Corneal reflex

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).[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 (i.e. it is the afferent).
  • 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, 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.

Contents

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 globus pallidus of the basal ganglia contains a blinking center that controls blinking. Nonetheless, the external stimuli are still involved. Blinking is linked with the extraocular muscles. Blinking is often concurrent with a shift in gaze, and it is believed that this helps the movement of the eye.

See also

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


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • corneal reflex — reflex blinking of both eyes normally elicited by lightly touching the cornea of one eye. This reflex is lost in deep coma, during general anaesthesia, and in death; it is therefore one of the tests used to confirm death …   The new mediacal dictionary

  • corneal reflex — 1. irritation of the cornea results in reflex closure of the lids; called also blink r., eyelid closure r., and lid r. 2. reflection of light from the cornea …   Medical dictionary

  • corneal reflex — 1. Physiol. the closing of the eyelids induced by touching the cornea lightly. 2. Ophthalm. the reflection of a keratoscope, as Placido s disk, on the surface of the cornea. * * * …   Universalium

  • corneal reflex — 1. Physiol. the closing of the eyelids induced by touching the cornea lightly. 2. Ophthalm. the reflection of a keratoscope, as Placido s disk, on the surface of the cornea …   Useful english dictionary

  • Corneal ulcers in animals — Large corneal ulcer in a dog A corneal ulcer, or ulcerative keratitis, is an inflammatory condition of the cornea involving loss of its outer layer. It is very common in dogs and is sometimes seen in cats. In veterinary medicine, the term corneal …   Wikipedia

  • Reflex — A reaction that is involuntary. The corneal reflex is the blink that occurs with irritation of the eye. The nasal reflex is a sneeze. * * * 1. An involuntary reaction in response to a stimulus applied to the periphery and transmitted to the… …   Medical dictionary

  • Reflex — For other uses, see Reflex (disambiguation). A reflex action, also known as a reflex, is an involuntary and nearly instantaneous movement in response to a stimulus.[1] A true reflex is a behavior which is mediated via the reflex arc; this does… …   Wikipedia

  • Corneal abrasion — Classification and external resources A corneal abrasion after staining with fluorescein. ICD 10 S …   Wikipedia

  • Corneal ulcer — For the condition in animals, see Corneal ulcers in animals. Corneal ulcer Classification and external resources ICD 10 H16.0 ICD 9 …   Wikipedia

  • Cushing reflex — (also referred to as the vasopressor response, the Cushing effect, the Cushing reaction, the Cushing phenomenon, the Cushing response, or Cushing s Law) is a physiological nervous system response to increased intracranial pressure (ICP) that… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”