Anatomy & Function of the Facial Nerve

• The facial nerve (CNVII) has two major divisions and controls the muscles of facial expression, including the frontalis muscle (raises the eyebrows), the orbicularis oculi muscle (closes the eyes), the zygomaticus muscles (raises the angle of the mouth)

Branches

• Greater petrosal nerve - provides parasympathetic innervation to lacrimal gland, sphenoid sinus, frontal sinus, maxillary sinus, ethmoid sinus, nasal cavity, as well as special sensory taste fibers to the palate via the Vidian nerve.
• Nerve to stapedius - provides motor innervation for stapedius muscle in middle ear
• Chorda tympani - provides parasympathetic innervation to submandibular gland and sublingual gland and special sensory taste fibers for the anterior 2/3 of the tongue.

Etiologies

• Paresis of the orbicularis oculi muscle leads to a diminished blink, incomplete eyelid closure (Lagophthalmos), impairment of the nasolacrimal pumping system
  • The blink reflex and lid position are critical to maintain the ocular surface
  • Each blink spreads the tear film over the ocular surface and allows for a continuous layer of moisture.
• Congenital
  • Moebius' Syndrome
• Acquired
  • Bell's Palsy
  • vascular lesions
• Tumors
  • Acoustic Neuroma
  • Parotid gland
  • temporal bone tumor
• Trauma

Symptoms

• Tearing, atonic eyelid

erms

Lagophthalmos: Patients with lagophthalmos have an inability to close eyelids. This may occur, for instance, in patients with Thyroid eye disease. Visit the lagophthalmos page

for more details.

Graves' disease is an autoimmune disease. It most commonly affects the thyroid, causing it to grow to twice its size or more (goiter), be overactive, with related hyperthyroid symptoms such as increased heartbeat, muscle weakness, disturbed sleep, and irritability. It can also affect the eyes, causing bulging eyes (exophthalmos). It affects other systems of the body, including the skin and reproductive organs. It affects up to 2% of the female population, often appears after childbirth, and has a female:male incidence of 5:1 to 10:1. It has a strong hereditary component; when one identical twin has Graves' disease, the other twin will have it 25% of the time. Smoking and exposure to second-hand smoke is associated with the eye manifestations but not the thyroid manifestations. Diagnosis is usually made on the basis of symptoms, although thyroid hormone tests may be useful, particularly to monitor treatment.