title: Laser in situ keratomileusis flap measurements: Comparison between observers and between spectral-domain and time-domain anterior segment optical coherence tomography.
abstract: OBJECTIVE
  To evaluate the between-observer (interobserver) and between-instrument (intraobserver) variability in flap thickness measurements after laser in situ keratomileusis (LASIK) using spectral-domain and time-domain anterior segment optical coherence tomography (AS-OCT).
  
  
  METHODS
  Singapore National Eye Centre.
  
  
  METHODS
  Evaluation of diagnostic test or technology.
  
  
  METHODS
  Two independent masked observers measured flap thickness 1 month after LASIK using spectral-domain (RTVue) or time-domain (Visante) AS-OCT. The measurements were taken at central (0.0 mm), -1.5 mm, and +1.5 mm locations. Measurements were repeated to assess between-instrument variability.
  
  
  RESULTS
  There was no statistically significant difference in mean flap thickness between the 2 observers at -1.5 mm, 0.0 mm, and +1.5 mm on spectral-domain AS-OCT and at -1.5 mm and +1.5 mm on time-domain AS-OCT (P < .01). There was a statistically significant difference between the 2 observers in the central (0.0 mm) values on time-domain AS-OCT (P=.0008). There was stronger interobserver correlation for spectral-domain AS-OCT at -1.5 mm (r = 0.82), 0.0 mm (r = 0.88), and +1.5 mm (r = 0.88) than for time-domain AS-OCT (r = 0.73, r = 0.62, and r = 0.79, respectively). There was no statistically significant difference in between-instrument measurements. There was stronger between-instrument correlation with spectral-domain AS-OCT than with time-domain AS-OCT at all locations. The mean standard deviation (measure of instrument repeatability) for spectral-domain AS-OCT was 4.19 μm.
  
  
  CONCLUSIONS
  Spectral-domain AS-OCT had closer agreement in between-observer and between-instrument measurements than time-domain AS-OCT and provided more consistent measurements of post-LASIK flap thickness.
authors.affiliation: Singapore National Eye Centre, National University of Singapore, Singapore.
authors.forename: Reece C
authors.initials: RC
authors.lastname: Hall
authors.forename: Farook K
authors.initials: FK
authors.lastname: Mohamed
authors.forename: Hla M
authors.initials: HM
authors.lastname: Htoon
authors.forename: Donald T
authors.initials: DT
authors.lastname: Tan
authors.forename: Jodhbir S
authors.initials: JS
authors.lastname: Mehta
mesh_terms: D000328:Adult; D001837:Body Weights and Measures; D003319:Corneal Stroma / Q000473:pathology* / Q000601:surgery; D005260:Female; D006801:Humans; D020731:Keratomileusis, Laser In Situ; D054018:Lasers, Excimer / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000601:surgery; D015588:Observer Variation; D011446:Prospective Studies; D015203:Reproducibility of Results; D013524:Surgical Flaps / Q000473:pathology*; D041623:Tomography, Optical Coherence / Q000295:instrumentation / Q000379:methods*; D055815:Young Adult