A Comparison of Different Corneal Iontophoresis Protocols for Promoting Transepithelial Riboflavin Penetration

Abstract

Citation: Gore DM, O'Brart DP, French P, Dunsby C, Allan BD. A comparison of different corneal iontophoresis protocols for promoting transepithelial riboflavin penetration. Invest Ophthalmol Vis Sci. 2015;56:7908-7914. DOI:10.1167/iovs.15-17569 PURPOSE. To measure corneal riboflavin penetration using different transepithelial iontophoresis protocols. METHODS.Freshly enucleated rabbit eyes were divided into nine treatment groups of 4 eyes. One group, in which 0.1% wt/vol riboflavin was applied for 30 minutes without iontophoresis after corneal epithelial debridement, acted as a control. The remaining groups were treated with an intact epithelium using different riboflavin formulations and varying iontophoresis current, soak, and rinse times. After riboflavin application, eyes were snap frozen in liquid nitrogen. Corneal cross sections 35 lm thick were then imaged immediately by two-photon fluorescence microscopy, using image processing software to quantify stromal riboflavin concentration at different corneal depths.RESULTS. In the epithelium-on iontophoresis treatment groups, greater stromal riboflavin penetration was achieved with higher-concentration riboflavin solutions, greater iontophoresis dosage, and longer solution contact times. A protocol utilizing 0.25% wt/vol riboflavin with benzalkonium chloride (BAC) 0.01% and two cycles of applied current and subsequent soaking (1 mA 5 minutes, soak 5 minutes; 0.5 mA 5 minutes, soak 5 minutes) achieved similar stromal riboflavin penetration to epithelium-off controls. The best-performing non-BACcontaining protocol produced stromal riboflavin penetration approximately 60% that of epithelium-off controls. Riboflavin solutions containing saline resulted in minimal stromal penetration. Riboflavin loading within the epithelium was equivalent to or higher than that in the subjacent stroma, despite rinsing the ocular surface with balanced salt solution.CONCLUSIONS. Modified iontophoresis protocols can significantly improve transepithelial riboflavin penetration in experimental corneal collagen cross-linking.

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

“…1,3,[7][8][9][10]13,14,20 In-vivo studies are needed to corroborate these findings and document any challenges of riboflavin administration in clinical patients. Rabbit samples were included in this study as a comparison to previous iontophoresis data collected in rabbits 21 and serve to validate our methodology. However, the authors acknowledge that use in horses and dogs is most clinically applicable.…”

“…21 Iontophoresis with higher concentrations of riboflavin, greater electrical current, and longer contact times was successful at overcoming the barrier effect of intact epithelium in rabbit corneas. 21 This provides an efficient alternative to the Dresden protocol. 1,3,[7][8][9][10]13,14,20 However, there are significant interspecies differences in corneal epithelium and stromal thickness.…”

“…Iontophoresis uses a voltage gradient to enhance the penetration of ionized riboflavin into the cornea. 21,22 Iontophoresis protocols improve transepithelial riboflavin penetration in an ex vivo rabbit model. 21 Iontophoresis with higher concentrations of riboflavin, greater electrical current, and longer contact times was successful at overcoming the barrier effect of intact epithelium in rabbit corneas.…”

“…21,22 Iontophoresis protocols improve transepithelial riboflavin penetration in an ex vivo rabbit model. 21 Iontophoresis with higher concentrations of riboflavin, greater electrical current, and longer contact times was successful at overcoming the barrier effect of intact epithelium in rabbit corneas. 21 This provides an efficient alternative to the Dresden protocol.…”

“…This is confirmed by the congruence of our findings with those previously reported for the rabbit with different methodologies. 21,22 A further limitation is the fact that the riboflavin penetration depth was not determined quantitatively. That is, the penetration depth was determined by a visual assessment of where the fluorescence intensity appeared to decrease by 50%.…”