Noninvasive real-time assessment of riboflavin consumption in standard and accelerated corneal crosslinking

Purpose: To estimate non-invasively riboflavin concentration in the corneal stroma using a novel UV-A theranostic device for corneal cross-linking. Methods: Fourteen human donor corneas were treated according to the conventional (UV-A irradiance of 3 mW/cm2 for 30 minutes) and rapid (10 mW/cm2 for 9 minutes) riboflavin/UV-A corneal cross-linking protocols using a theranostic UV-A device. A 20% dextran-enriched 0.1% riboflavin solution was used in all cases. The device consisted of a UV-A light source, a RGB camera, which acquires the fluorescence images of the cornea during treatment, and a single board computer for managing the overall operations and the raw data processing. Results: Preirradiation stromal soaking for 30 minutes achieved highly consistent intrastromal riboflavin concentration in all tissues (0.015%±0.003%). There were no differences between the kinetics curves of riboflavin consumption of the two UV-A irradiation protocols; intrastromal riboflavin concentration decreased exponentially with a constant energy rate of 2.8±0.2 J/cm2. Conclusion: In the 3-10 mW/cm2 range of power densities, the consumption of riboflavin in the stroma by UV-A irradiation is only energy dependent in accordance with the Bunsen-Roscoe law. The theranostic device was effective in estimating the intrastromal concentration of riboflavin non-invasively during treatment.