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M. Singh, H. A. Lin, A. Lai, J. Ng, C. K. L. Chee; Effect of Foveal Thickness on the Agreement Between Time Domain and Spectral Domain Optical Coherence Tomography Measurements. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4388.
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We hypothesized that there was poor agreement between time domain optical coherence tomography (TDOCT) and spectral domain OCT (SDOCT) in the quantitative assessment of macular thickness in eyes with macular edema. In this study we aimed to determine if thickening of the fovea affected the agreement between TDOCT and SDOCT measurements of foveal thickness (FT) and macular volume (MV).
We prospectively measured FT and MV with TDOCT (Stratus OCT) and SDOCT (Cirrus HD-OCT) (both Carl Zeiss Meditec, USA) in normal and edematous maculae using standardized protocols. Based on OCT measurement, eyes were classified as having a thickened macula if FT > 240 µm by Stratus OCT. Agreement in macular measurements between the two systems was determined by comparing the spans of the 95% confidence interval of the limits of agreement (LOA) on Bland-Altman plots.
183 eyes were included. Of these, 57 had thickened foveae based on FT > 240 µm by Stratus OCT. Considering all eyes together (n=183), mean FT and mean MV were greater with SDOCT than TDOCT (p<0.0001 for both). Comparing thickened with normal foveae, we found that the span of the 95% LOA for FT measurement between TDOCT and SDOCT was greater in thickened foveae than in normals (16.3 µm vs. 4.8 µm). Similarly the span of 95% LOA between TDOCT and SDOCT for MV was greater in thickened foveae than in normals (0.26 µm*3 vs. 0.089 µm*3
In thickened foveae there is poorer agreement between TDOCT and SDOCT measurements of FT and MV than in normals. Clinicians and researchers should be aware of this when using different OCT systems to evaluate patients with macular edema.
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