I do something that requires less mental focus. Music, chorus, exercise, or TV.
I have astigmatism, which requires glasses. Sometimes I read without glasses. That could be it.
Audio books aren’t a good example because I have hearing loss, and can’t focus on audio books for that reason.
I’ve had it, too. I’m the type of reader who reads everything all the way through. So, if a book is fairly long, I can wind up reading for 8-10 hours at a time. I deal with it by taking a nap for an hour or two.
It doesn’t feel like eyestrain, but I think that at least plays a part. It’s just so weird that eyestrain can cause foggy thinking. Maybe it’s because you have to use more mental energy to see. Or maybe it’s a coincidence, and your brain and eyes are just getting tired at the same time.
I do know that eyestrain was not the only problem back when I was detoxing from benzos. The reason I say this is that I would feel it at other times, too, even after just thinking with my eyes closed. The only way I can describe it is that I think it must be what people feel when they say they are thinking so hard it hurts. That was something I’d never experienced, and, like nearly everything else, was quite frightening.