Its typically believed that glasses were invented in the late 13th century; what was it like for people who needed them before they were invented? Were people just walking around blind? What was it like for the ancient Egyptian or even the ancient Roman empires?

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I have a completely unresearched and without any proof whatsoever theory.

Then we ask that you refrain from writing, thank you.

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It's hard not to come off as snarky on the internet, so I want to try to convince anyone I am not attempting to have any kind of sass in my response below (well, a little bit, but directed at those researchers, not op), just an assessment of eg the sources you provided. This is a little critical of reliance on fields where we can only hope the practitioners can be trusted. We all have to do that, but it doesn't always work. I'm coming from a position of the epistemology of scientific thought, how it's used, and how it's abused, and the downstream effects of this process - ie, working its way into commonplaces that other disciplines eventually feel confident taking as prima facie grounds to base their work on. University PR and gatekeeping, scholars that must publish or perish, the issues surrounding p and significance, filtering journals like Nature cause a lot of problems. In short, there may be more myopia prevalence now than in any given historical period, but that would be outside the area of expertise of the authors of these studies, and well outside the purview of the studies themselves, which are certainly flawed, but also attempt to claim more than they responsibly should, in an ideal world.

Taking the blog from Nature, for example, it isn't until well into the article that the authors start considering the counter-argument, that self-reported quantitative measures are not particularly reliable. I am particularly convinced more by the distance factor rather than light, and the advocate has just as much ethos as the study authors, but of course, the article is about those authors - that's how Nature works. The Nature authors completely abandon the possibility, and all discussion, in the next paragraph, and instead focus on animal studies of birds to double down on the assumption of the article itself. This is... not a good practice. Unfortunately, the research they cite is insufficient to 'prove' what the article suggests is being proven. There are enough problems with the study that if the null hypothesis had been replaced with "there is a gene that doesn't give you myopia if there's bright light," then they would have found in support of that hypothesis. Obviously, this is where the article starts from, in its historical survey. It could just as easily be a circular argument, its thesis lacks coherence.

On to the metastudy: Probably the first most damning part of the metastudy is the fact that they have 6 research questions, each one posed to answer a question that assumes the other research questions are to some extent already valid. Now, even though I am anonymous here, so I won't outright dismiss it, I will say that there are a lot of red flags one should look for in meta studies - their data charts and methods are, if anything, "hardened" against review. But saying that there are red flags doesn't mean that they are trying to obscure results, just that someone attempting to obscure results would do what they did, mixing methodologies, age groups, cohorts, interventions, styles, time periods, criteria, etc. across a vast cultural spectrum of optometric practices and criteria, and then applying transformations, multiplying statistical results by various factors without explanation.

Also, all the intervention studies in the metastudy were of Chinese students. There are features of this fact which are concerning for combining into the results of non-intervention studies of other groups. Also notable is that for these studies, the results were solely derived from surveys of the parents. Combined with the heavy promotion of an agenda later in section 4, we see again how there are so many publications with such low standards for reviewers that virtually any bias is allowed in if it is couched in somewhat vague terms, although here we do see straight advocacy without concession, very strange.

I wrote a ton more, but deleted it, because it can mostly be summed up by saying that excel will draw a regression line for any set of data points; it doesn't warn you when your data are bad, or stupid. For illustration any single paragraph from section 3 or 4 could be effectively analyzed in a methods class - or, hell, maybe even an ethics class, although it is certainly not abnormal across publications in general. Not because it's necessarily wrong, but one has to ask why all the obscure transformations, why all the manipulation of results.

The real problem, however, is explicitly this - however true it may be that myopia levels in East Asia have risen in the last 50 years and can be mitigated by additional sunlight hours (as reported by parents), this doesn't tell us anything fully productive about myopia incidence in medieval Europe 500-1000 years ago. There is simply too much noise between here and there to connect current research, in the current world, to such a distant point, and to assume these trends hold and have held true. I'm not saying I doubt the assertion, again; and it makes logical sense? That if these researchers are correct, then perhaps if a lot of time was spent medievally outdoors, then maybe the incidence was lower? But surely we must admit two things: a) a lot of things are different between our modern world and the medieval one - food, air, lifestyle, genes, parasite load, exposure to pathogens, exposure to specific pathogens - so that what is true of modernity might not therefore, and probably cannot be, true of such an earlier period, or if it is, it may not be for the same reasons, and b) that the measures and criteria of seeing-ness are very different in these two periods, namely, that tests of the type we now administer, and what we consider normal, would have been very different in an age that was very much pre-literate and pre-scientific (and I do mean pre-literate for everyone, in the larger sense of literacy as a community practice, where what you could read was mediated differently than it is now; thus, including even literate, well-read scholars in this batch, who would be considered not visually unimpaired in modernity, simply because the aids they had were different than the system now - I am trying really hard not to digress about Heath and literacy events and communities of practice and the layers of changing modes in the media of visual literacy between now and then). We learn to read academically, and these researchers know where people read, and so that is where they distorted things, where they knew they would attract non-specialists in meta-analysis.

tl;dr - you could easily be right, but those sources suck (their fault, fully, they should have done better), since your argument doesn't require it, no need to mention it when it's so obviously something that really pops out to readers who have anterior interests. No need to drop in an assumption that you don't need to defend. And yes, this is my day job, I try to keep scientists from making claims like these in their work, but they don't always listen or get it.

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