Antony Bhavna J, Stetson Paul F, Abramoff Michael D, Lee Kyungmoo, Colijn Johanna M, Buitendijk Gabriëlle H S, Klaver Caroline C W, Roorda Austin, Lujan Brandon J
School of Optometry, University of California Berkeley, CA, USA ; Vision Science Graduate Group, University of California Berkeley, CA, USA.
Carl Zeiss Meditec, Inc., Dublin, CA, USA.
Transl Vis Sci Technol. 2015 Jul 31;4(4):3. doi: 10.1167/tvst.4.4.3. eCollection 2015 Jul.
Off-axis acquisition of spectral domain optical coherence tomography (SDOCT) images has been shown to increase total retinal thickness (TRT) measurements. We analyzed the reproducibility of TRT measurements obtained using either the retinal pigment epithelium (RPE) or Bruch's membrane as reference surfaces in off-axis scans intentionally acquired through multiple pupil positions.
Five volumetric SDOCT scans of the macula were obtained from one eye of 25 normal subjects. One scan was acquired through a central pupil position, while subsequent scans were acquired through four peripheral pupil positions. The internal limiting membrane, the RPE, and Bruch's membrane were segmented using automated approaches. These volumes were registered to each other and the TRT was evaluated in 9 Early Treatment of Diabetic Retinopathy Study (ETDRS) regions. The reproducibility of the TRT obtained using the RPE was computed using the mean difference, coefficient of variation (CV), and the intraclass correlation coefficient (ICC), and compared to those obtained using Bruch's membrane as the reference surface. A secondary set of 1545 SDOCT scans was also analyzed in order to gauge the incidence of off-axis scans in a typical acquisition environment.
The photoreceptor tips were dimmer in off-axis images, which affected the RPE segmentation. The overall mean TRT difference and CV obtained using the RPE were 7.04 ± 4.31 μm and 1.46%, respectively, whereas Bruch's membrane was 1.16 ± 1.00 μm and 0.32%, respectively. The ICCs at the subfoveal TRT were 0.982 and 0.999, respectively. Forty-one percent of the scans in the secondary set showed large tilts (> 6%).
RPE segmentation is confounded by its proximity to the interdigitation zone, a structure strongly affected by the optical Stiles-Crawford effect. Bruch's membrane, however, is unaffected leading to a more robust segmentation that is less dependent upon pupil position.
The way in which OCT images are acquired can independently affect the accuracy of automated retinal thickness measurements. Assessment of scan angle in a clinical dataset demonstrates that off-axis scans are common, which emphasizes the need for caution when relying on automated thickness parameters when this component of scan acquisition is not controlled for.
光谱域光学相干断层扫描（SDOCT）图像的离轴采集已被证明会增加视网膜总厚度（TRT）测量值。我们分析了在通过多个瞳孔位置有意采集的离轴扫描中，使用视网膜色素上皮（RPE）或布鲁赫膜作为参考面获得的TRT测量值的可重复性。
从25名正常受试者的一只眼睛获取5次黄斑区的容积性SDOCT扫描。一次扫描通过中央瞳孔位置进行，随后的扫描通过四个周边瞳孔位置进行。使用自动方法对视网膜内界膜、RPE和布鲁赫膜进行分割。这些容积相互配准，并在9个糖尿病视网膜病变早期治疗研究（ETDRS）区域评估TRT。使用RPE获得的TRT的可重复性通过平均差异、变异系数（CV）和组内相关系数（ICC）计算，并与使用布鲁赫膜作为参考面获得的结果进行比较。还分析了另一组1545次SDOCT扫描，以评估典型采集环境中离轴扫描的发生率。
离轴图像中的感光细胞尖端较暗，这影响了RPE分割。使用RPE获得的总体平均TRT差异和CV分别为7.04±4.31μm和1.46%，而布鲁赫膜分别为1.16±1.00μm和0.32%。黄斑下TRT的ICC分别为0.982和0.999。第二组扫描中有41%显示出较大倾斜度（>6%）。
RPE分割因其靠近指状交叉区而受到混淆，指状交叉区是一个受光学斯泰尔斯-克劳福德效应强烈影响的结构。然而，布鲁赫膜不受影响，导致更稳健的分割，且对瞳孔位置的依赖性较小。
OCT图像的采集方式可独立影响自动视网膜厚度测量的准确性。对临床数据集中扫描角度的评估表明离轴扫描很常见，这强调了在扫描采集的这一组成部分未得到控制时，在依赖自动厚度参数时需要谨慎。
