Myopia seems to be gradually becoming the direction of human evolution. There are more and more people who have myopia, and there is a trend of youthfulness. The proportion of middle school students who wear glasses in urban and rural areas is not balanced.
More than 30 years ago, elementary and middle school students rarely wear glasses, especially in rural areas. Glasses are rare. Today, there are still fewer children wearing glasses in the countryside. According to statistics, the proportion of middle school students in urban myopia is 4 to 5 times that of rural areas.
Dimness in lighting is not easy to be short-sighted When the analysis of rural children with low myopia, many people will come down to learning, reading time is short, the operating pressure is small. Of course, this is the reason on the one hand.
However, when those children who had been studying under the lamp for many years, why did they improve their lighting conditions in the evening after going to university? In the past few years, they listened to an elderly person who came from the countryside and said that there are many urban myopia because of the lights. too bright. At the time, I just felt that this was reasonable, but I was not sure.
Once upon a time, we repeatedly emphasized the need to protect the children's vision. Its main measure is to improve the lighting of classrooms and libraries. Parents buy the best table lamps for their children and improve their nutrition. But the result is more and more myopia. Now we know that the desk lamp is a sight killer. The old man from the country was right. The glasses in the city were mostly because of the good lighting conditions.
So why is it not easy to be nearsighted under the dim lighting conditions? Let us first look at why we are shortsighted.
When viewing near objects, if the object is imaged behind the retina without being adjusted, of course, it is not clear. At this time, the contraction of the ciliary muscles generally increases the curvature of the lens and allows the object to be imaged on the retina. However, for a long time to see near objects, many signals formed by the contraction of the ciliary muscle lead to the gradual and long effect of the anteroposterior diameter of the eyeball. In this way, there is less need for contraction of the ciliary muscles, and the object can be imaged on the retina, forming a close-up vision adaptation.
However, the axial axis is elongated. When looking at distant objects, the imaging is in front of the retina. However, the eye muscles cannot be adjusted. Only the glasses can be used to correct the refractive power of the eye so that the distant objects can be imaged on the retina.
Therefore, the nature of myopia is the adaptive response of the axial axis to long-term visual appearance. This stretch cannot generally be reversed, or there is no condition for reversal, such as not being able to engage in close-range learning and work for a long time.
Why is it not easy to see myopia when the light is dark? There is a phenomenon called night myopia. It is the daytime vision that is clear, but you need to wear myopia at night. The reason for this is because at night, due to the difference in refraction, the imaging of the object is in front. There is a big difference between the refractive individuals at night, which is generally different from day 1 to 4D, with an average of about 1.3D.
Experiments have shown that keeping monkeys in a dark house can lead to hyperopia in monkeys. Therefore, in the darker light, the object is imaged in front of the light when the light is dark, and the light is behind when compared with the object in the bright table lamp. In this way, when the light is bright, the extensibility of the axial axis naturally adapts to a stronger response.
Home lighting should not be too bright to compare the difference in eye imaging position caused by different diopters under different light conditions. It is not difficult to understand why with the improvement of living conditions, the brightness of classrooms and home lighting has been increased, but the proportion of myopia has increased. Reasons. In view of this, the lightness of classrooms, libraries, etc. should be as strong as possible, and it needs to be re-evaluated objectively and scientifically in a new perspective.
How to prevent children's myopia First, home lighting should not be too bright. Children's books and assignments are generally relatively large, and it should not be a problem to see clearly. In addition, after studying at night for a while, go outside for a while.
Activity in darker light is a good fit for vision. The worst case is a bright desk lamp reading several novels and staying up late. It will take a few days if you donâ€™t wear glasses.
(The author of this article is Professor Wang Rui'an from the Fourth Military Medical University.)