A site for medical students - Practical,Theory,Osce Notes

How to elicit Corneal reflex?

The corneal reflex, also known as the blink reflex, is an involuntary blinking of the eyelids elicited by stimulation of the cornea. The purpose of this reflex is to protect the eyes from foreign bodies and bright lights (the latter known as the optical reflex)
The edge of  cornea  (limbus) is touched with  a  wisp of cotton, with the patient looking upward  in the opposite direction
  • The nasociliary branch of the ophthalmic branch (V1) of the 5th cranial nerve (trigeminal nerve) sensing the stimulus on the cornea(afferent fiber).
  • The temporal and zygomatic branches of the 7th cranial nerve (Facial nerve) initiating the motor response (efferent fiber).
  • The centre (nucleus) in the pons of brain stem.
  • Use of contact lenses may diminish or abolish the testing of this reflex.
  • Response is brisk closure of both the eyes
  • Stimulation should elicit both a direct and indirect or consensual response (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

An absent corneal reflex may be due to
  • Sensory loss in Vi (e.g. neuropathy or ganglionpathy)
  • Weakness or paralysis of the facial muscles (myopathy) 
  • Facial nerve (facial palsy, for example Bell's palsy) 
  • Brain stem disease.
For a myopathy to cause a loss of the blink reflex the weakness has to be very severe, example  chronic progressive external ophthalmoplegia (CPEO)