Iontophoresis transcorneal delivery technique for transepithelial corneal collagen crosslinking with riboflavin in a rabbit model

Abstract

Purpose: To evaluate a new iontophoresis transcorneal riboflavin delivery technique for transepithelial corneal collagen crosslinking (CXL).

Methods: ANIMALS: A total of 108 eyes from New Zealand white albino rabbits were included in this study. Corneas after riboflavin application by iontophoresis (n=25) were compared with corneas treated by conventional riboflavin application after de-epithelialization (n=16). Then I-CXL (n=18) was compared with C-CXL (n=9) 14 days after treatment. All these groups were compared with specific controls (n=40). METHODS: Iontophoresis involved the administration of a new formulation of charged riboflavin (Ricrolin® +) into cornea by applying a current of 1mA for 5 min. C-CXL was performed according to the Dresden protocol. MAIN OUTCOMES: Riboflavin diffusion in the eyes was investigated by two-photon microscopy in corneas and by high-performance liquid chromatography (HPLC) in corneas and aqueous humors. Stromal collagen structure modifications were analyzed using second harmonic generation imaging (SHG). Riboflavin diffusion in corneas was analyzed by measuring riboflavin emission at 500-550 nm with a two-photon microscope on corneal sections and riboflavin concentration in corneas and aqueous humors was measured by HPLC. Corneal stromal modifications were evaluated by analyzing the collagen fiber organization through SHG using a two-photon microscope.

Results: Images from two-photon microscope showed that after iontophoresis, riboflavin fluorescence and its diffusion throughout cornea were similar to that observed in a conventional application. In parallel, iontophoresis showed no more toxicity in the corneal epithelium than conventional application of riboflavin. Using HPLC, the corneal concentration of riboflavin was two-fold less after iontophoresis than after conventional application (936.2 ± 312.5 ng/ml and 1708 ± 908.3 ng/ml, respectively, p<0.05). Z-stack imaging using SHG showed that collagen fibers were more strongly interlinked, with a higher, lamellar organization in the anterior stroma 14 days after I-CXL or C-CXL as compared to controls.

Conclusions: This experimental study suggests that I-CXL is a promising alternative methodology for riboflavin delivery in crosslinking treatment, preserving the epithelium.

Keywords: 574 keratoconus