title: Corneal resistance to shear force after UVA-riboflavin cross-linking.
abstract: OBJECTIVE
  We evaluated whether UVA-riboflavin collagen cross-linking (CXL) increases transverse stromal shear moduli ex vivo, whether the shear moduli are greater in the anterior compared to the posterior stroma, and whether the shear moduli are affected by CXL.
  
  
  METHODS
  The resistance to unidirectional transverse shear of human (n = 18) and porcine (n = 42) corneas was measured in a custom engineered biaxial biomechanical setup at different hydrations. The corneas were separated into untreated, riboflavin solution-treated, and CXL-treated groups. The depth dependency of shear moduli within groups was assessed in femtosecond laser cut sheets. Dry weights were obtained for solids correction.
  
  
  RESULTS
  In porcine full-thickness buttons and 300 μm anterior sheets, a significantly increased unidirectional transverse shear modulus was detected in riboflavin-treated and CXL-treated groups compared to the respective untreated groups. There was no significant difference in shear modulus between riboflavin- and CXL-treated groups. In all groups, the shear moduli were greater in the anterior sheets compared to posterior sheets. Similar results were detected in human corneas.
  
  
  CONCLUSIONS
  A method for unidirectional transverse shear resistance measurement was developed. The shear moduli were greater in the anterior compared to the posterior sheets. Increase in shear moduli was observed in the riboflavin and CXL groups compared to the untreated group, indicating that the immediate effects of the riboflavin or CXL treatment may be due partly to ground substance/dextran-5-phosphate interaction.
authors.affiliation: Department of Ophthalmology, Aarhus University Hospital, Aarhus, Denmark. anders@soendergard.dk
authors.forename: Anders P
authors.initials: AP
authors.lastname: Søndergaard
authors.forename: Anders
authors.initials: A
authors.lastname: Ivarsen
authors.forename: Jesper
authors.initials: J
authors.lastname: Hjortdal
mesh_terms: D000818:Animals; D003094:Collagen / Q000494:pharmacology*; D003315:Cornea / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D003432:Cross-Linking Reagents / Q000494:pharmacology*; D004548:Elasticity; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012256:Riboflavin / Q000494:pharmacology*; D033081:Shear Strength / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D013552:Swine; D014466:Ultraviolet Rays
chemical_list: D003432:Cross-Linking Reagents; D003094:Collagen; D012256:Riboflavin
keywords: CXL; UVA; biomechanics; collagen; cornea; cross-linking; riboflavin; shear force; shear modulus; swelling pressure