The relationship between eyelid closure and associated eye movements: Normal patterns and disturbances in blepharospasm

Purpose: In blepharospasm involuntary eyelid closure may be accompanied by abnormal eye movements. To obtain better understanding in underlying neuropathological mechanisms we examined the relationship between blinks and eye movements in a group of normal controls.

Methods: During blinking, eye movements were evaluated at various gaze angles. Reflex blinks were elicited by electrical stimulation of the supra-orbital nerve. Horizontal and vertical eye positions were recorded with a double magnetic induction (DMI) ring method. Electromyographic (EMG) recording was performed bilaterally from the orbicularis oculi (OO) muscles, using surface electrodes.

Results: In controls, reflex, spontaneous and voluntary blinks were accompanied by disconjugate oblique eye movements. At different gaze angles the oblique eye movements of both eyes were directed nasally and downward. Unilateral electrical stimulation of the supra-orbital nerve showed, at low stimulus intensities, the classical bilateral late blink reflex at the OO concurrent with bilateral late eye movements. With increasing stimulus intensity, the amplitude of the corresponding eye movement increased by 2-6 degrees; the latency decreased by 70-40 ms. At stimulus intensities approximately 2-3 times above threshold the ipsilateral early blink reflex in OO could be observed together with an ipsilateral early eye movement at a latency of 10-15 ms.

Conclusions: A new, early ipsilateral and late bilateral eye movement component were identified during electrically elicited blink reflexes. Synchronized movements of eyelids and eyes and similarity of disconjugate eye movements in different types of blinks suggest a common neural generator, perhaps within the pons (pontine blinking centre). In blepharospasm accompanied by abnormal eye movements this generator may be disturbed.