title: Standard versus accelerated riboflavin-ultraviolet corneal collagen crosslinking: Resistance against enzymatic digestion.
abstract: OBJECTIVE
  To examine the effect of standard and accelerated corneal collagen crosslinking (CXL) on corneal enzymatic resistance.
  
  
  METHODS
  School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom.
  
  
  METHODS
  Experimental study.
  
  
  METHODS
  Sixty-six enucleated porcine eyes (with corneal epithelium removed) were assigned to 6 groups. Group 1 remained untreated, group 2 received dextran eyedrops, and groups 3 to 6 received riboflavin/dextran eyedrops. Group 4 had standard CXL (3 mW/cm(2) ultraviolet-A for 30 minutes), whereas groups 5 and 6 received accelerated CXL (9 mW/cm(2) for 10 minutes and 18 mW/cm(2) for 5 minutes, respectively). Trephined central 8.0 mm buttons from each cornea underwent pepsin digestion. Corneal diameter was measured daily, and the dry weight of 5 samples from each group was recorded after 12 days of digestion.
  
  
  RESULTS
  All CXL groups (4 to 6) took longer to digest and had a greater dry weight at 12 days (P < .0001) than the nonirradiated groups (1 to 3) (P < .0001). The time taken for complete digestion to occur did not differ between the standard and accelerated CXL groups, but the dry weights at 12 days showed significant differences between treatments: standard CXL 3 mW > accelerated CXL 9 mW > accelerated CXL 18 mW (P < .0001).
  
  
  CONCLUSIONS
  Standard and accelerated CXL both increased corneal enzymatic resistance; however, the amount of CXL might be less when accelerated CXL is used. The precise amount of CXL needed to prevent disease progression is not yet known.
  
  
  BACKGROUND
  No author has a financial or proprietary interest in any material or method mentioned.
authors.affiliation: From the Structural Biophysics Research Group (Aldahlawi, Hayes, Meek), School of Optometry and Vision Sciences, Cardiff University, Cardiff, and the Keratoconus Research Institute (O'Brart), Department of Ophthalmology, St Thomas Hospital, London, United Kingdom.
authors.forename: Nada H
authors.initials: NH
authors.lastname: Aldahlawi
authors.affiliation: From the Structural Biophysics Research Group (Aldahlawi, Hayes, Meek), School of Optometry and Vision Sciences, Cardiff University, Cardiff, and the Keratoconus Research Institute (O'Brart), Department of Ophthalmology, St Thomas Hospital, London, United Kingdom.
authors.forename: Sally
authors.initials: S
authors.lastname: Hayes
authors.affiliation: From the Structural Biophysics Research Group (Aldahlawi, Hayes, Meek), School of Optometry and Vision Sciences, Cardiff University, Cardiff, and the Keratoconus Research Institute (O'Brart), Department of Ophthalmology, St Thomas Hospital, London, United Kingdom.
authors.forename: David P S
authors.initials: DP
authors.lastname: O'Brart
authors.affiliation: From the Structural Biophysics Research Group (Aldahlawi, Hayes, Meek), School of Optometry and Vision Sciences, Cardiff University, Cardiff, and the Keratoconus Research Institute (O'Brart), Department of Ophthalmology, St Thomas Hospital, London, United Kingdom. Electronic address: meekkm@cardiff.ac.uk.
authors.forename: Keith M
authors.initials: KM
authors.lastname: Meek
mesh_terms: D000818:Animals; D003094:Collagen / Q000378:metabolism*; D003319:Corneal Stroma / Q000187:drug effects* / Q000378:metabolism; D003432:Cross-Linking Reagents; D005765:Gastrointestinal Agents / Q000494:pharmacology*; D010434:Pepsin A / Q000494:pharmacology*; D017319:Photosensitizing Agents / Q000494:pharmacology*; D012256:Riboflavin / Q000494:pharmacology*; D034421:Sus scrofa; D014466:Ultraviolet Rays
chemical_list: D003432:Cross-Linking Reagents; D005765:Gastrointestinal Agents; D017319:Photosensitizing Agents; D003094:Collagen; D010434:Pepsin A; D012256:Riboflavin