This all comes down my 20-20-20-20 rule.
The best advise for gamers is that a visual break should be taken every 20 minutes and involves looking at something 20 feet away from the device for 20 seconds and at the same time blinking 20 times ie 1 blink per second.
Fresh air is good too every 40 minutes or so and so a good walk also helps you to stretch out your neck and back which can contribute to eyestrain issues also.
Try it out, it really helps. If you have tried this and you feel you are still having eye problems you need to book now for an appointment for an eye examination.