title: Biomechanical property analysis after corneal collagen cross-linking in relation to ultraviolet A irradiation time.
abstract: OBJECTIVE
  To study the biomechanical effect of riboflavin-ultraviolet A irradiation (UVA)-induced collagen cross-linking (CXL) in porcine corneas using two different exposure times of 30 and 60 min.
  
  
  METHODS
  Seventeen enucleated porcine eyes were divided into three groups: group A, six eyes without any treatment, group B, six eyes treated by UVA CXL for 30 min, and group C, five eyes treated by UVA CXL for 60 min. Riboflavin (vitamin B2) was used as a photosensitizer in both groups of treatment. Then, the stress-strain behavior of all the specimens was measured to compare the corneal biomechanical properties among the three groups. The Young's modulus E of the mean curve of each group shows the stiffness of treated and untreated tissue. The stress data necessary for stretches of 6, 8, and 12% were used to perform the statistical analysis of the values.
  
  
  RESULTS
  Group B (riboflavin-UVA-CXL, 30 min, E = 46 MPa) showed a stiffer behavior than group A (control, E = 29 MPa) . Group C (60 min CXL, E = 28 MPa) showed lower stiffness than group B and a similar mechanical behavior than group A. The statistical analysis of the stress-strain curves showed significant differences in the corneal response between group B and the control at the three values of stretch considered, 6, 8, and 12% (p = 0.025, p = 0.025 and p = 0.037, respectively) and between group B and group C (p = 0.028, p = 0.028, and p = 0.028). No statistically significant difference was found between group C and control (p = 0.855, p = 0.715, and p = 0.584).
  
  
  CONCLUSIONS
  The application of 30-min UVA CXL treatment with riboflavin increased stiffness of the porcine corneal tissue. A 60-min UVA-radiated tissue presents lower stiffness than the 30-min treated tissue, showing a similar biomechanical behavior than the untreated corneas. A prolongation of the UVA irradiation time may cause structural weakening of the porcine corneas.
authors.affiliation: Group of Structural Mechanics and Materials Modelling, Aragón Institute of Engineering Research (I3A), Mechanical Engineering Department, University of Zaragoza, María de Luna 3, 50018, Zaragoza, Spain. elanchar@unizar.es
authors.forename: Elena
authors.initials: E
authors.lastname: Lanchares
authors.forename: María Angeles
authors.initials: MA
authors.lastname: del Buey
authors.forename: José Angel
authors.initials: JA
authors.lastname: Cristóbal
authors.forename: Laura
authors.initials: L
authors.lastname: Lavilla
authors.forename: Begoña
authors.initials: B
authors.lastname: Calvo
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena / Q000502:physiology; D003094:Collagen / Q000378:metabolism*; D003315:Cornea / Q000378:metabolism* / Q000528:radiation effects; D003319:Corneal Stroma / Q000378:metabolism / Q000528:radiation effects; D003432:Cross-Linking Reagents / Q000378:metabolism*; D004548:Elasticity / Q000502:physiology*; D017319:Photosensitizing Agents / Q000627:therapeutic use*; D011446:Prospective Studies; D012256:Riboflavin / Q000627:therapeutic use*; D013552:Swine; D013718:Tensile Strength / Q000502:physiology; D013997:Time Factors; D016896:Treatment Outcome; D014466:Ultraviolet Rays
chemical_list: D003432:Cross-Linking Reagents; D017319:Photosensitizing Agents; D003094:Collagen; D012256:Riboflavin