Long-term biomechanical properties of rabbit cornea after photodynamic collagen crosslinking.
OBJECTIVE
Photodynamic riboflavin/ultraviolet-A (UVA)-induced collagen cross-linking, which increases the biomechanical stiffness of the human cornea by about 300%, has been introduced recently as a possible treatment for progressive keratoconus. The present study was undertaken to evaluate the longterm biomechanical effects of this new cross-linking treatment as a necessary prerequisite to its clinical success.


METHODS
The corneas of the left eyes of nine male rabbits were cross-linked. The contralateral eyes served as controls. After removal of the central 7 mm of the epithelium, the corneas were treated with the photosensitizer riboflavin and UVA irradiation for 30 mins with an irradiance of 3 mW/cm(2) using a 370-nm UVA double diode. Groups of three animals were killed immediately after treatment and at 3 and 8 months, respectively. Biomechanical stress-strain measurements were performed using a microcomputer-controlled biomaterial tester on 4 x 10-mm corneal strips.


RESULTS
Corneal thickness in the treated rabbit cornea was 408 +/- 20 microm. A constant and significant increase in ultimate stress (of 69.7-106.0%), Young's modulus of elasticity (of 78.4-87.4%) and a decrease in ultimate strain (of 0.57-78.4%) were found over a time period of up to 8 months after cross-linking treatment.


CONCLUSIONS
Riboflavin/UVA-induced collagen cross-linking leads to a longterm increase in biomechanical rigidity which remains stable over time. These data support our previous longterm clinical observations and give hope that this new treatment will halt progressive keratoconus definitively.
Eye Laser Center, Department of Ophthalmology, Martin-Luther-University, Halle, Germany. gwollens@hotmail.com
Gregor
G
Wollensak
Elena
E
Iomdina
D000818:Animals; D001696:Biomechanical Phenomena; D003094:Collagen / Q000378:metabolism*; D003315:Cornea / Q000502:physiology*; D008297:Male; D010778:Photochemotherapy; D017319:Photosensitizing Agents / Q000627:therapeutic use*; D011817:Rabbits; D012256:Riboflavin / Q000627:therapeutic use*; D014466:Ultraviolet Rays
D017319:Photosensitizing Agents; D003094:Collagen; D012256:Riboflavin