Why do so many optical illusions not work for me?

[asdf]

is there something wrong with me? do they just not work on some people? I've been looking at a lot of them lately and out of a batch of, ie, 10, only 2 or 3 work on me? :/
i have meniere's disease, i don't know if that affects anything visual?
"If they are "illusions", how do you KNOW they aren't working?"

because underneath each picture there is a caption explaining what they are supposed to do