China is one of the countries with the highest proportion of myopic people in the world. The number of myopic people in our country has exceeded 700 million, and almost one in every two people is myopic.
Among them, more than 80% of those who have completed high school are myopic, and 35.6% of those who have completed primary school are myopic.
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However, most of us have very little knowledge about vision. Since I am also a myopic person, I often go to learn about this knowledge. I find that most of the knowledge about vision on the Internet is one-sided, or even Totally wrong.
For example, there is a question about whether myopic people will develop presbyopia as they get older. Most of the information shared on the Internet is wrong and extremely misleading.
Picture: Wearing reading glasses makes it difficult to see in the distance, so you often see elderly people reading in this posture while looking into the distance.
If you have ever tried to understand this topic, you will find many completely different answers.
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Some people will tell you that the vision of myopic people will improve as they get older. Some people will tell you that myopic people will no longer suffer from presbyopia. Some people may tell you that myopia and presbyopia will occur at the same time.
So, this is our topic today – will myopic people get presbyopia when they get old?
The correct answer is,Myopia and presbyopia are two completely different eye diseases. The mechanisms of the two diseases have almost no influence on each other. Moreover, one loses the ability to see far away, and the other loses the ability to see near. There is almost no influence on each other.
on the other hand,Presbyopia affects almost everyone who is old enough.
Therefore, as long as you were myopic when you were young, you will definitely get presbyopia when you are old – you will have two eye problems at the same time (although I personally dislike this answer, but it is the fact).
So why are there so many different answers?
There may be people around you who are nearsighted and have experienced vision improvement as they age, but to understand this, we must understand what exactly is affecting our vision.
If you are also myopic, you must know more or less that myopia is because light enters our eyes and is imaged in front of the retina, while in hyperopia, the opposite is true, and its light is imaged behind the retina.
As for why the front or back of the retina appears in the image, many people may not be sure.
What is the nature of presbyopia and myopia?
There are actually many factors that produce images on the retina. In other words, there are actually many reasons for our myopia. Just because it causes the same visual experience to us, it is collectively called myopia.
Figure: If there is a problem in any part of the process of light reaching the retina, the image may be deviated and cause myopia or hyperopia.
The imaging principle of our eyes is similar to that of a convex lens, except that it is a complex “convex lens system”. When light enters the eye, it needs to be deflected by the cornea, aqueous humor, lens, and vitreous body to finally form an image.
During this process, whether there is a problem with the refractive power of the cornea and lens, or the refractive index of the aqueous humor and vitreous body, light may not appear correctly on the retina, resulting in myopia.
However, for most people, the cause of myopia is not a problem with the power and refractive index of these eye structures;The axial length of the eye is elongated or the retina is pushed back, causing the structures of your eye to not appear on the retina when normal imaging, but in front of the retina.
Since the axial length of the eye only occurs when the body is growing, myopia usually only occurs in adolescence. Once adults, the axial length of the eye will not continue to grow, and the degree will not change.
Figure: Convex lens imaging
in addition,The reason why myopic eyes can see far away but cannot see near is because as the distance between objects shortens, the distance between you will be lengthened, making the image closer to the retina or more light appearing on the retina.(You can simulate the convex lens imaging yourself and it will become clear).
After understanding the causes of myopia, let’s learn about hyperopia (hyperopia is the so-called presbyopia mentioned above).
When we talked about eye imaging earlier, I don’t know if you found any problems. If the eye is imaged by a convex lens, then as the object distance changes (or when looking at objects at different distances), the image distance will also change. So why can our eyes It allows objects far and near to be imaged on the retina, allowing us to see clearly both far and near.
This is the most complex and intelligent part of the eye. It automatically adjusts the distance so that objects near and far can successfully hit the retina.
As for how to adjust the image distance, it is actually to adjust the shape of the lens through the ciliary muscle to change the radius of curvature of the lens, thereby changing the focal length.
