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Farhad Hafezi, Sabine Kling; Low-fluence-slow-irradiation corneal cross-linking induces the same biomechanical stiffening as the standard Dresden protocol. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4343.
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Corneal cross-linking (CXL) protocols that are currently used clinically vary in intensity and time, but share the same total fluence of 5.4 J/cm2. Although this fluence is considered safe, reducing the UV fluence while maintaining biomechanical efficacy would be beneficial in two ways: it would further reduce radiation exposure, and it would allow to treat corneas thinner than 400 µm.
Thirty-four freshly enucleated porcine corneas were de-epithelialized and soaked with 0.1%-hypoosmolar riboflavin solution during 30 minutes. Low-fluence-slow-irradiation CXL (30 min at 1.5 mW/cm2, fluence 2.7 J/cm2) was compared to standard CXL (30 min at 3 mW/cm2, fluence 5.4 J/cm2). Controls were soaked with riboflavin, but not exposed to UV light. Elastic (stress-strain) and viscoelastic (stress-relaxation) bi-dimensional testing was performed with a commercial stress-strain extensometer to quantify the biomechanical stiffening effect.
Corneas cross-linked with low and standard UV intensities had a significantly (p<0.001) higher elastic modulus (65.9±15.7 MPa and 67.1±15.6 MPa, respectively) when compared to controls (52.4±12.3 MPa). Also, the remaining stress after 120s of stress-relaxation was significantly (p≤0.013) higher after CXL with low and standard UV intensities (159±21 kPa and 158±25 kPa, respectively) compared to controls (135±20 kPa). Between CXL conditions, no difference (p=0.64) was observed with low and standard intensities.
The UV fluence for CXL may be reduced while maintaining the biomechanical efficacy by using a lower UV intensity and the same irradiation duration. This may open alleys in the treatment of extremely thin corneas.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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