Mechanism of Downbeat Nystagmus While Normal Subjects HaveHead Upside-down Position in Darkness

J Korean Neurol Assoc > Volume 18(6); 2000 > Article

Journal of the Korean Neurological Association 2000;18(6): 716-720.

정상인이 암실에서 머리를 거꾸로 할 때나타나는 하박안진의 발생 기전

단국대학교 의과대학 신경과학교실

Mechanism of Downbeat Nystagmus While Normal Subjects HaveHead Upside-down Position in Darkness

Jae Il Kim, M.D.

Department of Neurology, College of Medicine, Dankook University

Abstract

Background : Bohmer and Straumann have proposed that downbeat nystagmus is due to an asymmetry of the geom-etry of the vertical semicircular canals of the vestibular labyrinth. This hypothesis does not predict any sustained change in vertical nystagmus when subjects are placed in a head-upside-down position. Methods : Using the magnetic search coil technique, I measured vertical eye movements in darkness in three normal human subjects while they maintained head-erect or head-upside-down positions. Results : Two subjects had upbeat nystagmus and one downbeat nystagmus with their heads erect (slow-phase velocity < 1 deg/sec). All developed sustained nystagmus with quick phases directed towards their chins while in the head-upside-down position. Conclusions : These findings suggest that factors other than canal imbalance - otolithic or ocular - may also cause downbeat nystagmus. J Korean Neurol Assoc 18(6):716~720, 2000Key Words : Downbeat nystagmus, Semicircular canals, Otoliths, Cerebellum