Congenital oculomotor nerve palsy is a condition in which the third cranial nerve (oculomotor nerve, CN3) is impaired from birth. The oculomotor nerve innervates five extraocular muscles: the superior rectus, inferior rectus, inferior oblique, medial rectus, and levator palpebrae superioris, as well as the sphincter pupillae and ciliary muscle via parasympathetic fibers (from the Edinger-Westphal nucleus). Damage to this nerve results in restricted eye movement, ptosis, and pupillary abnormalities.
The causes of oculomotor nerve palsy in children are reported as 43–47% congenital, 13–23% traumatic, 10% tumor, and 7% aneurysm. The estimated incidence of congenital third, fourth, and sixth cranial nerve palsies combined is 7.6 per 100,000 people.
The exact mechanism of onset is unknown, but it is thought to result from peripheral nerve damage due to perinatal adverse events (such as birth trauma or hypoxia) rather than a developmental disorder within the brainstem.
QHow rare is congenital oculomotor nerve palsy?
A
Of pediatric oculomotor nerve palsy, 43–47% are considered congenital. The combined incidence of congenital third, fourth, and sixth cranial nerve palsy is 7.6 per 100,000 people, making it a relatively rare disease.
In newborns and infants, it is often discovered as ptosis or strabismus. Since infants cannot complain of symptoms, caregivers noticing the following abnormalities often leads to diagnosis.
Exotropia + hypotropia: Due to unopposed action of the superior oblique and lateral rectus muscles, the eye is abducted and depressed.
Restricted eye movements: Adduction, elevation, and depression are all impaired.
Ptosis: Severe ptosis due to complete paralysis of the levator palpebrae superioris muscle.
Pupillary dilation: Often accompanied by mydriasis due to damage to parasympathetic nerve fibers.
Incomplete palsy
Variable degree of eye movement restriction: The combination and severity of affected muscles vary among individuals.
Partial ptosis: Limited to mild to moderate drooping of the eyelid.
Pupil-sparing cases: Some cases do not involve the pupil. Cases with miosis are associated with aberrant regeneration.
Characteristic findings of congenital oculomotor nerve palsy include the following:
Oculomotor nerve aberrant regeneration: Observed in 1/3 to 1/2 of patients. During nerve regeneration after injury, misdirected connections form, causing eyelid and extraocular muscle movements in conjunction with jaw movements. Most noticeable during eating. In congenital cases, aberrant regeneration is reported in 61–93%.
Cyclic oculomotor spasms: A rare finding. Spasms lasting 10–30 seconds occur at regular intervals, causing eyelid elevation, adduction, miosis, and accommodation spasm. Considered a form of aberrant synkinesis.
Compensatory head posture: Tilting the head to facilitate fusion.
QWhat is oculomotor nerve aberrant regeneration?
A
When the damaged oculomotor nerve regenerates, it forms misdirected connections to muscles that are not the original targets. This causes eyelid elevation or eye movement with jaw movement. It is seen in 61–93% of congenital oculomotor nerve palsy cases and is most noticeable during eating (chewing).
The causes of congenital oculomotor nerve palsy are classified as follows.
Perinatal adverse events: Peripheral nerve injury due to birth trauma or perinatal complications is considered the most common cause. Mechanical injury during delivery is presumed, rather than a developmental disorder of the brainstem.
Trauma: Accounts for 13–23% of all pediatric oculomotor nerve palsy cases. Usually associated with severe head trauma.
Inflammation/infection: Oculomotor nerve palsy may appear as ophthalmoplegic migraine. It often occurs after a headache, but there are also cases unrelated to headache. MRI suggests involvement of inflammation, and aggressive anti-inflammatory therapy is recommended. With repeated attacks, the duration becomes longer, and some cases become permanent.
Tumor: Accounts for about 10% of pediatric oculomotor nerve palsy cases. Annual imaging is recommended for children with persistent oculomotor nerve palsy. There are reports of cases with acute unexplained complete oculomotor nerve palsy and no abnormalities on imaging, which were later found to be oculomotor nerve schwannoma years later.
Vascular lesions: Aneurysms account for about 7% of pediatric oculomotor nerve palsy cases.
QIs congenital oculomotor nerve palsy hereditary?
A
The inheritance pattern of congenital oculomotor nerve palsy itself is not established. However, CFEOM (congenital fibrosis of the extraocular muscles), a group of congenital cranial dysinnervation disorders (CCDDs), can have autosomal dominant (CFEOM1) or autosomal recessive (CFEOM2) inheritance patterns. If there is a family history of strabismus, differentiation from these conditions is necessary.
In children presenting with oculomotor nerve palsy for the first time, neuroimaging is recommended in all cases due to the possibility of underlying neurological lesions. Consultation with a pediatric neurologist is also advised.
MRI/MRA: This is the first-choice imaging test. SPGR provides high resolution even with thin slices (2–3 mm), and arteries appear as high signal. MRA is a non-invasive method for visualizing cerebral arteries without contrast agents, and is simple with high diagnostic value.
3D-CT Angiography: Three-dimensional imaging (volume rendering) using contrast agents is also useful.
Visual Acuity Test: Performed carefully using age- and maturity-appropriate methods to evaluate amblyopia.
Pupillary Examination: Checks for mydriasis or miosis. Useful for localizing lesions, but the absence of pupillary signs does not rule out oculomotor nerve palsy.
