Blinking is a frequent, often unnoticed behavior essential for eye health. A common question is whether our eyes continue to blink during sleep. Exploring eye function during both waking and sleeping states reveals the mechanisms governing these ocular movements.
The Science of Blinking
Blinking, the rapid closing and opening of eyelids, is a semi-autonomic process essential for eye health. Its primary function is to spread the tear film across the eye’s surface, providing lubrication and keeping the cornea moist. Blinking also helps to clear away dust, debris, and foreign particles, protecting the eye from irritants and potential harm. Additionally, tears deliver oxygen and nutrients to the cornea, which lacks blood vessels.
There are typically three classifications of blinks. Spontaneous blinks occur unconsciously and frequently, averaging about 14 to 17 times per minute in adults. Reflex blinks are rapid, involuntary responses to external stimuli, such as a sudden bright light or an object approaching the eye, offering immediate protection. Voluntary blinks, in contrast, are intentional actions, performed when a person chooses to close and open their eyelids.
What Happens to Your Eyes During Sleep
Humans do not blink during sleep because their eyelids are closed. This closure provides a protective barrier, reducing the need for the continuous lubrication and debris removal that blinking offers during waking hours. While the eyelids are shut, the eyes still exhibit characteristic movements depending on the sleep stage.
Sleep is broadly divided into two main categories: non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep. During NREM sleep, which includes deeper stages, eye movements significantly slow down and may even stop. Conversely, REM sleep is characterized by rapid, jerky eye movements, even though the eyelids remain closed. These rapid eye movements in REM sleep are thought to correlate with the brain’s activity during dreaming, potentially reflecting shifts in gaze within the dream environment.
Bell’s phenomenon, a protective reflex, occurs when the eyelids close. The eyeballs automatically roll upwards and slightly outwards, further shielding the cornea. This upward rotation protects the sensitive front surface of the eye, especially if eyelids do not fully close. With eyes closed and protected, the need for tear production and lubrication is significantly reduced.
When Eyes Don’t Fully Close During Sleep
While normal sleep involves fully closed eyelids, nocturnal lagophthalmos causes them to remain partially open during sleep. This inability to achieve complete eyelid closure exposes the eye’s surface to air and irritants. Even a small gap can lead to significant issues, as the eye loses protective benefits.
Nocturnal lagophthalmos can stem from various causes. Causes include issues with facial nerves, such as Bell’s palsy, which can weaken eyelid muscles. Structural eyelid problems, medical conditions like thyroid eye disease, or past eyelid surgeries can also contribute. In some instances, the cause remains unknown, though a familial tendency is observed.
Consequences of eyes not fully closing during sleep range from mild discomfort to severe eye health problems. Common symptoms include dry eyes, irritation, a gritty sensation, and redness, often worse upon waking. Prolonged exposure increases the risk of corneal abrasions, infections, and corneal damage or scarring, potentially affecting vision. Addressing nocturnal lagophthalmos is important to prevent complications and maintain ocular surface health.