The effects of sleep deprivation on oculomotor responses.

PURPOSE  Fatigue due to sleep deprivation is one of the main causes of accidents. An objective and efficient method for determining whether the person is tired could provide a valuable tool in accident prevention. In this study, we evaluated whether oculomotor responses related to pupillary light reflex and saccadic velocity can identify subjects with sleep deprivation and whether these objective values correlate with subjective feeling of sleepiness. METHODS  Thirteen normal subjects (5 male, 8 female) participated in a 4-day study. During the first two days following a full night's (8 hr in bed) sleep, they underwent baseline automated oculomotor testing using the FIT-2500-Fatigue-Analyzer. Following a third full night's sleep, participants were then sleep-deprived for 28 hr. Ten measurements of automated oculomotor tests were performed during the sleep deprivation period. Visually-guided saccadic velocity (SV), initial pupil diameter (PD), pupillary constriction latency (CL), and amplitude of pupil constriction (CA) were assessed using the FIT-2500-Fatigue-Analyzer. The FIT-index, which expresses the deviation of the ocular parameters from the baseline measurements, was calculated. Correlation of oculomotor parameters with the subjective Stanford Sleepiness Scale (SSS) was performed. RESULTS  We found that oculomotor measures showed a significant increase in CL (298.6 to 308.4 msec, P < 0.05) and calculated FIT index (3.4 to 16.8, P < 0.05) and a significant decrease in SV (64.8 to 59.6 deg/sec) during sleep deprivation. The SSS was found to significantly increase over the sleep deprivation period (2.05 to 5.05, P < 0.05) and was significantly correlated with the FIT-index (r > 0.66, P < 0.02). CONCLUSION  Evaluation of oculomotor responses, particularly CL and SV together with the FIT-index, might have practical applications for the assessment of an individual's state of alertness or fatigue. Correlation of the FIT-index to the SSS provides evidence for the potential usefulness of oculomotor function measurements in the detection of subjective sleepiness.