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Arthur Hammer, Olivier Richoz, Samuel Arba Mosquera, David Tabibian, Florence Hoogewoud, Farhad Hafezi; Corneal Biomechanical Properties at Different Corneal Cross-Linking (CXL) Irradiances. Invest. Ophthalmol. Vis. Sci. 2014;55(5):2881-2884. doi: https://doi.org/10.1167/iovs.13-13748.
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New corneal cross-linking (CXL) devices are capable of using higher UV-A light irradiances than used in original CXL protocols. The Bunsen-Roscoe law states that a photochemical reaction should stay constant if the delivered total energy is kept constant; however, little clinical data are available to support this hypothesis.
We investigated the biomechanical properties of four groups (n = 50 each) of porcine corneas. Three groups were exposed to riboflavin 0.1 % and UV-A irradiation of equal total energy (3 mW/cm2 for 30 minutes, 9 mW/cm2 for 10 minutes, and 18 mW/cm2 for 5 minutes). Controls were exposed to riboflavin 0.1% without irradiation. Young's modulus of 5-mm wide corneal strips was used as an indicator of corneal stiffness.
We observed a decreased stiffening effect with increasing UV-A intensity. Young's modulus at 10% strain showed significant differences between 3 mW/cm2 and 9 mW/cm2 (P = 0.002), 3 mW/cm2 and 18 mW/cm2 (P = 0.0002), 3 mW/cm2 and the control group (P < 0.0001), and 9 mW/cm2 and the control group (P = 0.015). There was no difference between 18 mW/cm2 and the control group (P = 0.064) and between 9 mW/cm2 and 18 mW/cm2 (P = 0.503).
The biomechanical effect of CXL decreased significantly when using high irradiance/short irradiation time settings. Intrastromal oxygen diffusion capacity and increased oxygen consumption associated with higher irradiances may be a limiting factor leading to reduced treatment efficiency. Our results regarding the efficiency of high-irradiance collagen cross-linking (CXL) raise concerns about the clinical efficiency of the new high-irradiance CXL devices already used in clinical practice without proper validation.
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