SOS - Boyfriend Has Headaches

Sorry if this is the wrong flair, I didn't see 'help' there.

So, my boyfriend and I used to play WoW constantly for about a year in our teens, back when Legion was still around. However, eventually he began getting bad headaches from looking at the game. He's able to play other games all day fine, including the other MMO Final Fantasy XIV, Overwatch anything that's not about to be stated. He's told me before the headaches also happen in games like Guild Wars 2 to a much lesser degree, and very rarely Smite and Smite 2. We've been together ten years, I know for a fact it's not a case of whether he wants to play or not; we've always loved playing together, and it sucks that we can't get in because the headaches it gives him.

We've tried...

1. Adjusting screen distance from face
2. Adjusting the screen in general
3. Blue light filter
4. Darkening the screen
5. Changing pretty much all the settings in the settings tab
6. Shifting hotbars so they're higher on the screen so he doesn't constantly look down at them
7. Drinking more water
8. He's updated his graphics drivers several times since Legion to be sure, and has switched PCs since then. The issues have been happening before then.

Is there anything you guys can think of that we should try? Addons, screen effects, anything? The next step for us as it would seem is just playing a period of time for like a week and seeing if he gets used to it, and the last thing either of us want is for him to hurt through any amount of time just to play the game; we really wanna play together but after so many attempts, it seems pointless.

Could what version of DirectX he has it on do something? Would playing it in a smaller window be a thing he could do? He could have done both of those, but I wanna gather a list of things we can try before this.

For the record, I'm gonna make him stop if he gets REALLY hurt at any point. I love WoW, but I love my boyfriend more than any game or anything money can buy. We've been together ten years, and been best friends since 2014.

I used a burner account because I promised him anonymity with this post.

Edit: Sorry for the late updates, Valentine's and all (we had a great one).

I've noticed a lot of people saying to have him checked by a doctor for Astigmatism. I've tried convincing him to go get checked out, but he had his eyes checked three years ago and refuses to get checked out again. This issue has been going on longer than three years, but didn't happen when we played back during Legion, so it started sometime between then. Unfortunately, I can't really force him to get himself checked out, so WoW will probably just be a no-go until something else comes up that makes him get checked.