基于傅里叶频谱分析设计的汉字近视力表

A Chinese near visual acuity chart based on Fourier Frequency spectrum

本研究介绍一种汉字近视力表。本视力表将傅里叶频谱分析和心理物理学测试应用于汉字视标的选择,筛选出可视性相似的汉字作为同一张视力表的视标。在视力表的设计中,每行视标的个数保持一致,每相邻两行视标之间的行间距为下一行视标的高度,每一行的字间距为该行所在字的字宽,视标的增率采用0.1对数单位,增加可重复测试的小视标及低对比度视力表等。因被检者的阅读习惯距离存在差异,故规定标准检查距离为40cm的同时设置25cm作为备选测量距离。将它应用于常规测试对预测被检者辨认汉字的阈值和早期发现与视觉有关的眼病有一定的临床价值。

Chinese characters were selected using Fourier Frequency spectrum analysis and psychophysical testing, so that all the visual targets in the same chart had equal legibility. The chart had the same number of visual targets on each row. The distance between 2 rows of visual targets was equal to the height of the lower-row visual targets; the distance between 2 visual targets was equal to the width of a single target in the same row. The sizes of visual targets on the chart were geometrically enlarged with an increasing rate at 0.1 log unit. Small targets for repeated tests and low contrast sensitivity test were also included in the chart. Two viewing distances （25 cm or 40 cm） could be selected according to individual needs. The use of this chart as a routine screening helps determine the size threshold in recognizing Chinese characters and detect vision threatening disorders in early stage.