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Radouil T Tzekov, Keith Zimmerman, David Richards, Ramesh Ayyala; Variability and repeatability of inner retinal macula layers segmentation by SD-OCT. Invest. Ophthalmol. Vis. Sci. 2019;60(9):145.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate variability and repeatability of inner retinal macular layers’ segmentation by two models of Spectralis SD-OCT (Heidelberg Engineering Inc., Carlsbad, CA).
This was a prospective observational study of normal volunteers. Posterior pole SD-OCT scans (8 x 8 grid) centered on the fovea were performed on the same day as three consecutive images of each eye were acquired on two models (2011 and 2017) of Spectalis SD-OCT by two operators. The same procedure was repeated in 2-3 weeks. The retinal nerve fiber layer (RNFL), the ganglion cell layer (GCL) and the inner plexiform layer (IPL) were segmented automatically by Spectralis software and a combined thickness: ganglion cell complex (GCC) was calculated. For each grid cell the root mean square (RMS) deviation from the mean of each set of three measurements, for each layer, was calculated and analyzed both in terms of absolute values and as a percent of the average thickness at that location.
Both eyes of 15 volunteers (5 men and 10 women) aged 34.4 +/- 12.2 years were imaged. The average RMS deviation among the three images varied as follows: 3.0-3.8 µm (RNFL), 2.1-2.2 µm (GCL), 1.9-2.1 µm (IPL), 3.2-4.2 µm (GCC) and there was no difference between right and left eyes (p>0.05). These ranges translated to 8.4-9.9% (RNFL), 6.7-7.5% (GCL), 6.9-8.9% (IPL) and 3.3-4.2% (GCC) of local retinal thickness. On both instruments and for both visits, all four layers showed a negative linear relationship between the thickness of the retinal layer and RMS error as percent of local thickness. The R2 ranged from 0.1116 to 0.5366 and the slopes of the regression ranged from -0.0090 to -0.0355; however, a sub-analysis based on similar range of layer thickness revealed no difference between the slopes (p>0.05). Analysis of the variation of the percent RMS error in terms of topography revealed distinct differences in the position of maximal % RMS error for each layer and this position was consistent between the 2011 and the 2017 model and between visits
These findings support our previous observation indicating that variability of SD-OCT measurement of individual retinal layers in the macula increases in areas where the thickness of the layers decreases. Detection of change in individual layer thickness over time (e.g. for measurement of glaucomatous progression) will therefore become more difficult at these regions.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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