title: Comparison of free-running vs. Q-switched Er:YAG laser photorefractive keratectomy (scanning mode) in swine eyes.
abstract: OBJECTIVE
  To examine morphology in plane and incisional corneal ablation (in vitro) induced by an Er:YAG laser (2.94 microm) in two modes: free-running and q-switched.
  
  
  METHODS
  Sequences of different fluences in each mode were applied to freshly enucleated pig eyes. Parameters of free-running mode were: pulse length 50 micros, fluences 1.21 to 4.77 J/cm2, frequency 80 Hz, spot size 500 microm FWHM, hexagonal spot shape. Parameters of q-switched mode were: pulse length 200 ns, fluences 0.79 to 2.33 J/cm2, frequency 20 Hz, spot size 500 microm FWHM, round spot shape.
  
  
  RESULTS
  Histology showed thermal damage of 10 to 25 microm in depth caused by the free-running mode compared with 4.5 to 7.5 microm by the q-switched mode. In both gross photography and scanning electron microscopic examination, the surface was more homogeneous and smoother in the q-switched mode.
  
  
  CONCLUSIONS
  Depending on the different application modes, both laser systems could be used for a defined corneal ablation in photorefractive keratectomy. At present, results using the Er:YAG laser are not as favorable as with the excimer laser.
authors.affiliation: Department of Ophthalmology, University of Ulm, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Kampmeier
authors.forename: S
authors.initials: S
authors.lastname: Schäfer
authors.forename: G E
authors.initials: GE
authors.lastname: Lang
authors.forename: G K
authors.initials: GK
authors.lastname: Lang
mesh_terms: D000818:Animals; D048429:Cell Size; D003315:Cornea / Q000601:surgery* / Q000648:ultrastructure; D004728:Endothelium, Corneal / Q000601:surgery / Q000648:ultrastructure; D066298:In Vitro Techniques; D054018:Lasers, Excimer; D008855:Microscopy, Electron, Scanning; D018903:Photorefractive Keratectomy / Q000379:methods*; D013552:Swine; D014945:Wound Healing