Proposal of Pupil Diameter Measurement Method and Restraint Stress in Albino Rats for Estimate of Autonomic Nervous System

The autonomic nervous system controls the size of the pupil diameter. In particular, the pupil diameter fluctuation, which constantly change the size of the pupil under constant illuminance, is correlated with the heart rate fluctuation commonly used in autonomic function estimation. Autonomic function estimation by pupil diameter fluctuation is still under development because albino rats often used in autonomic nervous function experiments. In this study, we propose a method to detect a pupil and measure pupil diameter by image processing of albino rats under near-infrared illumination without fixing eyelids. As a result of pupillary diameter measurement accuracy evaluation, the mean error rate of the measured value and the calculated value was 0.51%, and the correlation coefficient was 0.955 (p < 0.001), suggesting the usefulness of the proposed method. In addition, we obtained the pupil diameter fluctuation under restraint load using the proposed method, and examined whether autonomic nerve function can be estimated by frequency analysis. The analysis confirmed the tendency of autonomic nervous system function observed during restraint load, suggesting that autonomic nervous function estimation by pupil diameter fluctuation may be possible.