[zwarag]

What works quite well for me is to just take breaks. (I have +7 diopters with astigmatism and all the packages)

On MacOS there is an app called "Time Out" that dims the screen every 20 minutes for 20 seconds. It forces you to just relax for 20 seconds (you can set it up as you like). In the meanwhile you can either look at something that is far away (several meters or a good reason to learn metric), or just close your eyes and lean back.

There might be other Apps for other OSes but if you're into Arduino you can just smack a LED on the board and let it light up every 20 Minutes for ~20 seconds to have a reminder.

Additionally, I take a break every 4 hrs for at lest 20 minutes and go for a walk in the park, cook something, cuddle the cat or whatever.

[tpoacher]

Effectively this sounds like a somewhat stricter version of the pomodoro system, which prescribes a 5-minute "physical" break for every 25 minutes of uninterrupted focus.