Electromyographic studies of the motor function of the orbicularis oculi and the levator palpebra superioris of parkinsonian patients revealed: (1) no abnormalities during following movements; (2) tremor due to reciprocal phasic electrical activity in the levator and orbicularis during gentle lid closure; (3) no tremor but a rapid decline in electrical potential due to motor impersistence during forced lid closure; (4) persistence of orbicularis activity into the period of levator activity resulting in delayed lid opening during voluntary blinking; (5) coinhibition of both the orbicularis and the levator before and after a periodic blink; (6) increased latency and prolonged electrical activity in response to corneal stimulation; and (7) no decay in the nociceptive orbicularis response to glabellar tap. Comparison of these findings with electromyographic findings for peripheral muscles of patients with parkinsonism revealed some similarities.
LOEFFLER JD, SLATT B, HOYT WF. Motor Abnormalities of the Eyelids in Parkinson's Disease: Electromyographic Observations. Arch Ophthalmol. 1966;76(2):178–185. doi:https://doi.org/10.1001/archopht.1966.03850010180005
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