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Sabine Kling, David Tabibian, Olivier Richoz, Arthur Hammer, Amar Agarwal, Soosan Jacob, Farhad Hafezi; Biomechanical Efficacy of UV Cross-Linking Protocols in Thin versus Thick Corneas: The Effect of Oxygen, UV Absorption and Osmotic Pressure. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):1137.
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© ARVO (1962-2015); The Authors (2016-present)
To compare the current clinically used UV corneal cross-linking (CXL) treatment protocols for thin corneas with respect to oxygen, UV fluence and osmotic pressure.
Freshly enucleated murine (N=25) and porcine (N=38) eyes were used to study the effect of corneal thickness in the CXL treatment. The dependency on oxygen and the amount of UV absorption were evaluated for various epithelium-off CXL protocols, including standard CXL, contact lens assisted CXL, CXL after corneal swelling, contact lens control and riboflavin control. Treatment parameters were adapted according to the corneal thickness of the species used. Immediately after CXL, corneas were subjected to biomechanical testing, including pre-conditioning, stress-relaxation at 0.6 MPa and stress-strain extensiometry. A two-element Prony series was fitted to the relaxation curve for viscoelastic characterization.
Standard CXL was biomechanically most efficient; prior corneal swelling and CACXL reduced the long-term modulus by 6% and 15-20%, respectively. Oxygen reduction decreased the G∞ modulus by 14-15%, the G0 modulus by 2-5% and increased the G2 modulus by 22-31%. Reducing the amount of absorbed UV-energy decreased the G∞ modulus by 5-34%, the G0 modulus by 7-29% and the G2 modulus by 17-20%. The amount of absorbed UV-light was more important in porcine than in murine corneas.
Thin corneas have a higher oxygen availability, which potentially increases the efficacy of CXL. Clinical protocols for thin corneas should be revised to take advantage of this finding.
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