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鉴于国际视力表存在视标增率不匀、视力统计困难、低下视力不能用数值表示以及对数视力表又不易为一般人所理解,其数值更难为习惯所接受,故设计等比视力表。一、等比视力表的设计: (1)原理:本表遵照Weber-Fechner定律设计,即刺激按等比级数增加时,感觉按等差级数相应增加。如初刺激为I_1,后刺激增至I_2时,感觉的差异为△s, 则△s=(I_2-I_1)/I_2=K(常数) (2)依据:根据1862年巴黎国际眼科学会上统一规定,以一分视角为视角单位。一分视角等于0.000290888弧度,而5米距离的一分视角则等于5000×0.000290888=1.45(毫
In view of the existence of the International Table of Visual Ophthalmogram increases uneven rate of visual statistics, visual acuity difficulties, low visual acuity can not be expressed by numerical and logarithmic visual acuity chart is not easy for the average person to understand, its value is more difficult to accept by habit, so the design of visual acuity chart. First, the design of equal acuity chart: (1) Principle: This table follows Weber-Fechner’s law design, that is stimulated by an equal number of series increases, the feeling of increasing according to the number of differential series. If the initial stimulus for I_1, post-stimulus increased to I_2, the sensory difference is Δs, then △ s = (I_2-I_1) / I_2 = K (constant) (2) Basis: According to the 1821 Paris International Academy of Ophthalmology unified provisions , With a point of view for the perspective of units. A point of view is equal to 0.000290888 radians, while a point of view of a distance of 5 meters equals 5000 × 0.000290888 = 1.45