Brosnahan D, Norcia A M, Schor C M, Taylor D G
Department of Ophthalmology, Royal Hallamshire Hospital, Sheffield, UK.
Vision Res. 1998 Sep;38(18):2833-40. doi: 10.1016/s0042-6989(97)00441-0.
The present study quantified nasalward/temporalward biases in monocular optokinetic nystagmus (MOKN) and perceived velocity in patients with either early onset esotropia, late onset esotropia and in normals. MOKN was measured with low spatial frequency, small-field gratings drifting at 9.4 degrees/s. MOKN bias was quantified as the ratio of nasalward slow-phase velocity divided by the sum of temporalward and nasalward slow-phase velocities (N/(N + T)). Observers also rated the perceived velocity of gratings moving in nasalward and temporalward directions (3 or 9.4 degrees/s) using a two interval forced choice task. MOKN and perceived velocity biases were correlated negatively in both early onset and late onset groups in the perceptual task--nasalward moving targets were rated as slower than temporalward targets, but in the MOKN task, slow-phase gain was higher for nasalward than for temporalward targets. Oscillatory-motion, visual evoked potentials (VEPs), were recorded in response to 1 c/deg gratings undergoing apparent motion at 10 Hz in a subset of the observers. VEP direction biases were quantified by calculating the ratio of first harmonic response amplitudes to the sum of first and second harmonic amplitudes. Significant correlations were found between the direction biases obtained on all three measures. Perceived velocity and MOKN bias measures were also correlated negatively. Patients with early onset esotropia (infantile esotropia) had larger biases than late onset esotropes or normals on each measure and the biases were more frequently bilateral in the early onset patients. The pattern of result is consistent with early critical periods for the mechanism(s) underlying MOKN, perceived velocity and cortical responsiveness. A single site model for all three asymmetries is unlikely, at least in simple form, because of the negative correlation between MOKN and perceived velocity biases and because of the differences in relative magnitude between the perceptual and MOKN biases.
本研究对早发性内斜视、迟发性内斜视患者及正常人单眼视动性眼震（MOKN）向鼻侧/向颞侧的偏向以及感知速度进行了量化。使用空间频率低、以9.4度/秒漂移的小视野光栅测量MOKN。MOKN偏向被量化为向鼻侧慢相速度除以向颞侧和向鼻侧慢相速度之和的比值（N/(N + T)）。观察者还通过二区间强迫选择任务对向鼻侧和向颞侧方向移动的光栅（3或9.4度/秒）的感知速度进行评分。在感知任务中，早发性和迟发性组的MOKN与感知速度偏向均呈负相关——向鼻侧移动的目标被评为比向颞侧目标慢，但在MOKN任务中，向鼻侧目标的慢相增益高于向颞侧目标。在一部分观察者中，记录了对以10赫兹进行表观运动的1 c/deg光栅的振荡运动视觉诱发电位（VEP）。通过计算一次谐波响应幅度与一次和二次谐波幅度之和的比值来量化VEP方向偏向。在所有三种测量中获得的方向偏向之间发现了显著相关性。感知速度和MOKN偏向测量也呈负相关。早发性内斜视（婴儿型内斜视）患者在各项测量中的偏向均大于迟发性内斜视患者或正常人，且早发性患者中双侧偏向更为常见。结果模式与MOKN、感知速度及皮层反应性潜在机制的早期关键期一致。至少以简单形式而言，单一部位模型不太可能解释所有三种不对称性，因为MOKN与感知速度偏向之间存在负相关，且感知偏向与MOKN偏向在相对大小上存在差异。
