Assessing Errors Inherent in OCT-Derived Macular Thickness Maps

Abstract

SD-OCT has become an essential tool for evaluating macular pathology; however several aspects of data collection and analysis affect the accuracy of retinal thickness measurements. Here we evaluated sampling density, scan centering, and axial length compensation as factors affecting the accuracy of macular thickness maps. Forty-three patients with various retinal pathologies and 113 normal subjects were imaged using Cirrus HD-OCT. Reduced B-scan density was associated with increased interpolation error in ETDRS macular thickness plots. Correcting for individual differences in axial length revealed modest errors in retinal thickness maps, while more pronounced errors were observed when the ETDRS plot was not positioned at the center of the fovea (which can occur as a result of errant fixation). Cumulative error can exceed hundreds of microns, even under “ideal observer” conditions. This preventable error is particularly relevant when attempting to compare macular thickness maps to normative databases or measuring the area or volume of retinal features.

Macular structural characteristics in children with Down syndrome

“…Approximately 80 % of patients with Down syndrome are hyperopic, and their spherical equivalent is correlated with axial length [40]. 2) According to Odell and colleagues [39], after adjusting for shorter axial length, our data should demonstrate an even thicker central subfield in the Down syndrome group. In other words, adjusting for axial length confirmed our conclusion that CST was significantly different between the two groups.…”

“…Although axial length can affect CST results [39], we do not think it would have affected the results of this study, for two reasons. 1) We chose spherical equivalent-matched control subjects.…”

Longitudinal Analysis of Drusen Volume in Intermediate Age-Related Macular Degeneration Using Two Spectral-Domain Optical Coherence Tomography Scan Patterns

“…Using different scan densities for quantification of retinal thickness, only minimal changes in calculated retinal thickness measurements to a B-scan distance of up to 188 µm have been reported in systematic analyses based on cross-sectional imaging [37,38].…”

Lateral and axial measurement differences between spectral-domain optical coherence tomography systems

“…These differences may not affect disease management with uniform scanning protocols and manual measurements based on the small number of pixels required for the observed differences and the larger errors associated with automated segmentation, sampling density, and fixation variability. 7,[10][11][12][13] However, clinical studies gathering repeated measurements over time to evaluate disease modification may obtain statistically significant differences that remain within the range of instrument variability.…”

“…Previous studies have identified OCT-derived retinal thickness measurement variability due to differences in their segmentation algorithms, their reported axial resolutions in tissue, their scan density options, and their ability to correct for subject fixation. [7][8][9][10][11][12][13] Additional anatomic factors vary between individual patients, including axial length, refractive focal length, and macular curvature.…”