title: Determination of the excimer laser ablation rate in previously cross-linked corneas.
abstract: OBJECTIVE
  To evaluate the need for and quantify the extent of nomogram adjustments to compensate for potential changes in the amount of effective corneal stroma ablated in previously cross-linked corneas.
  
  
  METHODS
  Ex vivo porcine corneas were divided into two groups (the corneal cross-linking [CXL] group, n = 30; and the control group, n = 3): these experimental corneas underwent CXL including deepithelialization, instillation of riboflavin solution for 25 minutes, and ultraviolet-A irradiation at 9 mW/cm2 for 10 minutes. The control group was deepithelialized only. Four consecutive excimer laser ablations of 50 pm each were performed (AMARIS 750S; SCHWIND eye-tech-solutions, Kleinostheim Germany), and stromal bed thickness was measured with a built-in optical coherence pachymeter. To determine the potential influence of riboflavin, a third group (the riboflavin group, n = 12) underwent deepithelialization and instillation of riboflavin, but no ultraviolet-A irradiation.
  
  
  RESULTS
  The mean individual ablation depth across the four ablations was significantly smaller in cross-linked corneas (-17%) when compared to untreated control corneas (P < .001). A consistent reduction of 12% was observed via a cumulative analysis when assessing the relative isolated effect of CXL on the ablation rate. There was no significant effect from riboflavin in the deeper ablations, except for the first ablation (68.6 + 1.1 mm [range: 1 to 50 pm]). This may be due to a measurement error in pachymetric readings due to the thin film of riboflavin on the surface that resists even extensive rinsing.
  
  
  CONCLUSIONS
  CXL reduces the corneal ablation depth of excimer lasers in the anterior 200 pm of the porcine cornea by approximately 12%. Further clinical studies are needed to validate these findings in human corneas.
authors.forename: Olivier
authors.initials: O
authors.lastname: Richoz
authors.forename: Samuel
authors.initials: S
authors.lastname: Arba Mosquera
authors.forename: Sabine
authors.initials: S
authors.lastname: Kling
authors.forename: Arthur
authors.initials: A
authors.lastname: Hammer
authors.forename: Thomas
authors.initials: T
authors.lastname: Magnago
authors.forename: Martina M
authors.initials: MM
authors.lastname: Bosch
authors.forename: Farhad
authors.initials: F
authors.lastname: Hafezi
mesh_terms: D000818:Animals; D003094:Collagen / Q000378:metabolism; D063171:Corneal Pachymetry; D003319:Corneal Stroma / Q000187:drug effects / Q000473:pathology / Q000601:surgery*; D003432:Cross-Linking Reagents / Q000494:pharmacology*; D020731:Keratomileusis, Laser In Situ / Q000379:methods*; D054018:Lasers, Excimer / Q000627:therapeutic use*; D049451:Nomograms; D017319:Photosensitizing Agents / Q000494:pharmacology*; D012256:Riboflavin / Q000494:pharmacology; D013552:Swine; D014466:Ultraviolet Rays
chemical_list: D003432:Cross-Linking Reagents; D017319:Photosensitizing Agents; D003094:Collagen; D012256:Riboflavin