title: Nonlinear optical corneal collagen crosslinking of ex vivo rabbit eyes.
abstract: To determine whether riboflavin-induced collagen crosslinking (CXL) could be precisely achieved in the corneal stroma of ex vivo rabbit eyes using nonlinear optical excitation with a low numerical aperture lens and enlarged focal volume.
  
  
  
  Gavin Herbert Eye Institute, University of California Irvine, Irvine, California, USA.
  
  
  
  Experimental study.
  
  
  
  The corneal epithelium was removed and the corneas were soaked in 0.5% riboflavin solution. Using a 0.1 numerical aperture objective, a theoretical excitation volume of 150 μm × 3 μm was generated using 1 W of 760 nm femtosecond laser light and raster scanned with 4.4 μm line separation at varying effective speeds over a 4.50 mm × 2.25 mm area. Corneal sections were examined for collagen autofluorescence.
  
  
  
  Collagen autofluorescence was enhanced 2.9 times compared with ultraviolet-A (UVA) CXL. Also, increasing speed was linearly associated with decreasing autofluorescence intensity. The slowest speed of 2.69 mm/s showed a mean of 182.97 μm ± 52.35 (SD) long autofluorescent scan lines axially in the central cornea compared with 147.84 ± 4.35 μm for UVA CXL.
  
  
  
  Decreasing dwell time was linearly associated with decreasing autofluorescence intensity, approaching that of UVA CXL at a speed of 8.9 mm/s. Using an effective speed of 8.9 mm/s, nonlinear optical CXL could be achieved over a 3.0 mm diameter area in fewer than 4 minutes. Further development of nonlinear optical CXL might result in safer, faster, and more effective CXL treatments.
  
  
  
  None of the authors has a financial or proprietary interest in any material or method mentioned.
authors.affiliation: From the Department of Biomedical Engineering (Bradford, Brown, Juhasz, Jester) and the Department of Ophthalmology (Brown, Juhasz, Mikula, Jester), University of California, Irvine, California, USA.
authors.forename: Samantha M
authors.initials: SM
authors.lastname: Bradford
authors.affiliation: From the Department of Biomedical Engineering (Bradford, Brown, Juhasz, Jester) and the Department of Ophthalmology (Brown, Juhasz, Mikula, Jester), University of California, Irvine, California, USA.
authors.forename: Donald J
authors.initials: DJ
authors.lastname: Brown
authors.affiliation: From the Department of Biomedical Engineering (Bradford, Brown, Juhasz, Jester) and the Department of Ophthalmology (Brown, Juhasz, Mikula, Jester), University of California, Irvine, California, USA.
authors.forename: Tibor
authors.initials: T
authors.lastname: Juhasz
authors.affiliation: From the Department of Biomedical Engineering (Bradford, Brown, Juhasz, Jester) and the Department of Ophthalmology (Brown, Juhasz, Mikula, Jester), University of California, Irvine, California, USA.
authors.forename: Eric
authors.initials: E
authors.lastname: Mikula
authors.affiliation: From the Department of Biomedical Engineering (Bradford, Brown, Juhasz, Jester) and the Department of Ophthalmology (Brown, Juhasz, Mikula, Jester), University of California, Irvine, California, USA. Electronic address: jjester@uci.edu.
authors.forename: James V
authors.initials: JV
authors.lastname: Jester
mesh_terms: D000818:Animals; D003094:Collagen / Q000032:analysis* / Q000737:chemistry; D003315:Cornea / Q000737:chemistry*; D003319:Corneal Stroma / Q000737:chemistry*; D003432:Cross-Linking Reagents / Q000737:chemistry*; D017319:Photosensitizing Agents; D011817:Rabbits; D012256:Riboflavin; D014466:Ultraviolet Rays
chemical_list: D003432:Cross-Linking Reagents; D017319:Photosensitizing Agents; D003094:Collagen; D012256:Riboflavin