How is it possible that some ecstasy users see bar tables?

A side effect of MDMA, the active ingredient in ecstasy, is that your vision isn’t as good as it normally is. For example, you can’t focus as well because your eyes move quickly back and forth. Your brain likes to understand things. So it will then fill in things so that you can see things that are not there (hallucinate). People see bar tables for example, or fences or sunglasses. If you take a high dose, you will get hallucinations faster.