title: Assessment of UVA-Riboflavin Corneal Cross-Linking Using Small Amplitude Oscillatory Shear Measurements.
abstract: OBJECTIVE
  The effect of ultraviolet (UV)-riboflavin cross-linking (CXL) has been measured primarily using the strip extensometry technique. We propose a simple and reliable methodology for the assessment of CXL treatment by using an established rheologic protocol based on small amplitude oscillatory shear (SAOS) measurements. It provides information on the average cross-link density and the elastic modulus of treated cornea samples.
  
  
  METHODS
  Three fresh postmortem porcine corneas were used to study the feasibility of the technique, one serving as control and two receiving corneal collagen cross-linking treatment. Subsequently, five pairs of fresh postmortem porcine corneas received corneal collagen cross-linking treatment with riboflavin and UVA-irradiation (370 nm; irradiance of 3 mW/cm2) for 30 minutes (Dresden protocol); the contralateral porcine corneas were used as control samples. After the treatment, the linear viscoelastic moduli of the corneal samples were measured using SAOS measurements and the average cross-linking densities extracted.
  
  
  RESULTS
  For all cases investigated, the dynamic moduli of the cross-linked corneas were higher compared to those of the corresponding control samples. The increase of the elastic modulus of the treated samples was between 122% and 1750%. The difference was statistically significant for all tested samples (P = 0.018, 2-tailed t-test).
  
  
  CONCLUSIONS
  We report a simple and accurate methodology for quantifying the effects of cross-linking on porcine corneas treated with the Dresden protocol by means of SAOS measurements in the linear regime. The measured dynamic moduli, elastic and viscous modulus, represent the energy storage and energy dissipation, respectively. Hence, they provide a means to assess the changing physical properties of the cross-linked collagen networks after CXL treatment.
authors.affiliation: Emmetropia Mediterranean Eye Clinic Crete, Greece.
authors.forename: Ioannis M
authors.initials: IM
authors.lastname: Aslanides
authors.affiliation: Department of Materials Science and Technology, University of Crete, and Institute of Electronic Structure & Laser, Foundation for Research and Technology Hellas (FORTH), Crete, Greece.
authors.forename: Claudia
authors.initials: C
authors.lastname: Dessi
authors.affiliation: Emmetropia Mediterranean Eye Clinic Crete, Greece.
authors.forename: Panagiotis
authors.initials: P
authors.lastname: Georgoudis
authors.affiliation: Department of Chemistry, Laboratory of Bioinorganic Chemistry, University of Crete, Crete, Greece.
authors.forename: Georgios
authors.initials: G
authors.lastname: Charalambidis
authors.affiliation: Department of Materials Science and Technology, University of Crete, and Institute of Electronic Structure & Laser, Foundation for Research and Technology Hellas (FORTH), Crete, Greece.
authors.forename: Dimitris
authors.initials: D
authors.lastname: Vlassopoulos
authors.affiliation: Department of Chemistry, Laboratory of Bioinorganic Chemistry, University of Crete, Crete, Greece.
authors.forename: Athanassios G
authors.initials: AG
authors.lastname: Coutsolelos
authors.affiliation: Department of Ophthalmology, School of Medicine, University of Athens, Athens, Greece.
authors.forename: George
authors.initials: G
authors.lastname: Kymionis
authors.affiliation: Emmetropia Mediterranean Eye Clinic Crete, Greece 5Cardiff University School of Optometry, South Glamorgan, United Kingdom.
authors.forename: Achyut
authors.initials: A
authors.lastname: Mukherjee
authors.affiliation: Department of Chemistry, University of Crete, and Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas, Crete, Greece.
authors.forename: Theofanis N
authors.initials: TN
authors.lastname: Kitsopoulos
mesh_terms: D000818:Animals; D003094:Collagen / Q000378:metabolism; D003315:Cornea / Q000378:metabolism* / Q000502:physiology / Q000528:radiation effects; D004548:Elasticity / Q000502:physiology / Q000528:radiation effects; D012256:Riboflavin / Q000378:metabolism*; D033081:Shear Strength / Q000502:physiology / Q000528:radiation effects; D013552:Swine; D014466:Ultraviolet Rays; D014783:Viscosity / Q000528:radiation effects
chemical_list: D003094:Collagen; D012256:Riboflavin