title: A new nanosecond UV laser at 355 nm: early results of corneal flap cutting in a rabbit model.
abstract: OBJECTIVE
  A new 355 nm UV laser was used for corneal flap cutting in an animal model and tested for clinical and morphologic alterations.
  
  
  METHODS
  Corneal flaps were created (Chinchilla Bastards; n = 25) with an UV nanosecond laser at 355 nm (150 kHz, pulse duration 850 ps, spot-size 1 μm, spot spacing 6 × 6 μm, side cut Δz 1 μm; cutting depth 130 μm) and pulse energies of 2.2 or 2.5 μJ, respectively. Following slit-lamp examination, animals were killed at 6, 12, and 24 hours after treatment. Corneas were prepared for histology (hematoxylin and eosin [HE], TUNEL-assay) and evaluated statistically, followed by ultrastructural investigations.
  
  
  RESULTS
  Laser treatment was tolerated well, flap lift was easier at 2.5 μJ compared with 2.2 μJ. Standard HE at 24 hours revealed intact epithelium in the horizontal cut, with similar increase in corneal thickness at both energies. Irrespective of energy levels, TUNEL assay revealed comparable numbers of apoptotic cells in the horizontal and vertical cut at 6, 12, and 24 hours, becoming detectable in the horizontal cut as an acellular stromal band at 24 hours. Ultrastructural analysis revealed regular morphology in the epi- and endothelium, while in the stroma, disorganized collagen lamellae were detectable representing the horizontal cut, again irrespective of energy levels applied.
  
  
  CONCLUSIONS
  This new UV laser revealed no epi- nor endothelial damage at energies feasible for corneal flap cutting. Observed corneal swelling was lower compared with existing UV laser studies, albeit total energy applied here was much higher. Observed loss of stromal keratinocytes is comparable with available laser systems. Therefore, this new laser is suitable for refractive surgery, awaiting its test in a chronic environment.
authors.affiliation: Department of Ophthalmology, SALK/University Clinic, Paracelsus Medical University, Salzburg, Austria.
authors.forename: Andrea
authors.initials: A
authors.lastname: Trost
authors.forename: Falk
authors.initials: F
authors.lastname: Schrödl
authors.forename: Clemens
authors.initials: C
authors.lastname: Strohmaier
authors.forename: Barbara
authors.initials: B
authors.lastname: Bogner
authors.forename: Christian
authors.initials: C
authors.lastname: Runge
authors.forename: Alexandra
authors.initials: A
authors.lastname: Kaser-Eichberger
authors.forename: Karolina
authors.initials: K
authors.lastname: Krefft
authors.forename: Alfred
authors.initials: A
authors.lastname: Vogel
authors.forename: Norbert
authors.initials: N
authors.lastname: Linz
authors.forename: Sebastian
authors.initials: S
authors.lastname: Freidank
authors.forename: Andrea
authors.initials: A
authors.lastname: Hilpert
authors.forename: Inge
authors.initials: I
authors.lastname: Zimmermann
authors.forename: Günther
authors.initials: G
authors.lastname: Grabner
authors.forename: Herbert A
authors.initials: HA
authors.lastname: Reitsamer
mesh_terms: D000818:Animals; D017209:Apoptosis; D002452:Cell Count; D003315:Cornea / Q000473:pathology / Q000601:surgery*; D004195:Disease Models, Animal; D019573:Epithelium, Corneal / Q000648:ultrastructure; D020287:In Situ Nick-End Labeling; D020731:Keratomileusis, Laser In Situ / Q000379:methods*; D054018:Lasers, Excimer / Q000627:therapeutic use*; D046529:Microscopy, Electron, Transmission; D009216:Myopia / Q000473:pathology / Q000601:surgery*; D011817:Rabbits; D013524:Surgical Flaps; D016896:Treatment Outcome
keywords: corneal; histology; nanosecond UV laser; rabbit; refractive surgery