This forum seems great so thought I would post my findings over the last few years. I have been in "IT" as a dev, graphics designer and solution architect for 28 years now and have started to feel the burn 🙂 .... I get blurred vision now whereas five years ago I never did. Mostly, for me at least, I have a few triggers. So I break it down in two forms, phenomena and triggers, so to make it obvious to myself. My triggers, the causes, are closeness, I cannot use tablets and phones much, real life brightness contrast, so night time is worse for me, and flickering I am also sensitive to. I have more triggers but they are not the main ones. Like tiredness effects me but not so much. Then my phenomena is really a singular form, blurred vision or "digital blindness". So my visions gets to a point where I cannot read text. I dont get headaches much, migraines maybe once a year, but I really have to push myself, by using monitors for 18 hours a day for a week before I see any other phenomena.
So i thought I would explain what I see as potentials triggers from my research that it might help someone else figure out what their triggers are and thus find their solutions easier.

As humans we love to make things into "if and then" algorithms with singular instances of cause. We cannot quite cope with more then a few integers in any given equation. A bit like the big bang theory, now they have found a start older than the universe, it is all a bit stressful for them, all due to fixation on single integer math. So consider you might have 2-20 triggers. It is always better to test each potential trigger to see its effect and not stop once you think you have it. It seems most of us have 3-7 triggers for eye strain or digital blindness. A few things though .... 1. I have yet to see long term effects on computer monitors no radiation is not a factor although children do damage if on close screens too much it seems ..... 2. I am not your eye doctor I am just giving you my present best list of what I have found to help me with the problem.

So here my list of potential triggers. I really hope this helps you as much as it did me as I know the awful feeling of not being able to enjoy or work. You have my empathy in all cases.

