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Muhammed Alluwimi, William Swanson, Victor Malinovsky; Using Asymmetry Analysis to Reduce Normal Variability of Spectral Domain Optical Coherence Tomography (SD-OCT) Macular Thickness. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5491.
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To investigate the use of asymmetry analysis to reduce normal between-subject variability of macular thickness measurements using SD-OCT.
63 volunteers free of eye disease were recruited: 33 young subjects (ages 21 to 35 years), and 30 older subjects (ages 45 to 85 years). All participants passed a comprehensive ophthalmic examination within the past two years. Macular images were gathered with the Spectralis OCT (V 5.4, Heidelberg Engineering, GmbH), using the Posterior Pole asymmetry analysis. The image quality score was required to be 25 or greater. The overlay 8°×8° grid was manually centered on the fovea and aligned with the foveal-disc axis. This grid was divided into five zones per hemifield following the method of Um et al (2012 IOVS 53:1139), and asymmetry was computed as the difference between superior and inferior zone thicknesses. We assumed that the lowest variation and the highest density of ganglion cells will be found ~3° to 6° from the foveal center. This corresponds to zones 1 and 2, and has less vasculature than the other zones. For each zone and age group, between-subject standard deviations (SDs) were compared for retinal thickness (RT) versus asymmetry using an F-test. To account for repeated measures, p < 0.0125 was used for significance. Axial length (AL) and corneal curvature (CC) were measured with IOLMaster by the same operator and during the same imaging session.
For OD, asymmetry analysis reduced between-subject variability in zones 1 and 2 in both groups (F > 3.2, p < 0.001). SD for zone 1 dropped from 12.0 to 3.0 µm in the younger group and from 11.7 to 2.6 µm in the older group. SD for zone 2 dropped from 13.6 to 5.3 µm (younger) and from 11.1 to 5.8 µm (older). Combining all subjects, neither RT nor asymmetry showed a strong correlation with AL or CC (r2 <0.01) . Analysis for OS yielded the same pattern of results, as did asymmetry analyses between eyes (F >3.8, p < 0.0001).
Asymmetry analysis reduced between-subject variability and age effects. These findings demonstrate the potential usefulness of the RT asymmetry analysis for improving ability to detect glaucomatous damage of the macula.
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