Blinking

Blinking, a reflex to irritation of the sensory branches of the trigeminal nerve (cornea, conjunctiva, skin surrounding the eye, eyelashes) or to light stimulation. The centripetal arc of the reflex is either the trigeminal or optic nerve. The centrifugal arc is the branch of the facial nerve innervating the m. orbicul. palpebrarum. The arc of the blinking reflex to trigemerve irritation is closed in the region of the Varolian bridge and the oral part of the medulla oblongata. The blinking reflex to light stimulation requires for its implementation (at least in humans) the preservation of the cortical visual center (area striata, field 17). Under pathological conditions, blinking may be weakened or strengthened.-Weakening of blinking is observed primarily with destruction of the corresponding reflex arc; Thus, in lagophthalmos, observed with paralysis of the facial nerve, blinking movements are completely absent, tears do not move to the lacrimal canal, accumulate in the widely open eye and flow from it, i.e., there is a typical picture of peripheral paralysis of the facial nerve. Such a loss of blinking is also noted with damage to the branch of the trigeminal nerve. Then weakening of blinking is part of the picture of amimia, observed with general poverty of movements, characterizing the symptom complex of parkinsonism. And finally it characterizes the so-called Stellwag symptom, observed in Basedow's disease.-Strengthening of blinking (syn.: blepharospasmus clonicus, blepharoclonus, nictitatio, spasmus nictitans) is observed with various processes irritating the conjunctiva of the eye (conjunctivitis, etc.), often occurs in hysteria, and here also frequently combining with lacrimation and photophobia, and is especially characteristic of facial tic. In most cases with the latter, tics involve other parts of the face, but in some cases they may be limited to only blinking.