title: Cross-Linking Biomechanical Effect in Human Corneas by Same Energy, Different UV-A Fluence: An Enzymatic Digestion Comparative Evaluation.
abstract: OBJECTIVE
  To evaluate ex vivo the possible difference in corneal cross-linking (CXL) biomechanical effect of different ultraviolet-A (UV-A) irradiances.
  
  
  METHODS
  The study involved 25 human donor corneas, randomly allocated to 5 groups (n = 5 each). CXL was applied with UV-A irradiances of 3, 9, 18, 30, and 45 mW/cm2, maintaining equal cumulative energy dose of 5.4 J/cm2. UV-A was delivered on half of the cornea. The nonirradiated halves served as controls. Specimens were subjected to collagenase-A enzymatic digestion. The time to complete dissolution in each specimen was recorded.
  
  
  RESULTS
  Time to dissolution in group-A (3 mW/cm2 for 30 minutes) was 321 ± 13.4 minutes (range: 300-330) compared with 171 ± 8.2 (range: 165-180) for their control. In group-B (9 mW/cm2 for 10 minutes), it was 282 ± 19.6 minutes (range: 270-315) compared with 177 ± 6.7 (165-180) for their control. In group-C (18 mW/cm2 for 5 minutes), it was 267 ± 19.6 minutes (range: 240-285) compared with 177 ± 7.7 (range: 165-180) for their control. In group-D (30 mW/cm2 for 3 minutes), it was 252 ± 12.5 minutes (range: 240-270) compared with 180 ± 10.6 minutes (range: 165-195) for their control. In group-E (45 mW/cm2 for 2 minutes), it was 204 ± 17.1 minutes (range: 180-225) compared with 186 ± 8.2 minutes (range: 180-195) for their control.
  
  
  CONCLUSIONS
  The data in this ex vivo human corneal study indicate that the biomechanical effect of CXL studied by resistance to enzymatic digestion in human corneas is comparable between irradiances of 9, 18 and 30 mW/cm and seems to be reduced at a fluence of 45 mW/cm2.
authors: *Laservision.gr Clinical and Research Eye Institute, Athens, Greece; †Department of Ophthalmology, NYU Medical School, New York, NY; and ‡Neoscreen Laboratory, Athens, Greece.
authors: Anastasios J
authors: AJ
authors: Kanellopoulos
authors: Yannis L
authors: YL
authors: Loukas
authors: George
authors: G
authors: Asimellis
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D003094:Collagen / Q000378:metabolism*; D017364:Collagenases / Q000494:pharmacology*; D003315:Cornea / Q000187:drug effects / Q000502:physiology*; D003319:Corneal Stroma / Q000187:drug effects / Q000378:metabolism; D003432:Cross-Linking Reagents; D004307:Dose-Response Relationship, Radiation; D004548:Elasticity / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017319:Photosensitizing Agents / Q000494:pharmacology*; D012256:Riboflavin / Q000494:pharmacology*; D014019:Tissue Donors; D014467:Ultraviolet Therapy
chemical_list: D003432:Cross-Linking Reagents; D017319:Photosensitizing Agents; D003094:Collagen; D017364:Collagenases; D012256:Riboflavin