While complete eyelid closure is the typical and most beneficial state for human eye health during rest, certain conditions and biological adaptations challenge this common perception. This reveals a more complex reality regarding whether one can sleep without eyelids or with eyes open. The article explores eyelid function and the implications when they do not fully perform their role during sleep.
Eyelids and Their Functions
Eyelids serve as a protective barrier for the eyes, shielding them from external elements like dust, debris, and potential injury. They also regulate light exposure, which is important for the body’s natural sleep-wake cycle, as darkness signals melatonin production. Eyelids are also important for maintaining eye moisture. With each blink and during sleep, they distribute the tear film evenly across the eye’s surface, preventing dryness and washing away irritants.
When Eyes Don’t Close During Sleep
For humans, the inability of eyelids to close fully during sleep is known as nocturnal lagophthalmos. This involuntary condition affects up to 5% of individuals. Various factors can contribute, including damage to facial nerves from Bell’s palsy, stroke, or certain surgical procedures. Anatomical issues, like protruding eyes (proptosis), or weakened eyelid muscles due to aging or conditions like thyroid eye disease, can also prevent complete closure.
Many animals are adapted to sleep with their eyes open. Fish, for instance, lack eyelids entirely, so their eyes remain exposed during rest. Snakes also do not possess eyelids; instead, their eyes are covered by a transparent scale called a spectacle, allowing them to appear awake while sleeping. Some marine mammals, like dolphins, engage in unihemispheric sleep, where one half of their brain rests while the other remains active, allowing them to keep one eye open and stay vigilant. This highlights that while sleeping with eyes open is normal for some species, it is typically not for humans.
Health Impacts of Unclosed Eyes
When human eyes do not fully close during sleep, the exposed surface becomes vulnerable. Increased tear evaporation leads to dry eye syndrome, manifesting as discomfort, irritation, redness, and a gritty sensation upon waking. Lack of proper lubrication can also result in blurred vision, especially in the morning. Prolonged exposure of the cornea, the clear front surface of the eye, can lead to exposure keratopathy. This involves damage to the corneal surface due to persistent dryness, making the eye susceptible to abrasions, infections, and corneal ulcers. If left unaddressed, severe cases can cause corneal scarring, which may impair vision or lead to permanent vision loss.