[Clinicophysiological studies of orbicularis oculi reflex in brain stem diseases]

Orbicularis oculi reflex is consisted of two components; one is early reflex response (R1) which is 14.1 +/- 2.2 msec in latency, and the other is late reflex response (R2) that is 35.0 +/- 8.6 msec in latency (mean +/- 2SD). R1 is observed on the ipsilateral side of stimulation and R2 is visible bilaterally on ipsiand contralateral sides of stimulation. Clinically orbicularis oculi reflex can be recorded easily, however, its clinical and physiological significance has not been clearly solved. Orbicularis oculi reflex was tested on patients with the brain stem lesions of various kinds, and the factors influencing to the reflex pathways were examined, such as the site and the type of lesions, sleep, several anesthetics and the level of consciousness. Results obtained were as follows; 1) both R1 and R2 disappeared or prolonged in latencies by nuclear as well as peripheral facial nerve palsy, since the facial nerve was the final common pathway. 2) on cases of facial sensory disturbance R1 prolonged in latency with concomitant delay of R2 response. 3) both R1 and were attenuated as soon as the alpha rhythmicity of the EEG was disappeared. Administration of thiamylal also attenuated both the R1 and R2, however, ketamine (a dissociative anesthetic) enhanced the R1 in amplitude and suppressed R2. These findings indicated that the R1 and R2 were in some extent regulated from brain stem reticular formation and the orbicularis oculi reflex should be an useful diagnostic measure to detect imparied consciousness. 4) also the reflex should be used to know the extent of neoplastic process in the cerebellar hemisphere to the brain stem. 5) recovery curve of R1 from double shock stimuli (conditioned and test) indicated that this reflex was different from H wave of the spinal cord because of absent refractory period and shorter facilitatory period ranging between 40 to 60 msec.