Longer wavelengths pass through human body have systemic impact improves vision (nature.com)

Yet again we're back to balancing vitamin D and effects like these on vision, against skin cancer and cataract risk.

The theory re: myopia was that spending time indoors weakened the eye muscles because the eye didn't focus far and near.

Maybe it's due to the lack of these particular wavelengths.

As a teenager I had a small book "Better Eyesight Without Glasses" by Bates. It had a number of exercises two of which I recall were: palming your hands over your eyes, and facing the sun with eyes closed while moving your eyes around 'looking' about all with eyes closed. Each of these were to be done for a number of minutes.

I had good eyesight at the time so never knew how effective the exercises were but I always felt better after doing them.