Dynamics of the human eyeblink.

High-speed photography of eyeblinks in 4 subjects provided displacement and velocity time functions. The results from dynamic measurements made with a mechanical transducer connected physically to the upper eyelid gave estimates of the passive spring constant (Kp = 1.5 gmf/mm) and the passive viscosity (Bp = 0.09 gmf - sec/mm) of the eyelid. Noting the similarity between the reciprocal-innervation mechanisms in the eyelid and the eye-movement systems, a mathematical eyelid model was derived based on the well-known eye-movement model and using similar ideal mechanical-element representations. The model-simulation time course shows the essential characteristics of an eyeblink and suggests that the force program consists of reciprocally acting pulse forces during the downblink, and pulse-step forces during the upblink. When 1 mm of lid displacement is equated with 5 deg of eyeball rotation and when the main sequences for lid movements and for time-optimal saccadic eye movements are compared, the eyeblinks are not found to be time optimal for their various amplitudes.