title: Increased resistance of crosslinked cornea against enzymatic digestion.
abstract: OBJECTIVE
  Collagen-crosslinking using combined riboflavin/ UVA treatment has been developed by us as a new treatment for keratoconus by stiffening the collagenous matrix. Recently, we have started to use the same method for the treatment of corneal ulcers. The aim of the present study was to evaluate the influence of the crosslinking treatment on the resistance of the cornea against enzymatic degradation.
  
  
  METHODS
  60 enucleated porcine eyes were treated with the photosensitizer riboflavin and UVA-irradiation (370 nm; irradiance of 1, 2 or 3 mW/cm2) for 30 minutes and compared with 20 untreated control eyes. After crosslinking treatment, the corneal buttons were trephined and exposed to pepsin, trypsin and collagenase solutions. The extent of the corneal digestion was monitored daily. Selected cases were examined by light microscopy.
  
  
  RESULTS
  The corneal buttons crosslinked with riboflavin/ UVA at 3 mW/cm2 were dissolved only by day 13 following pepsin digestion and by day 14 following collagenase treatment versus 6 days in the untreated control corneas. Digestion by trypsin was observed on day 5 in buttons crosslinked at 3 mW/cm2 compared to day 2 in the control corneas. Microscopically, a prolonged preservation especially of the anterior portion of the crosslinked corneas could be demonstrated.
  
  
  CONCLUSIONS
  Photochemical crosslinking of the cornea using riboflavin and UVA results in a markedly increased resistance versus collagen digesting enzymes. The findings support the use of the new method in the treatment of corneal ulcers.
authors.affiliation: Department of Ophthalmology, Universitätsklinikum CGC, Fetscherstrasse 74, D-01307 Dresden, Germany. eberhard.spoerl@uniklinikum-dresden.de
authors.forename: Eberhard
authors.initials: E
authors.lastname: Spoerl
authors.forename: Gregor
authors.initials: G
authors.lastname: Wollensak
authors.forename: Theo
authors.initials: T
authors.lastname: Seiler
mesh_terms: D000818:Animals; D003094:Collagen / Q000378:metabolism*; D017364:Collagenases / Q000494:pharmacology; D003315:Cornea / Q000187:drug effects* / Q000378:metabolism; D003432:Cross-Linking Reagents / Q000494:pharmacology*; D010450:Endopeptidases / Q000494:pharmacology*; D010434:Pepsin A / Q000494:pharmacology; D017319:Photosensitizing Agents / Q000494:pharmacology*; D012256:Riboflavin / Q000494:pharmacology*; D013552:Swine; D014357:Trypsin / Q000494:pharmacology; D014466:Ultraviolet Rays
chemical_list: D003432:Cross-Linking Reagents; D017319:Photosensitizing Agents; D003094:Collagen; D010450:Endopeptidases; D014357:Trypsin; D010434:Pepsin A; D017364:Collagenases; D012256:Riboflavin