroidal space with 10 to 400 µl India ink, fluorescent riboflavin, dyed viscoelastic or fluorescent beads prior to freezing to visualize drug diffusion within the suprachoroidal space.

Results: : Suprachoroidal drug delivery was consistently achieved. In rabbits the dye spread laterally from the injection site towards the optic nerve covering over 25 % of the suprachoroidal surface. Similar coverage was noted in human and pig eyes. In no cases were there signs of dyes injected into the subretinal or vitreous tissue. Lyophilized globes were dissected into distinct entities e.g. sclera, uvea (iris, ciliary body and choroid), retina, vitreous, aqeous tissue thus permitting quantification and localization of injected dyes.

Conclusions: : Human, pig and rabbit whole globes have shown consistent suprachoroidal injections using a single microneedle. The suprachoroidal space can easily be visualized in situ ex vivo by dissecting frozen or lyophilized tissue. Monitoring and tracing drug delivery to the posterior segment of the eye is demonstrated. This teqnique may provide a more consistant approach to subretinal delivery of therapeutic agents.

Keywords: drug toxicity/drug effects • injection • choroid