Ocular motility test: Evaluate limitation of movement in each direction and determine whether it is complete or incomplete palsy.
External eye examination: Assess MRD1 (margin reflex distance 1), levator function, and Bell’s phenomenon. This provides essential information for surgical planning.
Treatment of congenital oculomotor nerve palsy requires a comprehensive approach that prioritizes amblyopia prevention while improving eye position and eyelid position. If an underlying disease is present, its treatment takes precedence.
Occlusion therapy: To prevent amblyopia, the healthy eye is patched while wearing fully corrective glasses. During patching, monitor for decreased vision in the healthy eye or reversal of fixation.
Prescription glasses: Correction of refractive errors.
Prism prescription: May be applied for mild deviations.
Botulinum toxin type A injection: Injected into extraocular muscles to improve eye alignment, but success rates vary.
The goal of strabismus surgery is to enable binocular fusion in primary gaze and during reading.
Recession and resection of horizontal rectus muscles: This is the most commonly performed procedure, as the majority of patients present with exotropia.
Transposition of horizontal muscles: Performed to correct vertical deviations.
Superior oblique weakening: May be used in combination for vertical deviations.
Surgical planning is often complicated by the involvement of multiple muscles and the presence of abnormal synkinesis.
Treatment of ptosis is essential to prevent amblyopia and ensure opportunities for binocular vision. Generally, it is recommended to perform strabismus surgery before eyelid surgery, because vertical muscle surgery can change eyelid position.
Frontalis Suspension
Indications: Recommended for severe ptosis with poor levator function (less than 3–4 mm).
Suspension material: Autologous fascia lata is the gold standard. It requires a second surgical site for harvesting from the lateral thigh. Autologous tissue can be used in children aged 3–6 years and older.
Synthetic materials: Silicone and others can be used, but the recurrence rate of ptosis is slightly higher.
Levator Advancement
Indications: Commonly used when levator function is 5 mm or more.
Procedure: The levator muscle is advanced to the anterior surface of the tarsal plate, and the aponeurosis is shortened to enhance eyelid opening.
Advantages: No second surgical site is required.
QAt what age is it best to undergo ptosis surgery?
A
When the visual axis is obstructed by ptosis, early surgical intervention is necessary to prevent amblyopia. If autologous fascia lata is used for frontalis suspension, the recommended age is 3 to 6 years or older, but surgery may be performed earlier using donor bank fascia lata or synthetic materials.
The oculomotor nucleus is a complex nucleus located in the midbrain tegmentum and has the following subnuclear structures.
Medial rectus, inferior rectus, and inferior oblique subnuclei: ipsilateral innervation
Superior rectus subnucleus: contralateral innervation (decussates within the nucleus)
Levator palpebrae superioris subnucleus: Located in the midline, innervates the levator palpebrae superioris muscles bilaterally (bilateral innervation)
Edinger-Westphal nucleus: Located rostral to the nuclear complex, innervates the ipsilateral sphincter pupillae and ciliary muscles
Runs ventrally from the nucleus in the midbrain tegmentum
Enters the subarachnoid space, passing above the superior cerebellar artery and below the posterior cerebral artery
Enters the lateral wall of the cavernous sinus
Passes through the superior orbital fissure into the orbit
Branches into superior branch (superior rectus, levator palpebrae superioris) and inferior branch (medial rectus, inferior rectus, inferior oblique, parasympathetic fibers)
Within the midbrain, the fibers run in order from rostral: parasympathetic fibers → inferior rectus and inferior oblique fibers → levator palpebrae superioris and superior rectus fibers. Parasympathetic (pupillary) fibers run in the most superficial dorsomedial layer of the oculomotor nerve, making them susceptible to compression lesions.
In congenital oculomotor nerve palsy, aberrant regeneration is observed in 61–93% of cases. During the process of nerve regeneration after injury, misdirected connections to muscles other than the original target are formed. Secondary connections with the ipsilateral trigeminal nerve may also develop, manifesting clinically as synkinesis of the eyelid and extraocular muscles with chewing (oculomotor synkinesis).
This is a rare phenomenon observed in some cases of congenital oculomotor nerve palsy. It is usually noticed from birth to a few years of age. The muscles innervated by the oculomotor nerve contract at regular intervals, lasting 10 to 30 seconds. During contraction, eyelid elevation, adduction, miosis, and increased accommodation occur, and between contractions, the oculomotor nerve palsy state returns. The underlying mechanism is not clear.
7. Latest Research and Future Prospects (Research Stage Reports)
CFEOM1 (Congenital Fibrosis of Extraocular Muscles Type 1): Mutations in KIF21A have been identified as the cause. KIF21A encodes a kinesin motor protein that transports substances along microtubules, and its abnormality leads to impaired axon guidance of the oculomotor nerve (CN3).
CFEOM3 (Congenital Fibrosis of Extraocular Muscles Type 3): Mutations in TUBB3 (neuron-specific beta-tubulin) or TUBB2B (another beta-tubulin) are responsible. Abnormalities in microtubule components lead to developmental defects of CN3 and CN4.
These studies deepen the understanding of the molecular mechanisms of axon guidance and may contribute to elucidating the etiology of congenital oculomotor nerve palsy and developing new treatments in the future.
Regarding ophthalmoplegic migraine, a cause of oculomotor nerve palsy in children, MRI has shown inflammatory findings around the oculomotor nerve, suggesting the effectiveness of aggressive anti-inflammatory therapy.
