Corneal Cross-linking: Intrastromal Riboflavin Concentration in Iontophoresis-Assisted Imbibition Versus Traditional and Transepithelial Techniques

PURPOSE: To determine differences in riboflavin concentration in the anterior, intermediate, and posterior stroma after 3 corneal cross-linking imbibition techniques (standard epithelial [epil-off, epi-on, and iontophoresis-assisted administration) of 0.1% riboflavin. DESIGN: Experimental laboratory investigation of human cadaver corneas not suitable for transplantation. METHODS: Ten corneas underwent imbibition with epi-on (n = 3), epi-off (n = 3), iontophoresis (n = 3), and saline exposure (control; n = 1). Femtosecond laser was used to produce 3 8-mm discs of the superficial' (0150 p.m), intermediate (150-300 mu m), and deep stroma ( > 300 gm). Riboflavin concentration was measured with high-performance liquid chromatography. The main outcome measure was riboflavin concentration at the 3 evaluated depths. RESULTS: The overall stromal concentration of riboflavin was 34.1 +/- 7.1 nig in epi-off, 7.2 +/- 3.7 mu g/g in epi-on, and 15.0 +/- 5.1 mu g/g in iontophoresis. The mean riboflavin content in the superficial slice in the epi-off group was about 2-fold greater than that of the iontophoresis group (50.5 +/- 5.3 mu g/g and 23.6 +/- 2.5 mu g/g, respectively) and 4-fold greater than that of the epi-on group (11.7 +/- 3.3 mu g/g). Similar differences among the 3 groups were observed for the intermediate and posterior stromal slices, presenting an evident reduction of riboflavin concentration with increasing depth in all groups. Slice depth-dependent decrease in riboflavin concentration was statistically significant (general linear model (GLM); F1,6 = 62.265, P < .001), as was the group-dependent variation (GLM; F2,6 = 20.268, P = .002) and the slice depth group interaction (GLM; F2,6 = 18.004, P = .002). CONCLUSIONS: Corneal cross-linking transepithelial iontophoresis imbibition yielded greater and deeper riboflavin saturation with respect to conventional epi-on, while maintaining the advantages of avoiding epithelial removal and shorter procedure time, but did not reach concentrations obtained with standard epi-off.