Which nerve has been anaesthetized to produce the inability to close the eye?

Correct answer: C. Facial nerve (CN VII)

• A. CN III supplies levator palpebrae superioris, which OPENS the upper lid. Its paralysis causes PTOSIS — a drooping lid that cannot be raised — the opposite of an inability to close.
• B. The optic nerve is purely SENSORY for vision. It has no motor function and cannot produce weakness of eyelid closure.
• C. CORRECT. The FACIAL NERVE. If the needle passes too far posteriorly and the solution is deposited within the PAROTID GLAND — through which the facial nerve and its branches run — a transient facial nerve palsy results. The temporal and zygomatic branches supply orbicularis oculi, so the patient cannot close the eye; the buccal and marginal mandibular branches produce the drooping mouth corner. It resolves as the anaesthetic wears off, in roughly 1 to 3 hours depending on the agent.
• D. V1 is sensory to the forehead, upper eyelid and cornea. Anaesthetising it would abolish the corneal reflex but would not weaken the muscle that closes the eye.

Note: Immediate management: cover the eye with a patch or have the patient close it manually and apply artificial tears, because the cornea is unprotected without a blink. Reassure the patient, document the event, and inform them it is temporary. The cause is depositing solution too far posteriorly — always contact bone before injecting, and withdraw slightly if you do not.