The corneal reflex is a protective blink when the cornea is touched. The sensory signal travels in the ophthalmic division of the trigeminal nerve and the blink is produced by the facial nerve supplying orbicularis oculi. Both eyes normally blink (direct and consensual responses).
| Nerve root | CN V (afferent), CN VII (efferent) |
|---|---|
| Area | Cornea, touched at its edge |
| How to test | While the patient looks to one side, the examiner gently touches the edge of the cornea with a wisp of clean cotton wool from the side and watches both eyes for a blink. |
| Muscles | |
| Nerve Supply | Ophthalmic nerve (trigeminal nerve, CN V1, via nasociliary branch); Facial nerve (CN VII) |
Protects the cornea from injury and drying by triggering a rapid blink.
If neither eye blinks when one cornea is touched, the sensory (trigeminal) side is affected; if only the touched eye fails to blink, the facial nerve on that side is affected. A reduced corneal reflex can be an early sign of a vestibular schwannoma pressing on the trigeminal nerve, and absence of the reflex is one of the brainstem tests used in determining brain death. Contact lens wearers may have a reduced response.
A tumour at the cerebellopontine angle can compress the trigeminal nerve and reduce the corneal reflex early, before obvious facial numbness.
In Bell palsy the touched eye on the affected side does not blink, though the other eye still does.
Loss of all brainstem reflexes, including the corneal reflex, is part of the clinical criteria for brain death.
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