Upper eyelid contour symmetry measurement with Bezier curves

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 Bezier 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. Bezier lines allow a quick and fast quantification of the lid contour, with a mean inter-observer variability of 3.9%.