Blinks and Associated Eye Movements

Abstract

Studies of blinks have revealed the reciprocal relationship between the innervation patterns of the levator palpebrae superioris (LP) and the orbicularis oculi (00) muscles (Gordon 1951; Bjork and Kugelberg 1953; Becker and Fuchs 1988; Evinger 1991; Aramideh et al. 1994a) resulting in a downward movement of the upper eyelid. Immediately prior to a blink, the discharge of the LP ceases whereas the 00 motoneurons produce a short high-frequency burst of activity. At the end of a blink the 00 actively turns off and the LP returns to its previous tonic activity either accompanied by an initial burst or not (Aramideh et al. 1994a). Concurrently the eye-globe makes a slight displacement of 1–2 millimeters back into the orbit (Evinger et al. 1984) and performs a horizontal, vertical (Collewijn et al. 1985; Riggs et al. 1987) and torsional rotation (Straumann et al. 1996). During blinks the rotation of the eye in straight-ahead position normally is directed nasally downward (Collewijn et al. 1985; Riggs et al. 1987). This rotation also depends on the initial eye position. Prolonged blinking or permanent closure of the eye may be accompanied by upward directed conjugate eye movements (Collewijn et al. 1985). To what extent the different extraocular muscles contribute to this combined translational and rotational movement is not yet known. Abnormalities of eye movements or eyelid movements or both have been reported in disorders of the basal ganglia and/or the midbrain. In essential blepharospasm occasionally eye movement disorders accompany the spasms of the eyelid closure (Aramideh et al. 1994b). This mutual interaction between some types of eye and eyelid movements may have a same origin.