title: The role of axial resolution of optical coherence tomography on the measurement of corneal and epithelial thicknesses.
abstract: OBJECTIVE
  Our purpose was to investigate the role of the axial resolution of optical coherence tomography (OCT) on the measurement of corneal and epithelial thickness by evaluating the repeatability and agreement among different OCT devices with different axial resolutions.
  
  
  METHODS
  twenty right eyes of 20 healthy subjects (AGE: 22.3 ± 1.3 years) and 18 eyes of 18 patients (age: 25.7 ± 6.8 years) after laser in situ keratomileusis (LASIK) refractive surgery were tested. Each subject was imaged using four OCT devices: ultra-high resolution OCT (UHR-OCT), ultra-long scan depth OCT (UL-OCT), commercial RTVue, and Visante. The OCT images obtained from UHR-OCT, UL-OCT, and RTVue were processed with a custom automated algorithm for measuring the central corneal thickness (CCT) and central epithelial thickness (ET). CCT measurements from pachymetry maps that were generated by RTVue and Visante were also obtained.
  
  
  RESULTS
  For both groups, the CCT and ET measured by UHR-OCT and UL-OCT were highly correlated with RTVue when the automated image processing algorithm was used. The CCT measurements from the RTVue and Visante pachymetry were thicker than those measurements obtained from the automatic algorithm. The coefficient of repeatability was less than 4.9 μm in the healthy subjects and 7.9 μm in the LASIK patients, and the associated intraclass correlation coefficient (ICC) was greater than 0.992 in both groups for the CCT measurements. For the ET measurements using UHR-OCT, UL-OCT and RTVue, the coefficient of repeatability was less than 2.2 μm in the healthy subjects and 4.8 μm in the LASIK patients with an ICC that was greater than 0.84.
  
  
  CONCLUSIONS
  The axial resolution of OCT may play a role in determining the precision with which the CCT and the ET can be measured, although it may not affect the measurement of results.
authors.affiliation: School of Ophthalmology and Optometry, Wenzhou Medical College, Zhejiang, China.
authors.forename: Lili
authors.initials: L
authors.lastname: Ge
authors.forename: Yimin
authors.initials: Y
authors.lastname: Yuan
authors.forename: Meixiao
authors.initials: M
authors.lastname: Shen
authors.forename: Aizhu
authors.initials: A
authors.lastname: Tao
authors.forename: Jianhua
authors.initials: J
authors.lastname: Wang
authors.forename: Fan
authors.initials: F
authors.lastname: Lu
mesh_terms: D000328:Adult; D000465:Algorithms; D003315:Cornea / Q000473:pathology*; D063171:Corneal Pachymetry; D003941:Diagnostic Techniques, Ophthalmological; D004847:Epithelial Cells / Q000473:pathology*; D005260:Female; D006801:Humans; D020731:Keratomileusis, Laser In Situ; D008297:Male; D009929:Organ Size; D015203:Reproducibility of Results; D041623:Tomography, Optical Coherence / Q000295:instrumentation*; D055815:Young Adult