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K. A. Soules, M. Durbin, T. Abunto, M. Horne, T. Callan, A. Singh-Walia; Effect of the Alignment Overlay Tool on Scan Placement Repeatability of the CirrusTm HD-OCT. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4238. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To determine the effect of the alignment overlay tool on scan placement repeatability of the Cirrus TM HD-OCT, a spectral domain optical coherence tomography instrument (Carl Zeiss Meditec, Dublin, CA).
Both eyes of 8 consented subjects with no known retinal disease were scanned on the Cirrus TM HD-OCT by 3 operators following an IRB approved protocol. Each eye was randomly assigned to have either a macular or optic nerve head (ONH) centered scan. The first operator performed a baseline scan on each eye. Subsequent scans by all operators were aligned to the baseline by using the alignment overlay tool.
The distance from the center of each repeat scan to the baseline scan was calculated. Table 1 below shows the mean distance (SD) of all repeat scans from the baseline:Table 1. Mean distance and SD of repeat scans from baseline, as measured from the center of each scan
In both macular and ONH scans, our results show good scan placement repeatability using the alignment overlay tool. All mean distances of repeat scans from baseline, as measured from the center of each scan, are within the desirable range. For macular scans, the desirable outcome is to repeat a scan within +/- 0.25 mm. Since the fovea is approximately 0.5 mm in diameter, and the central subfield is 1 mm in diameter, repeat scans within +/- 0.25 mm should not significantly affect retinal thickness measurements. In ONH scans, to achieve good reproducibility of RNFL average thickness values, the desirable outcome is to repeat the scan to within +/- 0.2 mm. of the baseline.
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