Conversion method of visual acuity chart and myopia degree

Abstract: the visual acuity chart is designed according to the principle of visual angle. The so-called angle of view is the angle formed by the light emitted from two external points through the nodes in the eye. Under normal circumstances, the human eye can distinguish the minimum distance between two points, and the angle of view formed is the minimum angle of view, that is, one point of view. The visual acuity chart is designed in one point of view.

the simplest and most intuitive way to check your eyesight is to use an eyesight chart. In the past, vision of 1.5 was the best. For some people with deep-rooted concepts, the current vision chart recording method is not intuitive, and the vision chart needs to be converted. The current visual acuity chart no longer adopts the decimal recording method of 0.1-1.5. We can often hear visual acuity of 5.0 and 4.0. This new method is called standard logarithmic recording method. The conversion rules of the two visual acuity charts are as follows:

and

visual acuity charts are designed according to the principle of visual angle. The so-called angle of view is the angle formed by the light emitted from two external points through the nodes in the eye. Under normal circumstances, the human eye can distinguish the minimum distance between two points, and the angle of view formed is the minimum angle of view, that is, one point of view. The visual acuity chart is designed in one point of view.

when measuring vision with an eye chart, The examinee should be 5 meters away from the visual acuity chart (if dissatisfied, mirror reflection can be used), and 1.0 or above is normal visual acuity. Generally, it is determined from the lower level of the visual acuity chart to the higher level until it cannot be recognized. However, in practice, because the visual acuity level of the whole group is not wrong, in order to save time, some examinees like to let the examinee distinguish from the most difficult.

Some friends of

do have poor eyesight. They still can’t see 0.1 e-Gap within 5 meters. At this time, let him approach until he can see clearly. At this time, his eyesight is: eyesight = 0.1 × Distance (m) / 5. If the e-notch on the visual acuity chart is still not visible within half a meter, the tester shall recognize the index, measure manual, light perception, etc. record the visual acuity according to the examination.

conversion of the value on the visual acuity chart and diopter

Let’s first understand the concept of diopter. The degree of myopia in people’s mouth is closely related to diopter. 1 diopter is defined as the focus of light passing through the lens at one meter behind the lens. If D is expressed and F is the focal length, there is the formula d = 1 / F. If the focal length of the lens is 0.5m, the diopter of the lens is 1 / 0.5 = 2. People like to call this 200 degrees.

many friends want to find out the relationship between vision and diopter (myopia) on the vision chart. In fact, these two concepts are independent of each other, and there is no absolutely accurate conversion relationship between them.

Generally speaking, the vision of ametropic people is not very good. The higher the diopter, the lower the naked eye vision. But this is not absolute. Some people have low diopter, but their eyesight is very low, because diopter is not the only factor affecting their eyesight. If the eyes have other diseases or retinal imaging function and optic nerve function are damaged, the vision will also be reduced. The same diopter does not mean that your vision cannot be changed, so friends with myopia don’t have to be too discouraged. Use reasonable intervention in time, and the slowly accumulated results will let you get rid of the trouble of frame mirror. The long-term use of young friends can also effectively control the growth of myopia, so that the degree of myopia will not deepen rapidly.