Marcus Gunn Syndrome – Healthnile.com

Marcus Gunn syndrome, also called jaw-winking syndrome, is a rare condition present at birth that links eyelid movement with jaw motion. It causes the upper eyelid to rise or “wink” when the jaw opens, shifts, or chews. This unusual connection happens because nerves that control the eyelid and the jaw connect in an unexpected way.

People with this syndrome often notice drooping of one eyelid, known as ptosis, along with the characteristic eyelid movement. The condition can vary in severity, sometimes affecting vision development and sometimes appearing only as a noticeable quirk. While usually seen on one side, it can rarely affect both eyes.

Definition of Symptom

Marcus Gunn Syndrome, also known as jaw-winking syndrome or Marcus Gunn phenomenon, is a rare condition present at birth. It involves an unusual link between the muscles that control the eyelid and the muscles used for chewing.

The most common sign is ptosis (drooping of the upper eyelid). When the person moves the jaw—such as during chewing, sucking, or opening the mouth—the drooping eyelid lifts suddenly, creating a “wink-like” motion.

This eyelid movement happens without the person trying to do it. Nerves for jaw movement and eyelid movement connect in a way that causes the eyelid to rise each time the jaw shifts in certain directions. Common triggers include:

Chewing
Sucking
Jaw thrusting or side movement
Smiling or talking

Some individuals may also have eyes that do not align properly (strabismus), which can appear alongside ptosis. In many cases, the eyelid movement is the only noticeable feature, but vision problems can occur if the drooping blocks normal sight.

Symptom	Description
Ptosis / Blepharoptosis	Drooping of the upper eyelid
Jaw-Winking	Eyelid lifts when jaw moves
Strabismus	Eyes may not align properly

The condition usually becomes less noticeable as children grow older.

Possible Causes/Diseases Condition

Marcus Gunn syndrome is a rare disease present at birth. It results from an unusual connection between the nerves that control eyelid movement and those that move the jaw. This miswiring causes the eyelid to rise or “wink” when the jaw moves.

In many cases, the condition appears sporadically without a clear family history. However, some families have reported the syndrome, and there is some evidence that it can be inherited in rare cases. The syndrome can appear alone or with other eye problems.

One frequent association is when the two eyes have unequal refractive power (anisometropia), which can increase the risk of a lazy eye (amblyopia) if not managed early. Marcus Gunn syndrome may also appear with broader genetic or developmental conditions. For example, some children with CHARGE syndrome also have Marcus Gunn syndrome.

Associated Condition	Possible Link to Marcus Gunn Syndrome
Anisometropia	May occur alongside and lead to vision problems
Familial Cases	Rare, sometimes inherited in families
Autosomal Dominant Inheritance	Suggested in limited cases
CHARGE Syndrome	Reported in some children with the syndrome

Other Non-Disease Causes

Marcus Gunn syndrome does not always arise from disease. In many cases, the unusual eyelid movement comes from nerve connections that form during early development. This means the condition can appear without any injury or illness.

The trigeminal nerve, which controls jaw muscles, and the oculomotor nerve, which lifts the eyelid, may connect abnormally. When this happens, movement of the jaw can trigger eyelid motion. This explains why chewing or smiling can cause the eyelid to rise. Jaw actions such as jaw protrusion, side-to-side shifts, or sucking may bring out the eyelid “wink.”

These are not harmful by themselves but highlight the nerve link. The pterygoid nerve, a branch of the trigeminal nerve that helps move the jaw, may also play a role in these responses. Some people notice the eyelid movement only during specific activities. Common triggers include:

Chewing food
Opening the mouth wide
Smiling or laughing
Shifting the jaw to one side

Nerve Involved	Usual Function	Effect in Marcus Gunn Syndrome
Trigeminal nerve	Controls jaw movement	Jaw motion causes eyelid lift
Oculomotor nerve	Lifts the upper eyelid	Responds when jaw moves
Pterygoid nerve	Moves jaw side-to-side	May trigger eyelid movement

How It Causes the Symptom

Marcus Gunn syndrome happens because of an unusual nerve connection that forms before birth. The trigeminal nerve, which controls jaw movement, connects incorrectly with the oculomotor nerve, which controls the muscle that lifts the eyelid.

Because of this, when a person chews, sucks, or moves the jaw, the eyelid also moves. The eyelid may rise or “wink” at the same time, even though the person is not trying to move it.

This effect is called synkinesis, which means one voluntary action triggers another involuntary action. In this case, the voluntary jaw movement leads to involuntary eyelid motion. Key points in the process:

Jaw movement → signals travel along the trigeminal nerve.
Misconnection → signals cross over to the oculomotor nerve.
Levator muscle activation → the eyelid lifts without intent.

The main muscle that raises the upper eyelid contracts during chewing or other jaw actions, creating the jaw-winking effect. In most people, the condition does not cause pain or other symptoms. However, in some cases the eyelid movement interferes with vision or creates cosmetic concerns. The symptom can appear in different ways:

Small, barely noticeable eyelid lift
Moderate winking with each bite or jaw shift
More obvious eyelid movement during chewing, sucking, or speaking

Possible Complications

Marcus Gunn syndrome can lead to vision problems linked to the abnormal eyelid movement. The most common are eyes that do not align properly (strabismus) and unequal refractive power (anisometropia), which can interfere with normal visual development.

Amblyopia (lazy eye) often develops in these cases, sometimes as a result of strabismus or anisometropia. In some cases, the drooping eyelid itself can block vision and contribute to amblyopia.

Complication	Possible Cause	Notes
Amblyopia (lazy eye)	Strabismus, anisometropia, eyelid block	May need patching or glasses
Strabismus	Eye misalignment	Often requires corrective care
Lagophthalmos	Post-surgery eyelid closure issues	Can cause corneal irritation
Suture granuloma	Reaction to surgical stitches	Usually managed locally

When To Seek Medical Attention

People with Marcus Gunn syndrome should seek medical care if eyelid movements interfere with vision or daily activities. A drooping eyelid that blocks the line of sight can affect learning, driving, or reading. Warning signs that need evaluation include:

Persistent or worsening drooping of the eyelid
Unequal vision between the eyes
Signs of lazy eye
Double vision or unusual eye movements

Parents should consult a doctor if a child shows eyelid twitching linked to jaw motion, especially if the child tilts the head to see better. Doctors may recommend surgery to correct eyelid position. Some people may benefit from glasses, patching therapy, or regular checkups. Timely care can reduce the risk of complications such as crossed eyes or lazy eye.

Patients and families can reach out to groups like the National Organization for Rare Disorders (NORD) or other patient organizations. These groups offer support, educational resources, and help with finding specialists. People interested in new therapies can ask about clinical trials. A doctor or patient organization can help find current studies and explain who can take part.

Situation	Action to Take
Eyelid blocks vision	Schedule an eye exam
Unequal eye movement	Seek pediatric eye care
Interest in new treatments	Ask about clinical trials
Need support	Contact patient organizations (e.g., NORD)