BLINK REFLEX

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BLINK REFLEX

INTRODUCTION : 

INTRODUCTION Blink reflex is the electrical analog of corneal reflex. The afferent limb of blink reflex is ophthalmic division of trigeminal nerve (which can be stimulated mechanically or electrically) and the facial nerve mediates the efferent arc. Blink reflex becomes useful in the evaluation of patients with : ● Involvement of trigeminal or facial nerve. ● Variety of polyneuropathies ● Multiple Sclerosis 12/18/2009 2

METHOD : 

METHOD Position of Patient : Lying on the couch with eyes closed. Recording Electrodes : Active electrode placed laterally over the orbicularis occuli muscles and reference placed on the side of the nose. Ground Electrode : Placed submentally on the neck or around the arm. 12/18/2009 3

METHOD : 

METHOD Stimulating Electrode : Supraorbital nerve is stimulated (Trigeminal Nerve) with cathode placed over the supraorbital foramen on one side and anode placed on the forehead. (Facial Nerve) : Facial nerve is stimulated at the stylomastoid foramen, with the cathode placed in front of the mastoid process. Responses may be obscured in part by stimulus artifact with supraorbital nerve, because the active recording electrode is then close to the stimulating cathode. 12/18/2009 4

PARAMETERS : 

PARAMETERS SWEEP VELOCITY (msec/div) : 5-10 SENSITIVITY (µv/div) : 200 FILTERS HIGH/LOW (KHz/Hz) : 10 KHz / 20Hz STIMULATION DURATION/RATE (msec/Hz) : 0.01msec/2 Hz INTERVAL : Between successive stimuli is set at atleast 30 sec to minimize interactions between them. (If R1 is not recorded easily, reduce the interstimulus interval to 5msec so that facilitation resulting from first stimulus permits R1 to be elicited.) 12/18/2009 5

REFLEX RESPONSE : 

REFLEX RESPONSE EARLY R1 COMPONENT Elicited only on the side that is stimulated. Relatively stable. Short lasting and of low amplitude. A disynaptic pathway between the main sensory nucleus of the trigeminal nerve and the ipsilateral facial nucleus. LATER R2 COMPONENT Present on both sides following unilateral stimulation. More variable. Long lasting and of higher amplitude. A polysynaptic connections between the spinal nucleus of the trigeminal nerve and bilateral facial nucleus. 12/18/2009 6 Two distinct components : Early R1 & Later R2

REFLEX RESPONSE : 

REFLEX RESPONSE EARLY R1 COMPONENT If latency > 13ms, then its abnormal Interside difference in latency < 1.2ms. LATER R2 COMPONENT If ipsilateral latency > 41ms and contralateral latency > 44ms, then its abnormal. The latency difference between ipsilateral and contralateral response recorded simultaneously following unilateral stimulation is < 5ms. The latency difference between R2 evoked by stimulation on each side in turn should be < 7ms. 12/18/2009 7

REFLEX RESPONSE : 

REFLEX RESPONSE 12/18/2009 8

REFLEX RESPONSE : 

REFLEX RESPONSE EARLY R1 COMPONENT Delay or absence indicates a disturbance of trigeminal or facial nerve or both on that side. LATER R2 COMPONENT Involvement of R2 indicates the site of lesion when R1 is abnormal. Trigeminal nerve lesions is characterized by bilateral delay or attenuation of R2 when the affected side of the face is stimulated. Facial nerve lesions is characterized by delay of R2 on the affected side, whichever side is stimulated. 12/18/2009 9

CLINICAL APPLICATION : 

CLINICAL APPLICATION In Bell’s Palsy, the response is initially nearly normal becoming abnormal after few days. R1 - delayed or abnormal during the first few weeks suggesting demyelination. In certain polyneuropathies - Direct response and R1 component delayed. Distinguishes between idiopathic trigeminal neuralgia (response is normal) and paratrigeminal neuralgia (response is abnormal). In comatose patients and acute phase of CVA - R2 delayed. 12/18/2009 10

CLINICAL APPLICATION : 

CLINICAL APPLICATION In hemifacial spasm or facial synkinesis following aberrant reinnervation there is spread of blink reflex into muscles other than orbicularis oris. In multiple sclerosis, the R1- delayed on one or both the sides and alterations in the R2 component is less specific. And if R2 is abnormal (with normal R1), it is suggestive of lateral medullary lesion. In Wallenberg’s syndrome, the R1 - normal and R2 - delayed or absent bilaterally with the stimulation of the affected side of the face. 12/18/2009 11

REFERENCES : 

REFERENCES The Electromyographer’s Handbook – Rajesh K. Sethi & (2nd Edition) Lowery Lee Thompson. Electromyography in Clinical Practice - Michael J. Aminoff (2nd Edition) Clinical Neurophysiology - UK Mishra & J Kalita (2nd Edition) www.google.com 12/18/2009 12