title: The efficacy of corneal cross-linking shows a sudden decrease with very high intensity UV light and short treatment time.
abstract: OBJECTIVE
  Standard treatment in cases of progressive keratectasia is UV-triggered corneal cross-linking. For irradiances larger than 10 mW/cm(2) and treatment times below 10 minutes, the scientific proof of a biomechanical strengthening effect is insufficient. The authors investigated the biomechanical strengthening of ex vivo corneal tissue treated with irradiances between 3 mW/cm(2) and 90 mW/cm(2) and illumination times from 30 minutes to 1 minute, respectively.
  
  
  METHODS
  A total of 100 porcine eyes received riboflavin + UV treatment (constant irradiation dose of 5.4 J/cm(2)) with different intensities and illumination times and were randomly assigned into 10 groups. A control group (80 eyes) was not irradiated but underwent the same treatment otherwise. Young's modulus at 10% strain was determined for each strip after uniaxial stress-strain measurement. A Kruskal-Wallis test was used for statistical analysis.
  
  
  RESULTS
  A statistically significant difference (α = 0.01) was found between the median value of Young's modulus of the treatment groups up to 45 mW/cm(2) (illumination times from 30 minutes to 2 minutes) compared with the control group. There was no statistically significant difference between the treatment groups from 50 mW/cm(2) up to 90 mW/cm(2) (illumination times of less than 2 minutes) and the control group.
  
  
  CONCLUSIONS
  The ex vivo results of corneal cross-linking performed in porcine corneas show that the Bunsen-Roscoe reciprocity law is only valid for illumination intensities up to 40 to 50 mW/cm(2) and illumination times of more than 2 minutes. Further experiments are necessary to validate these results for in vivo human corneal tissue. Additionally, safety aspects at high intensities must be investigated.
authors.affiliation: IROC Science to Innovation AG, Zurich, Switzerland. jeremy.wernli@irocscience.com
authors.forename: Jeremy
authors.initials: J
authors.lastname: Wernli
authors.forename: Silvia
authors.initials: S
authors.lastname: Schumacher
authors.forename: Eberhard
authors.initials: E
authors.lastname: Spoerl
authors.forename: Michael
authors.initials: M
authors.lastname: Mrochen
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena / Q000187:drug effects / Q000528:radiation effects; D003316:Corneal Diseases / Q000473:pathology* / Q000628:therapy*; D003432:Cross-Linking Reagents / Q000494:pharmacology*; D004108:Dilatation, Pathologic / Q000473:pathology / Q000628:therapy; D004307:Dose-Response Relationship, Radiation; D019573:Epithelium, Corneal / Q000187:drug effects / Q000473:pathology* / Q000528:radiation effects; D017319:Photosensitizing Agents / Q000494:pharmacology; D011897:Random Allocation; D012256:Riboflavin / Q000494:pharmacology*; D013552:Swine; D013997:Time Factors; D014467:Ultraviolet Therapy / Q000009:adverse effects / Q000379:methods*
chemical_list: D003432:Cross-Linking Reagents; D017319:Photosensitizing Agents; D012256:Riboflavin