I used to skip eye breaks until a blurry sight picture scared me straight
I thought taking regular breaks to rest my eyes was just for office workers, not for focusing on tiny parts like sear springs. After a long session, my vision got fuzzy and I almost misaligned a front sight. Now I set a timer for 20 minutes of work, then look at something far away for two minutes. It's made a huge difference in my precision and I don't get headaches anymore.
I saw a UC Berkeley article on eye strain from close-up tasks. It said looking far away gives your eye muscles a break, which explains why your timer helps. Glad you found something that works before making a big mistake.
Seriously? Every little thing becomes a health crisis now. Appreciate the backup @parker252, but maybe we can relax a bit before calling eye strain a near-miss disaster.