Marti Sarah, Bockisch Christopher J, Straumann Dominik
Neurology Department, Zurich University Hospital, Zurich, Switzerland.
Invest Ophthalmol Vis Sci. 2005 Jan;46(1):143-9. doi: 10.1167/iovs.04-0235.
Downbeat nystagmus (DBN) is a typical ocular motor sign in patients with lesions of the vestibulocerebellum. A vertical vestibular tone asymmetry, an upward shift of the eyes' null position for vertical gaze holding, or an imbalance of vertical smooth-pursuit signals have been proposed as mechanisms of DBN. The purpose of this study was to elaborate a possible link between an imbalance in the vertical smooth-pursuit system and DBN by relying on a healthy human model.
Healthy subjects (n=6) were exposed to continuous asymmetric smooth-pursuit stimulation over 20 minutes.
Prolonged asymmetric smooth-pursuit stimulation induced a drift lasting >5 minutes in the direction of the prior pursuit. Upward drift was faster than downward drift and showed eye-position dependence in accordance with Alexander's law, but no increase of drift velocity with lateral gaze. Upward drift violated Listing's law in three of four subjects tested.
An experimentally induced vertical smooth-pursuit imbalance leads to DBN in healthy human subjects. Accordingly, because in patients with cerebellar disease upward smooth-pursuit eye movements are typically better preserved than downward, the resultant sustained imbalance of vertical smooth-pursuit input may play a major role in the generation of DBN.
下跳性眼球震颤（DBN）是前庭小脑病变患者典型的眼球运动体征。垂直前庭张力不对称、垂直凝视保持时眼的零位向上移位或垂直平稳跟踪信号失衡被认为是DBN的发病机制。本研究的目的是通过健康人体模型阐述垂直平稳跟踪系统失衡与DBN之间可能存在的联系。
6名健康受试者接受了20分钟的持续不对称平稳跟踪刺激。
长时间的不对称平稳跟踪刺激导致在先前跟踪方向上持续超过5分钟的漂移。向上漂移比向下漂移更快，并且根据亚历山大定律表现出眼位依赖性，但漂移速度不随侧方凝视增加。在测试的4名受试者中有3名向上漂移违反了利斯廷定律。
实验诱导的垂直平稳跟踪失衡导致健康人体受试者出现DBN。因此，由于在小脑疾病患者中，向上的平稳跟踪眼球运动通常比向下的保存得更好，垂直平稳跟踪输入的持续失衡可能在DBN的产生中起主要作用。
