Corneal reflex

Corneal reflex — clear, oral-exam–ready explanation

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What the corneal reflex is

The corneal reflex is a protective brainstem reflex in which touching the cornea causes blinking of both eyes.

Components of the reflex (this structure wins marks)

1⃣ Receptor

  • Free nerve endings in the cornea

  • Highly sensitive (pain/touch)

2⃣ Afferent (sensory) limb

  • Cranial nerve V₁ (ophthalmic division of trigeminal nerve)

  • Pathway:

    • Cornea → nasociliary nerve → ophthalmic nerve (V₁)

    • Enters pons

    • Synapses in the spinal trigeminal nucleus

👉 Key point: The sensory limb is CN V₁.

3⃣ Central connections

  • Interneurons from the spinal trigeminal nucleus

  • Project bilaterally to the facial motor nuclei

👉 This bilateral projection explains blinking in both eyes.

4⃣ Efferent (motor) limb

  • Cranial nerve VII (facial nerve)

  • From facial motor nucleus

  • Innervates orbicularis oculi muscle

👉 Key point: The motor limb is CN VII.

5⃣ Response

  • Bilateral eyelid closure (blink)

One-line viva answer (perfect)

The corneal reflex is a protective blink reflex in which corneal stimulation is carried by the ophthalmic division of the trigeminal nerve to the spinal trigeminal nucleus, and the response is mediated bilaterally by the facial nerve to the orbicularis oculi.

Clinical testing (very high-yield)

  • Touch cornea lightly with cotton wisp

  • Normal: both eyes blink

  • If no blink in either eye: suspect V₁ lesion (afferent)

  • If only one eye doesn’t blink: suspect CN VII lesion (efferent) on that side

Quick localisation table

Finding

Likely lesion

No blink in either eye when right cornea touched

Right V₁

Right eye doesn’t blink, left does

Right CN VII

Reduced sensation but blinking intact

Partial V₁ sensory loss

Common exam traps ❌

  • ❌ Saying the afferent limb is CN VII

  • ❌ Forgetting that the response is bilateral

  • ❌ Calling it a cortical reflex (it is brainstem)