Prolonged orbicularis oculi activity

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Abstract
Background: Apraxia of lid opening (ALO) is a nonparalytic inability to open the eyes at will in the absence of visible contraction of the orbicularis oculi (OOc) muscle. Objective: To test the hypothesis that sustained activity of the OOc is a major factor in the difficulty in opening the eyes in this condition. Methods: Lid movement detected in an electromagnetic field and electromyogram activity of the septal and pretarsal portions of the OOc were recorded in 12 healthy control subjects and 12 patients with a clinical diagnosis of ALO. The latencies to onset and to complete eye opening and the time during which eye opening was sustained were measured and analyzed in relation to OOc activity. Results: The lid opening latencies and the lid movement duration were significantly increased in patients compared with control values. An abnormal persistence of OOc activity was present in 10 of the 11 patients with a delay in complete lid opening. The complete lid opening delay showed a strong positive correlation with the time it took to inhibit the OOc activity. This relationship fit the same linear regression in both groups. Conclusions: Patients with ALO show significant delays in eye opening. An abnormal persistence of OOc activity, detectable electromyographically but not clinically, could be the main factor contributing to the delay in lid opening in these patients.