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

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.