Hallucinogen persisting perception disorder in the context of Floater

Lysergic acid diethylamide, commonly known as LSD (from German Lysergsäurediethylamid) and by the slang names acid and lucy, is a semisynthetic hallucinogenic drug derived from ergot, known for its powerful psychological effects and serotonergic activity. It was historically used in psychiatry and 1960s counterculture; it is currently legally restricted but experiencing renewed scientific interest and increasing use.

When taken orally, LSD has an onset of action within 0.4 to 1.0 hours (range: 0.1–1.8 hours) and a duration of effect lasting 7 to 12 hours (range: 4–22 hours). It is commonly administered via tabs of blotter paper. LSD is extremely potent, with noticeable effects at doses as low as 20 micrograms and is sometimes taken in much smaller amounts for microdosing. Despite widespread use, no fatal human overdoses have been documented. LSD is mainly used recreationally or for spiritual purposes. LSD can cause mystical experiences. LSD exerts its effects primarily through high-affinity binding to several serotonin receptors, especially 5-HT_2A, and to a lesser extent dopaminergic and adrenergic receptors. LSD reduces oscillatory power in the brain's default mode network and flattens brain hierarchy. At higher doses, it can induce visual and auditory hallucinations, ego dissolution, and anxiety. LSD use can cause adverse psychological effects such as paranoia and delusions and may lead to persistent visual disturbances known as hallucinogen persisting perception disorder (HPPD).

Phencyclidine or phenylcyclohexyl piperidine (PCP), also known in its use as a street drug as angel dust among other names, is a dissociative anesthetic mainly used recreationally for its significant mind-altering effects. PCP may cause hallucinations, distorted perceptions of sounds, and psychotic behavior. As a recreational drug, it is typically smoked, but may be taken by mouth, snorted, or injected. It may also be mixed with cannabis or tobacco.

Adverse effects may include paranoia, addiction, and an increased risk of suicide, as well as seizures and coma in cases of overdose. Flashbacks may occur despite stopping usage. Chemically, PCP is a member of the arylcyclohexylamine class. PCP works primarily as an NMDA receptor antagonist.

Palinopsia (from Greek palin 'again' and opsia 'seeing') is the persistent recurrence of a visual image after the stimulus has been removed. Palinopsia is not a diagnosis; it is a diverse group of pathological visual symptoms with a wide variety of causes. Visual perseveration is synonymous with palinopsia.

In 2014, Gersztenkorn and Lee comprehensively reviewed all cases of palinopsia in the literature and subdivided them into two clinically relevant groups: illusory palinopsia and hallucinatory palinopsia. Hallucinatory palinopsia, usually due to seizures or posterior cortical lesions, describes afterimages that are formed, long-lasting, and high resolution. Illusory palinopsia, usually due to migraines, head trauma, prescription drugs, visual snow syndrome or hallucinogen persisting perception disorder (HPPD), describes afterimages that are affected by ambient light and motion and are unformed, indistinct, or low resolution.

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".