7th (Facial) Nerve - Ophthalmology PG Reference

Library note: Kanski's Clinical Ophthalmology (10th ed.) is available in full. AK Khurana and Duke-Elder are not in this library, so those sections are covered from standard knowledge below, clearly marked.

From Kanski's Clinical Ophthalmology, 10th Ed. (pp. 832-834)

Overview

• Innervates all facial muscles (motor)
• Stimulates secretomotor activity in the lacrimal gland, submandibular and sublingual salivary glands
• Carries taste from the anterior 2/3 of the tongue
• Controls the amplitude of sound from the inner ear (stapedius)

Anatomy (Fig. 19.80)

1. Crosses posterior cranial fossa alongside VIII nerve
2. Enters internal acoustic meatus
3. Enters facial canal in petrous temporal bone - roots fuse - form geniculate ganglion
4. Geniculate ganglion - gives off greater petrosal nerve (preganglionic parasympathetic to lacrimal gland + nasal mucous glands)
5. Continues → gives nerve to stapedius + chorda tympani (taste + parasympathetics to submandibular ganglion)
6. Exits through stylomastoid foramen
7. Divides into terminal branches at posterior edge of parotid gland - 5 branches: Temporal, Zygomatic, Buccal, Mandibular, Cervical

Key Features (Innervation Pattern)

• Dry eye: Loss of parasympathetic fibres (greater petrosal nerve) = reduced tear production + loss of anterior tongue taste
• Hyperacusis: Loss of stapedius function

Physical Signs - Localisation by Level of Lesion

Clinical Photo - 7th Nerve Palsy

Causes of Facial Nerve Palsy

Ophthalmological Complications

• Lagophthalmos (inability to close eye fully) → corneal exposure
• Paralytic ectropion (lower lid)
• Dry eye (loss of secretomotor to lacrimal gland)
• Watery eye / epiphora (from ectropion or "crocodile tears" in recovery)
• Synkinesis ("crocodile tears" = lacrimation during eating, from aberrant regeneration)
• Corneal exposure keratopathy - especially when V nerve also affected

Management (Kanski, p. 834)

1. Corneal protection - especially if 5th nerve also affected (lubricants, taping, tarsorrhaphy if needed)
2. Corticosteroids - In Bell palsy: prednisolone 60-80 mg/day for 1 week, then taper over 1 week - must start within 48-72 hours of onset
3. Antivirals (acyclovir or valaciclovir) - Added to steroids; reduces long-term sequelae (excessive tearing, abnormal facial movement) even though recovery rate is not improved
4. MRI brain - if palsy is slow in onset or has other neurological signs (to exclude intracranial pathology)
5. If bilateral - Chest X-ray + serum ACE (SACE) to exclude sarcoidosis
6. Surgery - Decompression is NOT beneficial in Bell palsy; reconstructive surgery for long-term paralysis offers partial improvement only

TIP (Kanski): If onset of facial nerve palsy is slow or other neurological signs are present, investigate with MRI to exclude intracranial pathology.

AK Khurana - Ophthalmology (from standard knowledge)

• Eyelids - Orbicularis oculi is innervated by the zygomatic and temporal branches of VII. Paralysis causes lagophthalmos.
• Corneal reflex - Efferent arc is VII nerve
• Bell's palsy chapter - Khurana emphasises:
  • UMN vs LMN palsy distinction (forehead sparing in UMN)
  • Bell's phenomenon (upward and outward rolling of eye on attempted closure - protective reflex) - important PG MCQ point
  • Paralytic ectropion management
• Secretomotor pathway - Greater petrosal nerve from geniculate ganglion → pterygopalatine ganglion → lacrimal gland

• Nerve of Wrisberg = nervus intermedius = sensory root of VII
• Crocodile tears = Bogorad syndrome (aberrant regeneration of greater petrosal nerve fibres into chorda tympani after Bell's palsy)
• Test for Bell's palsy recovery: Schirmer's test (lacrimation), stapedial reflex, taste (electrogustometry)

Duke-Elder (System of Ophthalmology) - from standard knowledge

• Nuclear anatomy: VII nerve nucleus lies in the pons. The VII nerve fibres loop around the VI nerve nucleus (forming the facial colliculus visible on the floor of 4th ventricle) - hence pontine lesions cause combined VI + VII palsy
• Efferent lacrimal pathway:
  • Hypothalamus → superior salivatory nucleus → nervus intermedius → geniculate ganglion → greater petrosal nerve → vidian nerve (nerve of pterygoid canal) → pterygopalatine ganglion → lacrimal nerve (branch of V1) → lacrimal gland
• Ectropion classification: Duke-Elder classifies paralytic ectropion as a separate type under lid malpositions
• Exposure keratitis: Covered extensively - neuroparalytic (V) vs lagophthalmos (VII) - both cause different patterns of corneal exposure
• Lagophthalmos from VII palsy causes inferior corneal exposure; neuroparalytic keratitis from V palsy causes loss of protective sensation with central exposure

High-Yield PG MCQ Summary