Upper eyelid contour symmetry measurement with Bézier curves

ABSTRACT Purpose: The purpose of the present work is to measure the interocular upper lid contour symmetry using a new method of lid contour quantification. Methods: The Bézier curve tool of the Image J software was used to extract the right and left upper eyelid contours of 75 normal subjects. Inter-observer variability of 29 right lid contours obtained by two independent observers was estimated using the coefficient of overlap of two curves and an analysis of the differences of the contour peak location. A two-way analysis of variance was used to test the mean value of the coefficient of overlap of the right and left contours in males and females and lid segments. The same analysis was performed to compare the location of the contour peak of the right and left contours. Results: The coefficient of contour overlap obtained by independent observers ranged from 93.5% to 98.8%, with a mean of 96.1% ± 1.6 SD. There was a mean difference of 0.02 mm in the location of the contour peak. Right and left contour symmetry did not differ between females and males and was within the range of the method variability for contour overlap and location of the contour peak. Conclusions: The upper eyelid contour is highly symmetrical. Bézier lines allow a quick and fast quantification of the lid contour, with a mean inter-observer variability of 3.9%.

摘要
目的：本研究旨在采用一种全新的睑轮廓量化方法，评估双眼上睑轮廓的对称性。
方法：使用ImageJ软件的贝塞尔曲线（Bézier curve）工具，提取75名正常受试者的双侧上睑轮廓。由两名独立观察者对29例右侧上睑轮廓进行测量，通过两曲线重叠系数及轮廓峰位置差异分析，评估观察者间变异。采用双向方差分析，检验男女受试者双侧睑轮廓重叠系数均值及眼睑节段的差异；并采用相同分析方法，对比双侧睑轮廓峰的位置差异。
结果：独立观察者测得的轮廓重叠系数介于93.5%~98.8%之间，均值为96.1%±1.6标准差（SD）。轮廓峰位置的平均差异为0.02mm。男女受试者间双侧睑轮廓对称性无显著差异，且该结果处于本方法轮廓重叠与轮廓峰位置的变异范围之内。
结论：上睑轮廓具有高度对称性。贝塞尔曲线可快速高效地实现睑轮廓的量化分析，观察者间平均变异率为3.9%。