Webcam-Based Pain Measurement Using Pupillary Diameter

Pupillometry can be used as a method for monitoring pain. There are experimental conditions under which standard pupillometry equipment cannot be used. Studying the effects of different pulse forms used for transcutaneous spinal cord stimulation (tSCS) is one such task. The aim was to create a system for recording pupil diameter based on a web camera because it can be synchronised with external equipment, which allows the diameter to be recorded simultaneously with other physiological signals. A markerless system for recording and analysing pupil diameter using deep neural networks was developed based on a commercially available web camera. The accuracy of this system was compared with the accuracy of measurements using manual analysis with ImageJ (version 1.54g). For validation, the system was tested in a study of the dependence of tolerance to tSCS on the shape of stimulating pulses, which involved volunteers (n = 12). The results of the developed pupillometry were compared with the pain rating scale traditionally used in such studies. The developed system is accurate in determining the pupil diameter, comparable to human accuracy. The pupillometry results reproduced those obtained using a subjective pain scale. This method was found to be a reliable method for recording nociceptive pupillary responses in electrophysiology.