Laboratory measurement of the absorption coefficient of riboflavin for ultraviolet light (365 nm).
OBJECTIVE
Corneal cross-linking (CXL) is an increasingly used treatment technique for stabilizing the cornea in keratoconus. Cross-linking (polymerization) between collagen fibrils is induced by riboflavin (vitamin B2) and ultraviolet light (365 nm). Although reported to reach a constant value at higher riboflavin concentrations, the Lambert-Beer law predicts a linear increase in the absorption coefficient. This work was carried out to determine absorption behavior at different riboflavin concentrations and to further investigate the purported plateau absorption coefficient value of riboflavin and to identify possible bleaching effects.


METHODS
The Lambert-Beer law was used to calculate the absorption coefficient at various riboflavin concentrations. The following investigated concentrations of riboflavin solutions were prepared using a mixture of 0.5% riboflavin and 20% Dextran T500 dissolved in 0.9% sodium chloride solution: 0%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4%, and 0.5%, and were investigated with and without aperture plate implementation. An additional test series measured the transmitted power at selected riboflavin concentrations over time.


RESULTS
In diluted solutions, a linear correlation exists between the absorption coefficient and riboflavin concentration. The absorption coefficient reaches a plateau, but this occurs at a higher riboflavin concentration (0.1%) than previously reported (just above 0.04%). Transmitted light power increases over time, indicating a bleaching effect of riboflavin.


CONCLUSIONS
The riboflavin concentration can be effectively varied as a treatment parameter in a considerably broader range than previously thought.
Iseli
Hans Peter
HP
Institute of Ophthalmic Surgery, Zurich, Switzerland. hanspeter.iseli@iroc.ch
Popp
Max
M
Seiler
Theo
T
Spoerl
Eberhard
E
Mrochen
Michael
M
D000042:Absorption; D003094:Collagen / Q000378:metabolism; D003319:Corneal Stroma / Q000378:metabolism; D003432:Cross-Linking Reagents; D006801:Humans; D007640:Keratoconus / Q000188:drug therapy / Q000378:metabolism; D017319:Photosensitizing Agents / Q000528:radiation effects* / Q000627:therapeutic use; D012256:Riboflavin / Q000528:radiation effects* / Q000627:therapeutic use; D012542:Scattering, Radiation; D013057:Spectrum Analysis; D014466:Ultraviolet Rays
D003432:Cross-Linking Reagents; D017319:Photosensitizing Agents; D003094:Collagen; D012256:Riboflavin