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G. J. Jaffe, I. C. Han; Retinal Thickness Measurements in Spectral Domain versus Time Domain Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1877.
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Spectral domain optical coherence tomography (SD-OCT) is a relatively new technology that provides improved image resolution and expedited image acquisition compared to time-domain OCT (TD-OCT) currently in widespread clinical use. The improved image resolution in SD-OCT has allowed for changes in segmentation algorithms to measure retinal thickness. In this study, we compare retinal thickness measurements (RTM) obtained by two different SD-OCT machines with RTM obtained by TD-OCT.
SD-OCT machines used in this study were the Cirrus HD-OCT (Carl Zeiss Meditec, Dublin, CA) and the Spectralis HRA+OCT (Heidelberg Engineering, Heidelberg, Germany). The Stratus (Carl Zeiss Meditec) TD-OCT was used for comparison. Patients who received volume scanning in a single session with either the Spectralis or Cirrus and the Stratus were identified via the Duke Eye Center OCT database. Images were reviewed for quality, and scans with gross inner/outer retina misidentification resulting in unusable thickness maps were excluded. RTM from the nine subfields were recorded from thickness maps generated by each machine, and an average thickness value was calculated for each subfield. The mean paired difference between RTM from either the Spectralis or Cirrus and the Stratus was then calculated and compared for each subfield, all subfields combined, inner ring (subfields 2-5), and outer ring (subfields 6-9).
Volume scans of 140 eyes from 89 patients were reviewed for the Spectralis-Stratus comparison. The mean paired difference for the central 1 mm subfield was 76.4 µm ± 38.3 µm. The difference across all subfields was 93.3 ± 52.5. For the Cirrus-Stratus comparison, scans of 72 eyes from 40 patients were reviewed. The mean paired differences for the central subfield and all subfields were 50.7 ± 30.4 and 44.8 ± 21.5 respectively. Interestingly, for Spectralis-Stratus, the average mean paired difference was greater for the outer (112.4 ± 52.8) versus inner ring (77.2 ± 47.4), and this discrepancy was noted to be statistically significant. For the Cirrus-Stratus, the opposite was observed, with the average mean paired difference of the inner ring (47.2 ± 24.3) being greater than the outer ring (41.9 ± 14.9) to a statistically significant degree.
Retinal thickness measurements obtained by SD-OCT (Heidelberg Spectralis and Zeiss Cirrus) is consistently greater than those obtained by TD-OCT (Zeiss Stratus). Consideration of these RTM differences between SD-OCT and TD-OCT is essential when using this information in clinical settings.
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