A. 5th Cranial nerve lesion
B. Brain-Stem lesion
C. 7th Cranial nerve lesion
D. All of the above
Ans:D. All of the above.
The test shown in the picture above represents corneal reflex test
- 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).
- 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 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).
the centre (nucleus) in the pons of brain stem.
- Interpretation: An absent corneal reflex can be due to sensory loss in V1-trigeminal nerve (e.g. neuropathy or ganglionpathy), weakness or paralysis of the facial muscles (myopathy) or facial nerve (facial palsy, for example Bell’s palsy) or brain stem disease.
- The examination of the corneal reflex is useful in unconscious patients and if present indicates that the lower brain stem is functioning. It is used as part of the assessment for determining if someone is brain dead; if the corneal reflex is present the person can’t be diagnosed with brain death.