Distance to screen - this seems to a very common trigger, with it seems, 40% of people being effected by this. It is best seen when using your phone for longer periods over 1 hour and reading content. Video is not so bad as our eyes move in a more erratic motion and focus differently. Note when you put down your device or leave your computer it is a good idea to massage the eyes and do some exercises. Blood flow and muscle strength seem to make a real positive difference.
PWM vs DC - This is another common one, especially on dimming screens, and most of us know the PWM issue. Non pwm screens are a really good idea generally as that type of flickering can actually change mental state and make you nervous potentially.
Brightness of screen - This is also a major one, even during the day, it is a good idea to turn down you brightness, direct proton flows at ones eyes can be a trigger. I had an old admin who could touch type like you never saw and her glasses were around an inch thick. Whether relative or not try not to stare at your screen constantly.
Dry eyes - this is also a major trigger it seems with people when they have been cycling or doing something that dries the eyes it can make things worse, although closing you eyes for 20-30 seconds usually remedies this for most. But those with chronic dry eyes can see more strain.
Eye sight - This seems to be a factor but actually a minor one so far as I can see. Those with 20 20 also get eye strain, and age seems to be more of a factor. And although I am not a nutritionist it seems have a partial or full raw diet for a few months, with eye & normal fitness exercising, seems to help people with bad eye sight with dramatic effects.
GPU drivers - This is a very general term due to different video rendering techniques that are beyond the specifics added here such as dithering. AMD recent drivers seem to be much better than Nvidia, but older drivers, 370 and earlier, Nvidia seems to be better. This would be different per person in some respects, with some generalisations as well. But it seems 3090. 3080, 2080 ti drivers can be triggers for some. Analysing what actually causes this is beyond me at present as it seems not to help whatever you do. I am not red or blue here, but I have noticed AMD are quite a bit better recent from Vega to 6000 series in most aspects for eye strain.
Fidelity - this works in two aspects. Again I prefer AMD here by a long shot, over the 6 or so years Nvidia have focused on FPS whereas the engineers in ATI seem to have focused on constant stable fidelity. YOu see this in a lot of technical reviews of course, but in this relativity, it helps with some with eye strain, the better the fidelity the less strain. However, the second part of this is strange, actual monitor fidelity is like riding a drunk donkey with a bot fly. It seems to effect almost everyone but completely differently. Some do well on 5k non-mat screens and some one 1080i only. I would say 1080p is better, generally for people, thn 1080i, but actually screen resolution is peculiar, but definitely a trigger. And as an addition here, and should not need to be said, dont be vain and put your fonts too small. This is also relative to fidelity as you cannot see 6pt. 🙂 But yes keep your font size reasonable with a nice font.
Font smoothing - again a weird trigger, you can disable this in Linux and Mac OS, not sure about windows (if it actually does disable) but this is really person dependent but worth testing.
Anti-aliasing - this seems to be quite common, including with DLSS (AMD too), and is a trigger for almost 30% of people. Remember this percentages are just my estimates from what I have read, seen, personal experience, but that is limited. You may find other results.
Polarisation & reflect natures - Polarising light sources and reflections in general seem to be a general trigger too effecting over 60% of people especially at night. Having two monitors, one glossy, if you really need, and the other matt seems to work a bit better and mitigates strain somewhat. Also having dark backgrounds, behind where you sit, in a well lit room helps a lot. Try not to sit with white walls behind you.
Sleepy face - Sleep and tiredness are a major factor as well. Bad sleep cycles and being tired form exercising or driving long distances trigger most of us. It is actually pretty high. This bleeds into the theory is is blood and muscle driven and that exercising and increasing metabolism helps drastically with digital eye stress and strain.
Stress - such as deadlines and panic doesn't just drop the IQ of an individual but also the eye sight apparently and has a direct relation to strain to a high percentage of us. Ever tried to take an IQ test right next to someone you hate? Seems you can drop 10-30 points! Same with an eye test .. so I would make sure when you go to the eye doctor you go with someone nice! 🙂
Blue light - most of you will know this one and it speaks for itself .... but I would add the frequency of the blue light matters a lot. It is not all blue light that is bad, only the top band, so consider this when testing for triggers.
V & H Flickering - Again a well known one, but note that are two axis, and people tend to only test one. Vertical and horizontal flickering should be avoided wherever possible as these seem to create strain under long term conditions.
Monitor contrast - something that gets ignored a lot but should be checked. Leave you contrast high and low over a few days to check if it effects. As with all testing you should find the perfect scenario, and then work backwards, so find something that feels really nice to work on and then start adding triggers.
Real life brightness contrast - so yes this is the night time or basement effect, bright screen relative to the environment around it, and effects over 80% of people given enough time I would say. Try and match blue light and brightness settings to your environment if possible. Turn down that brightness. Note that some monitors, screens and phones get more or start flickering if their brightness or contrast is changed from max or default.
Short note is not to worry too much as if you can watch TV all night you are going to be fine. There are scenarios where digital strain does not effect you. Hope that helps and makes you feel better. You just have to try and mimic that in your monitor or phone environment.
Frequency - Now this was one of the most interesting ones! It seems 60, 120, 180, 240 hz seems to be the best, less triggering, and I am not sure why. Many have discussed his is due to natural frequency rates, but I have found they are off digit, meaning 59.78, or 59.98, but then who knows what the actual final frequency is. But yes I would test to see if 60 hz or 120 hz feels better than other frequencies and you might be pleasantly surprised.
Flow consistency - now this is the hardest to explain without getting technical. I have tried to keep the language as simple as possible in this post but yeah constant flows is harder to explain. Best way to consider it is a sin wave. Like FPS, how consistent is it actually, does it stay at 120 hz all the time or is it fluctuating. Game devs do put this into their games, and there are settings to fix a refresh rate (one example), but this seems to be pretty important to most. Why many can game on a monitor for days and yet cannot read for more than 20 mins. Pulse rates, and scary monitor tech, all have frequency rates and keep them as close together as possible helps hugely. I am sorry I cannot define this better but at present this is really trial and error 70% of the time. But any kind of fluctuation seems bad if you are sensitive to it.
And finally dithering - switch it off wherever possible. It is the bane of the seeing world and poorly developed and implemented without any seemingly consideration for effects. You can add items like motion blur and other settings of the like to this as well, but dithering seems to be the worse.

Ok done. 20! 🙂 That turned out well.
I hope this helped. If you see I missed one let everyone know in the comments.
Again there are loads of solutions out there, test the above, test monitors before purchase, check drivers, use screen protectors with blue light reductions, etc ... three are always solutions so dont dismay. Just find your triggers and then you have your solutions.