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

Abstract

To estimate the noninvasive riboflavin concentration in the corneal stroma using a new ultraviolet-A (UVA) theranostic device for corneal crosslinking (CXL). Vision Engineering Italy srl, Rome, Italy. Experimental study. Fourteen human donor corneas were treated according to conventional (UVA irradiance of 3mW/cm2 for 30minutes) and rapid (10mW/cm2 for 9minutes) riboflavin-UVA CXL protocols using a theranostic UVA device. Five additional samples were treated by 0.5mW/cm2 for 9minutes and used as positive controls to determine riboflavin photodegradation under near ambient lighting conditions. A 20% dextran-enriched 0.1% riboflavin solution was used in all cases. The device consisted of a UVA light source; a red-green-blue 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. Preirradiation stromal soaking for 30minutes achieved highly consistent intrastromal riboflavin concentration in all tissues (mean 0.015%±0.003% [SD]). There were no differences in thekinetics curves of riboflavin consumption between the 2 UVA irradiation protocols; the intrastromal riboflavin concentration decreased exponentially, with a mean constant energy rate of 2.8±0.2J/cm2. In the control group, the intrastromal riboflavin concentration decreased quasilinearly. The theranostic device provided estimates of the intrastromal concentration of riboflavin noninvasively during treatment. In the 3 to 10mW/cm2 range of power densities, the consumption of riboflavin in the stroma by UVA irradiation was only energy dependent in accordance with the Bunsen-Roscoe law.