Purpose

To assess the impact of using different numbers of cells in calculations of the coefficient of variation (COV) value for normal and polymegethous endothelia

Methods

Four sets of 20 non-contact specular microscope images obtained from Caucasian individuals were assessed, and categorized according to the extent of polymegethism, i.e. grade 0 (none), grade 1 (mild), grade 2 (moderate) and grade 3 (substantial). Cell areas were measured manually and then values for between 2 and 100 cells were progressively added and averaged to generate COV estimates. These were then assessed in terms of their relative values (as percentages +/- SD) in relation to the value obtained on over 100 cells.

Results

For the 4 sets of endothelia with group-mean COV values of 25.8, 33.1, 45.1 and 56.8%, the reliability of the COV estimates realized asymptotic values of close to ±1.0, ±2.7, ±3.6 and ±5.0% with 90 cells, but with greater uncertainty with few numbers of cells, e.g. only to within ±3.4, ±5.3, ±6.1 and ±7.9% with 75 cells.

Conclusions

COV estimates for the corneal endothelium are dependent on the number of cells used in the calculations. It is recommended that every effort should be made to not only assess 75–100 cells per endothelial image, but that this number should be the same or very similar for all endothelial images in a particular data set so that the uncertainly (or estimated proportional error) in the estimates is balanced.

中文翻译：

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对角膜内皮细胞面积值的变异系数 (COV) 估计值进行标准化测量的细胞数量的重要性与隐形眼镜佩戴相关

目的

评估使用不同细胞数计算正常和多巨细胞内皮变异系数 (COV) 值的影响

方法

评估了从白种人个体获得的四组 20 张非接触镜面显微镜图像，并根据多变的程度进行分类，即 0 级（无）、1 级（轻度）、2 级（中度）和 3 级（严重） . 手动测量细胞面积，然后逐渐添加 2 到 100 个细胞的值并取平均值以生成 COV 估计值。然后根据它们相对于在 100 多个细胞上获得的值的相对值（以百分比 +/- SD 表示）进行评估。

结果

对于组平均 COV 值为 25.8、33.1、45.1 和 56.8% 的 4 组内皮，COV 估计的可靠性实现了接近 ±1.0、±2.7、±3.6 和 ±5.0% 的渐近值，90 个细胞，但在电池数量较少时具有更大的不确定性，例如仅在 ±3.4、±5.3、±6.1 和 ±7.9% 范围内使用 75 个电池。

结论

角膜内皮的 COV 估计值取决于计算中使用的细胞数量。建议应尽一切努力不仅评估每个内皮图像的 75-100 个细胞，而且对于特定数据集中的所有内皮图像，该数量应该相同或非常相似，以便不确定（或估计的比例误差） ) 在估计中是平衡的。