Thermomechanical behavior of collagen-cross-linked porcine cornea.
OBJECTIVE
Collagen cross-linking using combined riboflavin/UVA treatment has been shown to increase the biomechanical rigidity of the cornea and has been used successfully for the treatment of progressive keratoconus. From morphological and biochemical investigations, a different degree of cross-linking for the anterior and posterior stroma by the treatment is suggested. The present study was undertaken to better evaluate this effect by testing the thermomechanical behavior.


METHODS
Ten 10 x 5 mm corneal strips from porcine cadaver eyes enucleated within 5 h post mortem were cross-linked using the photosensitizer riboflavin and UVA irradiation (370 nm, irradiance = 3 mW/cm(2)) for 30 min and compared to ten untreated corneal strips and ten corneal strips cross-linked with 0.1% glutaraldehyde. The temperature in a water bath was raised from 60 to 95 degrees C with temperature increments of 1 degrees C per minute. The hydrothermal shrinkage of the corneal strips was measured in 2.5 degrees C steps using a micrometer. In addition, six 10-mm whole corneal buttons were cross-linked with riboflavin/UVA and immersed into water at 70 or 75 degrees C.


RESULTS
The maximal hydrothermal shrinkage for the untreated control specimens and the posterior portion of the riboflavin/UVA-treated corneas was at 70 degrees C, for the anterior portion of the cornea cross-linked by riboflavin/UVA at 75 degrees C and for glutaraldehyde-cross-linked cornea at 90 degrees C. In the cross-linked corneal buttons, a typical mushroom-like shape was observed at 70 degrees C and a cylinder shape at 75 degrees C.


CONCLUSIONS
The different degree of collagen cross-linking in the corneal stroma after riboflavin/UVA treatment is reflected by the differences in the maximal shrinkage temperature of the anterior and posterior portion. Therefore, in the corneas cross-linked with riboflavin/UVA a higher shrinkage temperature was observed for the anterior portion of the cornea (75 degrees C) compared to the posterior stroma (70 degrees C) due to the higher degree of cross-linking of the anterior stroma. The anterior localization of the cross-linking effect is advantageous for the endothelium and for the preservation of the anterior corneal curvature.
Spoerl
Eberhard
E
Department of Ophthalmology, Universitätsklinikum CGC, Dresden, Germany. eberhard.spoerl@uniklinikum-dresden.de
Wollensak
Gregor
G
Dittert
Dag-Daniel
DD
Seiler
Theo
T
D000818:Animals; D003094:Collagen / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D003315:Cornea / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D003432:Cross-Linking Reagents / Q000494:pharmacology; D004548:Elasticity; D005976:Glutaral / Q000494:pharmacology; D006358:Hot Temperature; D017319:Photosensitizing Agents; D012256:Riboflavin / Q000494:pharmacology; D013314:Stress, Mechanical; D013552:Swine; D014466:Ultraviolet Rays
D003432:Cross-Linking Reagents; D017319:Photosensitizing Agents; D003094:Collagen; D005976:Glutaral; D012256:Riboflavin