An Unintuitive Theory + Experiment: Negative Short-Term Response? [ended; inconclusive]

This is about a theory that sounds stupid but I find difficult to debunk. Could the eyes’ short-term axial length response be the opposite of its long-term response?


To our new public readers: hi, I’m a resident measurement fanatic. :nerd_face: I keep track of my eyes in multiple ways, including measuring their length with a Zeiss IOL Master to try figure out what exactly causes it to change.

This year, I haven’t been very successful at improving. Despite multiple experiments, I still could not find a useful cause-effect relationship, getting confusing results.


Looking back, also at older logs and diary entries, I’ve noticed a strange potential pattern: in the short term, my eyes often seem to react to changes in stimuli in the exact opposite way of predictions. :thinking:

I know, I know, it could be random and me grasping at straws. Well, maybe, but! :face_with_monocle:

This happened quite a few times, reaching back to spring 2018, when I returned from an outdoor event that lasted a few days, and measured bad distance acuity. Ever since, I’ve been confused at poor results right after weeks of cycling, or in times when I had been going to sleep earlier. And it’s not only subjective acuity. Some of the weirdest AL outliers were on the days after I returned from a vacation. Often, these bad results did not start a trend, but disappeared over time. Conversely, I sometimes had exceptionally good results after a week of heavy screen use, or just before a trend of worsening set in.

In recent weeks, since about the beginning of September, I’ve been trying to reduce consecutive screen time relative to outdoor breaks, with an emphasis on evenings. (There’s no clear starting date, but I remember looking for ideas and getting inspired by Jake’s three-hour-rule video on the 3rd, so around then. We also had an interesting chat since, where he mentioned stories of vacations that seemed to lead to worsening myopia.)

Now, have a look at the last year of my axial length measurements to see what happened next:

  • The azure points are a new average, added because the EMA has a systematic lag and timing is important here. The new average is calculated by looking both backward and forward in time. (4 weeks either way, linearly decreasing weight. Newest values not mature.)
  • The recent change my eyes did, circled in red, is a small but notable elongation. Subjective measurements consistently show a worsening too, and it’s quite consistent between eyes, so measurement error seems unlikely.

Long story short, it looks like being more careful about screen time made my eyes worse. What? :sweat_smile:

Some additional information:

  • The hump on the right eye marked as “also weird” coincides with a period in which I was hiking more often, using a -2.25 correction, which is relatively weak for me and may leave my left eye with excessive blur, but not the right. (My left eye is more myopic, despite the AL difference.)
  • The winter hump on the left eye began shortly after I stepped up my main distance glasses to -2.5, on 2020-01-10. Not sure if this is related.


It has long been suspected that changes in eye length start in the periphery and then move to central vision. This is underlined by rhesus monkey studies that showed that central vision is not important for the eyes’ adaptation.

Mechanically, I could imagine that eyes trying to begin shrinking only in the periphery could squeeze themselves from the sides, pushing central vision backwards until the change has propagated inwards, toward central vision. This would create a short-term elongation that reverts over time. I’m making this up without evidence, because it is the only plausible explanation I can think of.

A second theory that may be relevant here is that eyes adapt significantly during sleep, continuing to use whatever state of defocus they detected earlier. Long screen hours and late bedtime would muddy the eyes’ state of remembered stimulus, impeding the effectiveness of outdoor stimulus acquired earlier in the day.

Experiment & Call for Arguments

Right now, I am staying the course despite the negative response from my eyes, to test this theory.

Edit: to clarify, the biggest change I’m keeping up is being more strict on the three-hour rule: on a given day, three hours of accumulated screen-time should not be exceeded without undoing it 1:3 with quality outdoor time. So If I reach 3h, I have to be outdoors for a full hour to comply. This automatically puts a focus on evenings, since there is no quality outdoor time after dark. It’s not always possible to schedule this perfectly, so I’m aiming for high but not perfect complience and logging how well I’m keeping up.

