Sleeping with your eyes open: a fortuitous case of nocturnal lagophthalmos.

The eyes close at sleep onset, except for the 5% of the population in whom eyelid closure is only partial. This condition is called nocturnal lagophtalmos. We observed nocturnal lagophtalmos in a 67-year-old woman during video-polysomnography. She reported occasional eye redness, photophobia, and nocturnal tearing and was prescribed an eye lubricant for evening use. During video-polysomnography, her eyes were closed during N1 and N2 sleep but partially open during N3 sleep with occasional slow eye movements. Her eyes were wide open during REM sleep with numerous distinct rapid eye movements. This case illustrates changes in eyelid muscle tone as sleep deepens and the dynamics of eye movements during sleep.