The role of blink adaptation in the pathophysiology of benign essential blepharospasm
S. A. Hasan, R. S. Baker, W. S. Sun, B. R. Rouholiman, J. C. Chuke, D. E. Cowen and J. D. Porter
Department of Ophthalmology, University of Kentucky Medical Center, Lexington, USA.
OBJECTIVE: To investigate eyelid movements in patients with benign
essential blepharospasm (BEB), with an emphasis on the characterization of
the kinematics of normal and spastic blinks, assessment of interocular
differences, and further delineation of the role of adaptive blink
mechanisms in eyelid movement disorders. PATIENTS AND METHODS: The
electromagnetic search coil technique was used to record the metrics of
blinks 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 amplitude and peak
velocity. Moreover, the main-sequence slope was decreased bilaterally.
Spasms were bilateral and relatively conjugate. There was no change in the
coordination of normal blinking across the 2 eyelids. CONCLUSIONS: These
data demonstrate the operation of the adaptive regulation of blinking in an
eyelid movement disorder. The findings suggest that the adaptive regulation
of blink is a bilateral event. Blink-adaptive control systems can act on
the blink reflex excitability and main-sequence relationships, changing
these either together or independently. The hyperexcitable blink reflex of
BEB is met by what is believed to be an adaptive decrease in the
main-sequence slope that would decrease the strength of debilitating
spasms. Collectively, these data extend the knowledge of the
pathophysiology of BEB and, perhaps more important, establish the role of
blink system plasticity in eyelid movement disorders.
