Visual Hallucinations

    • Visual sensations that are not based on viewed objects, but are generated by endogenous neural activity (“seeing things that are not there”)
    • Mechanisms
      • Irritation of the outer retina, optic nerve, or vision-related cerebral cortex
      • Deafferentation of the vision-related cerebral cortex (“release hallucinations”)
    • Common causes of irritation of the outer retina: vitreous or retinal detachment, photoreceptor dysfunction
    • Common causes of irritation of the optic nerve: optic neuritis, ischemic optic neuropathy
    • Common causes of irritation of the vision-related cerebral cortex: migraine, ischemia, tumor, medications, or recreational drugs
    • Common cause of deafferentation of the vision-related cerebral cortex: blindness of any cause (Charles Bonnet Syndrome)
    • Brief flashes = aging, liquefying vitreous tugging on retina and deforming photoreceptors
    • Stationary white flickers = irritation of photoreceptors or vision-related cortex
    • Stationary, often multicolored, flickers = irritation of vision-related cortex by seizure
    • Episodic superimposition of previously viewed object on a newly viewed scene [“visual perseveration,” “palinopsia”] = irritation or deafferentation of vision-related cortex by various lesions
    • Geometric shapes that traverse a hemifield = migraine
    • Stationary complex patterns or figures = irritation of vision-related cortex by infarction, seizure, medications, recreational drugs; deafferentation of vision-related cortex by blindness (Charles Bonnet syndrome), sleepiness, schizophrenia, dementia
    • Flickering black and white dots or lines that interfere with visual clarity (“visual snow”) = visual hypersensitivity of psychogenic origin; very rarely irritation of photoreceptors by an outer retinal lesion
    • Retinal or vitreous detachment needs prompt surgical repair
    • Migraine needs reassurance and sometimes prophylaxis
    • Suspected vision-related cerebral cortex lesion needs brain imaging, electroencephalography, or other appropriate evaluation and treatment
    • Medications, recreational drugs need appropriate identification and withdrawal
    • Psychosis needs treatment
    • Charles Bonnet syndrome needs explanation, reassurance, and very rarely anxiolytic medication
    • Visual snow needs explanation, ruling out of an outer retinal lesion, and management of an underlying anxiety state

    Visual Hallucinations

    Visual Hallucinations