How does AF help with shortening axial length of the eye ball?

Dear community,

I went down 1 diopter within a year and I am very happy so far.

I understood that initial myopia is caused by too much close-up (near-induced transient myopia). By wearing glasses and especially due to hyperopic defocus, the eye ball elongates and the myopia gets worse (lens-induced myopia).

My understanding: Wearing glasses makes the ciliary muscle “weak” as we are not really using the muscle to focus, because glasses do the work for us. With AF we are actively contracting the ciliary muscle, which relaxes the muscle and helps us to see sharper without glasses. So it makes sense for me, that AF helps to reverse near-induced transient myopia.

But how does AF contribute to a shortening of the axial length of the eye ball, so I can also get rid of the lens-induced myopia?

Example: If I look at something at the edge of blur, my brain might say “we need to shorten the eye-ball” in order to see sharp again (myopic defocus). But if I do AF in that particular moment, I instantly see sharp, so the image hits my retina again. So my brain might think then, “oh everything is sharp again, we don’t need to shorten the eye ball”.

So is AF only helpful for near-induced transient myopia and if not, how does AF contribute towards the shortening of the eye ball? And what is really key for shortening the eye ball?

Thanks for any advice!
Baldy

Very good questions, and in spite of a good bit of rabbit-holing, I have not found the answer to either of these questions. I am not even sure if the eyeball does shorten, although a few members on the forum are measuring axial length, and may be able to tell us in a few years’ time whether their eyeballs have shortened or not.

There are other possible explanations for the improvements in vision, though a shorter eyeball is the desired one in view of reducing risk of retinal issues. It is possible that a reversal of the lengthening of the eyeball can result slowly as a result of consistently challenging the myopic homeostasis instead of pandering to it, but the potential pathways for this have not been investigated, as far as I have been able to find. The human studies on very small and transient changes in axial length are tantalising, but not sufficient for me to want to put all my eggs in the axial shortening basket. I am very open to finding evidence that wil prove me wrong.

Great to see that you have made some progress, and welcome to the forum. :grinning:

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Hey Ursa, many thanks for your quick reply and welcoming words.

My very own theory is the following (and I am certainly not sure if that is right); As long as we avoid any kind of hyperopic defocus (the “evil” of myopia), the eyeball will shorten over time, it happens very slowly but surely. It depends on age, genetics, diet, and many other factors how fast this happens. I mean, the same injury (e.g. a bruise) might take longer or shorter to heal depending on the person. For me, an elongated eyeball is not “natural” and I surely believe in the ability of the body to heal itself as long as it is not exposed to unnatural behavior (such as close-up for many hours). So as long as we avoid hyperopic defocus (i.e. use our distance vision glasses only for DISTANCE) and avoid bad habits the eyeball will shorten regardless of AF. That might be the reason why people see results even though they find AF many months later, but they maintain good habits in the meantime.

So only by maintaining good habits, the eye might heal naturally and get back to the “natural shape”.

In addition to that, with AF we are also pushing our focusing muscle (ciliary muscle) to get back to work. The ciliary muscle was more or less “on holiday” because the glasses did all the work for us. It is time to change that. If combined both, we might see the best results for vision improvement. I also think that pulling focus is more effective than pushing focus, as Jake already mentioned a few times. We want to see sharp far away, so it makes sense to train AF on objects that are far away instead of doing hours of print pushing or even using plus lenses for print pushing.

Again, that’s my very own theory. I am not a scientist; I might be completely wrong. So, take my words with caveat :wink: Cheers!

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And I am probably completely wrong, but it doesn’t matter. It has worked, and that is what matters to most people. It is my excessive curiosity that sends me down rabbit holes. :rabbit2: :rabbit2: :rabbit2: :rabbit2:

The EM theory is that the active focus tells your brain that yes, you can clear up a bit of blur - the clarity is there, you just need to focus a bit further out than your lens does normally. The body doesn’t like straining or working hard, but adapting to make its life easier - hence if your eye lens/muscle is doing a bit of work to get that bit of clarity, a shorter eyeball would save the body having to do that work so the signals are sent to shorten the eyeball.
That is the theory anyway. No one knows if it’s true or not.

That would however, be the exact reverse of what happens to lengthen your eyeballs in the first place i.e. eye having to work hard to bend the lens to accommodate up close so it lengthens the eyeball to “adapt to the close-up focus environment”. I guess it’s not such a big stretch of the imagination to think it could work in the opposite way too

unfortunately ,as far as I know it’s only been shown to work (a bit of myopic defocus) in growing eyes or non-human eyes not in adult humans.

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I have the following problem with this part of the hypothesis:
If the lens is already at its flattest, and the ciliary muscle at its most relaxed (their natural state for distance vision at 5 or more metres) I don’t see why they have to do a little extra work to see a bit more clearly at that distance. They would have to do a little extra flattening and relaxing beyond their natural limits, and I have no idea how one can make that happen. I am more inclined to think that it is either the extraocular muscles reshaping the cornea and the whole eyeball a little, or an extra effort of the visual cortex in image processing that gives a slightly clearer image… From there on, your path of logic follows. A better image often repeated, may start the process of axial shortening for the sake of eyeball economy.

