A new gyro-based method for quantifying eyelid motion

Purpose: We present an innovative method to quantify the eyeblink by using a miniature gyroscopic sensor (gyro), which is applied on the upper eyelid. Electrical Stimulation (ES) of the facial nerve is a promising technology to treat dysfunctional eyelid closure following facial paralysis. We used the new gyro-based method to evaluate the biomechanics of both the spontaneous and the ES-induced eyeblink, and to identify the best ES protocol. Methods: During blinking, eyelids rotate about the axis passing through the eye canthi, thus we propose to use a gyro for measuring the angular velocity of the upper eyelid (ωe ). The angular displacement of the eyelid (θe ) was calculated by integrating the ωe signal. Two indices were derived from θe: 1) the eyelid angular displacement during eye closure (C), calculated as the peak value of θe ; 2) the eyelid closure duration (D), calculated as the time interval between zero signal and the peak value of θe. In a healthy volunteer we used this method to quantify both the spontaneous eyeblink and the blinks elicited by different ES patterns. Results: For the spontaneous eyeblink, indices C = 14.0 ± 1.8° and D = 94.0 ± 10.8 ms were computed. By comparing C and D indices for spontaneous and ES cases, trains of 10 pulses with a frequency ranging from 200 Hz to 400 Hz proved to induce the most effective and natural-like eyeblinks. Conclusions: The new gyro-based method proved to be a valuable tool to provide dynamic and realtime quantification of eyelid motions. It could be particularly useful for evaluating the effective and natural-like eyeblink restoration provided by ES.