Pupillography as an objective indicator of fatigue

Abstract

Purpose. To determine whether parameters calculated from pupillary activity can identify subjects with sleep deprivation, and whether the objective values correlate with a subjective feeling of fatigue. Methods. pupil size in the dark was recorded continuously for 10 minutes in 12 healthy volunteers using an infrared video camera. Two recordings were made for each subject: after a full night’s sleep, and after 24 hours of sleep deprivation. Several parameters calculated from pupil size and activity were analyzed and compared with a subjective rating of the state of alertness provided by the participants in each test. Results. All pupillary parameters differed significantly between alertness and fatigue (p = 0.0076–0.0186). Changes in one of the parameters – average pupillary diameter – correlated with changes in the subjective level of sleepiness (r = -0.51, p = 0.028). Although the values of most parameters differed among subjects, an absolute value of more than 25 in one parameter, cumulative pupillary variability ratio, was always associated with sleep deprivation. Conclusion. On-line analysis of the pupillogram using the suggested parameters can be performed easily to produce a real-time assessment of an individual’s state of alertness or fatigue that correlates with his/her subjective assessment of this state.