Optimizing corneal riboflavin administration in ex vivo horse, dog, rabbit, and pig samples for use in corneal collagen cross-linking.

Purpose: Determine optimal iontophoresis times for riboflavin delivery to the corneal stroma across different species and compare these to corneal injection.

Methods: Ex vivo horse, dog, rabbit, and pig globes were treated with riboflavin administered with either iontophoresis for 2.5-20 minutes with or without corneal epithelium; or with purpose-designed precise corneal injection (PCI) application with intact epithelium. Immediately following riboflavin administration, samples were harvested, frozen, and sectioned. Riboflavin penetration was imaged using fluorescence microscopy.

Results: Horse samples processed with iontophoresis without epithelium for 2.5, 5, and 7.5 minutes, and processed with intact epithelium for 20 minutes, had mean percent stromal penetration (%SP ) of 63.4%, 93.8%, 100.0%, and 0.0% (respectively). Dog samples processed with iontophoresis without epithelium for 2.5 and 5 minutes, had %SP of 60.7% and 82.1% (respectively). Pig samples processed with iontophoresis for 5 minutes without and with epithelium had %SP of 63.3% and 35.1% (respectively). Rabbit samples processed with iontophoresis without epithelium for 2.5 and 5 minutes, had %SP of 81.8% and 100.0% (respectively). For all injected volumes, riboflavin was observed spanning throughout the corneal stroma, and lamellar separation was noted surrounding all sites of injection.

Conclusions: Both iontophoresis and injection via PCI needles provide efficient and effective means of riboflavin administration in ex vivo horse, dog, rabbit, and pig corneas. Epithelial debridement is required for stromal delivery of riboflavin using iontophoresis in horses. Following epithelial removal, riboflavin penetrated through the horse corneal stroma faster than all other species tested.