While it’s rare to be diagnosed with the condition—fewer than 200 clinical cases have been officially reported since 1955, mainly in children, and it doesn’t appear in any mainstream diagnostic handbooks—Alice-like symptoms appear to be relatively common. One survey study published in 1999 found that some 30 percent of participants had experienced at least one kind of visual distortion in their life. And around 16 percent of migraine patients in a recent study also reported symptoms of Alice in Wonderland syndrome throughout their life. Some researchers have theorized that Carroll experienced these symptoms himself because he was known to experience migraines.