Purpose:
To determine the feasibility of dosimetry by measuring riboflavin fluorescence as it diffuses in real time through a cornea, using a UVA-illumination slit and a camera with a filter.
Methods:
A UVA LED source illuminates a digital micromirror device (DMD) which then images a straight vertical slit onto a porcine eye. A camera (Basler acA1300-30gm) mounted with a long-pass filter is placed at a 45° angle to the eye. The camera detects the fluorescence of riboflavin through the cross-section of the cornea. Three porcine eyes with and 3 without epithelium are soaked with riboflavin solutions for different lengths of time and images are taken at regular intervals.
Results:
Cross-sectional images of the cornea show the diffusion of the riboflavin through the corneal thickness. Using ImageJ software (NIH), intensity profiles are plotted vs. corneal depth. Using Igor software (Wavemetrics, Inc.), a curve fitting is performed using the solution to Fick’s 2nd law of diffusion: Conc = C*[erfc(x/(2√Dt))] where C is initial concentration at boundary, is corneal depth, D is diffusion coefficient and t is time needed for diffusion. The software does the fit and calculates the best value for C and D. D Values obtained are comparable to those obtained using a Franz cell, showing this method accurately measures diffusion of riboflavin.
Conclusions:
Fluorescence measurements of riboflavin diffusing through cornea are used to calculate diffusion coefficients. This method can be implemented in a clinical device to accurately monitor real time riboflavin diffusion through the cornea, thus making it possible to more precisely deliver a particular dose during a cross-linking procedure and reduce dosage variance between patients.
Keywords: photodynamic therapy • imaging/image analysis: clinical • keratoconus