Fig. 1

Example of preprocessing a digital photograph for deriving measured indices. The images were converted to grayscale (a). On the image, the operator has marked the medial and lateral canthi (b). To build a palpebral fissure region of interest (ROI) with an interactive polygonal drawing approach, the operator would first click on the medial or lateral canthus, then drag the mouse along the eyelid contour, and then click on the opposite canthus (c). The image was then binarized, and a circle was formed around the eye, with the connecting line between the medial and lateral canthi serving as the diameter (d, e)