Adjust the brightness down, don't use your iPad in a dark room. Take breaks from your game every so often. Even every few minutes or between each round close your eyes for a little bit, or/and shift your focus across the room. Your focus is controlled by tiny muscles. Imagine with the rest of your body, holding one body part in position for a long period of time strains the muscle, well shifting the focus of your eyes helps with that.
There are plenty of simple artifiial tears. I'm not sure if I'd recommend blink simply because last time I looked at a bottle it was made in china and I have an intrinsic dislike of things made in China, but that may have changed. Regardless, artificial tears can help, resting your eyes, taking breaks, holding the iPad at different distanes from your face, they can all help.