title: Do different spectral domain OCT hardwares measure the same? Comparison of retinal thickness using third-party software.
abstract: OBJECTIVE
  Spectral-domain optical coherence tomographies (OCTs) from different companies do not give identical retinal thicknesses. The purpose of this study was to evaluate if differences in thickness when using a spectral domain Cirrus OCT or a Heidelberg Spectralis are due to hardware differences, or if they are caused by the segmentation algorithms.
  
  
  METHODS
  Thirty-seven healthy eyes were examined within the same session with a Cirrus OCT and a Spectralis OCT, the latter using averaged B-scans. Scans from similar positions and passing the fovea were analyzed by custom-made software. Thickness was analyzed at the fovea, the central 1-mm line and the 6-mm line.
  
  
  RESULTS
  When Cirrus and Spectralis scans were analyzed with the same software, the retinal thickness at the foveal center was 225.92 μm (SD 17.0) using the Cirrus and 228.70 μm (SD 18.4) using the Spectralis; the difference of 2.78 μm was not significant (p = 0.055). For the central 1 mm, the difference was 1.78 μm (p = 0.0414), and for all points out to 6 mm, the Spectralis retinal thickness was also significantly larger than the Cirrus thickness (p = 0.0052), though the mean difference was only 1.85 μm. Also for the RPE_OScomplex, Spectralis measured a greater thickness than did Cirrus, with a mean of 3.32 μm (p < 0.0001) for all points.
  
  
  CONCLUSIONS
  The retinal thicknesses from the Cirrus and from the Spectralis differed by 14 μm with the standard software of the instruments, and by less than 3 μm when analyzed with the same custom-made software, indicating that the major differences between the two SD-OCT systems are due to differences in their built-in software algorithms.
authors.affiliation: Department of Ophthalmology, Rigshospitalet - Glostrup, Ndr. Ringvej 57, DK-2600, Glostrup, Denmark. bisan@bisan.dk.
authors.forename: Birgit
authors.initials: B
authors.lastname: Sander
authors.affiliation: Department of Ophthalmology, Rigshospitalet - Glostrup, Ndr. Ringvej 57, DK-2600, Glostrup, Denmark.
authors.forename: Hajer Ahmad
authors.initials: HA
authors.lastname: Al-Abiji
authors.affiliation: Department of Ophthalmology, Rigshospitalet - Glostrup, Ndr. Ringvej 57, DK-2600, Glostrup, Denmark.
authors.forename: Mads
authors.initials: M
authors.lastname: Kofod
authors.affiliation: Department of Applied Mathematics and Computer Science, Technical University of Denmark, Richard Petersens Plads, Building 324, DK-2800, Kgs. Lyngby, Denmark.
authors.forename: Thomas Martini
authors.initials: TM
authors.lastname: Jørgensen
mesh_terms: D000368:Aged; D000465:Algorithms; D003941:Diagnostic Techniques, Ophthalmological / Q000295:instrumentation / Q000592:standards*; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012160:Retina / Q000033:anatomy & histology*; D012984:Software; D041623:Tomography, Optical Coherence / Q000295:instrumentation*
keywords: OCT; Outer segments; Retinal thickness; Segmentation; Spectral domain