Figure 1.

Image processing steps for irissometry. First, the limbus must be selected manually by using a computer mouse pointer (blue circle in top-left panel). Then, a startburst-like method calculates luminance changes per wedge (see #1 to #n in the top-left image of the right panel) across eccentricity, extending from the image center toward the limbus within a predefined suitable range. A pupil border per wedge (colored lines in top-right image) is detected based on the maximum luminance change above a predefined threshold (dotted line). In this study, the process was repeated (iterations) five times with an adjustment of the starting point for the wedge extensions per iteration, causing the pupil border to be detected at equal distance from the center of the pupil across wedges (bottom-left image depicts the luminance values of wedges across eccentricity for the first and last iterations). Within an iteration, detection of the pupil borders allowed calculation of the coordinates of the center of the pupil based on a circle fitted to the border points (cyan dot in bottom-right image), which served as a starting point instead of the image center (red dot) for the next frame. Finally, unique corner point features were detected between the pupil border and limbus, to be tracked from frame to frame (see bottom-left panel). Blinks or eye movements caused the pupil to deform, decreasing the fitted circular shape (see red surface) to a degree that could easily be detected using a predefined threshold.