I developed severe eye strain problems more than 10 years ago. Didn't have any issues before that, besides having myopia. I assume at the same time I developed an autoimmune disease which attacks my thyroid. It may effect eyes and other parts of the body. I developed dry eyes, floaters, light sensitivity, eye strain. I also have muscle discomfort and pain, which may also be related to eye muscle spasms. I had some success in improving my condition but it became worse again during the COVID pandemic. Spending too much time in isolation and staring at my computer for too long.
My symptoms started when I was working late nights, didn't get enough sleep, had a lot of stress and was staring at an LCD monitor non stop.
Things that helped me:
Makings sure that the humidity level is above 50%. Running a humidifier at night during the winter.
Following 20 20 20 rule while working on a computer.
Avoiding staring my smartphone as much as I can, only use it for sending messages and listening to podcasts/audiobooks.
Spending as much time as I can outside, rather than staring at screens.