Assessment of stromal riboflavin concentration-depth profile in nanotechnology-based transepithelial corneal crosslinking

Purpose: To determine the intrastromal concentration of riboflavin in nanotechnology-based transepithelial corneal crosslinking. Setting: Consiglio Nazionale delle Ricerche, Messina, Italy. Design: Experimental study. Methods: Six human donor sclerocorneal tissues were used to evaluate penetration of nanotechnology-based riboflavin 0.1% solution in the stroma through the intact epithelium. Three additional tissues were deepithelialized and soaked with dextran 20.0%-enriched riboflavin 0.1% solution for 30 minutes. After corneal soaking with riboflavin, all tissues were irradiated using a 10 mW/cm2 device for 9 minutes. Two-photon emission fluorescence (TPEF) axial scanning measurements were collected in all specimens before treatment and immediately after corneal soaking with riboflavin and ultraviolet-A (UVA) irradiation of the cornea. The absorbance spectra of each tissue were collected at the same time intervals. The TPEF signals and absorbance spectra were used to calculate the concentration-depth profile of riboflavin in the corneal stroma during treatments. Results: The mean stromal riboflavin concentration was 0.008%G0.003% (SD) and 0.017%G0.001% after transepithelial soaking with the nanotechnology-based solution and standard soaking, respectively (P Z .001). After UVA irradiation of the cornea, the mean consumption of riboflavin was 52% G 13% and 67% G 2% in the study group and control group, respectively (P < .01). Conclusions: The nanotechnology-based platform was effective in enriching the anterior stroma with riboflavin through the intact epithelium, although the riboflavin concentration-depth profile rapidly decreased across the mid and posterior stroma. The treatment-induced stiffening effect on the corneal stroma was not assessed in this study.