If you have any arguments, ideas, or opinions, especially reasons why this would be wrong and I’m making a bad choice, please speak up!

As usual, I’m going to make more measurements and update this thread later, so we can see where this goes. :upside_down_face:


One possible reason could be the amount of active focus, assuming that active focus is one of the factors that tells the eye to accomodate via axial shortening.

I can’t speak on your behalf, but at least for me I get a lot of opportunity for active focus practice while on my computer, more-so than outdoors. This is largely due to the fact that I’m more aware of the blur, what ‘type’ of blur it is, and just how much blur there is. Moreover, if lighting conditions are ideal, and the depth of field is increased past my usual blur horizon, I can simply move the screen further away until I have blur challenge. The lighting conditions outside are also way more likely to be a great deal brighter than indoors, meaning less blur challenge outdoors.


An alternative explanation to the same phenomena:
maybe the eye improves when it’s resting. So just like when you try to build muscles, if you go to the gym and lift weights (for the same muscle groups) for a week, every day, then your muscles won’t improve, they may even deteriorate. So just like for muscle building where you need a big stimulus, then a large amount of rest, the eye also needs the same. And when you have a long vacation with a lot of distance vision you practically strain your eyes. Which then first of all need some rest period to just get back to previous levels, and based on the amount of strain they may not even able to get back to previous levels. Of course with the right amount of strain (positive stimulus) they don’t deteriorate much and can also improve.

Honestly this could also explain what I experience in the last few months: maybe my problem is not that I have bad habits because of the home office, but I feared bad habits so much that now I’m constantly overdoing it :thinking:


I thought close work was a straining stimulus and distance was relaxing the ciliary. Are you saying AF is straining?

Not enough stimulus from things within your clear horizon? Too much too difficult to clear blur? Maybe there’s a pseudohyperopia phenomenon similar to pseudomyopia? Like your eyes tried to relax so much that tightening is difficult? Kind of like how static stretching should be for post-workout and dynamic stretching for warm-up?


I don’t know where my experience fits here, but I think my eyes’ short-term improvement could also be the opposite of long-term improvement response. (Don’t know about the axial, I measure mine in cms.)

My eyes improve better if I have less sleep than more sleep.
A few months ago, I tried to compare improvements between having 5 hours of sleep vs having 11-12 hours of sleep. So I deprived myself of good sleep for about 1 week and then binge slept for another 1 week. The pandemic was already happening and I stayed at home, so I was able to control most habits, and amount of AF snd screen time. For the extra waking hours of the 5 hours of sleep week, I literally do nothing. I don’t AF or do close-up work.

I expected that I’d get better results when I sleep longer, because when I lack sleep I feel more stressed and so do my eyes. But nope! I have very very small improvements during the 5 hours of sleep, and my cms got worse when I was sleeping well!

I didn’t know if my experiment sucked, or I’m just not being scientific at this at all, or binge sleeping is just somehow worse than lack of sleep.
Of course this was a short-term measurement, no idea on the long term manifestation of this. And now I am back to my normal 8.5 hours of sleep.


This may be an overvaluing of the benefits of outdoor stimulus. I have not noticed any improvement in vision after many hours outdoors and I think this is because I make no very specific demands for clearer vision when I am outdoors. I only do this for the few minutes, a few times a day, that I spend on conscious cow-pulling or power line clearing. At my screen I intentionally work some distance into the blur area so as to give my eyes a challenge. As I do not spend many hours at the screen, and only with text, and with regular breaks, I am challenging my myopic homeostasis all the time but without excessive strain. For other close or medium vision household or garden tasks, I make no effort to adjust the degree of clarity with AF, as it is rarely relevant. My vision improvement started with print pushing at the screen, and nothing else.
As I am uncorrected for all distances in spite of a big diopter gap, I am a black sheep (swan?) but insights gained from exceptions can also cast some light on what the underlying mechanisms are.

