Loss of Tryptophan Fluorescence Correlates With Mechanical Stiffness Following Photo-Crosslinking Treatment of Rabbit Cornea.

Purpose: A clinical treatment option for keratoconus involves the use of UV-initiated photo-crosslinking with riboflavin to increase corneal stiffness. Our study investigates whether endogenous fluorescence changes following treatment for keratoconus can be correlated to alterations in the stiffness of the cornea, thereby guiding treatment of keratoconus.

Methods: A total of 78 ex vivo rabbit eyes were treated with either riboflavin-dextran solution plus UV light, dextran solution plus UV light, or riboflavin-dextran solution only for half treatment (2.84 J/cm2), standard treatment (5.28 J/cm2), or prolonged treatment (15.84 J/cm2) times. Fluorescent spectroscopy was performed on all samples before and after treatment. The stress-strain relationship was measured for all samples using a uniaxial tensiometer following treatment.

Results: We found a dose-dependent decrease in the 290/340 nm excitation/emission fluorescence pair with increase in corneal stiffening following treatment that was significant (P < 0.01) for both standard (5.28 J/cm2 total fluence) and prolonged treatment (15.84 J/cm2) times. We did not observe a significant change in this excitation/emission pair for the dextran-plus-UV or riboflavin-only treatment groups.

Conclusions: Loss of fluorescence intensity at the 290/340 nm excitation/emission pair could offer a noninvasive, in situ measurement for guiding the photo-crosslinking treatment of keratoconus. Larger relative decreases in this pair are significantly correlated with longer treatment times and with increases in stiffness and Young's modulus.