THE ROLE OF BLINK ADAPTATION IN THE PATHOPHYSIOLOGY OF BENIGN ESSENTIAL BLEPHAROSPASM

Objective: To investigate eyelid movements in patients with benign ess ential blepharospasm (BEB), with an emphasis on the characterization o f the kinematics of normal and spastic blinks, assessment of interocul ar differences, and further delineation of the role of adaptive blink mechanisms in eyelid movement disorders. Patients and Methods: The ele ctromagnetic search coil technique was used to record the metrics of b links bilaterally in 5 patients with untreated BEB. Eyelid kinematics and the main-sequence (peak velocity vs amplitude) relationships were analyzed. Results: Patients with BEB exhibited a decrease in blink amp litude and peak velocity. Moreover, the main-sequence slope was decrea sed bilaterally. Spasms were bilateral and relatively conjugate. There was no change in the coordination of normal blinking across the 2 eye lids. Conclusions: These data demonstrate the operation of the adaptiv e regulation of blinking in an eyelid movement disorder. The findings suggest that the adaptive regulation of blink is a bilateral event. Bl ink-adaptive control systems can act on the blink reflex excitability and main-sequence relationships, changing these either together or ind ependently. The hyperexcitable blink reflex of BEB is met by what is b elieved to be an adaptive decrease in the main-sequence slope that wou ld decrease the strength of debilitating spasms. Collectively, these d ata extend the knowledge of the pathophysiology of BEB and, perhaps mo re important, establish the role of blink system plasticity in eyelid movement disorders.