MGJWP is usually sporadic, but a specific hereditary pattern in the form of autosomal dominant inheritance with incomplete penetrance has been reported on more than one occasion.¹,⁴ The precise pathogenetic mechanism of MGJWP remains unclear, and the most plausible theory is the concept of aberrant connection; however, it is the location of this alleged neural misdirection that is controversial.⁴ Traditionally, MGJWP was thought to occur when an abnormal branch of the trigeminal nerve is congenitally misdirected to the oculomotor nerve. This abnormal miswiring was thought to occur peripherally between the mandibular branch of the fifth cranial nerve or its anterior division, innervating the pterygoid muscles, and the superior branch of the third cranial nerve, innervating the levator muscle (trigemino-oculomotor synkinesis).⁵,⁶,⁷ Although this etiopathogenetic mechanism fails to explain the coexistence of ptosis, which is the second key component in MGJWP, it still appears repeatedly in the literature.⁶ Alternatively, the location of this aberrant connection or neural misdirection could be more central (cortical, internuclear, or infranuclear).⁴ This has led some authors to include MGJWP under the category of congenital cranial dysinnervation disorders where aberrant innervation of the ocular and facial musculature generally arises from abnormal development of cranial nerve nuclei or their axonal connections.⁸,⁹

It should be noted, however, that as early as 1959 Sano proposed an alternative theory, demonstrating electromyographically that the jaw wink is an exaggeration of a normal barely detectable physiologic cocontraction of the extraocular muscles innervated by the oculomotor nerve on the one hand and the muscles of mastication innervated by the trigeminal nerve on the other.¹⁰ Normally this primitive phylogenetic mechanism is kept in check by a higher central control. According to this hypothesis, this central inhibitory mechanism is “released” due to an unknown congenital brain stem lesion.¹¹ The presence of a primitive trigeminal-oculomotor neural circuit has recently been verified in an animal model, which argues in favor of this “release hypothesis”¹²; however, this “ephaptic coupling” or cross talk between adjacent axons directed to the levator muscle and the pterygoids is controversial.¹³

MGJWP accounts for 5% to 10% of all cases of congenital ptosis.¹,²,¹⁴ A slight preponderance for the left side has been noted by some authors,⁵,¹⁵ and disputed by others,¹,²,¹⁶,¹⁷ but sex distribution is essentially equal. Parents usually present with the infant very early in life complaining of eyelid flickering or rhythmic eyelid movements with feeding.¹⁸ Older children and adults usually present with partial unilateral
ptosis at rest, with paradoxical lid elevation occurring when moving the mandible sideways (Figure 38.1), with opening of the mouth (Figure 38.2), protruding the tongue, clenching the teeth, swallowing, or even when smiling (Figure 38.3).¹,²,¹⁹,²⁰ There are two major types of synkinesis in MGJWP. The first type is termed external (lateral) pterygoid-levator synkinesis and is characterized by synkinetic lid elevations when the jaw is thrust to the opposite side, projected forward, or opened widely. The second type, or the internal (medial) pterygoid-levator synkinesis, which is quite rare,³ is characterized by lid elevation that is triggered by clenching of the teeth, closing the mouth, or moving the jaw to the same side.³,⁵,²¹ In very young children it may not be possible to determine the exact movement that induces the wink.³ The degree of the synkinetic eyelid excursion varies from one patient to the other, often retracting the eyelid to a higher level than the normal unaffected side,²,²²,²³ and usually being more evident in downgaze. Although it is difficult to accurately quantify the amount of lid excursion with jaw movement, some authors grade the jaw wink into mild (2 mm or less), moderate (approximately 5 mm), or severe (7-8 mm or more).¹ The natural history of the jaw wink is that patients often remark that the synkinesis seems less prominent as they get older. Whether the jaw wink truly improves with age or whether patients acquire the ability to mask it is still a heavily contested issue, but the majority consensus is that it does not diminish and instead patients learn to mask the movement.¹,²,¹⁶,¹⁷ However, on more than one occasion we have encountered an adult patient who presents with a history of MGJWP but on examination fails to elicit any jaw wink at all or only exhibits the slightest jaw wink.

The degree of ptosis may be mild, moderate, or severe, and although rare, the jaw wink may even be observed in normal eyelids without ptosis.²⁰,²⁴,²⁵ As the wink improves or appears to improve with maturity, patients also learn to diminish their true ptosis through subtle sustained contractions of the jaw muscles.²⁶ This “habitual ptosis” is often of a lesser degree than the patient’s true ptosis.⁵ By learning to hide their ptosis by habitually maintaining an altered jaw position, these patients could be unconsciously or involuntarily putting to good use the same intimate neural connections that led to the jaw wink in the first place.²⁶

Irrespective of the presence or absence of habitual ptosis, any subtle movements of the jaw while the surgeon is assessing the levator may underestimate muscle function. Therefore, to get an accurate measure of levator function, it is important to assess levator excursion with the mouth closed² or better with the jaw completely immobilized by the examiner or an assistant.²⁶ In older individuals suspected of having habitual ptosis, it is important to instruct the patient to relax this isometric muscle contraction, although it is not always possible because some patients may be incapable of spontaneous relaxation of their jaw muscles after years of habitual contraction.⁵,²⁶

Various motility disorders have been described with MGJWP, but the most common is ipsilateral superior rectus underaction occurring in up to 76% of patients and may or may not be associated with hypotropia.¹,⁵,¹⁶,¹⁷,²²,²³,²⁵,²⁷ Conversely, some patients with MGJWP may present with hypotropia without superior rectus weakness.⁵ Less frequently reported ocular misalignment conditions include esotropia, exotropia, double elevator palsy, Duane retraction syndrome, and pseudo inferior oblique overaction.¹,²,³,²⁸,²⁹ Other associated ocular conditions include anisometropia in up to 25% of patients¹,¹⁷ and amblyopia in 30% to 60% of patients.¹,²,¹⁶,¹⁷ Amblyopia is multifactorial and is not exclusively of occlusive origin. Because eyelid drooping in MGJWP is not a constant phenomenon, amblyopia is rarely a consequence of the ptotic eyelid.¹⁶,¹⁷ Systemic associations are a rare occurrence in patients with MGJWP; however, it has been reported with Waardenburg syndrome, Rubinstein-Taybi syndrome, Hirschsprung megacolon, neuroblastoma, melanosis coli, profound deafness, and neurofibromatosis type 1.⁵,²¹,³⁰,³¹