Since childhood, parents have told their children that their eyes are the window of the soul, and they must take good care of them. However, there are still a large number of myopia. When you feel your vision is blurred, you have to go to the hospital to test your eyesight. At this time, you will find that the doctor will let you identify the capital letter E which always changes position. Maybe you have wondered why the English letter is used in the visual acuity chart Not Chinese characters? Why use the letter 'e' in the test table?
The first question we need to explain is why we use English letters instead of Chinese characters. This is because the European and American countries have been in a relatively leading position in modern vision measurement technology, so China has always introduced and used the alphabet test table; in addition, because most of the strokes of Chinese characters are more, it is difficult to achieve the purpose of accurate visual acuity measurement with Chinese characters. In addition, our country's "e table" is also suitable for people who can't read the Latin alphabet smoothly, but also for people who don't use the alphabet in their mother tongue.
However, why do test tables use the letter 'e'? Many people say that because 'e' is the first letter of the English word 'eyes', this explanation is not scientific. What we usually call visual acuity test is actually the ability of the eye to see far away. Its accurate definition is to measure the image on the smallest retina that can recognize its shape. The commonly used 'e' visual chart is designed according to the principle of visual angle, which is expressed by a formula, that is, v = 1 / A, and a is the angle of view. Under normal circumstances, the visual angle formed by the minimum distance between two points is the minimum angle of view, that is, one point angle of view. At a distance of 5 meters, the projection of 10 lines of "e" on the retina is exactly one point of view. We are familiar with the character "e" of equal length, each stroke or space is one fifth of the square. Therefore, this' e 'word is more in line with the strict angle resolution.
Of course, the measurement of visual acuity is not only determined by the visual chart, but also determined by a variety of conditions, affected by the surrounding environment, test standards and personal psychology and other factors. In our daily life, we need to pay attention to the illumination condition, glare interference, adaptability, motivation and expectation of the subjects.
Vision chart vision is widely used in medical treatment, prevention and a variety of physical examination standards, the use of standardized and unified visual chart is particularly important. Therefore, when designing and using the visual acuity chart in the future, the relevant departments need to consider: 1) formulate the national unified standard; 2) design reasonable and take into account the past habits; 3) try to be in line with the international standards; 4) in addition to the universal chart, design another visual chart for children about three years old, so that they can identify it more clearly.