Demer J L, Goldberg J, Porter F I
Jules Stein Eye Institute, UCLA 90024-7002.
J Vestib Res. 1990;1(2):109-22.
Telescopic spectacles, highly magnifying visual aids mounted in spectacle frames, markedly alter the visual consequences of head movements. To evaluate the effect of this altered visual feedback on head stability, angular head velocity of normally sighted and low vision subjects was measured in the roll, pitch, and yaw axes. Measurements were made under two postural conditions: (1) quiet standing; and (2) walking in place, as well as three visual conditions: (1) eyes closed; (2) unmagnified vision; and (3) vision with 4 x binocular telescopic spectacles. For normal subjects during quiet standing, both unmagnified vision and vision with telescopic spectacles tended to reduce spontaneous head velocity in all axes as compared to the eyes-closed condition. However, in low vision subjects neither unmagnified vision nor vision with telescopic spectacles produced significant changes in values of head velocity relative to those measured with eyes closed. Spontaneous head velocities for standing low vision subjects tended to be higher than in normal subjects, although not all differences were statistically significant. During walking in place, Fourier analysis demonstrated prominent frequency components related to harmonics of the walking frequency under all viewing conditions. In normal subjects, vision with telescopic spectacles, to a greater degree than unmagnified vision, reduced head velocity during walking in the roll and yaw, but not the pitch, axes. For low vision subjects, significant reductions in head velocity during walking were observed only during vision with telescopic spectacles. These findings indicate that vision reduces angular instability of the head during standing and walking. Magnification produced by telescopic spectacles further improves head stability under some conditions, although the effect of vision is least evident in the pitch axis. The stabilizing effect of vision is reduced in low vision subjects.
伸缩式眼镜是安装在眼镜架上的高放大倍率视觉辅助器具，它会显著改变头部运动的视觉效果。为了评估这种改变的视觉反馈对头部稳定性的影响，我们测量了视力正常和视力低下受试者在横滚、俯仰和偏航轴上的头部角速率。测量在两种姿势条件下进行：（1）安静站立；（2）原地行走，同时还设置了三种视觉条件：（1）闭眼；（2）无放大视觉；（3）佩戴4倍双目伸缩式眼镜的视觉。对于正常受试者，在安静站立时，与闭眼状态相比，无放大视觉和佩戴伸缩式眼镜的视觉都倾向于降低所有轴向上的自发头部速率。然而，对于视力低下受试者，无放大视觉和佩戴伸缩式眼镜的视觉相对于闭眼测量值而言，头部速率值均未产生显著变化。站立的视力低下受试者的自发头部速率往往高于正常受试者，尽管并非所有差异都具有统计学意义。在原地行走时，傅里叶分析表明，在所有视觉条件下都存在与行走频率谐波相关的突出频率成分。对于正常受试者，佩戴伸缩式眼镜的视觉比无放大视觉在更大程度上降低了行走时横滚和偏航轴（而非俯仰轴）上的头部速率。对于视力低下受试者，仅在佩戴伸缩式眼镜的视觉期间观察到行走时头部速率有显著降低。这些发现表明，视觉可降低站立和行走期间头部的角不稳定性。伸缩式眼镜产生的放大作用在某些条件下进一步改善了头部稳定性，尽管视觉效果在俯仰轴上最不明显。视力低下受试者中视觉的稳定作用减弱。
