occurs in the case of a unilateral lower motor neuron palsy
is the visible vertical rotation of globe on closing the affected eye (1)
it is seen when the patient attempts to shut the eye on the affected side which causes upward movement of the eyeball and incomplete closure of the eyelid.
this provides a test of infranuclear competence
only a positive response is helpful
some normal subjects do not show a Bell's phenomenon.
in unconscious patients, a fairly strong corneal stimulus may induce a Bell's phenomenon. If it does, it indicates midbrain-low pons intactness, i.e. cranial nerves III-VII. With structural brainstem lesions above the pons, Bell's phenomenon disappears but the jaw may deviate to the opposite side in the corneal pterygoid reflex.
bilateral Bell's phenomenon (2)
is found in the following conditions
myasthenia gravis
sarcoidosis
bilateral Bell's palsies
congenital facial diplegia
muscular dystrophy
motor neuron disease
Guillain-Barré syndrome (rare)
if an oblique of horizontal ocular deviation is evoked during forcible lid closure, it is said to signify a temporoparietal lesion on the side opposite to the deviation and is called by Cogan 'spasticity of conjugate gaze.'
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