China has one of the highest myopic population in the world, with more than 700 million myopic people in our country, and almost one out of 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 myopia.
However, most of us have very little knowledge about vision, because I am also a myopic group, so I often go to learn about this knowledge, and I find that most of the knowledge about vision on the Internet is one-sided, or even completely wrong.
For example, there is a question about whether people with myopia will get presbyopia when they are older, and most of the sharing on the Internet is wrong and extremely misleading.
Pictured: You can't see far away with reading glasses, so you often see older people reading and looking away in this way
If you've ever tried to understand this topic, you'll find a lot of completely different answers, some will tell you that myopic people will see better when they get older, others will tell you that myopic people won't get presbyopia anymore, and others will tell you that myopia and presbyopia can go hand in hand.
So, that's our topic today – will myopic people get presbyopia when they get old?
The correct answer is that myopia and presbyopia are two completely different eye diseases, and the two have almost no effect on each other in terms of pathogenesis, and one has lost the ability to see far away, and the other has lost the ability to see near places, and the two diseases have almost no effect on each other.
Presbyopia, on the other hand, affects almost everyone who is old enough.
So, if you were short-sighted when you were young, you're bound to get presbyopia when you're old – you'll have both eye problems at the same time (although I personally don't like this answer very much, but it's just the way it is).
So why are there so many different answers?
You may be close to people who are really nearsighted and have experienced vision improvement in old age, but to understand this, we must understand what exactly is affecting our vision.
If you are also nearsighted, you must know more or less that myopia is caused by the fact that the light enters our eyes and is imaged in front of the retina, while in the case of farsightedness, it is the opposite, and its light is imaged behind the retina.
As for why imaging appears in front or behind the retina, many people may not be clear.
What is the nature of presbyopia and myopia?
There are actually many factors in the retina, in other words, there are actually many reasons for our myopia, but because it causes us to feel the same vision, so we are collectively called myopia.
Figure: Problems at any point in the process of light reaching the retina can cause the image to be skewed and cause nearsightedness or farsightedness
The imaging principle of our eyes is similar to that of the convex lens, except that it is a complex "convex lens system", and the light entering the eye needs to pass through the deflection of the cornea, aqueous humor, lens, and vitreous humor for final imaging.
During this process, whether it is the refractive power of the cornea and lens, or the refractive index of the aqueous humor and vitreous, it can cause light to not appear correctly on the retina, resulting in myopia.
However, for most people, the cause of myopia is not a problem with the refractive power and refractive index of these eye structures, but rather a longer eye axis or a backward retina that causes your eye structures to not appear on the retina when imaged normally, but in front of the retina.
Because the eye axis only occurs when the body is developing, myopia usually only occurs in adolescence, and once the eye axis is an adult, it will not continue to develop, and the power will not change.
Figure: Convex lens imaging
In addition, the reason why the myopic eye can see far and not near is because as the distance between objects is shortened, your distance will be lengthened, so that the image is closer to the retina or more light appears on the retina (you can simulate the downward lens imaging yourself).
After understanding the causes of myopia, let's learn about farsightedness (farsightedness is the so-called presbyopia mentioned above).
When we talked about eye imaging earlier, I don't know if you found the problem, if the eye is imaging with a convex lens, then with the change of object distance (or looking at objects at different distances), the image distance will also change, so why can our eyes make objects near and far image on the retina, and let us see clearly near and far?
This is the most complex and intelligent part of the eye, which automatically adjusts the distance so that objects near and far can 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, so as to change the radius of curvature of the lens, thereby changing the focal length.
As with myopia, there are many factors that can cause farsightedness, but there are two main causes of regular farsightedness, both of which are caused by the inability of the eye to adjust its focus well.
One is that the lens hardens and loses elasticity with age, making it difficult to change its radius of curvature, and the other is that the ciliary muscle, which is used for accommodation, deteriorates with age, making it impossible to adjust to image recent objects on the retina.
Whether it is the hardening of the lens or the function of the ciliary muscle, it is related to age, so as long as you are old enough, you will basically have farsightedness 100%.
Have you noticed that most people's myopia is that the eye axis is too long, resulting in the farther away objects from the retina, so that the more difficult it can see, and most normal farsightedness is because the eyes cannot change the focus, so that near objects appear behind the retina, and the two are unrelated processes.
Therefore, the idea that myopia will not get presbyopia or that myopia and presbyopia will cancel each other out is just a myth, and there is almost no physical impact between the two.
But, as we said earlier, why do some people with myopia experience improved vision as they age?
Why do some people with myopia get better when they get older?
First of all, there are people who do exist, but this is a rare case.
I've looked up a lot of information as to why this is the case, and I'm pretty sure that there are two main reasons for this (and maybe you wouldn't like me to wonder why).
One of the most important reasons is that these people are experiencing large lesions in their eyes, because the lesions of the eyes cause their focal length to change, and the result is like a natural addition of myopic glasses.
These conditions include, but are not limited to, diabetes (especially the recent onset of hyperglycemia), cataracts, lens dislocation, corneal edema, macular edema, and tumors behind the eye.
The most common of these is cataracts, which are the precursors of the lens, which can improve myopia by changing the way light "bends" when it enters the eye, or changes its focal length, which can also worsen myopia.
We mentioned earlier that lens sclerosis is also the cause of presbyopia, which is probably why some people feel that their myopia is improved by presbyopia, but this is not caused by myopia and hyperopia offsetting, presbyopia still exists, but myopia is improved due to the change of focal length.
Another reason is not a good thing, because when you were young, the myopia was not matched, and it was matched.
Because when we are young, our ciliary muscles are very functional, so you will not have too much discomfort when your power is higher, because the ciliary muscles adjust the shape of the lens to adapt to your higher prescription glasses.
But as you get older and the function of the ciliary muscle declines, it becomes unable to adapt to the higher myopia degree, so you feel like your power is lower.
Similarly, we mentioned earlier another factor in the function of the ciliary muscles that affects presbyopia, so some people feel that their myopia has improved because of presbyopia.
In fact, there is another situation that must be mentioned, that is, some people with high myopia, the impact of presbyopia on them 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 close enough, its image will be far enough in front of the retina, and if you have farsightedness at this time, it will cancel each other out because the hyperopia pulls the image of the closer object down the back of the retina.
However, if you correct your eyesight at this time, or if you wear glasses, then the effects of presbyopia will become apparent.
At last
A lot of people think that myopia can be changed in some way, but it turns out that once you are really nearsighted, then it is permanent, unless some surgery is done to correct the refractive power.
Therefore, it is necessary to take 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, and there are glasses that can solve both myopia and farsightedness, but it is said that the comfort is very poor.
ps：
This article only refers to one case, my family, she was myopic when she was young, and she got presbyopia when she was older, she did not experience myopia improvement, only experienced presbyopia getting worse and worse, and needed two pairs of glasses to wear.
The rest of the content is purely my own search for information, as well as the speculation of physics knowledge, I am not a professional, if you have any questions, please consult a professional.