Development of a Pupillary Plant Model for Investigating the Effects of Range Nonlinearity on Pupil Size Variability Signal

Pupil Size Variability (PSV), referring to the continuous fluctuation of pupil size without visual accommodation or light stimulation, results from the coupling of cardiovascular regulation signals from the brainstem to the pupil. This phenomenon can provide useful trend data for assessing the condition of the Autonomic Nervous System (ANS). It has been proposed that PSV can be monitored through a mobile health (m-health) system in the form of smart eyewear. The pupillary plant displays a range nonlinearity (RNL) property, causing the level of pupil size fluctuations to change nonlinearly with the mean pupil size. Before PSV can be accurately used to estimate ANS condition, a deeper understanding of the biomechanical mechanisms behind RNL is required. A model incorporating the biomechanical properties of the pupillary muscle plant and the regulation of the ANS has been developed to simulate PSV under the effects of RNL. Our study found that RNL contributes to a nonlinear lowpass filtering effect. The simulation results suggest that a compensation technique will be necessary for estimating ANS condition based on PSV.