Voluntary, spontaneous, and reflex blinking in Parkinson's disease

Abstract

Blinking, a motor act consisting of a closing and an opening eyelid movement, can be performed voluntarily, spontaneously, and reflexly. In this study we investigated the kinematic features of voluntary, spontaneous, and reflex blinking in patients with Parkinson's disease (PD), OFF and ON dopaminergic treatment. Patients were asked to blink voluntarily as fast as possible. Spontaneous blinking was recorded for a minute during which the subjects just relaxed. Reflex blinking was evoked by electrical stimulation on the supraorbital nerve. Eyelid movements were recorded with the SMART analyzer motion system. Patients OFF therapy paused longer than controls during voluntary blinking but not during spontaneous and reflex blinking. The blink rate tended to be lower in patients OFF therapy than in controls and the spontaneous blinking had abnormally low amplitude and peak velocity. Finally, in patients OFF therapy the excitability of the neural circuit mediating the closing phase of the reflex blinking was enhanced. Dopaminergic treatment shortened the pause during voluntary blinking and increased the blink rate. In PD patients the longer pauses between the closing and opening phase in comparison to normal subjects, suggest bradykinesia of voluntary blinking. PD patients also display kinematic abnormalities of spontaneous blinking and changes in the excitability of the closing phase of reflex blinking.

Distribution of spontaneous inter-blink interval in repeated measurements with and without topical ocular anesthesia

“…The nervous system regulates logarithmically the inter-blink interval in a symmetrical manner. This characteristic seems to be invariable and it would be interesting to determine whether the inter-blink time intervals also follow a Log Normal distribution in the presence of conditions that affect blink rate such as psychosis (13) , Parkinson's disease (5) , sleep deprivation (14) , drug use (8) , and dry eye, as well as the rates induced by refractive surgery such as LASIK (15) . …”

“…These patterns may be the expression of an intrinsic feature of each individual determined by mesencephalic dopaminergic activity. Although the hypothesis of blinking rate central regulation is well accepted in neuropsychology (4)(5)(6)(7)(8)(9) , there are several lines of ophthalmologic evidence showing that the condition of the ocular surface modulates the blink rate (1,(10)(11) . A classical example is the reduced blink rate that occurs after topical ocular anesthesia (12) .…”

Increasing Stimulation Parameters Relieves Acquired Eyelid Apraxia after Deep Brain Stimulation of the Subthalamic Nucleus

“…Eye lid apraxia is a non-paralytic motor abnormality characterized by difficulty in initiating opening of the eyelids [7,8]. Premotor control of lid-eye coordination by extrapyramidal and mesencephalic circuitries has been suggested and dopaminergic involvement was further substantiated by analysis of blinking rates in patients with PD [9]. Regarding the pathogenesis of eyelid apraxia, the distance from subthalamic nucleus to optic tracts, substantia nigra and red nucleus is only 3 mm which is very close.…”

Bereitschaftspotential preceding eyelid blinks in Parkinson’s disease

“…Voids in the dopaminergic and nondopaminergic circuits have been involved in this pathophysiology, generating an imbalance between inhibition and excitation, deficits and compensation 4,5,6 . Changes in the dopaminergic pathways explain, at least in part, disturbances in the kinematics of spontaneous eyelid blink 7,8,9 , and the voluntary one 10 and in the blink reflex habituation of PD…”

“…Pharmacological treatment with dopaminergic medications, considered the gold standard 12,13 , results in partial problem-solving of bradykinesia as it improves the speed of movement 7,8,10 , but not its rhythm and amplitude…”