title: Riboflavin/UVA collagen cross-linking-induced changes in normal and keratoconus corneal stroma.
abstract: OBJECTIVE
  To determine the effect of Ultraviolet-A collagen cross-linking with hypo-osmolar and iso-osmolar riboflavin solutions on stromal collagen ultrastructure in normal and keratoconus ex vivo human corneas.
  
  
  METHODS
  Using small-angle X-ray scattering, measurements of collagen D-periodicity, fibril diameter and interfibrillar spacing were made at 1 mm intervals across six normal post-mortem corneas (two above physiological hydration (swollen) and four below (unswollen)) and two post-transplant keratoconus corneal buttons (one swollen; one unswollen), before and after hypo-osmolar cross-linking. The same parameters were measured in three other unswollen normal corneas before and after iso-osmolar cross-linking and in three pairs of swollen normal corneas, in which only the left was cross-linked (with iso-osmolar riboflavin).
  
  
  RESULTS
  Hypo-osmolar cross-linking resulted in an increase in corneal hydration in all corneas. In the keratoconus corneas and unswollen normal corneas, this was accompanied by an increase in collagen interfibrillar spacing (p<0.001); an increase in fibril diameter was also seen in two out of four unswollen normal corneas and one unswollen keratoconus cornea (p<0.001). Iso-osmolar cross-linking resulted in a decrease in tissue hydration in the swollen normal corneas only. Although there was no consistent treatment-induced change in hydration in the unswollen normal samples, iso-osmolar cross-linking of these corneas did result in a compaction of collagen fibrils and a reduced fibril diameter (p<0.001); these changes were not seen in the swollen normal corneas. Collagen D-periodicity was not affected by either treatment.
  
  
  CONCLUSIONS
  The observed structural changes following Ultraviolet-A cross-linking with hypo-osmolar or iso-osmolar riboflavin solutions are more likely a consequence of treatment-induced changes in tissue hydration rather than cross-linking.
authors.affiliation: Structural Biophysics Research Group, School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom.
authors.forename: Sally
authors.initials: S
authors.lastname: Hayes
authors.forename: Craig
authors.initials: C
authors.lastname: Boote
authors.forename: Christina S
authors.initials: CS
authors.lastname: Kamma-Lorger
authors.forename: Madhavan S
authors.initials: MS
authors.lastname: Rajan
authors.forename: Jonathan
authors.initials: J
authors.lastname: Harris
authors.forename: Erin
authors.initials: E
authors.lastname: Dooley
authors.forename: Nicholas
authors.initials: N
authors.lastname: Hawksworth
authors.forename: Jennifer
authors.initials: J
authors.lastname: Hiller
authors.forename: Nick J
authors.initials: NJ
authors.lastname: Terill
authors.forename: Farhad
authors.initials: F
authors.lastname: Hafezi
authors.forename: Arun K
authors.initials: AK
authors.lastname: Brahma
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Quantock
authors.forename: Keith M
authors.initials: KM
authors.lastname: Meek
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D003094:Collagen / Q000378:metabolism*; D003319:Corneal Stroma / Q000187:drug effects* / Q000378:metabolism / Q000528:radiation effects*; D003432:Cross-Linking Reagents / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D007640:Keratoconus / Q000378:metabolism*; D008875:Middle Aged; D012256:Riboflavin / Q000494:pharmacology*; D014466:Ultraviolet Rays
chemical_list: D003432:Cross-Linking Reagents; D003094:Collagen; D012256:Riboflavin