Guyton D L, Cheeseman E W, Ellis F J, Straumann D, Zee D S
Wilmer Ophthalmological Institute, Johns Hopkins University School of Medicine, Baltimore, USA.
Trans Am Ophthalmol Soc. 1998;96:389-424; discussion 424-9.
Dissociated vertical deviation (DVD) has eluded explanation for more than a century. The purpose of this study has been to elucidate the etiology and mechanism of DVD.
Eye movement recordings of six young adults with DVD were made with dual-coil scleral search coils under various conditions of fixation, illumination, and head tilt. Horizontal, vertical, and torsional eye movements were recorded for both eyes simultaneously. Analyses of the simultaneous vertical and torsional movements occurring during the DVD response were used to separate and identify the component vergence and version eye movements involved.
Typically, both horizontal and cyclovertical latent nystagmus developed upon occlusion of either eye. A cycloversion then occurred, with the fixing eye intorting and tending to depress, the covered eye extorting and elevating. Simultaneously, upward versions occurred for the maintenance of fixation, consisting variously of saccades and smooth eye movements, leading to further elevation of the eye behind the cover. The cyclovertical component of the latent nystagmus became partially damped as the DVD developed.
In patients with an early-onset defect of binocular function, the occlusion of one eye, or even concentration on fixing with one eye, produces unbalanced input to the vestibular system. This results in latent nystagmus, sometimes seen only with magnification. The cyclovertical component of the latent nystagmus, when present, is similar to normal vestibular nystagmus induced by dynamic head tilting about an oblique axis. Such vestibular nystagmus characteristically produces a hyperdeviation of the eyes. In the case of cyclovertical latent nystagmus, the analogous hyperdeviation will persist unless corrected by a vertical vergence. A normal, oblique-muscle-mediated, cycloversion/vertical vergence is called into play. This occurs in the proper direction to correct the hyperdeviation, but it occurs in an exaggerated form in the absence of binocular vision, probably as a learned response. The cycloversion/vertical vergence helps damp the cyclovertical nystagmus (a cyclovertical "nystagmus block-age" phenomenon), aiding vision in the fixing eye. But this mechanism also produces unavoidable and undesirable elevation and extortion of the fellow eye, which we call DVD.
分离性垂直偏斜（DVD）已困扰人们一个多世纪。本研究旨在阐明DVD的病因及机制。
对6例患有DVD的年轻成年人，在不同的注视、照明和头部倾斜条件下，使用双线圈巩膜搜索线圈记录眼动。同时记录双眼的水平、垂直和扭转眼动。通过分析DVD反应期间同时发生的垂直和扭转运动，来分离和识别所涉及的集合和版本眼动成分。
通常，单眼遮挡时水平和旋转性隐性眼球震颤均会出现。然后发生旋转运动，注视眼内旋并趋于下转，被遮盖眼外旋并上转。同时，为维持注视会出现向上的版本运动，包括不同形式的扫视和平滑眼动，导致被遮盖眼进一步上抬。随着DVD的发展，隐性眼球震颤的旋转性成分会部分减弱。
在双眼功能早期缺陷的患者中，单眼遮挡，甚至仅用单眼注视，都会向前庭系统输入不平衡的信号。这会导致隐性眼球震颤，有时仅在放大情况下可见。隐性眼球震颤的旋转性成分（若存在）类似于动态头部绕斜轴倾斜所诱发的正常前庭眼球震颤。这种前庭眼球震颤通常会导致眼球过度偏斜。对于旋转性隐性眼球震颤，类似的过度偏斜将持续存在，除非通过垂直集合进行纠正。正常的、由斜肌介导的旋转/垂直集合开始发挥作用。它会以正确的方向发生以纠正过度偏斜，但在缺乏双眼视觉时会以夸张的形式出现，可能是一种习得的反应。旋转/垂直集合有助于减弱旋转性眼球震颤（一种旋转性“眼球震颤阻滞”现象），辅助注视眼的视力。但这种机制也会不可避免地导致另一只眼出现不必要的上抬和外旋，即我们所说的DVD。
