Pupillography as an objective indicator of fatigue

Purpose. to determine whether parameters calculated from pupillary activity can identify subjects with sleep deprivation, and whether the objective va lues 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 sl eep deprivation. Several parameters calculated from pupil size and activity were analyzed and compared with a subjective rating of the state of alertn ess 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 sl eepiness (r = -0.51, p = 0.028). Although the values of most parameters dif fered among subjects, an absolute value of more than 25 in one parameter, c umulative pupillary variability ratio, was always associated with sleep dep rivation. Conclusion. On-line analysis of the pupillogram using the suggested paramet ers can be performed easily to produce a real-time assessment of an individ ual's state of alertness or fatigue that correlates with his/her subjective assessment of this state.