| Corneal reflex | |
|---|---|
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| Purpose | Examination of corneal reflex is part of some neurological tests. |
Thecorneal reflex, also known as theblink reflex oreyelid reflex,[1] is an involuntaryblinking of theeyelids elicited by stimulation of thecornea (such as by touching or by a foreign body), though it could result from any peripheral stimulus. Stimulation should elicit both a direct and consensual response (response of the opposite eye). The reflex occurs at a rapid rate of 0.1 seconds. The purpose of this reflex is to protect theeyes from foreign bodies and bright lights (the latter known as the optical reflex).[2] The blink reflex also occurs when sounds greater than 40–60dB are made.[3]
The reflex is mediated by:
Use ofcontact lenses may diminish or abolish the testing of this reflex.
The optical reflex, on the other hand, is slower and is mediated by thevisual cortex, which resides in theoccipital lobe of the brain. The reflex is absent in infants under nine months.
The examination of the corneal reflex is a part of someneurological exams, particularly when evaluatingcoma, such asFOUR score. Damage to the ophthalmic branch (V1) of the trigeminal 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.
When awake, the lids spread the tear secretions over the corneal surface, on a typical basis of 2 to 10 seconds (though this may vary individually). However, blinking is not only dependent on dryness and/or irritation.[citation needed] A brain area, theglobus pallidus of thebasal ganglia, contains a blinking center that controls blinking. Nonetheless, the external stimuli are still involved. Blinking is linked with theextraocular muscles. Blinking is often concurrent with a shift in gaze, and it is believed that this helps the movement of the eye.[4]
The corneal reflex is a contraction of the orbicularis oculi in response to light touch of the cornea. It is polysynaptic, the afferent limb of the reflex being the ophthalmic division of the fifth cranial nerve, the efferent limb running in the seventh nerve