The phenomena of seeing things that are not present or a visual perception that does not reconcile with the physical, consensus reality. There are many psychophysiologic, psychobiochemical, and psychological causes. Numerous disorders can involve visual hallucinations but they don't always indicate a disorder.
Treatment options will depend on the syndrome identified. Visual pathway disorder hallucinations may be treated with reassurance and the knowledge that the hallucinations will resolve in time, although may re-occur if the visual pathway lesion progresses. For non-distressing, visual-only brainstem/cholinergic hallucinations without persistent secondary delusions, patients may be managed with reassurance, although the experiences are likely to persist and progress. For brainstem /cholinergic syndrome hallucinations that are distressing, multi-modality or with persistent delusions (or visual pathway syndrome hallucinations that are persistent and distressing) largely anecdotal treatment options include cholinesterase inhibitors, anti-convulsants and atypical antipsychotics.
Peduncular hallucinosis is an uncommon syndrome of isolated visual hallucinations in color described as vivid images of people, animals, scenes, or geometric patterns recognized by patients as not being real. Sleep disorder may also be present. The anatomic localization is typically in the thalamus or midbrain, with the etiology usually being vascular disease -- or less often, tumor.
Hallucinogenic drugs (including mescaline, psilocybin, and lysergic acid diethylamide [LSD]) are agonists of serotonin 5-HT2A receptors; they do not always produce true hallucinations unless they are used at high doses. The effects also depend to some degree on the mood of the user and the situation in which the drug is used. Other drugs often considered to be hallucinogenic include phencyclidine (PCP), ecstasy, atropine, and dopamine agonists.
When caused by organic factors there may be impaired consciousness. Organic causes include hallucinogenic drugs, epilepsy, delirium due to toxic agents or alcohol/barbiturate withdrawal states. Psychogenic causes include schizophrenic psychosis, which typically occurs in the setting of clear consciousness.
Complex visual hallucinations, such as the image of a child, can occur in a limited portion or throughout the visual field. Formed or complex visual hallucinations usually result from lesions of the visual association cortices in the temporal, occipital, or parietal lobes. The images can be stationary or moving, single or multiple, or enlarged or diminished in size.
Complex visual hallucinations may affect some normal individuals on going to sleep and are also seen in pathological states, often in association with a sleep disturbance. The content of these hallucinations is striking and relatively stereotyped, often involving animals and human figures in bright colours and dramatic settings. Conditions causing these hallucinations include narcolepsy-cataplexy syndrome, peduncular hallucinosis, treated idiopathic Parkinson's disease, Lewy body dementia without treatment, migraine coma, Charles Bonnet syndrome (visual hallucinations of the blind), schizophrenia, hallucinogen-induced states and epilepsy.
Simple visual hallucinations include spots of white light, colored or geometric forms, or positive scotomas (e.g., "heat waves" surrounding a black hole). Photopsias, sparks, or flashes of light, are the most common simple visual hallucination. Simple visual hallucinations arise from a dysfunction in the visual pathways from the eye to the primary visual cortex or, less often, from irritative lesions of the visual association cortex and medial temporal lobe.
Visual hallucinations in the adult have been stated to result from lesions anywhere in the visual pathway, including the retina, brainstem pathways and occipital lobe. Some researchers suggest that isolated visual hallucinations in older adults, often with visual impairment, and frequently sedentary and sensorially deprived, may be an indication of early stages of dementia.
Most reported hallucinations are auditory, and visual hallucinations tend to reflect neurologic rather than psychiatric disease.
Before diving deep into the patient’s visual psyche, it is worth pausing to consider whether the symptom being described is vivid visual imagery. Visual images appear in the mind’s eye and are under some degree of volitional control, as opposed to hallucinations and illusions which are externally located, unpredictable and outside volition (in the sense that one cannot choose to make a hallucination of, say, a face turn into that of a chair).
Hallucinations are usually seen by only one individual. Hallucinations are false perceptions that occur in the absence of appropriate external stimuli, whereas illusions are misinterpretations of external stimuli that are, in fact, present. Delusions are different from both illusions and hallucinations. They are beliefs, not perceptions.
Hallucinations come from “within,” although subjects react to them as if they are coming from external sources. Although hallucinations are mostly described in people having psychiatric disorders, they sometimes occur in healthy people as well. They can occur upon falling asleep (hypnagogic hallucinations) or upon waking (hypnopompic hallucinations).
Absinthe, widely known as the ‘Green Fairy‘ was banned across Europe in the early 20th century after it became the purported cause of absinthism, the symptoms of which included hallucinations, tremors and convulsions. It turns out that absinthism was probably just alcoholism. German scientists put old bottles of the substance to the test and found that the liquid is 70 percent alcohol (140 proof) and 0 percent hallucination.