The difficulty many people face in closing a single eye independently, known as winking, is a common observation pointing to a fascinating interplay between human anatomy and neurological programming. While the necessary muscles exist, the brain is fundamentally wired to coordinate the eyes and eyelids as a synchronized unit. Unilateral eye closure requires overriding the deeply ingrained protective mechanisms that govern our facial movements. Understanding this challenge involves exploring the specific muscles, the brain’s preference for bilateral action, and the learned nature of the winking skill.
The Muscles Required for Independent Eye Closure
The physical ability to close the eye rests almost entirely on the single, ring-shaped muscle known as the orbicularis oculi. This muscle encircles the eye socket and is responsible for all eyelid closure, from the gentle, involuntary blink to the forceful squint. The orbital portion of the orbicularis oculi is primarily responsible for the voluntary, sustained closure required for winking.
Winking requires a deliberate, isolated contraction of the orbicularis oculi on one side of the face. This contraction must be decoupled from its partner, the levator palpebrae superioris, which raises the upper eyelid and keeps the eye open. The levator palpebrae superioris is controlled by the Oculomotor Nerve (Cranial Nerve III), while the orbicularis oculi is controlled by the Facial Nerve (Cranial Nerve VII). Successfully winking means simultaneously relaxing the opener muscle and forcefully contracting the closer muscle on one side, without triggering the same action on the other.
Why Our Brain Prefers Closing Both Eyes
The primary reason winking is difficult stems from how the brain organizes motor commands for facial movements. The orbicularis oculi muscle on both sides is innervated by the Facial Nerve (Cranial Nerve VII), which originates in the brainstem. Although the nerve is distinct for each side, the brain’s motor cortex often issues a single, coordinated signal to both nerves.
Blinking is the most frequent eyelid movement and is a protective, reflexive action involving the simultaneous firing of both orbicularis oculi muscles. This deeply ingrained, bilateral synchronization is managed by brainstem circuits, allowing for rapid, unconscious eye protection. Voluntary winking demands that higher cortical centers, such as the frontal eye field, send a specific command to decouple this built-in bilateral program. The brain must consciously inhibit the signal traveling to the contralateral orbicularis oculi while activating the ipsilateral one. This requires greater cognitive effort and more complex neural pathways than a simple, synchronized blink.
Developing the Skill of Winking
The ability to wink is not an innate reflex but a learned motor skill requiring practice to refine neural decoupling. For many individuals, one side of the face is naturally easier to control, often due to subtle asymmetries in facial muscle strength or motor cortex dominance. Studies using functional magnetic resonance imaging (fMRI) show that winking activates larger areas of the brain’s motor control centers, including the frontal and parietal cortices, compared to simple blinking.
When a person learns to wink with their “difficult” eye, the brain strengthens the connections between the voluntary control centers and the muscles. Learning to wink on a previously difficult side activates similar cortical areas as those used by people who can wink bilaterally without training. The common difficulty with the left eye may reflect natural motor dominance, where the brain has prioritized neural pathways for right-side control. Consistent practice helps the brain build the necessary, isolated motor program to perform the unilateral action successfully.
When Loss of Control Signals a Health Issue
While struggling to close one eye may be a normal consequence of brain programming or lack of practice, the sudden or complete inability to close an eye is a serious concern. This loss of control usually indicates a problem affecting the Facial Nerve (Cranial Nerve VII), which supplies motor function to the orbicularis oculi. The most common cause of this sudden weakness is Bell’s Palsy, a condition causing temporary paralysis or weakness on one side of the face.
Bell’s Palsy symptoms appear suddenly, often over 48 to 72 hours. Symptoms include an inability to fully close the eye, a drooping eyebrow, and weakness in the lower face, such as a lopsided smile. Because the eye cannot close properly, patients often experience eye dryness and require lubrication to prevent corneal damage. Other conditions, such as a stroke or physical trauma, can also damage the Facial Nerve, leading to similar symptoms of facial paralysis. If a person experiences a sudden onset of facial weakness or complete inability to close an eye, they should seek medical attention immediately.