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David Tabibian, Sabine Kling, Arthur Hammer, Olivier Richoz, Farhad Hafezi; No additional biomechanical effect of CXL after repeated in vivo treatment in mice. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):1136.
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© ARVO (1962-2015); The Authors (2016-present)
To analyze and compare corneal biomechanics of single and multiple corneal cross-linking in the mouse eye.
The corneas of C57BL/6 mice were divided into in two groups. In the first group, corneas were cross-linked once (day 1), in the second group a second CXL was performed at 72 hours (day 4) after the initial procedure (n=3 each). Untreated corneas served as controls (n=3). Biomechanical measurements were performed at day 7. The CXL procedure was adapted to the anatomy of the mouse eye, using 0.27%-riboflavin for 20 minutes and UVA irradiation (365 nm, 9mW/cm2) for 2:50 minutes in an epi-off procedure. After irradiation, mice were sacrificed, corneas were excised and mounted on a customized 2D-flap-holder. The biomechanical measurement consisted of three parts: (i) pre-conditioning, (ii) stress relaxation during 120 s and (iii) stress-strain curve until break.
After a relaxation period of 120 seconds, highly significant (p<0.001) differences in the stress-strain curves were found between controls and single cross-linked corneas. No significant differences (p=0.70) were measured between 1x and 2x cross-linked corneas. The stress remaining after relaxation was 355 ± 25.2 kPa in riboflavin controls, 457 ± 34.1 kPa in 1x cross-linked corneas and 463 ± 22.2 kPa in 2x cross-linked corneas.
Repeated cross-linking does not further increase corneal biomechanical stiffness in the mouse cornea in vivo. This might indicate that the stiffness of the cornea cannot be arbitrarily augmented over certain levels.
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