title: Comparison of fourier-domain and time-domain optical coherence tomography for assessment of corneal thickness and intersession repeatability.
abstract: OBJECTIVE
  To compare Fourier-domain optical coherence tomography (FD-OCT) with time-domain OCT (TD-OCT) for agreement in corneal pachymetry in the central (2-mm) zone and paracentral (2- to 5-mm) zone, minimum corneal thickness, and instrument intersession reliability in candidates with normal cornea.
  
  
  METHODS
  Prospective comparative trial.
  
  
  METHODS
  The study was performed at a tertiary care ophthalmic hospital. One hundred normal candidates with no ocular pathology except mild refractive error were included. FD-OCT and TD-OCT were used for pachymetric analysis within 15 minutes of each other. Repeat testing on both machines was done on the next day. One eye from each patient was randomly selected for analysis of both comparison and reliability.
  
  
  RESULTS
  The mean thickness was significantly more for FD-OCT (difference being 5.8, 11.1, and 19.2 mum for central, paracentral, and minimal thickness). Highest correlation, best linear fit, and smallest range of 95% limits of agreement (LoA) was seen for central corneal thickness, followed by paracentral and minimum corneal thickness (R(2) values for the 3 best fit lines were 0.93, 0.86, and 0.58, respectively). In terms of intersession reliability, FD-OCT was better (coefficients of reliability <1.5% vs 4.5% of TD-OCT) with smaller 95% LoA range, suggesting its better performance.
  
  
  CONCLUSIONS
  The corneal thickness measurements between TD-OCT and FD-OCT were highly correlated but not similar. Conversion equations may be used for central and paracentral, but not for minimum, corneal thickness. Even though both the OCT instruments had good reliability, FD-OCT was better.
authors.affiliation: Dr Agarwal's Eye Hospital and Eye Research Centre, Chennai, India.
authors.forename: Gaurav
authors.initials: G
authors.lastname: Prakash
authors.forename: Amar
authors.initials: A
authors.lastname: Agarwal
authors.forename: Soosan
authors.initials: S
authors.lastname: Jacob
authors.forename: Dhivya Ashok
authors.initials: DA
authors.lastname: Kumar
authors.forename: Athiya
authors.initials: A
authors.lastname: Agarwal
authors.forename: Rumki
authors.initials: R
authors.lastname: Banerjee
mesh_terms: D000328:Adult; D001837:Body Weights and Measures; D003315:Cornea / Q000033:anatomy & histology*; D005260:Female; D005583:Fourier Analysis; D006801:Humans; D008297:Male; D011446:Prospective Studies; D015203:Reproducibility of Results; D013997:Time Factors; D041623:Tomography, Optical Coherence / Q000295:instrumentation / Q000379:methods*; D055815:Young Adult