Illusory palinopsia

Illusory palinopsia is a subtype of palinopsia, a visual disturbance defined as the persistence or recurrence of a visual image after the stimulus has been removed. Palinopsia is a broad term describing a heterogeneous group of symptoms, which is divided into hallucinatory palinopsia and illusory palinopsia. Illusory palinopsia is likely due to sustained awareness of a stimulus and is similar to a visual illusion: the distorted perception of a real external stimulus. Illusory palinopsia is caused by migraines, hallucinogen persisting perception disorder (HPPD), prescription drugs, and head trauma, but is also sometimes idiopathic. Illusory palinopsia consists of afterimages that are short-lived or unformed, occur at the same location in the visual field as the original stimulus, and are often exposed or exacerbated based on environmental parameters such as stimulus intensity, background contrast, fixation, and movement. Illusory palinopsia symptoms occur continuously or predictably, based on environmental conditions. The term is from Greek: palin for "again" and opsia for "seeing". Illusory palinopsia is often worse with high stimulus intensity and contrast ratio in a dark adapted state. Multiple types of illusory palinopsia often co-exist in a patient and occur with other diffuse, persistent illusory symptoms such as halos around objects, dysmetropsia (micropsia, macropsia, pelopsia, or teleopsia), Alice in Wonderland Syndrome, visual snow, and oscillopsia. Illusory palinopsia consists of the following four symptom categories. Prolonged indistinct afterimages are unformed and occur at the same location in the visual field as the original stimulus. Stimulus intensity, contrast, and fixation length affects the generation and severity of these perseverated images. For example, after seeing a bright light such as a car headlight or a camera flash, a persistent afterimage remains in the visual field for several minutes. Patients often report photophobia, which can restrict their ability to perform outdoor activity.