First caveat is that I’m new here. Have been reading stuff over on the wiki rather than here. (Kind of testing its role as the intro to all this stuff.) Apologies if it has been discussed here many times already, but a quick search found one mention - https://community.endmyopia.org/t/brith-text-on-dark-background-inhibits-myopia/2354/5 - perhaps it didn’t get much discussion there because it drifted onto it from the original topic.
The wiki says several times that hyperopic defocus causes myopia. Which seems fair. There’s plenty of animal studies cited (though I’ve not read them). With animal studies, you can put as strong a lens as you like on the eye, and there’s not a lot they can about it.
The wiki rather implies that it is the cause of myopia. A subtle difference, perhaps, but it’s confusing me. Actually, doesn’t just imply it. eg at https://wiki.endmyopia.org/wiki/Differentials#Why_are_differentials_worn.3F it is definitely saying it is the cause.
First, I should make sure I understand the term: it is seeing a blurred image because the light is focused behind the retina. Now, is this properly blurred, like you’d have with myopic defocus due to uncorrected myopia. Or just a tiny bit out of focus - similar to the point you’re aiming for with active focus. Such as depicted at the bottom of https://endmyopia.org/focal-calculator/calc.html ?
If (or rather, when) I’m wearing glasses and and can’t quite see something clearly up close, I take my glasses off. I don’t sit there with sustained blur doing nothing about it. (I suppose if I wore contacts that might be slightly harder.) Prior to covid, I’d meet friends to play boardgames, wearing (what I’m calling) normalised, but if I have to try to read tiny print on cards, I have to take my glasses off to help my poor probably-presbyopic eyes.
Otherwise, accommodation automatically deals with the hyperopic blur - it’s the whole reason the lens is there, to increase the overall focusing power of the eye when objects get closer.
So if we are talking about just a tiny bit of blur (because the feedback is imprecise or the ciliarly muscle is lazy and so the accommodation doesn’t go quite far enough to completely resolve the blur, and it basically acts like active focus in reverse and acts as a stimulus to elongate the eye. That makes sense.
The wiki (and the thread mentioned above) does touch on an alternative hypothesis :
" Even if hyperopic blur is not induced by the lenses, the accommodation system is being constantly stressed and this encourages eye axial lengthening"
To me, that sounds pretty plausible as the stimulus which could lead to induced myopia.
Am I missing something ?