Eyelid movements. Mechanisms and normal data.

This study provides a comprehensive description of upper eyelid movement in normal human subjects. Using the magnetic search coil technique to monitor lid position and modified skin electrodes to record orbicularis oculi electromyographic (EMG) activity, the authors found that the basic eyelid movements, blinks, and saccadic lid movements, can be uniquely and reliably characterized by their amplitude-maximum velocity relationships. The data show that similar increases in levator palpebrae activity produce the upward lid movements that accompany upward saccadic eye movements as well as the upward phase of a blink. The lid movements that accompany downward saccadic eye movements arise almost exclusively from the passive downward forces and relaxation of the levator palpebrae muscle. In contrast, active orbicularis oculi contraction and the passive downward forces act together to generate lid closure with a blink. These normative data and techniques provide the basis for the clinical analysis of lid motility by which abnormal lid movements can be compared with normal lid kinematics.