Evaluation of the methods for pupil size estimation: on the perspective of autonomic activity.

The purpose of This work is to find the optimal calculation method about pupil size to estimate an activity of autonomic nerve system. To evaluate its state, we have to calculate an accurate pupil size from the image of free-rotated and yawed eye for 5 minutes. But calculation of the pupil size from image takes a long time. So we suppose three methods which considered cost (time), accuracy and evaluate for each. 'Method' 1 is to calculate the vertical pupil diameter from images, 'method 2' is to calculate the pupil size from whole image (method 2-1; by binarization and method 2-2; by binarization with shape evaluation) and 'method 3', the most accurate method, is from three-dimensional transformation of pupil image. As a result, for seven subjects, each method is takes about 6, 44, 124, 311 minutes to evaluate five-minute images (300,000 pixels/frame, 30 frames/sec). Also, the result of correlation between the parameter Lf/Hf ratio of heart rate variability, commonly used method for estimate the state of autonomic nerve system, and it of pupil size variability is, for each case, 0.34, 0.2, 0.69, 0.69.