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J Biomech. 2019 Aug 27;93:209-212. doi: 10.1016/j.jbiomech.2019.06.011. Epub 2019 Jun 27.

Two-year changes in corneal stiffness parameters after accelerated corneal cross-linking.

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Noor Research Center for Ophthalmic Epidemiology, Noor Eye Hospital, Tehran, Iran.
Rio de Janeiro Corneal Tomography and Biomechanics Study Group, Rio de Janeiro, RJ, Brazil; Federal University of the State of Rio de Janeiro (UNIRIO), Brazil.
St Paul's Eye Unit, Royal Liverpool and Broadgreen University Hospital, Liverpool, United Kingdom.
Humanitas University, Department of Biomedical Sciences, Pieve Emanuele Milan, Italy; Humanitas Clinical and Research, Rozzano, Italy.
Department of Ophthalmology & Visual Science, Department of Biomedical Engineering, The Ohio State University, Columbus, OH, USA.
Eye Research Center, Farabi Eye Hospital, Tehran University of Medical Sciences, Tehran, Iran.
Noor Ophthalmology Research Center, Noor Eye Hospital, Tehran, Iran. Electronic address:


The objective of this non-randomized trial was comparison of two-year changes in dynamic corneal response (DCR) between 18 mW/cm2 (5- min) and 9 mW/cm2 (10-min) cross-linking (CXL) protocols, using novel stiffness parameters and correlating them to clinical indices. The two groups were evaluated before and 2 years after the procedure using Corvis ST (Oculus Optikgeräte GmbH, Germany) and DCR parameters such as deformation amplitude ratio at 1 mm and 2 mm (DA ratio-1 mm and DA ratio-2 mm) and integrated radius and stiffness parameters at A1 (SP-A1). Two-year follow-up was completed for 16 of the 30 eyes in the 5-min group and 21 of the 25 eyes in the 10-min group; data from those who were lost to follow-up was not included in the analyses. Mean age at baseline was 21.7 ± 4.9 and 21.5 ± 5.2 years in the 5- and 10-min groups, respectively (P = 0.895). At 2 years after CXL, in the 5-min group, the reduction in integrated radius (-1.12 ± 1.27 mm, P = 0.003) was significant, and the increase in SP-A1 (7.11 ± 14.86 mmHg/mm, P = 0.075) was borderline, while in the 10-min group, the decrease in DA ratio-2 mm (-0.43 ± 0.58, P = 0.003) and integrated radius (-1.89 ± 1.72 mm, P < 0.001), and increase in SP-A1 (7.67 ± 10.92 mmHg/mm, P = 0.004) were significant. In both groups, the strongest and significant correlation was observed between DCR parameters and changes in radius of curvature. In conclusion, results indicated corneal strengthening with both protocols especially with the 9 mW/cm2. Corvis ST indices can provide "in vivo" biomechanical evidence on the efficacy of CXL that may occur prior to clinical indices.


18 mW/cm(2) protocol; 9 mW/cm(2) protocol; Accelerated corneal cross-linking; Corneal stiffness; Dynamic corneal response

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