China has one of the highest rates of nearsightedness in the world, with over 700 million nearsighted individuals in the country. Roughly one out of every two people is nearsighted.
Among those who have completed high school education, over 80% are nearsighted, while even among those who have completed primary school, 35.6% are nearsighted.
However, most of us have a very limited understanding of vision. As a member of the nearsighted population myself, I often seek to learn more about this topic. I have found that much of the information on the internet regarding vision is one-sided and, in some cases, completely inaccurate.
For instance, there is a common question about whether nearsighted individuals will develop presbyopia as they age. The majority of information shared online on this topic is incorrect and highly misleading.
Image: Wearing reading glasses makes it difficult to see things far away, which is why you often see elderly people reading with this posture, trying to read while looking into the distance.
If you've ever tried to understand this topic, you'll find many completely different answers.
Some may tell you that people with nearsightedness will have improved vision as they age, while others may say nearsighted individuals won't develop presbyopia. Some might even mention that nearsightedness and presbyopia can coexist.
So, our topic today is: Do nearsighted people develop presbyopia as they age?
The correct answer is that nearsightedness and presbyopia are two completely different eye conditions with almost no impact on each other's disease mechanisms. One affects the ability to see things far away, while the other affects the ability to see things up close, with little overlap in their conditions.
On the other hand, presbyopia affects almost all individuals as they reach a certain age.
Therefore, if you were nearsighted when you were young, you will likely develop presbyopia as you age - experiencing both eye issues simultaneously (even though personally, I may not like this answer, it is indeed the reality).
So, why are there so many different answers?
You may indeed have seen nearsighted individuals whose vision improved as they aged, but to understand this, we must delve into what exactly influences our vision.
If you are nearsighted, you probably know to some extent that nearsightedness occurs because when light enters our eyes, it focuses in front of the retina, while farsightedness is the opposite, with light focusing behind the retina.
As for why the focus appears in front of or behind the retina, many people may not be very clear about it.
What is the essence of presbyopia and nearsightedness?
There are actually many factors that contribute to the focus being in front of the retina. In other words, the reasons for our nearsightedness are actually numerous, but because they result in a similar visual sensation for us, we collectively refer to them as nearsightedness.
Image: Any problem in the process of light reaching the retina can cause deviations and lead to myopia or hyperopia.
The imaging principle of our eyes is similar to that of a convex lens, except it is a complex "convex lens system." Light entering the eye needs to pass through the cornea, aqueous humor, crystalline lens, and vitreous humor for refraction, ultimately forming an image.
During this process, issues with the refractive power of the cornea and crystalline lens, as well as the refractive index of the aqueous humor and vitreous humor, can cause light to not focus correctly on the retina, resulting in myopia.
However, for most people, the cause of myopia is not due to issues with the refractive power and refractive index of these eye structures, but rather due to the elongation of the eye axis or the backward displacement of the retina, causing the normal imaging of your eye structures to appear in front of the retina instead of on it.
Since the elongation of the eye axis only occurs during physical development, myopia typically occurs during adolescence. Once adulthood is reached, the eye axis stops elongating, and the degree of myopia does not change further.
Image: Imaging with Convex Lens
Furthermore, the reason why nearsighted eyes can see far away but not up close is because as the distance of the object shortens, your focal length is elongated, resulting in the image being closer to the retina or more light appearing on the retina (you can simulate imaging with a convex lens to understand this better).
Now that we understand the cause of nearsightedness, let's delve into farsightedness (which is what was previously referred to as presbyopia).
When discussing imaging of the eye earlier, you may have noticed a question arising. If the eye functions like a convex lens for imaging, then as the object distance changes (or when looking at objects at different distances), the image distance also changes. So, how is it that our eyes can form images of objects at both near and far distances on the retina, allowing us to see clearly at all distances?
This is the most complex and intelligent part of the eye. It automatically adjusts the focal length, ensuring that objects at various distances are successfully focused on the retina.
