title: Enzymatic Resistance of Corneas Crosslinked Using Riboflavin in Conjunction With Low Energy, High Energy, and Pulsed UVA Irradiation Modes.
abstract: OBJECTIVE
  To investigate the effect of various riboflavin/ultraviolet light (UVA) crosslinking (CXL) protocols on corneal enzymatic resistance.
  
  
  METHODS
  A total of 66 enucleated porcine eyes, with the corneal epithelium removed, were divided into 6 groups. Group 1 remained untreated. Groups 2 to 6 received riboflavin/dextran for 30 minutes. Group 3 underwent standard CXL (SCXL) with 3 mW/cm(2) UVA for 30 minutes (total energy dose 5.4 J/cm(2)). Groups 4 and 5 underwent high intensity CXL (HCXL) using 30 mW/cm(2) UVA for 3 minutes (5.4 J/cm(2)) and 30 mW/cm(2) for 4 minutes (7.2 J/cm(2)), respectively. Group 6 was exposed to 8 minutes of 30 mW/cm(2) UVA in a 10-second on/10-second off pulsed-radiation mode (p-HCXL; 7.2 J/cm(2)). A central 8-mm disk from each cornea was submerged in pepsin digest solution at 23°C and measured daily. After 13 days, the dry weight was recorded from 5 samples in each group.
  
  
  RESULTS
  The CXL-treated corneas took longer to digest than nonirradiated corneas (P < 0.0001). Differences in digestion time also were observed between CXL groups, such that, HCXL (5.4 J/cm(2)) < SCXL (5.4 J/cm(2)) < HCXL (7.2 J/cm(2)) < p-HCXL (7.2 J/cm(2); P < 0.0001). The dry weight of the SCXL (5.4 J/cm(2)) group was higher than the HCXL (5.4 and 7.2 J/cm(2); P < 0.001) and p-HCXL 7.2 J/cm(2) (P <0.05) groups. No difference was detected between the HCXL and p-HCXL 7.2 J/cm(2) groups.
  
  
  CONCLUSIONS
  The intensity and distribution of the crosslinks formed within the cornea vary with different UVA protocols. The precise location and amount of crosslinking needed to prevent disease progression is unknown.
authors.affiliation: Structural Biophysics Research Group, School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom 2Cardiff Institute for Tissue Engineering and Repair (CITER), Cardiff University, Cardiff, United Kingdom.
authors.forename: Nada H
authors.initials: NH
authors.lastname: Aldahlawi
authors.affiliation: Structural Biophysics Research Group, School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom 2Cardiff Institute for Tissue Engineering and Repair (CITER), Cardiff University, Cardiff, United Kingdom.
authors.forename: Sally
authors.initials: S
authors.lastname: Hayes
authors.affiliation: Keratoconus Research Institute, Department of Ophthalmology, St. Thomas' Hospital, London, United Kingdom.
authors.forename: David P S
authors.initials: DP
authors.lastname: O'Brart
authors.affiliation: Structural Biophysics Research Group, School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom 2Cardiff Institute for Tissue Engineering and Repair (CITER), Cardiff University, Cardiff, United Kingdom.
authors.forename: Alina
authors.initials: A
authors.lastname: Akhbanbetova
authors.affiliation: Structural Biophysics Research Group, School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom 2Cardiff Institute for Tissue Engineering and Repair (CITER), Cardiff University, Cardiff, United Kingdom.
authors.forename: Stacy L
authors.initials: SL
authors.lastname: Littlechild
authors.affiliation: Structural Biophysics Research Group, School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom 2Cardiff Institute for Tissue Engineering and Repair (CITER), Cardiff University, Cardiff, United Kingdom.
authors.forename: Keith M
authors.initials: KM
authors.lastname: Meek
mesh_terms: D000818:Animals; D003094:Collagen / Q000378:metabolism; D003315:Cornea / Q000187:drug effects* / Q000378:metabolism; D003319:Corneal Stroma / Q000378:metabolism; D003432:Cross-Linking Reagents; D004351:Drug Resistance; D005765:Gastrointestinal Agents / Q000494:pharmacology*; D006801:Humans; D010434:Pepsin A / Q000494:pharmacology*; D010778:Photochemotherapy; D017319:Photosensitizing Agents / Q000494:pharmacology*; D011829:Radiation Dosage; 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