Several techniques using autonomic nervous system equilibrium recording parameters allow assessment of pain in the awake subject or nociception in the patient under general anesthesia. The main objective of these monitoring techniques is to allow a more rational use of analgesics in non-communicating patients (extreme ages of life, neurological or psychiatric pathology, anesthetic awakening, resuscitation patients) or intraoperatively, avoiding over- or under-dosing with opioids, thus improving the hemodynamic stability of the most fragile patients while minimizing the phenomena of postoperative hyperalgesia. Videopupillometry now allows a simple assessment of pain in patients awake or under general anesthesia. Only dynamic tests, such as the measurement of the pupillary dilatation reflex to pain or the photomotor reflex, can provide information, a posteriori, on the imbalance induced by the stimulation, and thus provide information on the balance of pain / analgesia or nociception / antinociception at a given moment. In the same way, the monitoring of the variability of the pupillary diameter appears as a dynamic measure likely to bring information on the balance pain / analgesia, with the advantage of being able to be carried out continuously.