title: Measurement of pupil centroid shift and cyclotorsional displacement using iris registration.
abstract: OBJECTIVE
  To estimate the amount and nature of pupil centroid shift and cyclotorsion occurring between preoperative wavefront measurement and refractive surgery.
  
  
  METHODS
  This retrospective study comprised 183 eyes of 92 patients who had wavefront-guided LASIK using iris registration. We analyzed the pupil centroid shift and cyclotorsional displacement occurring between preoperative wavefront measurements and during the laser procedure. The eyes were measured by the WaveScan Wavefront system (VISX, Santa Clara, Calif., USA) and refractive surgery was performed with the VISX STAR S4 excimer laser system.
  
  
  RESULTS
  The mean magnitude of shifts in the location of pupil center was 0.26 +/- 0.16 mm horizontally, 0.20 +/- 0.16 mm vertically and 0.37 +/- 0.13 mm vectorally. 162 eyes (88.5%) experienced more than 0.2 mm of shift. The mean amount of torsion was 2.58 +/- 1.56 degrees for 83 eyes showing incyclotorsion and 2.94 +/- 1.87 degrees for 100 eyes showing excyclotorsion. 117 eyes (63.9%) experienced more than 2 degrees of cyclotorsion and 21 eyes (11.5%) experienced more than 5 degrees of cyclotorsion.
  
  
  CONCLUSIONS
  Pupil centroid shift and cyclotorsion occur in the majority of eyes undergoing laser treatment. The amount of pupil centroid shift and cyclotorsion shown in this study is considerable. Accurate compensation for cyclotorsion and pupil centroid shift may maximize the potential of visual quality of customized ablations.
authors.affiliation: Department of Ophthalmology and Visual Science, Kangnam St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea.
authors.forename: Shin Hae
authors.initials: SH
authors.lastname: Park
authors.forename: Minjung
authors.initials: M
authors.lastname: Kim
authors.forename: Choun-Ki
authors.initials: CK
authors.lastname: Joo
mesh_terms: D000328:Adult; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007498:Iris / Q000033:anatomy & histology*; D020731:Keratomileusis, Laser In Situ / Q000379:methods*; D011300:Preoperative Care; D011680:Pupil; D012029:Refraction, Ocular; D054140:Refractive Surgical Procedures; D012189:Retrospective Studies; D014102:Torsion Abnormality / Q000175:diagnosis* / Q000209:etiology*; D014792:Visual Acuity; D055815:Young Adult