title: Influence of corneal collagen crosslinking with riboflavin and ultraviolet-a irradiation on excimer laser surgery.
abstract: OBJECTIVE
  Riboflavin/ultraviolet A (UVA) cross-linking (CXL) of corneal collagen is a novel method of stabilizing corneal mechanical properties and preventing progression of keratectasias. This study was conducted to investigate whether CXL influences ablation rate, flap thickness, and refractive results of excimer laser procedures ex vivo.
  
  
  METHODS
  Corneal epithelium was removed from enucleated porcine eyes, and CXL was performed with riboflavin 0.1% and UVA radiation (365 nm, 3 mW/cm(2)) for 30 minutes. Control eyes received epithelial abrasion only. Diffusion of riboflavin through the cornea was assessed by using infrared-excited, two-photon microscopy of riboflavin autofluorescence, combined with second-harmonic generation of fibrillar collagen. During phototherapeutic keratectomy, corneal thickness was measured by optical coherence pachymetry. During LASIK for myopia, the flap thickness of microkeratome cuts was measured and the induced refractive change assessed by Placido topography. Data were analyzed by Shapiro-Wilk test and Student's t-test.
  
  
  RESULTS
  Multiphoton imaging showed a rapid (30-minute) and even distribution of riboflavin throughout the corneal stroma. No difference in ablation rate was measured in treated and untreated corneas (P = 0.90). Mean flap thickness was increased by 44% in cross-linked corneas (P < 0.01). After LASIK for myopia of 4 to 25 D, the mean corneal refractive change was reduced in CXL-treated eyes by 20.1% (P < 0.05). This effect was less pronounced in thinner flaps.
  
  
  CONCLUSIONS
  CXL reduces the amount of refractive change after LASIK for myopia. Although the laser ablation rate is unaffected, CXL results in an increased flap thickness. This study suggests the need for adjustment of microkeratome and laser parameters for LASIK after CXL and indirectly endorses the theory of a direct stiffening effect of CXL.
authors.affiliation: Department of Ophthalmology, University of Würzburg, Würzburg, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Kampik
authors.forename: Bernhard
authors.initials: B
authors.lastname: Ralla
authors.forename: Sabine
authors.initials: S
authors.lastname: Keller
authors.forename: Markus
authors.initials: M
authors.lastname: Hirschberg
authors.forename: Peter
authors.initials: P
authors.lastname: Friedl
authors.forename: Gerd
authors.initials: G
authors.lastname: Geerling
mesh_terms: D000818:Animals; D003094:Collagen / Q000378:metabolism*; D003319:Corneal Stroma / Q000187:drug effects* / Q000378:metabolism / Q000601:surgery; D005486:Flavin Mononucleotide / Q000494:pharmacology*; D020731:Keratomileusis, Laser In Situ; D054018:Lasers, Excimer; D010778:Photochemotherapy; D017319:Photosensitizing Agents / Q000494:pharmacology*; D012029:Refraction, Ocular / Q000502:physiology; D013524:Surgical Flaps; D013552:Swine; D014466:Ultraviolet Rays
chemical_list: D017319:Photosensitizing Agents; D005486:Flavin Mononucleotide; D003094:Collagen