Corneal reflex

The corneal reflex, also known as the blink reflex, is an involuntary blinking of the eyelids elicited by stimulation (such as touching or a foreign body) of the cornea, 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).^[1] The blink reflex also occurs when sounds greater than 40-60 dB are made.^[2]

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.
• the 7th cranial nerve (facial nerve) initiating the motor response.
• possibly mediated by a medullary center.

Use of contact lenses may diminish or abolish this reflex.

The optical reflex, on the other hand, is slower and is mediated by the cortex (outer covering) of the occipital real 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.

Rates

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). But blinking is not only dependent on dryness and/or irritation. A brain area, the globulus pallidus of the caudate nucleus, a cell mass between the base and outer material of the brain contains a blinking center that controls blinking. Nonetheless, the external stimuli are still involved. Blinking is linked with the extraocular muscles. Blinking is often simultaneous with a shift in gaze, and it is believed that this helps the movement of the eye.

See also

• Reflex

References

1. ^ "eye, human."Encyclopædia Britannica from Encyclopædia Britannica 2006 Ultimate Reference Suite DVD 2009
2. ^ Garde, M.M., & Cowey, A. (2000). "Deaf hearing": Unacknowledged detection of auditory stimuli in a patient with cerebral deafness. Cortex 36(1), 71-80

External links

• -751501308 at GPnotebook