A group of military servicemen were deprived of sleep for 65 h while they carried out a simulated military mission with a high visual workload. Their performance in a series of near vision tests was monitored. In general, the visual system was found to be resilient to the stress of sleep loss, the subjects experiencing mild symptoms of asthenopia (eyestrain). However, after 48 h without sleep there was a reduction in amplitude of convergent fusional reserves and a decrease in contrast sensitivity to a spatial frequency of 6 cycles/degree. A disruption in diurnal rhythms for these parameters was suggested. The results are considered in terms of the maintenance of visual efficiency and comfort with loss of sleep, and have implications for both the military and civilians involved in shift work and long work schedules.