Try to take frequent breaks, as regularly as possible. Mark from HR can’t be around for your regular kitchen chats at the office, but that doesn’t mean you can’t stretch your legs, rest your eyes and check out what’s happening outside throughout the day.
But if you can only remember one rule, let it be the 20-20-20 rule: every 20 minutes look away from the screen for 20 seconds, at something that’s 20 feet away. That way, you’re giving your eyes the regular breaks they need.