Since reading your post, I have gone down a bit of a rabbit hole on the role of peripheral defocus on the development of myopia and the elongation of the eye in children. But I have found nothing on its potential role in axial shortening. Your hypothesis is indeed counter-intuitive. I would be tempted to look for a simpler and more elegant hypothesis - lack of challenge. This might also explain your ‘also weird’ data points.

What I find most interesting about your data is that axial length can change rapidly, even though only by a small amount, and the fact that your more myopic eye is shorter.

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This is the rationale behind print pushing, a short and elegant theory. Problem is, despite trying various things, I never managed to confirm it as a reliable way of improving. It’s certainly not a bad thing to do, but by itself, it doesn’t seem to suffice.

I’d not be surprised if it’s something like this. Though I find it difficult to make this concrete and match it to my history. Look at this example from last year’s outdoor experiment:


This is the right eye, but the left qualitatively did the same thing. The gap was a cycling tour, weeks of maximum distance stimulus. Before it, I was already on my experimental high-outdoor-time prescription for well over a month.

If there were a simple rule like “too much stimulus makes the eyes worse,” I shouldn’t have had such significant improvement after the tour. And what is it with the outliers right after the tour?

There is also a theoretical problem with this: would such an error be stable enough to survive evolution? In stone age, long breaks from distance vision were in short supply. Wouldn’t people with such unstable eyes have gotten runaway myopia and died?

This could explain why my left eye was responding poorly compared to the right when I was using -2.25, while the left did this weird late-winter hump when I was using -2.5.

But this only works with the short-term responses upside-down. :sweat_smile:

Similar problem is the right eye’s response pattern around April, which went from getting worse to getting better without me changing anything (knowingly). On top of that, the recent response going the opposite way seems excessive, given that I didn’t make any extreme change. Can the mechanism be this picky?

Thing is, the level of challenge varied between the eyes, and also a lot as I switched back and forth between -2.5 and -2.25 for distance. A lack of challenge should be more dangerous to the left eye, but it’s the right that is bouncing around.

The “also weird” points don’t have a clear direction. The eye gets longer first, but then has an improvement trend that undoes it and more. I’d love a simpler theory, but don’t understand how to match it to the data.

Oh, it can change even more rapidly, see my response to David. But that doesn’t seem sustainable. If the theory is correct, it only “worked” because I lost the stimulus at the end, paying with many months of no improvement.

I’d not get hung up on my myopic eye being shorter. The AL difference is less than the change I’ve already seen. For comparison, my brother’s eyes are roughly a millimeter shorter, and he’s still (low) myopic.


I know this theory seems silly. But there doesn’t seem to be a strong argument against it, which is surprising given how strongly it goes against expectations.

Keep 'em coming, please! If this is just nonsense, I’m putting my eyes at risk by continuing.


Based on my knowledge of at least one group of stone-age hunter gatherers (the Khoisan) this was not the case. Only a small part of the day (and not every day, depending on the success of the hunt the day before) was spent on hunting and there were plenty of close vision activities like making ostrich eggshell beads, sewing the few clothes they did wear, and preparing small poisoned arrow heads. They also spent hours just sitting around a fire, cooking and talking. They actually spent fewer hours a day ‘earning a living’ than modern humans do.


The analogy I go with for AF (though I don’t know if it contradicts science) is, instead of thinking of it as muscle strengthening I think of it as muscle stretching. You push through discomfort in the former, you relax through pain in the latter, but both create micro-traumas in the tissue that might be healed for the better during sleep.


I mean different kind of strain. @Salt’s analogy is good, muscle can be strained with both lifting too much weight, and can also be overstretched. Both causes strain, but obviously a different strain caused by different mechanism.


