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Muneeswar Gupta Nittala, Ranjith konduru, Humberto R. Gracia, Srinivas R. Sadda; Effect of OCT Volume Scan Density on Thickness Measurements in Diabetic Macular Edema. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1332.
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To evaluate the impact of reducing B-scan density on retinal thickness measurements using spectral domain optical coherence tomography (SD-OCT) in eyes with diabetic macular edema (DME).
We retrospectively collected OCT data for 64 eyes of 43 patients undergoing imaging for DME using the Cirrus HD-OCT 512 x 128 macular cube protocol. For each case, raw OCT data was imported into the 3D-OCTOR software and retinal thickness maps were generated using all 128 B-scans, as well as a lower density of B-scans ranging from every other scan to only two scans (every 64th B-scan). Maps were generated before and after manual correction of retinal boundary segmentation errors. The foveal central subfield (FCS) and total retinal volume (TRV) values were used to compare thickness maps of varying densities.
The mean difference in FCS retinal thickness and TRV increased as the B-scan density was reduced, particularly when the density was reduced to fewer than 16 B-scans over 6 mm. At a density of 16 B-scans, the mean absolute difference in FCS thickness was 2.43 microns (0.79%), with a maximum of 10.1 microns (4.09%). At this density, the mean difference in total retinal volume was 0.002 ml (0.82%), with a maximum difference of 0.01ml (5.13%). Manual correction of OCT segmentation errors resulted in a difference in FCS thickness of ≥10 microns in only 12.5% of cases, with a maximum difference of 115.7 microns.
A minimum of 16 equally spaced B-scans appears necessary to generate retinal thickness measurements similar to those produced using all 128 B-scans in eyes with DME. Manual correction of segmentation errors appeared to have a clinically meaningful effect in a small minority of cases. These results may have implications for the design of SD-OCT imaging and grading protocols in clinical trials of DME, particularly when using multiple SD-OCT instruments that acquire varying numbers of B-scans.
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