Pardhan S, Gilchrist J, Beh G K
Department of Optometry, University of Bradford, West Yorkshire, England.
Optom Vis Sci. 1993 Nov;70(11):914-22.
The detectability of a signal decreases in the presence of externally added visual noise. A linear relation exists between the energy of a signal at threshold and the spectral density of the added visual noise. This relation, represented by contrast detection in noise function, allows a given loss in contrast sensitivity (CS) to be attributed to an increase in the internal intrinsic noise and/or a decrease in the detection efficiency of the observer. Intrinsic noise gives a measure of the random background noise within the visual system, whereas detection efficiency is a measure of how effectively the observer utilizes the available stimulus information. Recent work shows that neural dysfunction produces a decrease in the detection efficiency, whereas optical deficits produce a change in the intrinsic noise only. We investigated whether the CS loss in cataract can be attributed to either a change in intrinsic noise, in detection efficiency, or both. Contrast detection in noise functions was measured for 10 uniocular cataract patients. Comparison between the two eyes showed no significant difference in detection efficiency, although the intrinsic noise increased significantly in the cataractous eye. The data suggest that detection efficiency may provide a measure of neural visual function behind a cataract and, conversely, that intrinsic noise provides a measure of the visual effect of the cataract itself. We discuss the implications of intrinsic noise as a measure of cataract for both clinical assessment and research.
在存在外部添加的视觉噪声的情况下，信号的可检测性会降低。阈值处信号的能量与添加的视觉噪声的频谱密度之间存在线性关系。这种关系由噪声中的对比度检测函数表示，它使得对比度敏感度（CS）的给定损失可以归因于内部固有噪声的增加和/或观察者检测效率的降低。固有噪声衡量视觉系统内的随机背景噪声，而检测效率则衡量观察者有效利用可用刺激信息的程度。最近的研究表明，神经功能障碍会导致检测效率降低，而光学缺陷只会导致固有噪声发生变化。我们研究了白内障患者的CS损失是否可归因于固有噪声的变化、检测效率的变化或两者兼而有之。对10名单眼白内障患者测量了噪声中的对比度检测函数。两只眼睛之间的比较显示检测效率没有显著差异，尽管白内障眼的固有噪声显著增加。数据表明，检测效率可能提供白内障背后神经视觉功能的一种衡量指标，相反，固有噪声提供了白内障本身视觉效应的一种衡量指标。我们讨论了将固有噪声作为白内障的一种衡量指标对临床评估和研究的意义。
