Micropsia is a condition affecting human visual perception in which objects are perceived to be smaller than they actually are. Micropsia can be caused by optical factors (such as wearing glasses), by distortion of images in the eye (such as optically, via swelling of the cornea or from changes in the shape of the retina such as from retinal edema, macular degeneration, or central serous chorioretinopathy, by changes in the brain (such as from traumatic brain injury, epilepsy, migraines, prescription drugs, and illicit drugs), and from psychological factors.

Dissociative phenomena are linked with micropsia, which may be the result of brain lateralization disturbance. Micropsia is also commonly reported when the eyes are fixating at (convergence), or focussing at (accommodation), a distance other than that of the object in accord with Emmert's law. Specific types of micropsia include hemimicropsia, a form of micropsia that is localized to one hemisphere of the brain and can be caused by brain lesions. Related visual distortion conditions include macropsia, a less common condition with the reverse effect, and Alice in Wonderland Syndrome, a condition that has symptoms that can include both micropsia and macropsia.