Effects of 24-hour and 36-hour sleep deprivation on smooth pursuit and saccadic eye movements

Sleep restrictions and sleep deprivation have become common in modern society, as many people report daily sleep below the recommended 8 hours per night. This study aimed to examine the effects of sleep deprivation on oculomotor performance by recording smooth pursuit and saccadic eye movements after 24 and 36 hours of sleep deprivation. Another objective was to determine whether detected changes in oculomotor performance followed fluctuations according to a circadian rhythm and/or subjective Visuo-Analogue sleepiness Scale scores. Oculomotor responses were recorded from 18 subjects using electronystagmography, and comprised measurements of accuracy (i.e., the percentage of time the eye movement velocity was within the target velocity boundaries), velocity and latency. Continuous EEG recordings were used to validate that subjects had remained awake throughout the 36-hour period. Our findings showed that sleep deprivation deteriorated smooth pursuit gain, smooth pursuit accuracy and saccade velocity. Additionally, the ratio between saccade velocity and saccade amplitude was significantly decreased by sleep deprivation. However, as the length of sleep deprivation increased, only smooth pursuit gain deteriorated further, whereas there were signs of improvement in smooth pursuit accuracy measurements. The latter observation suggests that smooth pursuit accuracy might be affected by the circadian rhythm of alertness. Surprisingly, high subjective scores of sleepiness correlated in most cases with better saccade performance, especially after 36 hours of sleep deprivation, suggesting that awareness of sleepiness might make subjects perform better during saccade assessments. To conclude, oculomotor function clearly decreased after sleep deprivation, but the performance deteriorations were complex and not necessarily correlated with subjectively felt sleepiness.