Sleeping with your eyes open is more than just a metaphor for being observant. Some people really do sleep with their eyes open—and it can damage their eyes and vision. Being unable to close the eyelids is called lagophthalmos. If this only happens during sleep, it's called nocturnal lagophthalmos. This doesn't mean the eyes are wide open, though. In most cases, the lids will close most of the way but not completely. Even a small opening in the eyelids can dry out the eyes overnight. Over time, the eyes can become chronically dry and uncomfortable, leading to exposure keratopathy, scratches on the eye, corneal abrasions and corneal ulcers. Click here to read the full story from the American Academy of Ophthalmology.