You can get apps which tell you once an hour (think you can change the interval) to do some sort of stretch - gives you a different one each time.
Ideally, you should have 5 minutes screen break each hour; that doesn't mean not working, but could be a meeting or a phone call where you make notes in a pad of paper. Or it could be a loo break or walking to get a coffee. (I do not necessarily practise what I preach here...)
It's also good to change your focal length for a bit, so if you are in sight of a window that you can look out of, do so, especially if you can see some distance, or to the far end of the office or something.
You should be able to claim back the costs of your sight test from your employer, if you’re a use of display screen equipment. If you need corrective glasses because of your DSE use, you can also claim back some costs of that (but not if you just happen to be short-sighted, or need reading glasses because of your age.)
I also recommend getting a workplace assessment, to make sure your desk and so on is set up in the best way to minimise physical problems. If you need any corrective equipment (e.g. footstool, wrist pad, screen shield,) your employer should provide that.
I spend many hours a day staring at screens, and before that, I spent many hours a day reading books. I guess it depends what you're used to.