Regan D, Bartol S, Murray T J, Beverley K I
Brain. 1982 Dec;105 (Pt 4):735-54. doi: 10.1093/brain/105.4.735.
This article extends our previous reports that multiple sclerosis can cause a visual dysfunction better described as a distortion than as a blurring of vision. An earlier paper reported that multiple sclerosis spares visual acuity in some patients while reducing visual sensitivity for less fine detail. Specifically, these patients experience a loss of contrast sensitivity for low and/or intermediate spatial frequencies, while contrast sensitivity for high spatial frequencies is unimpaired. We report here that some patients also lose spatial frequency discrimination, so that these patients cannot tell which of two clearly visible gratings has the higher spatial frequency even though control subjects accurately report which grating has the higher spatial frequency. One way of regarding this discrimination loss is in terms of a deterioration of the ability to discriminate size. Contrast sensitivity was measured over the spatial frequency range 1 to 20 cycles/deg using the von Békésy tracking method for 10 patients. (20 eyes) and 16 control subjects (32 eyes). The limit of normality was taken as 2.5 standard deviations from the control mean (99 per cent confidence). Spatial frequency discrimination was measured using the criterion-free method of temporal two-alternative forced choice over the spatial frequency range 2 to 16 cycles/deg for 10 patients (20 eyes), and for 14 to 26 control eyes at each spatial frequency. Three control subjects were studied more extensively over the range 1 to 20 cycles/deg. Control subjects could discriminate two spatial frequencies that differed by more than about 5 per cent. This held for all spatial frequencies tested. Grating contrast had little effect on discrimination, provided that all test gratings were clearly visible. The normal limit for discrimination threshold was set at 2.5 standard deviations from the control mean. Seven of 10 patients have abnormal contrast sensitivity at one or more spatial frequencies. Six of 10 patients had abnormal discrimination at one or more spatial frequencies. At any given spatial frequency the correlation between the magnitudes of sensitivity loss and discrimination loss was weak, though an eye that was less sensitive than its fellow also tended to have poorer discrimination. A more subtle relationship between sensitivity loss and discrimination loss was clearly shown by one patient. Sensitivity loss was restricted to spatial frequencies below 8 cycles/deg, while discrimination loss in the same eye was restricted to spatial frequencies above 8 cycles/deg. We propose that this finding can be straightforwardly understood if discrimination is determined by the relative activities of different spatial frequency channels analogously, to the way opponent-colour mechanisms determine colour discrimination.
本文扩展了我们之前的报告，即多发性硬化症可导致一种视觉功能障碍，这种障碍更确切地说是一种视觉扭曲而非视力模糊。较早的一篇论文报道，多发性硬化症在一些患者中不影响视敏度，但会降低对较精细细节的视觉敏感度。具体而言，这些患者在低空间频率和/或中等空间频率下的对比敏感度下降，而高空间频率下的对比敏感度未受影响。我们在此报告，一些患者还丧失了空间频率辨别能力，以至于这些患者无法分辨两个清晰可见的光栅中哪个具有更高的空间频率，尽管对照组受试者能准确报告哪个光栅的空间频率更高。看待这种辨别能力丧失的一种方式是从辨别大小能力的退化角度来考虑。使用冯·贝凯西跟踪法，对10例患者（20只眼）和16名对照受试者（32只眼）在1至20周/度的空间频率范围内测量对比敏感度。正常范围的界限设定为比对照均值低2.5个标准差（99%置信度）。使用无标准的时间二择一强迫选择法，在2至16周/度的空间频率范围内对10例患者（20只眼）以及在每个空间频率下对14至26只对照眼测量空间频率辨别能力。对3名对照受试者在1至20周/度的范围内进行了更广泛的研究。对照受试者能够分辨相差超过约5%的两个空间频率。在所有测试的空间频率下均如此。只要所有测试光栅都清晰可见，光栅对比度对辨别能力影响不大。辨别阈值的正常界限设定为比对照均值低2.5个标准差。10例患者中有7例在一个或多个空间频率下对比敏感度异常。10例患者中有6例在一个或多个空间频率下辨别能力异常。在任何给定的空间频率下，敏感度丧失程度与辨别能力丧失程度之间的相关性较弱，尽管一只眼比其对侧眼敏感度低时，其辨别能力往往也较差。一名患者清楚地显示出敏感度丧失与辨别能力丧失之间更微妙的关系。敏感度丧失仅限于低于8周/度的空间频率，而同一眼的辨别能力丧失仅限于高于8周/度的空间频率。我们提出，如果辨别能力是由不同空间频率通道的相对活动决定的，类似于对立颜色机制决定颜色辨别，那么这一发现就可以直接理解。
