A Closed-Loop Stimulation System Supplemented with Motoneurone Dynamic Sensitivity Replicates Natural Eye Blinks

Objective. The authors are designing an implantable device that will electrically stimulate a paretic eyelid when electrodes implanted into the contralateral healthy orbicularis oculi muscle detect a spontaneous blink activity. As a novelty, the stimulation pattern includes the dynamic sensitivity of motor units, thus obtaining complete eyelid closure, tailored on the kinematics of the natural eye blink. Study Design. A preliminary study was performed on 10 healthy subjects, to observe, first, the kinematics of their natural eye blink and, second, the eye blink stimulated by a dynamic vs nondynamic pattern. Setting. A microaccelerometer taped onto the left upper eyelid detected its kinematics. A dedicated LabView software built up and triggered the stimulation pattern. A webcam recorded the behavioral effect. Subjects and Methods. The kinematics of spontaneous eye blinks was detected. Then, an epicutaneous stimulation of the facial nerve branch for the left orbicularis oculi muscle was performed on the same subjects. Muscle recruitment curves were studied, and acceleration of the bionic blink was measured and compared with the natural one. Results. Kinematics of the natural eyelid is highly variable within subjects. The stimulation pattern frequency was set case by case in order to obtain the desired eyelid acceleration of the contralateral eye. A custom-fit dynamic stimulation leads to a symmetrical natural-like eye blink. Conclusions. By adding the dynamic pulse, the authors were able to tailor a bionic eye blink, which was hardly distinguishable from the subject's natural one.