4. Neuro-Ophthalmology and Seventh Nerve Paresis

Seventh nerve paresis - facial weakness

Definition: Seventh nerve paresis refers to weakness in the muscles controlled by the facial nerve (Cranial Nerve VII).

  • It is also known as facial weakness.

  • interruption of the seventh nerve itself (lower motor neurone paresis)

Involvement of all facial muscles on the affected side due to direct interruption of the seventh nerve.

  • Potential Causes:

    • Vascular Problems: Often associated with conditions like diabetes.

    • Trauma: Any injury that impacts the facial nerve.

    • Tumours: Growths that can compress the nerve.

    • Inflammation:

      • Viral Infections: Such as varicella zoster virus leading to Ramsay–Hunt syndrome.

      • Sarcoidosis.

    • Bell’s Palsy:

      • Diagnosis of exclusion.

      • Commonly idiopathic in nature

  • Clinical Considerations:

    • Ask the patient when symptoms began; rapid onset may suggest Bell’s palsy.

    • Evaluate for slow development of symptoms as it can indicate other, more serious issues.

    • Check the region of the ear for associated rashes or vesicles.

Symptoms and Signs

Ophthalmic:

  • Sore and/or watery eye

  • Blurred vision (corneal exposure)

  • Incomplete eyelid closure

  • Lower lid paralytic ectropion

  • Cornea: punctate epithelial loss

  • Reduced tear film (if lacrimal gland affected)

  • Epiphora (lacrimal pump mechanism failure)

Other Symptoms

  • Problems with speech, eating, and drinking.

  • Drooping of the outer angle of the mouth.

  • Inability to purse lips or puff out cheeks.

  • Changes in taste perception.

Upper Motor Neuron Paresis: Seventh nerve paresis

  • Pathophysiology: Compromise of input from higher centres to the facial nerve nuclei leads to weakness of lower facial muscles on the contralateral side.

  • Common Cause: Most frequently caused by a stroke.

  • Key Distinction: The eye is not involved as the upper facial muscles, including the orbicularis oculi, receive bilateral innervation from the brainstem.

    • unlikely to present to optometrist as eye is not commonly affected.

Management of Seventh Nerve Paresis

  • Referral: All patients with new-onset facial nerve weakness should be assessed to identify the underlying cause.

  • Corneal Protection: Essential due to risk of exposure:

    • Possible methods include:

    • Wearing a patch.

    • Taping the eyelids closed at night.

    • Using copious lubricating eye drops.

    • Scleral contact lenses.

    • Surgical option: Tarsorrhaphy (surgical eyelid closure).

Bell’s Palsy

  • Description: Most common cause of facial nerve paresis, characterized by acute onset unilateral weakness.

  • Diagnosis: Considered idiopathic, making it a diagnosis of exclusion. Possibly due to viral or inflammatory conditions.

  • Typical Onset: Facial droop occurs within 72 hours.

  • Demographics: Most common between ages 15 and 60, affecting both sexes equally.

  • Prognosis: Approximately 70% of patients regain full facial function within three weeks.

  • Treatment Options:

    • Systemic steroids, usually prednisone.

    • Antivirals (e.g., acyclovir) may be prescribed, often in combination with steroids.

Acoustic Neuromas

  • Impact on Facial Nerve: Can lead to weakness in the facial nerve,

  • can affect CN V (trigeminal nerve), CN VI (abducens nerve), and CN VIII (vestibulocochlear nerve).

  • Symptoms Associated with Acoustic Neuromas: in addition to 7th nerve palsy patients

    • Tinnitus (ringing in the ears).

    • Hearing loss.

    • Diminished corneal sensitivity.

    • Diplopia (double vision).

    • Papilledema (swelling of optic nerve head).

  • Clinical Consideration: In patients with sixth and seventh nerve paresis, always check corneal sensitivity on both sides.