Marcus Gunn jaw-winking syndrome, also known as the Marcus Gunn Phenomenon, is a rare congenital eye condition characterized by involuntary movement of the upper eyelid. This condition is a form of trigemino-oculomotor synkinesis, an abnormal co-contraction between two different muscle groups. In individuals with this condition, the upper eyelid moves in response to movements of the jaw. It is present from birth and represents one of the most common types of congenital abnormal ocular innervation.
The Defining Physical Characteristics
The most noticeable sign of Marcus Gunn jaw-winking syndrome is unilateral ptosis, or a drooping upper eyelid, in the resting state. This droop typically affects only one eye, causing it to appear lower than the other when the jaw is still. The severity of this initial ptosis can vary widely among affected individuals.
The jaw-winking movement involves the involuntary, rhythmic elevation and retraction of the affected eyelid whenever the jaw muscles are stimulated. This movement can be triggered by common actions such as chewing, sucking, opening the mouth wide, or thrusting the jaw to the side.
The excursion of the eyelid during a jaw movement can range from barely perceptible to quite pronounced, temporarily eliminating the difference between the eyelids. The rapid upward movement makes the affected eye appear to wink or flutter, and the eyelid quickly returns to its ptotic position once the jaw movement ceases. This synkinetic movement is considered cosmetically significant if the eyelid elevates by two millimeters or more.
The Underlying Neurological Mechanism
Marcus Gunn jaw-winking syndrome is a consequence of an aberrant neural connection that developed before birth. The condition is rooted in a miswiring between two distinct cranial nerves that control separate muscle groups. Specifically, the issue involves a pathological link between the motor branch of the Trigeminal Nerve (Cranial Nerve V) and the Oculomotor Nerve (Cranial Nerve III).
The Trigeminal Nerve branch normally innervates the pterygoid muscles, which are responsible for moving the jaw during actions like chewing. The Oculomotor Nerve’s superior division controls the levator palpebrae superioris muscle, which is the primary muscle for lifting the upper eyelid. In this synkinesis, the signal intended to contract the jaw muscle accidentally crosses over to the eyelid muscle.
When a person attempts to move their jaw, the electrical impulse travels not only to the pterygoid muscle but also simultaneously stimulates the levator palpebrae superioris on the same side of the face. This unintended electrical impulse causes the involuntary and rapid elevation of the droopy eyelid.
Diagnosis and Management Options
Diagnosis of Marcus Gunn jaw-winking syndrome relies primarily on clinical observation, as the characteristic jaw-to-eyelid synkinetic movement is distinct. Healthcare providers, often ophthalmologists, confirm the condition by observing the eyelid’s response to various jaw movements. While the condition itself is non-progressive and stable, associated vision problems must be carefully assessed.
A significant concern is the potential for amblyopia, or “lazy eye,” which is decreased vision in one eye due to poor visual development. Amblyopia can result either from the ptotic eyelid blocking the visual axis or from associated conditions like strabismus, which is misalignment of the eyes. If amblyopia is present, it must be treated with corrective eyewear or occlusion therapy, such as patching the stronger eye, before considering surgical correction of the eyelid.
Management options range from simple observation to surgical intervention, depending on the severity of the ptosis and the degree of the jaw-winking phenomenon. For mild cases where the ptosis does not impair vision and the synkinesis is not cosmetically significant, a watch-and-wait approach is often adopted. Many individuals learn to subtly adjust their jaw movements over time, which can make the winking less noticeable.
Surgical intervention is considered for moderate to severe cases, particularly if the ptosis causes amblyopia or if the jaw-winking is highly noticeable. For mild ptosis with insignificant winking, a levator resection procedure may be performed to tighten the eyelid-lifting muscle. If the jaw-winking is pronounced, the preferred approach is a more complex surgery involving the ablation of the levator muscle on the affected side. This procedure is followed by a frontalis sling operation, which connects the eyelid to the eyebrow muscle, allowing the forehead to lift the eyelid instead of the now-disabled levator muscle.