Recently, while listening to episode 273 (I think) of The Talk Show podcast, John spoke about having eye problems and that he had switched to full time dark mode and moved the text size slider one notch up on his iPhone. As I am always happy to try new things, I thought I'd give it a go and I have to say that I love it.
If you are not sure of the process I have some screen shots below of the process, first switching to full time dark mode (iOS 13 required).
The next is increasing the text size, which could be increased more if you like.
I also added the text size quick adjust to the Control Centre screen just incase I want to switch back.
Lastly, as an added bonus, another trick I employed last year was turning off Night Shift, which reduces the blue light at certain times of the day. I am now just using the True Tone feature that newer Apple devices have. This allows the screen to adjust colour temperature to match the surrounding environments. This means that at night when I'm using on my "yellow" bedside light the screen also adjust. I highly recommend this change too.