Peer-reviewed

Corneal cross-linking: Intrastromal riboflavin concentration in iontophoresis-assisted imbibition versus traditional and transepithelial techniques – Accepted Manuscript

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Abstract: Purpose: The present study aimed at determining differences in riboflavin concentration in the anterior, intermediate and posterior stroma after three corneal cross-linking imbibition techniques (standard Epi-off, Epi-on and Iontophoresis-assisted administration) of 0.1% riboflavin.Design: Experimental laboratory investigation of human cadaver corneas not suitable for transplantation.Methods: 10 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 three 8mm discs of the superficial (0-150μm), intermediate (150-300μm) and deep stroma (>300μm). Riboflavin concentration was measured with High-Performance Liquid Chromatography. The main outcome measure was riboflavin concentration at the three evaluated depths.Results: The overall stromal concentration of riboflavin was 34.1±7.1 μg/g in Epi-off, 7.2±3.7 μg/g in Epi-on and 15.0±5.1 μg/g in Iontophoresis. The mean riboflavin content in the superficial slice in the Epi-off group was about two-fold greater than that of the Iontophoresis group (50.5±5.3 μg/g and 23.6±2.5 μg/g, respectively) and four-fold greater than that of the Epi-on group (11.7±3.3 μg/g). Similar differences among the three 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<0.001), as was the group-dependent variation (GLM; F2,6=20.268, p=0.002) and the slice depth-group interaction (GLM; F2,6=18.004, p=0.002).Conclusions: Corneal cross-linking transepithelial ionotphoresis 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.