title: Dynamic torsional misalignment of eyes during laser in-situ keratomileusis.
abstract: OBJECTIVE
  To determine the amount and characteristics of dynamic torsional misalignment of eyes during excimer ablation in laser in-situ keratomileusis (LASIK).
  
  
  METHODS
  Retrospective trial for evaluation of dynamic intraoperative torsional misalignment of 179 eyes that underwent LASIK for correction of myopia and/or astigmatism. Patients were treated with the Keracor 217z excimer laser implementing 25 Hz dynamic eye tracker ACE 100 (both Technolas Perfect Vision, Munich, Germany). From dynamic torsional misalignments, temporal power spectra were obtained by Fourier analysis up to a frequency of 12.5 Hz and an amplitude of ±15° from initial torsional status (limited by the tracking system). The f90, f95, and f99 criteria were defined as the frequency below which 90 %, 95 %, and 99 % of misalignments occur. A Wilcoxon rank sum test was performed to detect differences of f90, f95, and f99 in groups' gender, age, and eye (if both eyes underwent surgery at same day). Multiple regression analysis (MRA) was performed to evaluate possible preoperative predictors of f90, f95, and f99.
  
  
  RESULTS
  Fourier analysis showed a dominance of high-frequency, low-power dynamic torsional misalignment. Mean f95 threshold of rotational movements was 4.89±2.12 Hz (median 4.54, ranging from 0.44 to 9.23 Hz). Wilcoxon rank sum test showed no differences in f90, f95, and f99 between groups' gender, age, and eye. MRA revealed age, gender, and optical zone as preoperative predictors on intraoperative f90, f95, and f99.
  
  
  CONCLUSIONS
  Dynamic intraoperative torsional misalignments of eyes undergoing LASIK are dominated by low-frequency (slow), high-power (large) movements, with 95 % being slower than 4.89Hz regarding the spectrum analyzed (0-12.5Hz, ±15°). Movements can be predicted preoperatively by eye treated, patients' gender, and age in pre-LASIK diagnostics.
authors.affiliation: Department of Ophthalmology, Goethe University, Frankfurt Theodor-Stern-Kai 7, 60590, Frankfurt am Main, Germany.
authors.forename: Mehdi
authors.initials: M
authors.lastname: Shajari
authors.affiliation: Department of Ophthalmology, Goethe University, Frankfurt Theodor-Stern-Kai 7, 60590, Frankfurt am Main, Germany.
authors.forename: Jens
authors.initials: J
authors.lastname: Bühren
authors.affiliation: Department of Ophthalmology, Goethe University, Frankfurt Theodor-Stern-Kai 7, 60590, Frankfurt am Main, Germany. kohnen@em.uni-frankfurt.de.
authors.forename: Thomas
authors.initials: T
authors.lastname: Kohnen
mesh_terms: D000328:Adult; D001251:Astigmatism / Q000601:surgery; D005260:Female; D005583:Fourier Analysis; D006801:Humans; D007431:Intraoperative Complications; D020731:Keratomileusis, Laser In Situ / Q000009:adverse effects*; D054018:Lasers, Excimer / Q000009:adverse effects*; D008297:Male; D009216:Myopia / Q000601:surgery*; D015835:Ocular Motility Disorders / Q000209:etiology*; D012189:Retrospective Studies; D014102:Torsion Abnormality / Q000209:etiology*
keywords: Dynamic torsional misalignment; Eye movements; LASIK; Misalignment