title: Potentiation of femtosecond laser intratissue refractive index shaping (IRIS) in the living cornea with sodium fluorescein.
abstract: OBJECTIVE
  To assess the effectiveness of intratissue refractive index shaping (IRIS) in living corneas and test the hypothesis that it can be enhanced by increasing the two-photon absorption (TPA) of the tissue.
  
  
  METHODS
  Three corneas were removed from adult cats and cut into six pieces, which were placed in preservative (Optisol-GS; Bausch & Lomb, Inc., Irvine, CA) containing 0%, 0.25%, 1%, 1.5%, or 2.5% sodium fluorescein (Na-Fl). An 800-nm Ti:Sapphire femtosecond laser with a 100-fs pulse duration and 80-MHz repetition rate was used to perform IRIS in each piece, creating several refractive index (RI) modification lines at different speeds (between 0.1 and 5 mm/s). The lines were 1 mum wide, 10 microm apart, and approximately 150 microm below the tissue surface. The RI change of each grating was measured using calibrated, differential interference contrast microscopy. TUNEL staining was performed to assess whether IRIS or Na-Fl doping causes cell death.
  
  
  RESULTS
  Scanning at 0.1 mm/s changed the RI of undoped, living corneas by 0.005. In doped corneas, RI changes between 0.01 and 0.02 were reliably achieved with higher scanning speeds. The magnitude of RI changes attained was directly proportional to Na-Fl doping concentration and inversely proportional to the scanning speed used to create the gratings.
  
  
  CONCLUSIONS
  IRIS can be efficiently performed in living corneal tissue. Increasing the TPA of the tissue with Na-Fl increased both the scanning speeds and the magnitude of RI changes in a dose-dependent manner. Ongoing studies are exploring the use of IRIS to alter the optical properties of corneal tissue in situ, over an extended period.
authors.affiliation: University of Rochester Eye Institute, Rochester, New York 14642, USA.
authors.forename: Lana J
authors.initials: LJ
authors.lastname: Nagy
authors.forename: Li
authors.initials: L
authors.lastname: Ding
authors.forename: Lisen
authors.initials: L
authors.lastname: Xu
authors.forename: Wayne H
authors.initials: WH
authors.lastname: Knox
authors.forename: Krystel R
authors.initials: KR
authors.lastname: Huxlin
mesh_terms: D000818:Animals; D017209:Apoptosis; D002415:Cats; D003315:Cornea / Q000187:drug effects / Q000503:physiopathology / Q000601:surgery*; D004305:Dose-Response Relationship, Drug; D019793:Fluorescein / Q000494:pharmacology*; D005456:Fluorescent Dyes / Q000494:pharmacology*; D020287:In Situ Nick-End Labeling; D054018:Lasers, Excimer; D012029:Refraction, Ocular / Q000502:physiology*
chemical_list: D005456:Fluorescent Dyes; D019793:Fluorescein