Origin of eye and eyelid movements during blinking

Studies of blinks have revealed the reciprocal relationship between innervation patterns of the levator palpebrae superioris (LP) and the orbicularis oculi (OO) muscles, resulting in a downward movement of the upper eyelid. Immediately before a blink, tonic activity of LP ceases followed by OO muscle activity. At the end of a blink, OO actively turns off and LP returns to its previous tonic activity either accompanied by an initial burst or not.1, 2 Concurrently with blinking the eye‐globes rotate in a horizontal, vertical, and torsion direction. In general, eye rotation depends on the initial eye position, which is in straight‐ahead position directed nasally and downward.3-8 In addition to during blinking, the eye‐globes make a slight displacement of 1 to 2 mm back into the orbits. Prolonged blinking or permanent eye closure is accompanied by upward conjugate eye movements (Bell's sign).

In patients with essential blepharospasm (involuntary eyelid contractions) eye movement disorders may, occasionally, accompany eyelid spasms and may consist of lateral and oblique deviations limited to one eye and deviations in all directions. Furthermore, deviations may be tonic and/or phasic, may occur in conjunction with eyelid closure, and persist after the opening of the eyelids. Convergence spasms and regular and macrosquare wave jerks have been demonstrated also.9 We report on observations obtained by simultaneous recordings of eye and eyelid movements together with electromyography (EMG) recordings of the OO muscle in a group of seven healthy subjects and in a patient with an intrinsic brainstem lesion.