Visual hallucination


Visual hallucination

Description, Causes and Risk Factors:

Visual hallucinations are common clinical phenomena that occur in a wide variety of ophthalmologic, neurologic, medical and psychiatric disorders. As many as 75% of delirious patients manifest visual hallucinatory phenomena, and when hallucinations dominate the clinical presentation, a patient may be misdiagnosed as suffering from an idiopathic psychiatric disorder.

A visual hallucination may be defined as a visual sensory perception without external stimulation or, more operationally, as a behavioral syndrome in whihc a patient claims to see something or behaves as if he or she sees something that an observer cannot see. In contrast, delusions are abnormal beliefs that are endorsed by patients as real, that persists in spite of evidence to the contrary and that are not part of pateints culture or subculture. Hallucinations per se are recognized as false sensation phenomena, but when they coexist with delusions, a patient may endorse them as real. Hallucinations by themselves are not evidence of psychosis.

Visual hallucinations can be produced by ophthalmologic disease, neurologic disorders, toxic and metabolic disturbance, psychiatric disorders and a variety of miscellaneous conditions.

Among ophthalmologic diseases, total or partial blindness is commonly assoicated with visual hallucinations. The blindess may be a product of injury to the globe or may be the result of catract formation, macular degeneration, or retinal disease. Hallucinations associated with blindness have been called phantom vision to express their similarity to the phantom-like phenomenon. Hallucinations occuring with blidness may be either formed or unformed, but formed hallucinations predominate. Unformed hallucinations of ocular origin occur with retinal traction and with glaucoma. Retinal traction gives rise to brief unformed flashes of light as a result of retinal detachment or rapid ocular movement. Acute glaucoma with a sudden increase in intraocular pressure may result in the appearance of hallucinated rainbow surrounding objects. The sudden occurrence of visual hallucinations in the elderly is known as Charles Bonnet Syndrome. Formerly considered idiopathic disorder, the syndrome has been found to be assoicated with an ocular pathologic disorder in most cases. Hallucinatory images arising from ocular disease must be distinguished from entoptic phenomena such as opacities in the vitreous humor or seeing elements of one's own retinal circulation.

Optic nerve disease gives rise to unformed visual hallucinations when the nerve is inflammed. Patients with optic neuritis frequently experience bright, transient flashes of light when moving their eyes horizontally.

Brain-stem lesions produce a unique type of visual hallucination syndrome known as peduncular hallucinosis. The hallucinations are product of vascular, neoplastic or other structural involvement of the pons or midbrain and are usually accompained by disturbances of the sleep wake cycle and by cranial nerve palsies. The hallucinations typically occur in the evening and consist of geometric patterns, more complex kaleidoscopic scences of landscapes, flowers, birds, animals or people of visions of miniature animals and beings.

Hemispheric lesions may cause ictal hallucinations during the course of a seizure or they may produce "release" hallucinations assoicated with a visual field defect. Release hallucinations occur with hemispheric infarctions, tumors, or other destructive lesios of the geniculocalcarine pathways. The images are often complex regardless of the lesion location, consisting of complex visual patterns or identifiable images of objects, animals or people. They are usually located within the visual field defect, and they may be influenced by environmental factor such as opening, closing, or moving the eyes. They are typically novel visual experiences rather than visual memories. Release hallucinations are more common with right-sided than with left-sided lesions, and the inciting lesion is often an infarction in the distribution of the right posterior cerebral artery.

Migraine is a well-known cause of visual hallucinations. Fortification spectra (zig-zag lines, often with an associated scotoma) are the most frequent type of hallucination, but patients who have migraines may experience every variety of hallucinatory image from simple unformed lines and spots to highly complex, formed scenes. Visual distortions, including macropsia and micropsia may also occur. Such sensory distortions have been called the "Alice-in-Wonderland" syndrome.

Narcolepsy may produce visual hallucinations that are confined to those instants just as one is falling asleep or just one is awakening. A patients level of arousal is usually depressed and the hallucinations have a dreamlike quality. The patient may see geometric patterns, landscape, faces or figures, and there may be associated visual distortions.

