Purppse. Parkinson disease patients exhibit the paradox of decreased blink rate accompanied by a hyperexcitable blink reflex. We examined blinking in Parkinson disease in an attempt to further understand the consequences that dopamine depletion has upon eyelid kinematics and main sequence (peak velocity versus amplitude) characteristics of blinks. Methods. The electromagnetic search coil technique was used to record the metrics of blinks bilaterally in subjects with Parkinson disease. An age-matched population served as control. Results. Neurologic evaluations and spontaneous blink rates were consistent with the diagnosis of Parkinsonism. The most striking finding in Parkinson disease patients was a differential effect upon spontaneous and voluntary blink kinematics. Mean blink down-phase amplitude was dramatically reduced for spontaneous blinks, but remained in normal range for voluntary blinks, when compared to age-matched controls. There also was a disparate response in the slope of the peak velocity versus amplitude relationship for the two classes of blinks. Downphase main sequence slope was at control values or slightly decreased for spontaneous blinks, while the same patients showed significant elevation of main sequence slope for voluntary blinks. The interocular coordination of eyelid movements was decreased for both spontaneous and voluntary blinks, as amplitude and peak velocity of down phases were less tightly matched for the two eyelids in comparison to the control population. Conclusions. In contrast to patients with other neurologic disorders affecting blink (e.g., blepharospasm, Bell's palsy), eyelid kinematics in Parkinson patients exhibited changes that were dependent upon the type of blink. The finding that spontaneous blinks were hypometric, while voluntary blink amplitudes fell into normal range, suggests that dopamine may exert differential control over different classes of blink. Main sequence slope measures are particularly useful in understanding the effects of Parkinsonism on the neural control of eyelid movement. We interpret the blink down-phase main sequence slope as an indicator of aggregate orbicularis oculi motoneuron activity. Thus, the increase in the voluntary downphase slope value for voluntary blinks reflects an enhanced orbicularis motoneuron recruitment that is not seen in spontaneous blinks. Supported by EY10760, the Benign Essential Blepharospasm Research Foundation, and Research to Prevent Blindness. None.
|Journal||Investigative Ophthalmology and Visual Science|
|State||Published - 1997|
ASJC Scopus subject areas
- Sensory Systems
- Cellular and Molecular Neuroscience