I’m reading a bunch of Ophthalmology and Vision Therapy texts right now. One recurring theme (especially in vision therapy) is that you can train up all of these different visual systems to get them working properly, just like you can train your muscles in the gym.
Nowadays people spend a lot of time indoors and on screens and in “crappy indoor lighting”. So your pupils over time get stuck with a limited range of motion in where they’ve adjusted to your screen brightness and the indoor lights, and most people never really get out and walk around for a couple of hours in just the moonlight or starlight. Here in New York City it never really gets completely dark because there are streetlights on every corner, lighted signs, etc. So as a city kid you’re pretty much always in “medium brightness”.
If you lived a more primitive life somewhere you’d get lots of bright sunlight during the day, and lots of darkness at night, and your pupils would go through their whole range of motion from very-low-light conditions to bright sunshine.
I’m a big fan of sunglasses, as a practical matter I’d just use them especially in Australia (aren’t you guys right under a giant hole in the ozone layer?) But if you wanted to get better with your naked eyes under the bright sun you could ease into it, maybe practice without sunglasses for a minute or two each day, and gradually ease into it.
In harsh outdoor sunlight your pupils have to contract all the way and stay there, which is probably hard to do if you’re not used to it or haven’t done it often. The farmer does it all the time. I would guess that he’s likely to get cataracts when he gets old though.