Toxic and metabolic disorders are among the most common causes of visual hallucinations. The hallucinations may be the sole manifestation of the toxic encephalopathy or they be one expression of a complex delirious state. Visual hallucinations are present in 40%-75% of patients in metabolic encephalopathies associated with cardiopulmonary insufficiency, uremia, hepatic disease, endocrine disturbance, vitamin deficiency.

Visual hallucinations have also been induced by many drugs and toxins including stimulants, antiparkinsonian agents, antidepressants, analgesic, and nonsteroidal anti-inflammatory agents, anticonvulsants, cardiovascular agents, antibiotics, hormonal agents. Visual hallucinations may also be promient in withdrawal syndromes when the use of alchohol, opiates, or sedative-hypnotics is abruptly discontinued.

Various idiopathic psychiatric disorders can also produce visual hallucinations.

Symptoms:

In some types of visual hallucinations, vision is simply distorted. People may see halos, streaks of color, tracers, and other artifacts in their vision which do not actually exist. These types of visual hallucinations are often associated with recreational drug use. Distortion of vision may last a few seconds to several days, depending on the cause.

In other visual hallucinations, visions are entirely false. People may see people, animals, or objects which are not there, or may be transported into scenes which don't actually exist. A common type of visual hallucination seen among elderly patients is a hallucination of a dead loved one; people may claim to be able to see a dead spouse, for example, and may even carry on conversations with the hallucination.

Diagnosis:

Given the broad variety of potential etiologies of visual hallucinations outlined previously, it is clear that an accurate diagnosis is required before effective treatment can be initiated. A thorough history and clinical examination are the most vital elements of a workup for visual hallucinations. Associated symptoms and characteristics of the visual hallucinations themselves may help direct diagnosis. The elicitation of signs or symptoms of psychosis, inattention, Parkinsonism, impaired vision, or headache will narrow the diagnosis and prompt further diagnostic studies. An EEG is potentially the most revealing diagnostic study, since it can not only highlight seizure activity, but also detect delirium, and CJD (Creutzfeldt-Jakob disease). An MRI of the brain can uncover tumors or infarcts that may be responsible for Anton's syndrome or peduncular hallucinosis, and may also show the characteristics "pulvinar sign" associated with CJD.

Treatment:

Since effective treatment of visual hallucinations is entirely dependent on the underlying cause, care should be taken to ensure diagnostic accuracy, especially since treatments that may be beneficial for one cause of visual hallucinations may exacerbate another. For example, benzodiazepines are the treatment of choice for delirium tremens, but they will almost certainly worsen a delirium due to any other cause.

Neuroleptic medications (i.e., dopamine antagonists) are the mainstay of treatment for visual hallucinations due to primary psychotic illness. These medications are also beneficial for the management of delirium (in which hallucinations are thought to be due to release of endogenous dopamine), with intravenous haloperidol having the most evidence for safety and efficacy.

Unfortunately, due to their dopamine-blocking activity, most neuroleptics will significantly exacerbate parkinsonian symptoms in patients with DLB or dementia associated with Parkinson's disease. Quetiapine and clozapine have a niche role in the treatment of these patients, since their very low affinity for dopamine receptors renders them less likely to cause this serious adverse effect. As with other forms of Alzheimer's dementia, cholinesterase inhibitors may have some benefit in posterior cortical atrophy.

More focal causes of visual hallucinations may require more focal treatment. Seizures may be treated with anticonvulsants, tumors with surgery and radiation, and migraines with triptans or ?-blockers. Unfortunately, some causes of visual hallucinations (e.g., CJD) have no definitive treatment. For these patients, neuroleptics may minimize visual hallucinations and distress. Most patients with visual hallucinations, regardless of cause, will benefit from the reassurance of their caregivers. Some may also benefit from more formal psychotherapeutic interventions (e.g., cognitive behavioral therapy) directed to improve insight.

NOTE: The above information is for processing purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.

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