[delecti]

At least if wikipedia's summary is to be believed, that's one of the less supported of many potential theories. https://en.wikipedia.org/wiki/Myopia#Environmental_factors

Their summary seems to suggest that the biggest factor is exposure to daylight. So then even reading outside ought theoretically protect against nearsightedness.

[sumy23]

> People, and children especially, who spend more time doing physical exercise and outdoor play have lower rates of myopia,[30][29][31][32][33] suggesting the increased magnitude and complexity of the visual stimuli encountered during these types of activities decrease myopic progression. There is preliminary evidence that the protective effect of outdoor activities on the development of myopia is due, at least in part, to the effect of long hours of exposure to daylight on the production and the release of retinal dopamine.

That sounds like a fair bit of support to me.

[delecti]

> The near work hypothesis, also referred to as the "use-abuse theory" states that spending time involved in near work strains the intraocular and extraocular muscles. Some studies support the hypothesis, while other studies do not.[3] While an association is present, it is not clearly causal.[3]

This is what I meant. The GP comment included "and thereby not focusing their eyes over longer distances", which I interpreted to be in contrast to spending time indoors and looking at things close to you. So it's not that things far from you are protective, but specifically variety seems to be. So I think we mostly agree.

[JumpCrisscross]

Can’t find it now, but there is also a comparative development study showing myopia and indoor electrification setting in together in different countries. Though that paper speculated blue light content, with a developing eye hard coded to “tune” its length on the assumption of sunlight.