An illusion in detail uses your eyes to get into your mind. Depending on the illusion, you might have different reactions. For example, if you watch a lot of tv, you might start seeing the characters you've seen a lot.
The way it travels through you eye is through retina colour palate. Since they're tainted lenses, they're clear enough for an image to travel back and forth between your brain and your mind
Illusions can also effect our dreams and nightmares. If we see an image enough to create illusions then we can in the dream world. We do have eyes in our dreams right? In our dreams we might see actions,images or even characters