AGI My thinking is the effect is more than just the eyes, the brain is also interpreting these flashes and constant focus adjustments, and it works similar to a localized seizure. I made a post about this but I don't think many people agree. They feel pain in their eyes so they figure it is a an eye problem. But like you suggested, the fact that it happens instantly means there is more to it. I wold like to add that this doesn't mean people here have epilepsy, but the mechanism is similar. Rapid patterns interpreted by the brain can cause an overload.
From listening to others, most people didn't start with instant eye pain and severe symptoms. They usually got the eyestrain and dry eyes which they tolerated, but over time they became super sensitive like you mentioned. I believe this super sensitive reaction that occurs is the body's aversion to the light source. The same way that if you eat something and get sick from it, even just an image or smell of that food in the future can cause a strong queasy feeling. Same with people who drink too much of a certain type of alcohol and get sick. Simply the smell of that alcohol again can trigger sick feelings. This is a documented reaction of the body to stimuli or other things that are harmful.
These displays can be toxic to people's brains, and after a while the brain becomes averse to even a few seconds of exposure and tries to send you signals to avoid it the same it makes you feel sick if you smell an alcohol or food that just got you sick.
Now if you take a break you will return to normal but in my experience it takes a few months of no use or limited use of screens. This is another reason I am positive the real effect is on the brain, brain changes can take months to return to normal. Eye muscles will recover in a few days after over-use.
Like I said, I think people are too obsessed with this being an eye issue because that's where they are feeling the symptoms at first, but the eyes don't do anything or process anything, the brain does. That's also why people report feeling "off" after just a few minutes of using the screen or having unrelated cognitive symptoms.
I would say though if you are having those strong symptoms, you have to take some time off of screens if at all possible, or limit the use as much as you can. You will notice your symptoms start to drop off. But I understand that can be hard if your work involves a lot of screen time.
That's one of the reason I suggested people get an epilepsy test if they have the means and time to do it and are having very bad symptoms and sensitivity to other light. You will sometimes test positive, and if you do you may be able to take some time off work either via medical leave or get on some sort of compensation for medical reasons. This is only for people having severe symptoms though, if someone is just having dry eyes I would not bother with this test.
Anyway, hope you find some solutions and I'll post whatever I can find out testing different setups.