The blink reflex consists of bilateral reflex contraction of the orbicularis oculi muscles. This may be induced by:
- Mechanical stimulus:
- Examples include percussion over the supraorbital ridge (glabellar tap reflex, Myerson’s sign, nasopalpebral reflex): this quickly habituates with repetitive stimulation in normal individuals; touching the cornea (corneal reflex); stroking the eyelashes in unconscious patients with closed eyes ("eyelash reflex").
- Visual stimulus:
- Sudden visual stimulus approaching the eyes (menace reflex, threat reflex, visuopalpebral reflex): the stimulus should be unexpected since the reflex can be voluntarily suppressed; failure to respond to a stimulus moving into the temporal field of vision may indicate a hemianopic field defect in patients unable to comply with standard confrontation visual field testing. Care should be taken to avoid generating air currents with the hand movement as this may stimulate the corneal reflex which may simulate the visuopalpebral reflex. It is probable that this reflex requires cortical processing: it is lost in persistent vegetative states. Loss of this reflex may occur in Balint’s syndrome, ascribed to inability to recognize the nearness of the threatening object.
- Acoustic stimulus:
- Sudden loud sounds (acousticopalpebral reflex).
The final common (efferent) pathway for these responses is the facial nerve nucleus and facial (VII) nerve, the afferent limbs being the trigeminal (V), optic (II), and auditory (VIII) nerves respectively. Electrophysiological study of the blink reflex may demonstrate peripheral or central lesions of the trigeminal (V) nerve or facial (VII) nerve (afferent and efferent pathways, respectively). It has been reported that in the evaluation of sensory neuronopathy the finding of an abnormal blink reflex favors a nonparaneoplastic etiology, since the blink reflex is normal in paraneoplastic sensory neuronopathies.
Auger RG, Windebank AJ, Lucchinetti CF, Chalk CH. Role of the blink reflex in the evaluation of sensory neuronopathy. Neurology1999; 53: 407-408
Liu GT, Ronthal M. Reflex blink to visual threat. Journal of Clinical Neuro-ophthalmology 1992; 12: 47-56