In most cases, pupils change size based on the light and dilate, meaning that appear larger, when you're in a darker room. But your pupils may also change size based on injuries, drug use ...

Larsen, MDMedically reviewed by Christine L. Larsen, MD If you have your pupils dilated for an eye exam, they may stay ...

Pupils usually dilate in a dark environment to help the eye take in more light. But with this illusion, there is "no reason" for the eye to change shape, "because nothing is changing in the world ...