Abnormalities of Facial Movement
The ophthalmologist may be asked to evaluate CN VII weakness, which is frequently seen in clinical settings. Assessment of CN VII includes testing not only motor function, but also sensory and autonomic functions. Motor function can be readily assessed by observation. With the patient at rest, any asymmetry of facial expression or eyelid blink is noted. The palpebral fissure on the side of CN VII paresis will be wider as a result of the relaxed tone of the orbicularis oculi muscles. The clinician can test the various muscle groups by asking the patient to smile, to close the eyes forcibly, and to wrinkle the forehead. The degree to which the eyelashes become buried on each side can reveal subtle orbicularis oculi weakness. The corneal blink reflex provides a functional assessment of CN VII and CN V.
Testing autonomic functions such as salivation and lacrimation as well as testing sensation can help localize CN VII lesions. Cutaneous sensation can be tested along the posterior aspect of the external auditory canal. Lesions of CN VII from the cerebellopontine angle to the geniculate ganglion typically impair all functions of the nerve, whereas lesions distal to the geniculate ganglion affect only certain functions, depending on their location (Fig 11-8).
Figure 11-8 Distribution and topical diagnosis of CN VII lesions. Peripheral lesions result in facial monoplegia, including the orbicularis oculi and frontalis muscles, as well as:
Supranuclear facial palsy: contralateral weakness of lower two-thirds of the face with accompanying weakness of the orbicularis oculi muscle; retained expression
Nuclear facial palsy: facial monoplegia (congenital) plus CN VI nucleus involvement (ipsilateral gaze palsy) and frequent ataxia; occasional Horner syndrome
Cerebellopontine angle: decreased tearing, dysgeusia, loss of salivary secretion, loss of taste from anterior two-thirds of tongue, hearing impairment, nystagmus, vertigo, ataxia, and adjacent CN findings (CN V, CN VI)
Geniculate ganglionitis (Ramsay Hunt syndrome, herpes zoster oticus): findings are the same as in cerebellopontine angle, but the brainstem and other CNs are not involved
Isolated ipsilateral tear deficiency due to involvement of vidian nerve or sphenopalatine ganglion (accompanying CN VI palsy with cavernous sinus involvement)
Fallopian canal: involvement of nerve to stapedius muscle, dysacusis, involvement of chorda tympani, loss of taste to anterior two-thirds of tongue, impaired salivary secretion
Distal to chorda tympani: isolated paralysis of facial muscles
Distal to branching of CN VII after it leaves stylomastoid foramen: only certain branches of CN VII are affected (localized facial; bilateral CN VII palsy may result from weakness)
In addition, bilateral CN VII palsy may result from congenital conditions (Möbius syndrome), sarcoidosis, Guillain-Barré syndrome, or neurofibromatosis type 2 (bilateral acoustic neuromas). GSPN = greater superficial petrosal nerve.
(Illustration by Christine Gralapp.)
Any aberrant facial movements at rest or during volitional movement should be noted (see Fig 11-4). After any facial neuropathy, but most commonly as a result of Bell palsy, regenerating axons may reinnervate different muscles from those originally served; such aberrant regeneration can cause synkinetic movements. In this situation, the involved facial muscles may remain weak. When axons originally destined for the orbicularis oculi reinnervate the lower facial muscles, each blink may cause a twitch of the corner of the mouth or a dimpling of the chin. Conversely, movements of the lower face—such as pursing the lips, smiling, or chewing with the mouth closed—may produce involuntary eyelid closure.
Other disorders of aberrant facial innervation include lacrimation caused by chewing (crocodile tears), in which fibers originally supplying mandibular and sublingual glands reinnervate the lacrimal gland by way of the greater superficial petrosal nerve. This syndrome usually develops after severe injury to the proximal CN VII and may be accompanied by decreased reflex tearing and decreased ability to taste from the anterior two-thirds of the tongue.
Excerpted from BCSC 2020-2021 series: Section 5 - Neuro-Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.