As for adjusting focal length, it's done by the ciliary muscles altering the shape of the lens, changing its curvature radius and thus adjusting the focal length.
Similar to nearsightedness, there are various factors that can cause farsightedness. However, the two main reasons for common farsightedness are both related to the eye's inability to adjust the focal length effectively.
One reason is that the lens hardens and loses elasticity with age, making it difficult to change its curvature radius. The other reason is that as one ages, the function of the ciliary muscles responsible for adjustment deteriorates, leading to an inability to focus close objects onto the retina.
Both the hardening of the lens and the decline in ciliary muscle function are age-related, so as you get older, farsightedness is almost guaranteed to occur.
Did you notice that for most people, nearsightedness is caused by having an elongated eyeball, which makes distant objects focus in front of the retina, leading to blurry vision? On the other hand, most cases of farsightedness occur because the eye cannot adjust its focus properly, causing close objects to focus behind the retina. These two conditions are unrelated processes.
Therefore, the belief that nearsightedness prevents presbyopia (farsightedness with age) or that they cancel each other out is simply a myth. Physically, they have little to no impact on each other.
However, as mentioned earlier, why do some nearsighted individuals experience improved vision as they age?
Why do some nearsighted people see better as they get older?
Indeed, such cases exist, but they are relatively rare.
After researching extensively, I am now confident that there are two main factors contributing to this phenomenon (perhaps you, like me, may not want to know why).
One of the most significant reasons is that these individuals are undergoing significant eye changes, which alter their focal length, similar to naturally wearing nearsighted glasses.
According to my findings, these conditions include but are not limited to diabetes (especially with recent high blood sugar levels), cataracts, dislocated lenses, corneal edema, macular edema, and tumors behind the eye.
Among these, cataracts are the most common. The precursor to cataracts is lens hardening, which changes how light bends or the focal length of the eye, thus improving nearsightedness (although these eye conditions could also worsen nearsightedness).
We mentioned earlier that the hardening of the crystalline lens is also a cause of presbyopia. This is probably why some people feel that their myopia has improved due to presbyopia, but it is not a cancellation of myopia and hyperopia. Presbyopia still exists; it's just that myopia has improved due to changes in focal length.
Another reason is not a good thing either; it's because when you were young, your myopia prescription was not matched correctly, and it was overcorrected.
When we are young, our ciliary muscle is strong, so even if your prescription was overcorrected, you wouldn't feel much discomfort because the ciliary muscle adjusted the shape of the crystalline lens to accommodate your higher prescription.
However, as you age, the function of the ciliary muscle decreases, making it unable to adapt to higher myopia prescriptions, so you feel that your prescription has decreased.
Similarly, as we mentioned earlier, the ciliary muscle function affects another factor of presbyopia, so some people feel that their nearsightedness has improved due to presbyopia.
In fact, there is another situation worth mentioning: some highly myopic individuals may not be as affected by presbyopia (this may be why some people think highly myopic individuals won't get presbyopia).
This is because even if highly myopic individuals look at objects up close, the image will still be far enough in front of the retina. When you also have hyperopia at this point, it will pull the image of this closer object behind the retina, canceling each other out.
However, if you correct your vision at this point or wear glasses, the impact of presbyopia will become apparent.
Many people believe that myopia can be changed in some way, but the fact is, once you are truly myopic, it is permanent unless corrected through surgery to change the refractive power.
Therefore, taking care of your eyes is necessary.
Although presbyopia is usually unavoidable, which is not very friendly to myopic individuals, there are now glasses available that can address both myopia and hyperopia simultaneously, but they are said to be uncomfortable.
PS:
This article is based on a single case study, my family member. When she was young, she was nearsighted, and as she got older, she developed presbyopia. She did not experience an improvement in her myopia but only experienced worsening presbyopia, needing to switch between two pairs of glasses.
Other content is purely based on my own research and speculation of physics knowledge. I am not a professional, so if you have any questions, please consult a professional.
