Patel Nimesh B, Wheat Joe L, Rodriguez Aldon, Tran Victoria, Harwerth Ronald S
College of Optometry, University of Houston, Houston, Texas 77204, USA.
Optom Vis Sci. 2012 May;89(5):E652-66. doi: 10.1097/OPX.0b013e318238c34e.
An assessment of the retinal nerve fiber layer (RNFL) provides important information on the health of the optic nerve. There are several non-invasive technologies, including spectral domain optical coherence tomography (SD OCT), that can be used for in vivo imaging and quantification of the RNFL, but often there is disagreement in RNFL thickness between clinical instruments. The purpose of this study was to investigate the influence of scan centration, ocular magnification, and segmentation on the degree of agreement of RNFL thickness measures by two SD OCT instruments.
RNFL scans were acquired from 45 normal eyes using two commercially available SD OCT systems. Agreement between RNFL thickness measures was determined using each instrument's algorithm for segmentation and a custom algorithm for segmentation. The custom algorithm included ocular biometry measures to compute the transverse scaling for each eye. Major retinal vessels were identified and removed from RNFL measures in 1:1 scaled images. Transverse scaling was also used to compute the RNFL area for each scan.
Instrument-derived global RNFL thickness measured from the two instruments correlated well (R(2) = 0.70, p < 0.01) but with significant differences between instruments (mean of 6.7 μm; 95% limits of agreement of 16.0 μm to -2.5 μm, intraclass correlation coefficient = 0.62). For recentered scans with custom RNFL segmentation, the mean difference was reduced to 0.1 μm (95% limits of agreement 6.1 to -5.8 μm, intraclass correlation coefficient = 0.92). Global RNFL thickness was related to axial length (R = 0.24, p < 0.01), whereas global RNFL area measures were not (R(2) = 0.004, p = 0.66). Major retinal vasculature accounted for 11.3 ± 1.6% (Cirrus) or 11.8 ± 1.4% (Spectralis) of the RNFL thickness/area measures.
Sources of disagreement in RNFL measures between SD-OCT instruments can be attributed to the location of the scan path and differences in their retinal layer segmentation algorithms. In normal eyes, the major retinal vasculature accounts for a significant percentage of the RNFL and is similar between instruments. With incorporation of an individual's ocular biometry, RNFL area measures are independent of axial length, with either instrument.
对视神经纤维层（RNFL）的评估可为视神经健康状况提供重要信息。有多种非侵入性技术，包括光谱域光学相干断层扫描（SD OCT），可用于RNFL的活体成像和定量分析，但临床仪器之间的RNFL厚度测量结果常常存在差异。本研究旨在探讨扫描中心位置、眼放大率和分割方法对两种SD OCT仪器测量RNFL厚度一致性的影响。
使用两种市售SD OCT系统对45只正常眼进行RNFL扫描。采用每种仪器的分割算法和一种自定义分割算法来确定RNFL厚度测量结果之间的一致性。自定义算法包括眼生物测量指标，用于计算每只眼睛的横向缩放比例。在1:1比例的图像中识别并去除主要视网膜血管对RNFL测量结果的影响。横向缩放比例还用于计算每次扫描的RNFL面积。
两种仪器测量得到的基于仪器的总体RNFL厚度相关性良好（R(2)=0.70，p<0.01），但仪器之间存在显著差异（平均差异为6.7μm；一致性界限95%为16.0μm至-2.5μm，组内相关系数=0.62）。对于采用自定义RNFL分割的重新定位扫描，平均差异降至0.1μm（一致性界限95%为6.1至-5.8μm，组内相关系数=0.92）。总体RNFL厚度与眼轴长度相关（R=0.24，p<0.01），而总体RNFL面积测量结果则不然（R(2)=0.004，p=0.66）。主要视网膜血管系统占RNFL厚度/面积测量值的11.3±1.6%（Cirrus）或11.8±1.4%（Spectralis）。
SD-OCT仪器之间RNFL测量结果存在差异的原因可归因于扫描路径位置及其视网膜层分割算法的不同。在正常眼中，主要视网膜血管系统在RNFL中占相当比例，且仪器之间相似。纳入个体眼生物测量指标后，无论使用哪种仪器，RNFL面积测量结果均与眼轴长度无关。
