Myopic defocus in the evening is more effective at inhibiting eye growth


Study Pontification Time! Myopic defocus in the evening is more effective at inhibiting eye growth than defocus in the morning: Effects on rhythms in axial length and choroid thickness in chicks.

“Animal models have shown that myopic defocus is a potent inhibitor of ocular growth: brief (1–2 h) daily periods of defocus are sufficient to counter the effects of much longer periods of hyperopic defocus, or emmetropic vision. While the variables of duration and frequency have been well-documented with regard to effect, we ask whether the efficacy of the exposures might also depend on the time of day that they are given. We also ask whether there are differential effects on the rhythms in axial length or choroidal thickness.”

All right, so this chickens and don’t count yours before they hatch, and all that.

Fascinating here at the very least is just how much research is out there, how much we already know and discover about eyesight and myopia … and how not even the top line of any of it exists anywhere in the retail optometry narrative.

(yes yes of course, we know why - patentable products, profit, quick fixes, etc etc)


Did you see the lady in the Facebook group forum whose job it is to summarize research papers and turn them into programs?

I’m interested to see what she comes back with.

I am already deep into the chicken manure. :rooster: :chicken:
Inhibiting ocular growth in growing chicks is not the same as ocular shortening in human adults. If myopic defocus had been enough, I would be emmetropic by now after living in considerable myopic defocus for 30 years. But it does seem to have inhibited additional ocular lengthening in those years.
Ocular shortening has been measured in people with increasing hyperopia, so the mechanism exists. This is probably the result of increasing use of plus lenses for distances that don’t need them (and not only age). Sounds familiar.


I guess it makes sense, in the evening the defocus would be stronger due to weaker light.


Unless you pull your book/ sewing/ screen closer to compensate… but yes, it would happen naturally, almost like nature saying, hey! time to look far away into dream oblivion, sun’s down! take a rest.
However, I think in this study they purposefully caused myopic defocus in the chick eyes, I would guess by removing or reducing minus lenses.

I think there are a lot of way our bodies respond to natural rhythms, but we have become disconnected for the sake of rapid progress and ‘freedom’ from the harsh realities of being organic bodies.

Yea. Always curious about these blips on the radar, sometimes gems come out of it.

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Evening? Low light? Certain amount of time before sleep?

Really need to differentiate those.

Other problem is: if it inhibits all eye growth, are you inhibiting shortening, too? Since shortening is a type of growth.

When I read this study abstract a while back, my takeaway was we don’t need huge amounts of hours of blur. 1-2 hrs was sufficient.

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I think this study is a red herring in our context. It applies to growing chicks, and might be interesting for trying to prevent myopia progression in young children whose eyes have not yet finished growing.
Eye studies in primates are possibly more relevant to us, and in my recent post Myopia in Man and Beast, there is an abstract of a study in which dim light (DL) was shown to increase myopia in monkeys.

Correction: I reread the abstract, and this is the conclusion
‘Thus, DL appears to reduce the efficiency of emmetropization and, in the case of lenstreated monkeys, the ability of myopic defocus to slow ocular growth. Thus, DL can increase the risk of myopia.’


I’ve got a laundry list of opinions on this one in particular. :joy:

But then … people tell me, “oh if only you had a study, people would take you seriously”. And I think of the endless research like this one just as example, where the discussion is not if stuff is possible or whether myopia is genetic - but rather several levels ahead, with intricate details of what specific aspect of stimulus may create the most opportunity for change.

Like being asked to create a wheel as proof of concept, while there’s a highway full of cars right outside.

Probably why I just keep focused on trying to maximize a reliable avenue to simply reduce one’s myopia, skipping a lot of the theorizing (and arguments in that community). Of course though, most times when running into these study scenarios, feeling highly tempted to write a slight alteration of a few of the main course sessions with tweaks, and see what people experience. :laughing:

This argument always bugs me just a bit, as much as its recurring and even obviously obvious in relevance. They use chicks for a reason (not just because exploring chicken myopia is in itself so interesting). Surprisingly similar eye biology. Very similar stimulus response. And while growth plays various roles, the stimulus at large continues to function past maturity.


Oh, I am interested in chicken myopia, but to go to the extent of turning this into guidelines for taking your glasses off in the evening rather than at other times turns it into a red herring for me (equally tasty :wink:).

Also, the chickens didn’t spend ten years in front of a screen before starting their EM journey :smile:.

I have a suspicion that the key to my stuttering improvement is among the above. That is: variation of duration, frequency, and time of day of stimuli.

At least, that would explain why I sometimes improve great despite doing considerable screen work, while at other times I struggle despite considerable outdoor time.

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Hi! So far I’m finding the fundamentals discussed here are true.

Lighting conditions and rates of change keep coming up, but data insufficient for me to question the wisdom much yet.

Change rates in baby chickens is astounding, and recovery rate is faster than progression in baby chicks.

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I always think it’s funny coming from a place where people are making a thing work–like endmyopia, whole food plant based diets, debt elimination–and there is research “pointing the way,” vaguely, somewhere over yonder, somewhere in the vicinity of the thing people are making work for vision improvement, weight and disease control, and financial success in the face of “structural flaws in today’s economy.”

It does not make the researchers look nearly as smart as they probably really are. Glacial progress is progress nonetheless.

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They’re all in their own little worlds. It take a lot of brain power to become experts in these narrow and deep fields, it takes even more brain power and imagination to become an expert in a field and then make a radical departure from it. Many of them are smarter than you and I, but have spent so much time diving deep they don’t know how to go wider any more…

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Ok, specifically about this paper:

Frist of all, I hope these researchers had assistants, 5:30 AM to 7:30 PM is a brutal work schedule.
Measurements were taken every 6 hours… And we talk about measurable change over months… 6 hours! Granted, the young are growing at a rapid rate and therefore adapt more quickly, but this could apply to humans in growth spurts.

Data for “noon” was similar to that of “evening”. The title emphasises evening, but noon might be just the same.

The chicks getting 2 hours a day plus lenses vs 22 hours a day minus lenses had the same diopter difference, but vastly different baselines. chicks are born farsighted and naturally become nearsighted with growth, so those wearing plus lenses would be slowing natural progression, while minus lenses would be accelerating it.

The link only points to the abstract. I have requested a full text copy, the authors may respond. I want to see the graphs of the daily cycles and long term changes. I want to see the method of the experiment and see if ambient lighting was controlled, if the experimental lighting used a sunrise/sunset emulation or just on/off, and the colors of the lights used. There are a lot of different variables in this experiment, were there enough chicks in each group for statistically significant results?

Also, caution should be used in applying “inhibiting eye growth” factors to “promoting eye shrinkage”. We lack the information to say if the factors inhibit change or if they favor shorter eyes.

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The abstract does not tell us if there was weaker light.

Indeed, just an assumption from my part. Evening being a factor can only make sense either if there’s weaker light or the chicken has been awake for a specific length of time. But unless they made sure to prevent chicken from napping and sleeping the whole time, I’m more incline to suspect a change of lighting.

By two weeks old, chicks do a lot less day sleeping (source, me, I’ve raised baby chickens). I suspect they had a light on a timer, but was there window exposure? Was the experimental light on a sunrise/sunset simulation or just on/off?

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I know, right?!

Interesting part is here we can easily take 10-20 people at any given time and ask them to try a variation like this for a few months (if only we could buy them all Lensmasters, too). I personally have been guilty of ignoring evenings largely (“over it” at that point with tasks and things), and one might wonder if there’s a nugget there - or otherwise variations we haven’t experimented with.

At the end of the day (figuratively speaking) I like to keep things as simple as possible. But also, ideally widely ranging effective.