title: Effect of limbal marking prior to laser ablation on the magnitude of cyclotorsional error.
abstract: OBJECTIVE
  To evaluate the residual registration error after limbal-marking-based manual adjustment in cyclotorsional tracker-controlled laser refractive surgery.
  
  
  METHODS
  Two hundred eyes undergoing custom surface ablation with the iVIS Suite (iVIS Technologies) were divided into limbal marked (marked) and non-limbal marked (unmarked) groups. Iris registration information was acquired preoperatively from all eyes. Preoperatively, the horizontal axis was recorded in the marked group for use in manual cyclotorsional alignment prior to surgical iris registration. During iris registration, the preoperative iris information was compared to the eye-tracker captured image. The magnitudes of the registration error angle and cyclotorsional movement during the subsequent laser ablation were recorded and analyzed.
  
  
  RESULTS
  Mean magnitude of registration error angle (absolute value) was 1.82°±1.31° (range: 0.00° to 5.50°) and 2.90°±2.40° (range: 0.00° to 13.50°) for the marked and unmarked groups, respectively (P<.001). Mean magnitude of cyclotorsional movement during the laser ablation (absolute value) was 1.15°±1.34° (range: 0.00° to 7.00°) and 0.68°±0.97° (range: 0.00° to 6.00°) for the marked and unmarked groups, respectively (P=.005). Forty-six percent and 60% of eyes had registration error >2°, whereas 22% and 20% of eyes had cyclotorsional movement during ablation >2° in the marked and unmarked groups, respectively.
  
  
  CONCLUSIONS
  Limbal-marking-based manual alignment prior to laser ablation significantly reduced cyclotorsional registration error. However, residual registration misalignment and cyclotorsional movements remained during ablation.
authors.affiliation: SynsLaser Kirurgi, Oslo, Norway. chenxianjun1101@gmail.com
authors.forename: Xiangjun
authors.initials: X
authors.lastname: Chen
authors.forename: Aleksandar
authors.initials: A
authors.lastname: Stojanovic
authors.forename: Filip
authors.initials: F
authors.lastname: Stojanovic
authors.forename: Jon Roger
authors.initials: JR
authors.lastname: Eidet
authors.forename: Sten
authors.initials: S
authors.lastname: Raeder
authors.forename: Haakon
authors.initials: H
authors.lastname: Øritsland
authors.forename: Tor Paaske
authors.initials: TP
authors.lastname: Utheim
mesh_terms: D000328:Adult; D003316:Corneal Diseases / Q000175:diagnosis* / Q000209:etiology; D006801:Humans; D007498:Iris / Q000033:anatomy & histology*; D054018:Lasers, Excimer / Q000627:therapeutic use*; D016850:Limbus Corneae / Q000033:anatomy & histology*; D008875:Middle Aged; D012030:Refractive Errors / Q000517:prevention & control; D014102:Torsion Abnormality / Q000175:diagnosis* / Q000209:etiology; D055815:Young Adult