First, it’s not so simple that people in the past had all the time distance vision. If you put homo sapiens in a evolutionary historical settings, there was a lot of close-up, just different type than what we have. First of all if you walk barefoot, you have to look a lot to the ground. Not totally close-up, more like middle distance, but different than watching the horizon. Then you have tool making. Grinding stone to a knife takes a lot of time and lot of close-up. Same for creating pots and bowls. And as @Ursa said there were low amount of time constantly looking into the distance. Only hunting. Otherwise they did some close-up thing. Yes, with a lot of looking up and focal plane changes. But not staring at the distance for hours. Also let’s not forget that a lot of time was spent in dark and/or with fire light. Again, not really possible to have distance vision.
In other words, unless you are hunting or guarding the tribe, there is not much interesting thing in the distance. All interesting thing (people, tools, meals) are in close-up.
Of course I can totally mistaken here, we should check with some anthropologist :slight_smile:

Second, we have to differentiate between having a kind of vision / stimulus all of your life and trying to reverse your eyesight to “normal”. It’s like if you going barefoot since you are child and never wear shoes, your feet can tolerate much more than if you try to go barefoot as an adult. Of course if you are careful as an adult and gives a few years of training for your feet it will develop the same tolerance… but if you just start to use it like you’ve never wear shoes you will just damage it. In evolutionary setting people never got myopic and never had hours of unchanged close-up focal distance. So evolution never had to deal with reversing this condition.

But maybe it was not too much. It was perfectly the right amount. If I understand it correctly what we see here, that right after the stimulus your eyes were “tired” and “needed rest” (ie.: longer axial length), but because they had the right amount of stimulus, they could improve fast after it.

Also I’m pretty sure that there is some lag between stimulus and vision changes. Most likely because actually building up / broking down cells takes time. So it won’t happen that you do a heavy stimulus day, and next day you have better vision. Which could explain some of your

Did you had lot of distance vision before this week of heavy screen use? If yes, it may happen that the lag is even a week, so you saw the improvements from the positive stimulus before the heavy close-up started.

What is exactly your experiment currently? I could not really find it in the opening post.


Not disagreeing here. Question is, isn’t a cycling tour – or any typical outdoorsy activity I’d do – fairly similar? We’d stop to stay somewhere for the night, eat and prepare food, do stuff on the bikes, look at the map, visit attractions that have indoor stuff, maybe play a card game or write some messages, etc. It’s really hard to find an outdoor activity where you’re staring at the distance nonstop. So when I try to imagine historical activities and what outdoor activities today look like, I can’t see a major difference, especially when compared to books and screens in artificial light.

Of course! But isn’t this addressed by reducing the lens power slowly? Small amounts of myopia probably happened, or else why would the eyes be able to reverse that at all?

Thing is, I’ve been trying to fit a lag period into my log for over a year now, and can’t find a solution. Something like one week doesn’t match at all… often, I changed something, saw no effect and kept going, and (seemingly?) got a response that only started about a month later.

But a pure lag of over a month? Smeared-out response, maybe, but this is just weird. I can’t imagine how the biology would even implement it. And that’s on top of the problem that I can’t find a clear cause-effect link using such a lag… it somehow roughly works, but is really murky.

Not necessarily. This isn’t a clear-cut thing or experiment though, more like a number of times where I thought, huh, that’s unexpected. And this response time appears to be really fast, on the order of a few days. Sometimes, I’d go hiking for just two days, and after that I’d think, whew, why did my distance vision get worse?

Ah, sorry. I added a clarification to the OP. Biggest change is to be more strict about undoing near work with quality outdoor time at least 1:3 before reaching three hours of accumulated screen time.

Jake also gave me tips that I’m trying to incorporate but aren’t as easy to quantify; main focus on paying attention to how screen time affects my vision and seeking out engaging outdoor activities. Though this happened after the AL jump. The weird jump follows shortly after the evening changes / consecutive screen-time limitation, with many weeks of no noteworthy changes to my behavior before it.

I may have been doing more screen work prior to the worsening, but it wasn’t unusual and included more outdoor time than prior periods like this that weren’t followed by such an obvious worsening on both eyes.

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You are right there.

Not necessarily. You can have two type of strain: too big work in short time frame and too long time frame (even for small work). Reducing slowly solves the first problem, but does not solves the latter.

