Bell’s Phenomenon, Bell’s Sign
Bell’s phenomenon or sign is reflex upward, and slightly outward, deviation of the eyes in response to forced closure, or attempted closure, of the eyelids. This is a synkinesis of central origin involving superior rectus and inferior oblique muscles. It may be very evident in a patient with Bell’s palsy (idiopathic facial nerve paralysis) attempting to close the paretic eyelid. The reflex indicates intact nuclear and infranuclear mechanisms of upward gaze, and hence that any defect of upgaze is supranuclear. However, in making this interpretation it should be remembered that perhaps 10-15% of the normal population do not show a Bell’s phenomenon.
Bell’s phenomenon is usually absent in progressive supranuclear palsy and is only sometimes spared in Parinaud’s syndrome
Bell C. On the motions of the eye, in illustration of the use of the muscles and nerves of the orbit. Philosophical Transactions of theRoyal Society, London 1823; 113: 166-186.