For new parents, observing a baby’s every expression and movement is a source of wonder. Sometimes, they may notice a peculiar and startling reflex: every time their baby sucks on a bottle, chews, or moves their jaw, one of their eyelids rhythmically jumps upward. This unusual and often surprising movement is the hallmark of Marcus Gunn Jaw-Winking Phenomenon. It is a rare, congenital condition that creates an abnormal connection between the nerves that control chewing and the nerve that lifts the eyelid. While the “winking” can be alarming to witness, it is crucial for parents to understand that this is not a sign of a dangerous neurological disease. It is a benign “mis-wiring” of the nerves that a child is born with. Management is focused on ensuring normal vision development and, in some cases, considering surgical options to improve the cosmetic appearance.

Marcus Gunn phenomenon, also known as Marcus Gunn jaw-winking or pterygoid-levator synkinesis, is a rare genetic condition that is a type of congenital ptosis.

• Congenital means it is present at birth.
• Ptosis is the medical term for a drooping upper eyelid.
• Synkinesis is the medical term for an involuntary movement that occurs in one part of the body when another part moves voluntarily.

In Marcus Gunn phenomenon, a child is born with a droopy eyelid (ptosis) on one side. The unique feature is that this droopy eyelid paradoxically and rapidly retracts, or “winks,” upward whenever the jaw is moved in a specific way.

To understand this, it is helpful to use an analogy. Think of the nerves in the head as a complex electrical panel in a house, with separate, dedicated circuits for every function.

• One circuit, controlled by the “eyelid switch” (the oculomotor nerve), powers the levator muscle, which lifts the eyelid.
• A completely separate circuit, controlled by the “jaw switch” (the trigeminal nerve), powers the pterygoid muscles, which are used for chewing.
• In Marcus Gunn phenomenon, it is as if during the initial wiring of the house (fetal development), a few wires from the “jaw circuit” were accidentally cross-wired and connected into the “eyelid circuit.”
• Now, whenever the jaw switch is flipped during sucking, chewing, or opening the mouth, it not only powers the jaw muscles but also sends an unintended jolt of electricity to the eyelid muscle, causing it to jump open.

This abnormal, cross-wired connection between the nerve that controls the jaw and the nerve that controls the eyelid is the core feature of the syndrome.

In my experience, parents are often puzzled when they notice their baby’s eyelid lifts every time they suck, chew, or move their jaw, this quirky eyelid movement is a hallmark of Marcus Gunn phenomenon.

The direct cause of Marcus Gunn phenomenon is a congenital aberrant connection between branches of two different cranial nerves. Specifically, motor nerve fibers that should only go to the pterygoid muscles (jaw muscles controlled by the trigeminal nerve) have an abnormal connection with the nerve fibers that supply the levator palpebrae superioris muscle (the eyelid-lifting muscle controlled by the oculomotor nerve).

This mis-wiring of the nerves is a developmental error that occurs in the womb. The exact reason why this faulty connection forms is unknown. It is not caused by any action or inaction of the mother during pregnancy but is considered a random developmental anomaly.

I’ve had to explain to concerned families that this isn’t due to birth trauma or external injury, it’s a congenital nerve wiring variant, not a progressive disorder.

Marcus Gunn phenomenon is a congenital condition that a child is born with. It is not contagious.

• Sporadic Occurrence: The vast majority of cases (around 95%) are sporadic. This means the faulty nerve connection occurs by chance in an individual, with no other affected family members.
• Inherited Form: In a small number of cases (about 5%), the condition can be inherited from a parent. In these rare familial cases, the inheritance pattern is typically autosomal dominant. This means an affected parent has a 50% chance of passing the trait on to each of their children.

The signs of Marcus Gunn phenomenon are present from birth and are usually noticed in early infancy, often when the baby is feeding.
The two hallmark signs of the condition are:

1. Congenital Ptosis: The child has a droopy upper eyelid on one side (unilateral). The severity of the droop can range from very mild to severe, where the eyelid partially or completely covers the pupil.
2. The Jaw-Wink: The droopy eyelid retracts (lifts or “winks” upward) in response to the stimulation of the jaw muscles. This paradoxical movement is typically triggered by:
   • Sucking on a bottle or pacifier in infants.
   • Chewing or opening the mouth wide.
   • Moving the jaw to the side opposite the affected eye.
   • Clenching the teeth.

Associated Eye and Vision Problems
While the jaw-winking itself is harmless, the associated ptosis can lead to serious vision problems if it is not properly monitored and managed by an eye doctor.

• Amblyopia (“Lazy Eye”): This is the most serious potential complication. If the droopy eyelid covers the pupil for a significant part of the day, it blocks clear images from reaching the brain. Over time, the brain will start to ignore the blurry input from that eye and will only “learn” to see with the unaffected eye. This can lead to a permanent loss of vision in the droopy eye that cannot be corrected with glasses later in life.
• Strabismus (Misaligned Eyes): Children with Marcus Gunn phenomenon have a higher incidence of strabismus, where the eyes do not line up in the same direction.
• Anisometropia: A significant difference in the refractive error (the prescription for glasses) between the two eyes is also common, which can also contribute to the development of amblyopia.

