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 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.