Department of Ophthalmology and Visual Sciences, Fundus Photograph Reading Center, College of Engineering, Mechanical Engineering-General, University of Wisconsin-Madison, Madison, WI 53717, USA.
Invest Ophthalmol Vis Sci. 2011 Nov 1;52(12):8558-61. doi: 10.1167/iovs.11-7917.
Studies have used central retinal arteriolar (CRAE) and central retinal venular (CRVE) calibers, measured from images produced with computerized image analysis, to detect risk factors for systemic diseases. The authors explored suboptimal image focus as a possible contributing factor to artificially larger vascular caliber measurements.
From the reading center image collections, 30 digital retinal images were selected for optimum quality. Image analysis software was used to derive nine progressively blurred versions of the originals. IVAN measurement software was used to measure CRAE and CRVE in the original and the blurred series derived from them. To check the adequacy of the simulation, progressively defocused series of images were taken of several volunteers.
For CRAE, each level of simulated blurring produced a statically significant increase in apparent vessel caliber from the original (P<0.01, Wilcoxon signed rank test). For an average CRAE of 160 μm, mean broadening with minimal/moderate/severe blurring was 3 μm/12 μm/33 μm. For CRVE, every blurring level beyond the first was found to be significant (P<0.01). From an average CRVE of 200 μm, mean broadening ranged from 0 to 11 μm with minimal to severe blurring. Analysis of the progressively defocused series taken of volunteers yielded similar results overall.
Suboptimal focus can result in erroneously larger vessel caliber measurements. Slight blurring has a minimal effect, but more severe blurring has a progressively greater effect.
已有研究利用计算机图像分析得出的中央视网膜小动脉（CRAE）和中央视网膜小静脉（CRVE）的直径来检测系统性疾病的危险因素。作者探讨了图像聚焦不佳可能是人为增大血管直径测量值的一个原因。
从阅读中心的图像库中选择 30 张具有最佳质量的数字视网膜图像。使用图像分析软件对原始图像进行九次逐渐模糊的处理。使用 IVAN 测量软件对原始图像及其衍生的模糊系列中的 CRAE 和 CRVE 进行测量。为了检查模拟的充分性，对几名志愿者的一系列逐渐失焦的图像进行了拍摄。
对于 CRAE，每一级模拟模糊都导致与原始图像相比，表观血管直径出现显著增加（P<0.01，Wilcoxon 符号秩检验）。对于平均 CRAE 为 160μm，最小/中度/严重模糊时的平均增宽分别为 3μm/12μm/33μm。对于 CRVE，第一级以后的每一级模糊都有显著差异（P<0.01）。对于平均 CRVE 为 200μm，最小到严重模糊时的平均增宽范围从 0 到 11μm。对志愿者进行的逐渐失焦系列分析总体上得出了相似的结果。
图像聚焦不佳可能导致血管直径测量值出现错误地增大。轻微模糊的影响最小，但更严重的模糊会产生逐渐增大的影响。
