An objective tool to measure the effect of botulinum toxin in blepharospasm and hemifacial spasm

Background and purpose It is challenging to assess patients with blepharospasm (BSP) and hemifacial spasm (HFS) as these patients exhibit a wide range of amplitudes of eyelid movements. In order to quantify these movements, a mathematical algorithm, i.e. Fast Fourier Transform, can be employed to convert the signal from the time domain to the frequency domain. The result of this quantification represents the energy generated during the eyelid movements. In order to objectively assess the therapeutic effects of botulinum toxin (BoNT) in these patients, we evaluated the energy generated by the upper eyelid during spontaneous eyelid movements before and after treatment. Methods A total of 39 patients with BSP and HFS were evaluated before and 30 days after receiving onabotulinum toxin A injections. A high‐speed camera and micro light‐emitting diodes were used to register the spontaneous eyelid movements. The result of the quantification obtained using Fast Fourier Transform permitted assessment of the activity associated with the eyelid movements. Results We studied 78 eyelids. The total energy generated during spontaneous eyelid movements was significantly reduced after treatment in the patients with BSP ( P = 0.0018) and on the affected side in the patients with HFS ( P = 0.0058). Conclusions The assessment of the energy generated by the upper eyelid during spontaneous eyelid movements enabled us to measure the therapeutic effects of BoNT in patients with these conditions. The use of this system could enable customized and fine adjustments to BoNT doses based on each patient’s needs.