Blink reflex in man in response to stretching of extraocular muscles?

Abstract

An unilateral oculo-palpebral reflex evoked by weakly tapping the eyeball is described. It has a latency of 8–9 msec and a well-synchronized aspect. It is often followed by a silent period lasting 20–80 msec and is accompanied by a reciprocal inhibitory pause in the homolateral frontal muscle. It is unaffected by local anesthesia of the homolateral supra and infraorbital nerves, but is abolished by a homolateral retrogasserian neurotomy. Our results suggest that this short-latency blink reflex is produced by the stretching of extraocular muscles. It seems, therefore, likely that it originates in extraocular muscle spindles whose primary afferents are known to run with the ophthalmic branch of the trigeminal nerve. This reflex response can be facilitated by voluntary activation of the opposite orbicularis oculi muscle and in spastic hemiplegic patients it is potentiated on the affected side. Stronger tapping of the eyeball evokes a bilateral blink reflex with characteristics of a nociceptive reflex. It is suggested that this reflex originates in pain receptors located in extraocular muscles.