How to measure eyesight?_industry news_
Vision testing is basically familiar to everyone. When entering a higher school, vision will be measured, and vision will be measured in the physical examination. However, many people are not so clear about measuring vision, and they do not understand the conversion of vision. At present, there are two types of vision charts for measuring vision, one is the new vision chart and the other is the old vision chart. Let's learn how to measure vision. At present, the most commonly used measurement in China is the use of the international standard eye chart, which is composed of 12 lines of 'E' characters with different openings and directions, and the measurement is from 0.1-2.0 (or from 4.0-5.3). The eye chart is designed according to the principle of viewing angle. The so-called viewing angle is the angle formed by the light rays emitted by two points outside the eye through the nodes in the eye. Under normal circumstances, the viewing angle formed by the minimum distance between two points that the human eye can distinguish is the minimum viewing angle, that is, one point of viewing angle. The eye chart is designed in units of one point of view. At present, there are two measurement ranges of the eye chart, one is from 0.1-2.0, and the other is from 4.0-5.3. Among them, the counting table of 0.1-2.0 is called 'standard logarithmic vision chart\The 'standard logarithmic vision chart' and the 'decimal recording vision chart' can be converted to each other through a formula. The conversion formula of the vision chart is as follows: Five-point recording method u003d 5-lg (1/decimal recording method), Note: Five The fractional recording method is the test value of the 'standard logarithmic vision chartWe often hear visual acuity 5.0, 4.0, etc. This new method is called standard logarithmic recording. The standard visual acuity chart test vision includes distance vision and near vision to check distance vision. my country usually uses the international standard visual acuity chart and the logarithmic visual acuity chart created by Miao Tianrong in my country. During the examination, the examinee was sitting at a distance of 5m from the visual acuity chart. The international standard visual acuity chart 1.0 or the logarithmic visual acuity chart 5.0 was at the same level as the eye to be examined. The subject quickly said the direction of the optotype gap, and recorded the font size of the smallest optotype line that was right. The visual acuity of a normal person is 1.0 or 5.0. When the visual acuity is lower than 0.1, the visual acuity can be gradually approached and calculated by 0.1×d/5 (d is the distance from the visual chart when the examinee sees the line clearly). When examining near vision, my country usually uses the Jaeger's near vision chart and the E standard near vision chart designed by Xu Guangdi in my country. The eye chart should be placed in a well-lit place, or illuminated with fluorescent lamps. A normal person can see clearly at a distance of 30cm under normal light. 10th Behavior 1.0. If the distance between the eye chart and the eye is changed due to myopia or hyperopia, the changed distance will be recorded together. The conversion rules of the visual role are the following old new dimensions 0.1 4.0 6500.12 4.1 550.3 4.5 300-3500.4 4.6 2500.5 4.7 2000.6 4.8 1500.8 4.9 1001.0 5.01.2 5.11.5 5.2 Nearcast and Differentiation Relationship between people Closely, 1 diopter is defined as a ray of light passing through the lens forming a focal point one meter behind the lens. Denoted by D, and f represents the focal length, there is the formula Du003d1/f. If the focal length of the lens is 0.5 meters, then the diopter of this lens is 1/0.5u003d2, which is customarily called 200 degrees. There is no absolutely accurate conversion relationship between the visual acuity and the diopter (myopia) on the eye chart. Because some people's poor vision is closely related to many factors, such as some eye diseases, retinitis, optic neuritis, macular degeneration, etc., will affect vision.