A study of stromal riboflavin absorption in ex vivo porcine corneas using new and existing delivery protocols for corneal cross-linking

Abstract

Purpose To indirectly measure stromal riboflavin penetration using commercially available riboflavin solutions and new and existing epithelium-off, trans-epithelial and iontophoresis-assisted delivery protocols. Methods Forty porcine eyes were divided into eight groups. Group 1: Ricrolin applied to the de-epithelialised cornea for 30 min; Group 2: epithelium-intact, no treatment; Groups 3-5: epithelium-intact, 30-min application of Ricrolin TE, Mediocross TE or ParaCel/Vibex, respectively. Group 6: epithelium-intact, Ricrolin+ iontophoresis-assisted delivery for 5 min; Group 7: epithelium-intact, Ricrolin+ iontophoresis-assisted delivery for 5 min with a 20-min riboflavin soak; and Group 8: epithelium-intact, Ricrolin+ iontophoresis-assisted delivery for 5 min, 15-min soak and another 5 min of iontophoresis. After a saline wash, light transmission spectra were obtained from each cornea, before and after epithelial removal. Results Corneas in groups 1 and 8 showed a distinct riboflavin absorption peak between 400 and 520 nm. The optical density of the corneas in groups 3-7 did not differ significantly from that of the untreated corneas (group 2). Conclusions A modification to the standard iontophoresis trans-epithelial technique resulted in successful penetration of riboflavin into the stroma and appears to offer the most promise for epithelium-on cross-linking.