Kim Eon, Ehrmann Klaus
Vision Cooperative Research Centre, Sydney, New South Wales, Australia.
Clin Exp Optom. 2012 Jul;95(4):432-41. doi: 10.1111/j.1444-0938.2012.00724.x. Epub 2012 May 9.
The aim was to study the reliability of measurements of the RTVue (Optovue, Fremont, CA, USA) anterior segment optical coherence tomographer (AS-OCT) and assess how results can be improved by analysing raw optical coherence tomography data with customised image analysis software and applying correction factors.
Five RTVue AS-OCT instruments (ver. 4.0) were assessed by imaging gauge blocks of three different lengths, single/stepped glass plate (microscope slides) and flat window glass to check for width, depth and linearity of the measurement scans. Five repeats per calibration tool were imaged and averaged. Raw data were exported and loaded into customised image analysis software written in LabWindows/CVI for further analysis. Using two calibration balls with different radii, measurement scans were validated. Repeatability of the optical coherence tomographs and the edge detection procedure were checked and statistical analyses performed.
Variations ranging from 0.01 to 1.93 mm in scan width and 0.1 to 0.17 mm in scan depth were found between the five instruments. Slight curvature distortion of 0.06 ± 0.01 mm (mean and standard deviation) was found in the raw images. By isolating the three sources of image distortion and applying individual correction factors, accuracy for corneal curvature measurements could be improved to better than 0.1 mm. Manual edge detection limited the coefficient of repeatability value to 0.06 and 0.08 mm for anterior and posterior radii of curvature, respectively. The coefficient of repeatability of corneal thickness measurements was less than 8 µm.
Accuracy of the RTVue AS-OCT varied between instruments. By applying calibration scale factors calculated by customised software, accuracy of thickness and curvature values of the anterior eye was improved. The achievable precision is sufficient to detect clinically relevant corneal curvature variations.
本研究旨在探讨美国加利福尼亚州弗里蒙特市Optovue公司生产的RTVue眼前节光学相干断层扫描仪（AS - OCT）测量结果的可靠性，并评估通过使用定制图像分析软件分析原始光学相干断层扫描数据及应用校正因子如何提高测量结果。
对五台RTVue AS - OCT仪器（版本4.0）进行评估，通过对三种不同长度的量规块、单/阶梯玻璃板（载玻片）和平板窗玻璃成像，检查测量扫描的宽度、深度和线性度。对每个校准工具进行五次重复成像并求平均值。导出原始数据并加载到用LabWindows/CVI编写的定制图像分析软件中进行进一步分析。使用两个不同半径的校准球对测量扫描进行验证。检查光学相干断层扫描仪和边缘检测程序的可重复性并进行统计分析。
五台仪器之间的扫描宽度变化范围为0.01至1.93毫米，扫描深度变化范围为0.1至0.17毫米。在原始图像中发现了0.06±0.01毫米（平均值和标准差）的轻微曲率畸变。通过分离图像畸变的三个来源并应用单独的校正因子，角膜曲率测量的准确性可提高到优于0.1毫米。手动边缘检测将前、后曲率半径的可重复性系数值分别限制为0.06和0.08毫米。角膜厚度测量的可重复性系数小于8微米。
RTVue AS - OCT的准确性在不同仪器之间有所差异。通过应用定制软件计算的校准比例因子，提高了眼前节厚度和曲率值的准确性。可达到的精度足以检测临床上相关的角膜曲率变化。
