Corneal Reflex

The corneal reflex, also known as the blink reflex, is an involuntary blinking of the eyelids elicited by stimulation of the cornea (such as by touching or by a foreign body), or bright light, though could result from any peripheral stimulus. Stimulation should elicit both a direct and consensual response (response of the opposite eye). The reflex consumes a rapid rate of 0.1 second. The evolutionary purpose of this reflex is to protect the eyes from foreign bodies and bright lights (the latter known as the optical reflex). The blink reflex also occurs when sounds greater than 40-60 dB are made.

The reflex is mediated by:

• the nasociliary branch of the ophthalmic branch (V₁) of the 5th cranial nerve (trigeminal nerve) sensing the stimulus on the cornea, lid, or conjunctiva (i.e. it is the afferent).
• the temporal and zygomatic branches of the 7th cranial nerve (Facial nerve) initiating the motor response (i.e. it is the efferent).
• possibly mediated by a medullary center.

Use of contact lenses may diminish or abolish the testing of this reflex.

The optical reflex, on the other hand, is slower and is mediated by the visual cortex, which resides in the occipital lobe of the brain. The reflex is absent in infants under 9 months.

The examination of the corneal reflex is a part of some neurological exams, particularly when evaluating coma. Damage to the ophthalmic branch (V₁) of the 5th cranial nerve results in absent corneal reflex when the affected eye is stimulated. Stimulation of one cornea normally has a consensual response, with both eyelids normally closing.