Clinically, I check for associated issues like ptosis or strabismus, as some children with this condition also have amblyopia or require vision monitoring.

The diagnosis of Marcus Gunn phenomenon is made entirely by clinical observation. It does not require any blood tests, X-rays, or imaging scans. The diagnosis is typically made by a pediatric ophthalmologist (a children’s eye doctor) or an oculoplastic surgeon.

The diagnostic process involves a comprehensive eye examination:

• Observation: The doctor will carefully observe the child’s eyelids both at rest and during jaw movement. They will have the child chew on something or give an infant a bottle to elicit and confirm the characteristic jaw-winking movement.
• Measurement of Ptosis: The doctor will precisely measure the degree of eyelid droop.
• Assessment of Vision: The most important part of the exam is to test the vision in each eye separately to check for amblyopia.
• Evaluation of Eye Alignment and Motility: The doctor will check for any associated strabismus.
• Refraction: A measurement of the child’s refractive error is performed (often after using dilating eye drops) to check for any significant nearsightedness, farsightedness, or astigmatism that might require glasses.

In my experience, further testing isn’t usually needed unless there’s suspicion of other eye abnormalities, ophthalmology referral helps confirm and monitor for visual development.

The management of Marcus Gunn phenomenon is focused on two primary goals:

1. Treating any associated vision problems to ensure the healthy development of sight.
2. Improving the cosmetic appearance of the eyelid, if desired.

1. Non-Surgical Management (Focus on Vision)

The first and most important part of treatment is to address any amblyopia or significant refractive error. This is essential for protecting the child’s vision.

• Observation: For very mild cases where the ptosis does not cover the pupil and there are no other vision problems, no treatment may be necessary other than regular monitoring.
• Amblyopia Treatment: If amblyopia is present, treatment must be started right away. This typically involves patching the “good” eye for several hours a day. This forces the brain to use and process images of the weaker, ptotic eye, stimulating normal vision development.
• Corrective Eyeglasses: Glasses will be prescribed to correct any significant astigmatism or difference in prescription between the two eyes.

2. Surgical Treatment

Surgery for Marcus Gunn phenomenon is a highly specialized procedure performed by a pediatric oculoplastic surgeon. The decision to proceed with surgery is complex and is based on several factors, including the severity of the ptosis, the severity of the wink, the risk to vision, and the cosmetic concerns of the family and child.

• The Surgical Dilemma: A simple surgery to just lift the droopy eyelid (a levator resection) can make the jaw-winking movement even more noticeable, as the lid will now jump from a higher starting position to an even higher one. Therefore, the surgical approach must address both the ptosis and the wink.
• Surgical Options:
  • Levator Muscle Resection: In cases with mild ptosis and a mild wink, a surgeon may perform a procedure to simply tighten the eyelid-lifting muscle.
  • Frontalis Sling Procedure: This is a common approach for severe ptosis. The surgeon disconnects the eyelid from its abnormal levator muscle and then uses a “sling” (made of a silicone rod or tissue from the patient’s own thigh) to connect the eyelid to the powerful frontalis muscle in the forehead. The child then learns to lift their eyelid by raising their eyebrow.
  • Bilateral Frontalis Sling with Levator Extirpation: This is often considered the gold standard for achieving the best cosmetic and functional symmetry. In this more complex procedure, the surgeon detaches the levator muscle on the affected side (to eliminate the wink) and may also detach it on the unaffected side. They then perform a frontalis sling procedure on both eyelids. This allows the child to lift both eyelids symmetrically by raising their eyebrows, which eliminates the jaw-winking and creates a more balanced appearance.

Clinically, I consider surgical correction only if there’s significant ptosis affecting vision or if the asymmetry causes social or psychological concern as the child grows older.

Marcus Gunn Jaw-Winking Phenomenon is a rare and fascinating congenital condition that results from a harmless “cross-wiring” of the nerves supplying the jaw and the eyelid. While the involuntary winking movement can be startling, it is not a sign of a dangerous neurological disease and often improves with age. The most critical aspect of care is not the wink itself, but the associated droopy eyelid (ptosis) and its potential to cause a permanent loss of vision from amblyopia if left unmanaged. Therefore, the cornerstone of management is a comprehensive evaluation and regular follow-up with a pediatric ophthalmologist to ensure that vision is developing properly in both eyes. In my experience, once parents understand that this is a benign, non-progressive condition, their anxiety eases significantly.

1. American Association for Pediatric Ophthalmology and Strabismus (AAPOS). (n.d.). Marcus Gunn Jaw-Winking Phenomenon. Retrieved from https://aapos.org/glossary/marcus-gunn-jaw-winking-phenomenon
2. National Organization for Rare Disorders (NORD). (2022). Marcus Gunn Phenomenon. Retrieved from https://rarediseases.org/rare-diseases/marcus-gunn-phenomenon/
3. American Academy of Ophthalmology (AAO). (2023). Ptosis: Congenital. Retrieved from https://eyewiki.aao.org/Ptosis:_Congenital