The Impact of a Blue-Blocking Filter Over One Eye on Health and Performance Outcomes and Its Implications for Night Workers

The higher risk for cancer documented among night-shift nurses compared to the day-shift nurses possibly results from lower melatonin levels associated with exposure to light at night in the work environment. Research demonstrates that eliminating spectral power <530 nm to both eyes prevents light-induced nocturnal melatonin suppression, and complete occlusion of one eye reduces melatonin suppression relative to that when both eyes are open. This study investigated whether filtering short wavelengths from one eye using a blue-blocking filter, rather than occluding one eye, would maintain high melatonin levels, alertness, and visual performance. This crossover, within-subjects study ran for six nights. Subjects experienced one of six light conditions involving combinations of binocular versus monocular and filtered versus unfiltered vision per night. Normalized melatonin concentration area under the curve (AUC_n) served as the primary outcome and the numerical verification (NVT) and go/no-go (GNG) performance tasks, pupil area, and subjective sleepiness (Karolinska Sleepiness Scale [KSS]) served as secondary outcomes. Both filtered and unfiltered monocular light conditions resulted in significantly greater melatonin AUC_n than the unfiltered binocular light condition. Performance at the NVT and at the GNG was not affected by filtering one eye compared to the unfiltered binocular light condition, nor did it affect KSS ratings. Melatonin AUC_n positively correlated with pupil area for corresponding light conditions. In conclusion, filtering one eye can help preserve melatonin levels in night workers while maintaining alertness and visual performance, which could be a simple and effective solution for improving health in night-shift nurses.