Like myopia, there are many factors that can cause hyperopia, but there are two main causes of conventional hyperopia, both of which are caused by the inability of the eyes to adjust the focus well.
One is that the lens will harden and lose elasticity with age, making it difficult to change its radius of curvature; the other is that the function of the ciliary muscle for adjustment becomes worse with age, making it impossible to adjust to image nearby objects. appear on the retina.
Both the hardening of the lens and the function of the ciliary muscle are related to age, so as long as you are old enough, you will almost certainly develop hyperopia.
Have you noticed that most people's myopia is caused by the eye axis being too long, which causes objects farther away from the retina to be seen more clearly, while most normal hyperopia is caused by the inability of the eyes to change the focal length, making the near vision blurry. Objects appear behind the retina, and the two are unrelated processes.
so,It is just a myth that myopia will not cause presbyopia or that myopia and presbyopia will cancel each other out. Physically, the two will have almost no impact.
But, as we said earlier, why do some people with myopia experience improvements in their vision as they age?
Why do some people with myopia improve their vision as they age?
First of all, such people do exist, but they are rare cases.
I've done a lot of research on why this happens, and now I'm pretty sure it's mainly due to two factors (maybe you, like me, don't want to know why).
One of the most important reasons is,The eyes of these people are experiencing major lesions, because the lesions of the eyes cause the focal length to change, and the result is like a natural pair of myopia glasses.
I found out here that these conditions include but are not limited to diabetes (especially recent hyperglycemia), cataracts, lens dislocation, corneal edema, macular edema and retroocular tumors.
The most common of these is cataracts. The precursor to cataracts is the hardening of the lens, which changes the way light “bends” when it enters the eye, or changes its focal length, thus improving myopia (of course, these eye diseases may also worsen myopia).
We mentioned earlier that lens sclerosis is also the cause of presbyopia. This is probably why some people feel that their myopia is improved by presbyopia. However, this is not caused by the offset between myopia and hyperopia. Presbyopia still exists, but myopia is improved due to the change in focal length. That’s all.
Another reason is not a good thing,It's because your myopia degree was not matched when you were young, and it was too high.
Because when we are young, our ciliary muscle function is very strong, so if your prescription is higher, you will still not have much discomfort, because the ciliary muscle adapts to your higher prescription glasses by adjusting the shape of the lens.
But as you age, the ciliary muscle function declines, and it becomes unable to adapt to higher degrees of myopia, so you feel that your degree of myopia has decreased.
Similarly, we mentioned earlier that ciliary muscle function affects another factor in presbyopia, so some people feel that their myopia has improved due to presbyopia.
In fact, there is another situation that must be mentioned, that is, for some people with high myopia, the impact of presbyopia is not so obvious (this may be the reason why some people think that people with high myopia will not get presbyopia).
This is because even if a person with high myopia sees an object that is close enough, its image will be far enough in front of the retina. If you still have farsightedness at this time, the image of the closer object will be pulled down the retina because of the farsightedness. behind, and cancel each other out.
However, if you correct your vision at this time, or wear glasses, the effects of presbyopia will become obvious.
at last
Many people think that myopia can be changed in some way, but it turns out that once you are really myopic, it is permanent unless you undergo some surgery to correct the refractive power.
Therefore, it is necessary to take good care of your eyes.
In addition, although presbyopia is usually unavoidable, which is not very friendly to people with myopia, there is no need to be too pessimistic. There are now glasses that can solve both myopia and hyperopia, but it is said that the comfort is very poor.
PS:
This article only refers to one case, my family member. She was myopic when she was young, and got presbyopia when she got older. She did not experience improvement of myopia, only experienced that presbyopia became more and more serious, and she needed two pairs of glasses. Wear it.
Other aspects of the content are purely based on my own search for information and speculation on physics knowledge. I am not a professional. If you have any questions, please consult a professional.
Editor in charge: Shang Shangwen Q