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yeah I don’t know which muscle is working, but that’s the theory that somehow one of your eye muscles is working to get the extra clarity during AF (even though you are relaxed during it) and your body gets the signal that it’d be easier to shorten the eyeball to get the light focussed on the retina

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Because the axial length is not correct.

I have a hypothesis for that :wink: But I cannot rule out your explanations too.

I have another theory, possibly junk but I’ll throw it out there.

All materials’ refractive indexes are dependent on the wavelength of the light passing through it. The amount that a material refracts ie “bends” light is dependent on the wavelength. For a given material it will refract red light (on one side of the spectrum) at a different strength than blue/violet light (on the other side of the spectrum). This will be either very slight (eg a lens with low chromatic aberration) or great (eg a rainbow).

During hyperopic defocus (what makes the eye longer) one side of the light spectrum gets focused on the retina sharper than the wavelengths at the other side of the spectrum. Not completely such that is causes blur or noticeable chromatic aberration, but enough that it’s detected by the biology. Since all of the spectrum is not completely in focus the eye length adjusts such that it rests in the mid-point of the visible spectrum.

Conversely during slight myopic defocus (as advised to stay on the threshold of in EM) the opposite end of the spectrum comes into focus sharper than the rest on the retina just about enough to be detectable, but imperceptible. This causes the biology to shorten the eyeball to once again try to rest the axial length in the middle of the wavelength of the visible spectrum. The AF we do may get just the right amounts of the picture in focus, and in the correct direction wavelength wise, that it triggers the change in the eye.

They do a check for this at optometrists (duochrome/bichrome tests) involving the green and red panels. They get the alignment balanced for distance vision but it’d be interesting to see the results of the same “prescription” during close-up.

H

I don’t know if it does. I think what you’re doing is avoiding excessive blur, essentially. Hyperopic defocus seems to be a really strong stimulus for changing the eye, maybe stronger than mypopic defocus.

But the way the eye is set up (being able to focus closer for near via the ciliary muscle), it has a built-in mechanism for avoiding lots of hyperopic defocus. Problem is, the glasses that a lot of myopic people wear (and their habits and resulting recalibrated accommodation/vergence) mess up the that whole thing.

By doing active focus, you get rid of that (hyperopic) blur, or strain, whatever you want to call it.

If you’re talking about myopia, then it’s actually the opposite. I initially thought the same as you when looking at diagrams, because in a 2d diagram they always should the ciliary muscle on either side of the lens, as if it were two sperate muscles. In reality it is a single muscle, like a sphincter, that wraps around the lens.

Trying to focus up-close means you have to contract the ciliary muscle to see clearly. To achieve distance vision the ciliary muscle must relax. So AF would most likely not include contracting the ciliary muscle. The specific mechanisms behind how AF operates have yet to be proven.

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Obviously, but there is a slight language misunderstanding. It would be nice if they could do a little extra relaxing, but as they are at their limit, they cannot, and it would not be work, unless you call relaxation work.

Yes, you do, and I looked at it with interest.

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[quote=“Ursa, post:6, topic:13666”]

I remember having read somewhere that the crystalline lens and cornea get flatter in the long term to compensate eye growth, mostly in childhood. One hypothesis was, once the lens’ ability to reduce power is exhausted, myopia kicks in. In this scenario, the eyeball was over-elongating long before wearing glasses
from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3075061/

A second theory has been proposed based on longitudinal ocular growth data from emmetropic and myopic children. This theory asserts that mechanical tension created by the crystalline lens or ciliary body restricts equatorial ocular expansion and causes accelerated axial elongation.28, 29 The mechanical tension theory proposes that there are factors that produce a larger than normal eye size in children at risk for myopia (Figure 1). Ciliary-choroidal tension in the anterior portion of the globe reaches a critical point where proportional expansion of the globe during eye growth is no longer possible. Once equatorial growth is restricted, there is accelerated axial growth. Myopia results from excess elongation that is uncompensated because the crystalline lens can no longer decrease in power by thinning and stretching.28, 29 A second consequence of reaching this critical point is that the tension results in an increase in the amount of effort required to accommodate, thereby producing an increased accommodative lag23 and AC/A ratio.3

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Yes, I have read that as well. I wonder if the cornea retains some ability to flatten as a result of the stimulus of trying to clear myopic defocus. This might be an explanation for the reduction in myopia with the EM method rather than axial shortening. This finding also supports my questioning of how much of initial myopia is lens-induced. I have no problem with the concept of lens-aggravated myopia.

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My cornea average power has flattened by 0.5 D after EM according to keratometry.
But I did EOM exercises just before keratometry and that might be the case.

3 months after resuming full correction it returned to its previous values.

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Interesting and it migh suggest that you keep on with gentle EOM exercises and not wear full correction.