title: Noninvasive intratissue refractive index shaping (IRIS) of the cornea with blue femtosecond laser light.
abstract: OBJECTIVE
  To test the feasibility of intratissue refractive index shaping (IRIS) in living corneas by using 400-nm femtosecond (fs) laser pulses (blue-IRIS). To test the hypothesis that the intrinsic two-photon absorption of the cornea allows blue-IRIS to be performed with greater efficacy than when using 800-nm femtosecond laser pulses.
  
  
  METHODS
  Fresh cat corneas were obtained postmortem and cut into six wedges. Blue laser pulses at 400 nm, with 100-fs pulse duration at 80 MHz were used to micromachine phase gratings into each corneal wedge at scanning speeds from 1 to 15 mm/s. Grating lines were 1 μm wide, 5 μm apart, and 150 μm below the anterior corneal surface. Refractive index (RI) changes in micromachined regions were measured immediately by recording the diffraction efficiency of inscribed gratings. Six hours later, the corneas were processed for histology, and TUNEL staining was performed to assess whether blue-IRIS causes cell death.
  
  
  RESULTS
  Scanning at 1 and 2 mm/s caused overt corneal damage in the form of bubbles and burns. At faster scanning speeds (5, 10, and 15 mm/s), phase gratings were created in the corneal stroma, which were shown to be pure RI changes ranging from 0.037 to 0.021 in magnitude. The magnitude of RI change was inversely related to scanning speed. TUNEL staining showed cell death only around bubbles and burns.
  
  
  CONCLUSIONS
  Blue-IRIS can be performed safely and effectively in living cornea. Compared with near-infrared laser pulses, blue-IRIS enhances both achievable RI change and scanning speed without the need to dope the tissue with two-photon sensitizers, increasing the clinical applicability of this technique.
authors.affiliation: The Institute of Optics, University of Rochester, Rochester, New York, USA.
authors.forename: Lisen
authors.initials: L
authors.lastname: Xu
authors.forename: Wayne H
authors.initials: WH
authors.lastname: Knox
authors.forename: Margaret
authors.initials: M
authors.lastname: DeMagistris
authors.forename: Nadan
authors.initials: N
authors.lastname: Wang
authors.forename: Krystel R
authors.initials: KR
authors.lastname: Huxlin
mesh_terms: D000818:Animals; D017209:Apoptosis; D002415:Cats; D002470:Cell Survival; D003315:Cornea / Q000473:pathology / Q000601:surgery*; D005240:Feasibility Studies; D020287:In Situ Nick-End Labeling; D053685:Laser Therapy / Q000295:instrumentation*; D054140:Refractive Surgical Procedures / Q000379:methods*