The use of a light visor during night work by nurses

Five nurses have been investigated for the two nights of a rapidly rotating shift schedule on four occasions: once with normal ward lighting (40 lux on average) and three times while wearing a light visor (Bio-Brite Inc., MD, USA). The visor was worn for four periods of 40 minutes each, at about 2 hour intervals during each night shift, the intensity giving 400-600, 1500 and 3200 lux for the three studies. The nurses recorded subjective evaluations of mood, physical fitness, sleepiness and fatigue, and carried out some performance measures (Simple Auditory Reaction Time, Flicker Fusion Frequency, Search and Memory test) at the start, middle and end of each night shift. Plasma cortisol was measured at the end of the shift, and 6-sulphatoxymelatonin was measured in urine collected at the middle and end of each shift. Oral temperature was also recorded for 48 h covering the two shifts. No significant effects of light treatment (even at 3200 lux) upon within-shift decline in mood and performance were seen. The acceptability of the wearer of the visor was moderate since the upper visual field was impaired and, at the highest light intensity, there was difficulty in seeing clearly objects in the dimly-lit environment. Furthermore, no significant falls in melatonin excretion and cortisol excretion were noted, but there was some evidence that the circadian rhythm of oral temperature was stabilised by the light visors. This is thoroughly desirable in rapidly rotating shift systems.