My screens are both Samsung T260 1920x1200, 25.5", which gives .286 dot pitch.
I'm running them at 120dpi instead of 96 dpi, which scales things up by 25%. That is simply nowhere near enough. Until tonight, I was zooming in web pages at ~150%. Now I'm trying 200%, which given the 25% boost from the higher DPI, really translates into someone viewing at 96DPI at 250% ... it seems to help ...
I was already using an 18 point monospace font for coding - I've just bumped it up to 24 point ... but that's like using a 30pt font on a 96dpi rendering ... it's HUGE. BUT I can read it with noticeably less strain, so here's hoping ...
Your strategy seems to be to make things larger, as if you were trying to cope with a minification (as in optics, not programming) problem. Have you experimented with radical adjustments to the distance of the object your eyes are focusing on? Relaxed the human eye focus is at infinity; think scanning the horizon for threats, with occasional refocusing on a near object before going back to scanning for stuff moving in the distance. Focusing on something a meter away all day long for years on end isn't what the eye does gracefully.
trying 200%, which given the 25% boost from the higher DPI, really translates into someone viewing at 96DPI at 250% ... it seems to help ...
I didn't have your condition (in my case just plain old "eye fatigue"), but realizing focal length was the root cause and adjusting for it led to a dramatic improvement after years of experimenting with image scaling in exactly the same way you are. Image scaling helped with the symptoms (I could see what was happening easier) without any effect on the root cause.. In my case the difference was immediate and dramatic enough to notice after a weekend of playing games on a friends projector, leading to my adjusting my work environment for longer focal distances, so perhaps you could find out if focal length is or is not a factor in your condition just as quickly if you haven't already.