Towards a Mobile Phone Pupillometer

It is said that the eyes are the windows of the soul. Although rather poetic, such a statement becomes clearly more relevant if we acknowledge that dynamic changes in pupillary dimensions convey a great amount of information, regarding the general psychological and neurophysiological condition of the observed person. Most commonly used pupillometers are rather expensive, and may require highly controlled experimental setups to be used. Those can limit greatly the applicability of the devices in practise. Based on a basic smartphone and a cardboard support, originally proposed for virtual reality applications, we developed a portable pupillometer, which can be used in natural, as well as controlled stimuli conditions. The proposed device fits the category of monocular video pupillometers, meaning that it continuously measures one of the user’s eyes, while the other may receive pre-determined visual stimulation. To help validating the use of the pupillometer, we measured the evolution of pupillary dimensions during a standard “ice bucket” hand test. The results followed quite accurately the behaviour reported in literature, with increases of pupillary diameters in the order of 15% to 20%, as a result of placing or removing the subject’s hand. Recorded pupillary reaction response times were about 2.6 s, which suggest an interplay between the sympathetic and parasympathetic nervous system controlling activity.