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Types and time course of the alterations induced in monkey blink movements by botulinum toxin
J D Porter1, R S Baker, M W Stava
1Department of Anatomy and Neurobiology, University of Kentucky Medical Center, Lexington 40536-0084.
Abstract:
The alterations induced in eyelid movement metrics subsequent to unilateral injections of botulinum toxin type A into the orbicularis oculi muscle were studied in chronic alert monkeys using the search coil technique. Botulinum toxin caused rapid paralysis of blinks in the treated eyelid. The amplitude and peak velocity of blinks generated by this eyelid remained at or below 20% of that of the fellow, untreated eyelid for 10-20 days. Blink amplitude gain increased linearly thereafter, attaining control values by 40-60 days after injection. Recovery of blink peak velocity was slower. The adaptive alterations in blink duration that were observed during the acute phase of toxin paralysis suggest that the mechanisms responsible for blink reflex plasticity may produce bilateral adjustments in eyelid function. Taken together, these data establish a quantitative data base that can be exploited in order to: (1) better understand the neural adaptive mechanisms that operate during eyelid movements and (2) allow quantitative comparisons between current treatment protocols that employ botulinum toxin and protocols that may lead to improvements in the treatment of chronic eyelid spasm (blepharospasm).
Insights
Botulinum toxin type A temporarily paralyzes eyelid blinks, with recovery taking 40-60 days. This study quantifies blink recovery, aiding understanding of eyelid movement plasticity and blepharospasm treatments.
Area of Science:
- Neuroscience
- Ophthalmology
- Motor Control
Background:
- Botulinum toxin type A is used to treat conditions like blepharospasm.
- Understanding its precise effects on eyelid movement is crucial for optimizing treatment.
Purpose of the Study:
- To quantitatively analyze the effects of botulinum toxin type A on eyelid movement metrics.
- To investigate the adaptive changes in blink function following toxin-induced paralysis.
Main Methods:
- Unilateral injections of botulinum toxin type A into the orbicularis oculi muscle of chronic alert monkeys.
- High-precision search coil technique to measure eyelid movement metrics.
Main Results:
- Rapid paralysis of blinks in the treated eyelid, with amplitude and peak velocity reduced to below 20% of the control eyelid for 10-20 days.
- Gradual recovery of blink amplitude gain, reaching control levels by 40-60 days post-injection.
- Slower recovery of blink peak velocity observed.
Conclusions:
- Botulinum toxin type A induces significant, quantifiable alterations in eyelid movement.
- Adaptive changes suggest potential bilateral adjustments in blink reflex plasticity.
- Provides a quantitative basis for understanding neural mechanisms and comparing botulinum toxin treatment protocols for blepharospasm.