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Jeremy Wernli, Silvia Schumacher, Eberhard Spoerl, Michael Mrochen; The efficacy of corneal cross-linking shows a sudden decrease with very high intensity UV-light and short treatment time. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1611.
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Standard treatment in case of progressive keratectasia is UV-triggered corneal cross-linking. For irradiances larger than 10 mW/cm2 and treatment times below 10 min the scientific proof of a biomechanical strengthening effect is insufficient. The authors investigated the biomechanical strengthening of ex-vivo corneal tissue treated with irradiances between 3 mW/cm2 and 90 mW/cm2 and illumination times from 30 minutes to 1 minute, respectively.
100 porcine eyes received riboflavin+UV treatment (constant irradiation dose of 5.4 J/cm2) with different intensities and illumination times and were randomly assigned into 10 groups. A control group (80 eyes) was not irradiated but underwent the same treatment otherwise. Young’s modulus at 10% strain was determined for each strip after uniaxial stress-strain measurement. A Kruskall-Wallis test was used for statistical analysis.
A statistically significant difference (α=0.01) was found between the median value of Young’s modulus of the treatment groups up to 45 mW/cm2 (illumination times from 30 min to 2 min) compared to the control group. There was no statistically significant difference between the treatment groups from 50 mW/cm2 up to 90 mW/cm2 (illumination times of less than 2 min) and the control group.
The ex vivo results of corneal cross-linking performed in porcine corneas show that the Bunsen-Roscoe reciprocity law is only valid for illumination intensities up to 40 to 50 mW/cm2 and illumination times of more than 2 min. Further experiments are necessary to validate these results for in vivo human corneal tissue. Additionally, safety aspects at high intensities must be investigated.
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