In vitro effect of corneal collagen cross-linking on corneal hydration properties and stiffness.
BACKGROUND
The purpose of this study is to evaluate in-vitro the immediate effect of corneal collagen cross-linking (CXL) on corneal hydration and stiffness.


METHODS
Forty-two corneal buttons from freshly enucleated porcine eyes were immersed in riboflavin 0.1% in dextran 20% dilution for 3 h in order for their hydration to reach equilibrium. Corneal buttons where divided into two groups; the first group was stored in dark conditions while the other group was irradiated with UV radiation (370 nm) for 30 min to simulate CXL according to the clinically applied protocol. After irradiation, all corneas were immersed in dextran 20% solution for 3 additional hours. Subsequently, each button underwent weighing, thickness measurement, and was mounted in a special device for the measurement of force versus deformation by compression. Finally, all corneal buttons were dehydrated for 48 h in a desiccating oven set at 62 °C and weighed again to obtain their dry mass. Hydration (%) of each button was calculated.


RESULTS
Mean corneal hydration in the irradiated and the non-irradiated group of corneas was 69.8 and 72.2%, respectively (p < 0.001). Differences in thickness and compressibility were not statistically significant. Thickness and hydration were positively correlated (Pearson's r = 0.714, p < 0.001).


CONCLUSIONS
CXL causes corneal dehydration that can be detected immediately after the procedure. This phenomenon may contribute to increased mechanical stiffness of the cornea. A change in stiffness by means of compressibility could not be detected in porcine corneas.
Institute of Vision and Optics (IVO), University of Crete, Medical School, 71003, Heraklion, Crete, Greece. kontadas@yahoo.com
Georgios A
GA
Kontadakis
Harilaos
H
Ginis
Nikolaos
N
Karyotakis
Alexandros
A
Pennos
Iro
I
Pentari
George D
GD
Kymionis
Ioannis G
IG
Pallikaris
D000818:Animals; D001834:Body Water / Q000502:physiology*; D003094:Collagen / Q000378:metabolism*; D003315:Cornea / Q000502:physiology; D063171:Corneal Pachymetry; D003319:Corneal Stroma / Q000378:metabolism*; D003432:Cross-Linking Reagents / Q000494:pharmacology*; D004548:Elasticity / Q000502:physiology*; D017319:Photosensitizing Agents / Q000494:pharmacology; D018583:Pliability / Q000502:physiology*; D012256:Riboflavin / Q000494:pharmacology; D013552:Swine; D014466:Ultraviolet Rays; D014882:Water-Electrolyte Balance
D003432:Cross-Linking Reagents; D017319:Photosensitizing Agents; D003094:Collagen; D012256:Riboflavin