Zee D S
School of Medicine, Johns Hopkins University, Baltimore, Maryland, USA.
J Vestib Res. 1996 Nov-Dec;6(6):395-401.
Alternating skew deviation, in which the side of the higher eye changes depending upon whether gaze is directed to the left or the right, is a frequent sign in patients with posterior fossa lesions, including those restricted to the cerebellum. Here we propose a mechanism for alternating skews related to the otolith-ocular responses to fore and aft pitch of the head in lateral-eyed animals. In lateral-eyed animals the expected response to a static head pitch is cyclorotation of the eyes. But if the eyes are rotated horizontally in the orbit, away from the primary position, a compensatory skew deviation should also appear. The direction of the skew would depend upon whether the eyes were directed to the right (left eye forward, right eye backward) or to the left (left eye backward, right eye forward). In contrast, for frontal-eyed animals, skew deviations are counterproductive because they create diplopia and interfere with binocular vision. We attribute the emergence of skew deviations in frontal-eyed animals in pathological conditions to 1) an imbalance in otolithocular pathways and 2) a loss of the component of ocular motor innervation that normally corrects for the differences in pulling directions and strengths of the various ocular muscles as the eyes change position in the orbit. Such a compensatory mechanism is necessary to ensure optimal binocular visual function during and after head motion. This compensatory mechanism may depend upon the cerebellum.
交替性斜视，即较高眼的一侧会根据注视方向是向左还是向右而改变，是后颅窝病变患者常见的体征，包括那些局限于小脑的病变。在此，我们提出一种与侧眼动物头部前后俯仰时耳石 - 眼反射相关的交替性斜视机制。在侧眼动物中，对静态头部俯仰的预期反应是眼球的旋转。但如果眼球在眼眶内水平旋转，偏离初始位置，也会出现代偿性斜视。斜视的方向将取决于眼球是向右（左眼向前，右眼向后）还是向左（左眼向后，右眼向前）。相比之下，对于正眼动物而言，斜视是适得其反的，因为它们会产生复视并干扰双眼视觉。我们将正眼动物在病理状态下出现斜视归因于：1）耳石 - 眼反射通路的失衡；2）眼动神经支配成分的丧失，而在眼球在眼眶内改变位置时，这种成分通常可纠正各眼肌牵拉方向和力量的差异。这样一种代偿机制对于确保头部运动期间及之后的最佳双眼视觉功能是必要的。这种代偿机制可能依赖于小脑。
