一般视功能可用各种方法检查,但视觉最重要功能之一的形觉,主要是以视力来评价的。这是用浓淡分明的视标,检查能够识别视标最小到何种程度。即测定Landolt环等的分离阈值(解像界限)。这种方法较为简便,在眼科临床上是一种重要而不可缺少的检查方法,无疑今后也会继续使用。但只检查分离阈值不能严格表现出视觉的形觉功能。例如辨认浓淡不清楚物体的能力,仅靠视力的测定,就无法明确了解。又如视标的形状或对比不同,测得的视力也不同。总之,视力检查是在一定条件之下,对特定能力的比较评价具有重要的意义,但对视功能仅能提供某一方面的情况。从更广的范围用定量的功能函数作为评价视觉的形觉功能的手段,在光学领域内研究发展起来的空间频率特性(Modulation Transfer Function-以下略称MTF)的概念已被引进视觉系统。(译者注:MTF又称空间对比传递函数- The general visual function can be checked by various methods, but the shape of one of the most important functions of vision is mainly evaluated by visual acuity. This is the use of shades of the visual target, check to identify the smallest possible extent to the target. The determination of Landolt ring separation threshold (resolution limit). This method is relatively simple, clinically an important and indispensable examination method in ophthalmology, and will undoubtedly continue to be used in the future. However, checking only the separation threshold can not strictly show the visual form function. For example, the ability to identify shades of unclear objects can not be clearly understood based solely on the determination of visual acuity. Another example is the shape of the visual target or contrast, the measured visual acuity is also different. In short, visual acuity test is under certain conditions, the comparative evaluation of specific abilities is of great significance, but the visual function can only provide some aspects of the situation. The concept of the Modulation Transfer Function (MTF), developed in the field of optics, has been introduced into the vision system by using a quantitative function as a means of evaluating the visual shape function over a wider area. (Translator’s Note: MTF, also known as spatial contrast transfer function -