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A. P. Soendergaard, J. Hjortdal, M. Misfeldt, A. Ivarsen; Corneal Distribution of Riboflavin Prior to Collagen Cross-Linking. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5468.
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To evaluate the distribution of riboflavin in the corneal stroma prior to UVA-induced collagen cross-linking.
In porcine eyes, the central corneal epithelium was removed, and 0.1% riboflavin-5-phosphate (dissolved in 20% Dextran T-500) was applied to the stromal surface for 5, 10, or 20 minutes (4 corneas in each group). The central 7.5-mm cornea was trephined, and the corneal buttons were placed on glass slides for immediate laser-scanning confocal microscopic examination. Using an excitation wavelength of 458 nm, average fluorescence intensity above 530 nm was recorded at 10 µm intervals through the thickness of the specimen. The riboflavin concentration in corneal stroma was estimated from fluorescence intensities of standardized solutions of riboflavin. Intensity profiles were generated by plotting average fluorescence as a function of depth. Background fluorescence was determined in 4 untreated corneas.
Average corneal thickness was 846 ± 34 µm as determined with optical pachymetry. A linear correlation between measured fluorescence intensity and riboflavin concentration was observed in standardized concentrations (R2 = 0.95, p = 0.02). In riboflavin treated corneas fluorescence intensity peaked within the first 150 µm followed by a steep decline to baseline (Figure). Longer riboflavin treatment times caused only slightly more fluorescence in deeper corneal layers. Background fluorescence could not be detected in untreated corneas.
The distribution of riboflavin appears to be predominantly located to the anterior 150 µm stroma, even after 20 minutes application. Surprisingly, the application time seems to have little influence on the depth of riboflavin penetration into the corneal stroma.
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