Yeah no, that sounds unreasonable. I have experience of having a week of lag in other body functions, but I can hardly imagine something longer than that. I can imagine some kind of month long moving average though. I thinking in the ballpark of having some cell level remodeling, which needs one months to complete (cell turnover can be pretty slow in the body: ). The body starts it when it reaches some stimulus threshold, but obviously more stimulus happens during the remodeling which in some way affects the process. So maybe some really high positive stimulus in the beginning can start a process and direction of change which does not influenced too much with ongoing stimulus, because somehow the start is more heavily weighted? Somehow? Or maybe the direction is determined the beginning, so if it starts to the correct direction then even negative input result only just in less change (but still in positive direction). And if in the beginning the direction is bad then even the most high quality positive stimulus can only result in not much worsing. I’m not sure, I just really guessing here.

But it’s pretty sure that this stimulus - axial length thing is not straightforward and not direct. And there is definitely no connection between the amount of stimulus with the speed of the improvement.


I always go on about people into sports improving faster or at least, more reliably.

This is a good example:


Maybe the stress of keeping track and measuring and trying to theorize has you over thinking things. And your mind can’t let improvements happen because it doesn’t understand the data.

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To me your theory makes sense. Of course, we can’t prove anything, but it is a possible explanation.

Another thing I can think of is the fact that the eye elongates partly to deal with the stress put on it by close-up, right? So it’s stressed and gets longer to “relax” a bit that way. Maybe due to all the good habits (AF etc) your eyes are a bit stressed and react in the same good ol’ way they’re used to - elongate to release stress. However, now instead of relief, there’s more (positive) stress, so the eyes/brain/whatever realizes that’s not the way to go and goes in the other direction.

To me that would also make sense, but it depends on how quickly all of this happens and also how quickly the eye can adapt. Maybe any form of elongation is purely temporary to test the waters, so to speak, more a small stretching of the eye or something and not a real change/elongation, and when it seems to help with relaxing (and/or we get stronger glasses) it stays like that/elongates for real. When it doesn’t (lots of distance vision, AF, etc) it tries the other way around. Of course, this assumes that the shape of the eye can slightly change temporarily within a few weeks without much trouble.

I do wish we had more science around this, it’s really interesting.

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On a cycling tour, are you looking out in the distance as you ride or paying attention to the road directly in front to avoid oncoming potholes?

Recently I began resistance training after a ~10-year hiatus – I train intensively to failure once every 4-7 days. Qualitatively, my vision appears to deteriorate for 2-4 days following training, and after that it appears much better than it was pre-training.

I have only recently noticed this and haven’t done any measurements to confirm, but perhaps this would conform to a 1-step back 2-steps forward hypothesis.


When I was cycling I probably spent much of my time looking just ahead of the front tire. Especially on a climb or when really pushing myself. Now downhill sections or just joy rides would be more distance vision.

I’m trying to take that same step. My 17 year old son is now officially stronger than I am. He’s lifted consistently the last couple years. Oh to be young again.


Very mixed. Sometimes I go through forests, then of course I’m looking down ahead most of the time, but often I’m just leasurely going down a cycleway, then I’m looking at the distance a lot.

My eyes seem to have much more difficulty focusing as everything is moving and there’s not much time to fixate each object I’m looking at. This could be a problem for stimulus? The two long tours across foreign countries in 2018 and 2019 seemed to have a positive effect (after some lag), but during these, there were so many other distance activities that it’s hard to tell whether the actual cycling was the stimulus or maybe something else entirely.

Mini Update

The left eye’s averages have continued to worsen, though at a slower rate, while the right eye’s have not. Huh? :thinking:

No graph for now since I seem to be having noise issues and this “result” could be random. There should be better data in about two weeks.

Compared to the last ~20 months I have detailed measurements for, my left eye’s current behavior is abnormal. I’d really like to know how I caused this. Currently trying to keep conditions as constant as possible. The decrease in daylight is making this more difficult, but if I shift my sleep time back at just the same rate… :nerd_face: :sweat_smile: