Alice in Wonderland syndrome is a neurological condition that affects perception where objects appear smaller, larger, closer, or farther away than they actually are. However, the patient remains lucid and can easily distinguish real objects from imagined ones, even when the patient is also hallucinating. It's usually temporary and can be caused by migraines, brain tumors, or hallucinogenic drugs. It's fairly common during childhood, and can often appear spontaneously at the onset of sleep. It becomes much rarer in people over the age of 30.
It can commonly appear with other perceptual difficulties, such as a slowing or speeding up of time, altered sense of touch, or more alarmingly to most patients, an altered sense of body image.
The exact mechanism of the condition isn't well understood. However, during perceptual difficulties, it's clear that the eyes themselves aren't involved and operate normally.