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Bell's phenomenon

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

Authoring team

  • Bell's phenomenon
    • 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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