In one approach to patients with visual hallucinations and illusions, the general categories (see Table 12.1 ) should be considered first. The neurologic examination, for example, should exclude an altered sensorium due to a mass lesion or a toxic or metabolic disturbance a hemiparesis or hemisensory loss suggestive of a hemispheric mass lesion ataxia, third nerve palsy, or vertical gaze paresis consistent with a mesencephalic process (see Peduncular Hallucinations ) nystagmus and imbalance associated with a brainstem or vestibular lesion or evidence of Parkinson’s or Alzheimer’s disease.ĭiagnostic and Treatment Considerations (Overview) We also prefer to perform formal visual field testing in almost every patient with a visual hallucination or illusion to exclude a field deficit. Even mild visual loss in the setting of macular degeneration or optic atrophy can be associated with release hallucinations, and these may be missed without a careful examination. Particular attention should be paid to visual acuity, color vision, pupillary reactivity, and the ophthalmoscopic examination. The neuro-ophthalmic examination of a patient with visual hallucinations or illusions is directed toward excluding afferent pathway disease or another responsible lesion of the nervous system. Investigation into predisposing underlying conditions, such as metabolic disturbances, visual loss, psychiatric illnesses, alcohol intake, and drug use (illicit, recreational, or otherwise), is also extremely important. Insight is characteristic of release visual hallucinations (see later discussion), for instance, whereas a schizophrenic with psychotic hallucinations might not be able to differentiate the hallucination from reality. The patient should be asked whether he or she knows if the perception is a hallucination or not. For instance, a visual hallucination followed by a headache suggests migraine, while one followed by limb twitching and then loss of consciousness is suspicious of a seizure. With such individuals, encouragement from family members is often helpful.Īccompanying neurologic symptoms also can be very helpful in the diagnosis. In some instances, patients with hallucinations or illusions are reluctant or ashamed to admit they have them because they fear a diagnosis of psychosis or dementia. In addition, their frequency, duration, and repetitiveness should be established. The examiner can ask whether the visual symptoms are monocular or binocular, but usually the patient has never checked or cannot make this distinction. For illustrative purposes, it is often helpful to have him or her draw on paper or on the computer what is perceived. The patient should be asked to detail the hallucinations or illusions, with particular attention to their content, complexity, and static or dynamic features. All too often the examination is unrevealing.

The history is paramount in these patients, because the diagnosis is frequently made based on the clinical setting and the detailed description of the visual symptoms.

History and Examination in Patients With Visual Hallucinations or Illusions Other evidence of an occipital lobe lesion Other motor or sensory manifestations of seizuresĬlinical evidence of Parkinson’s disease, dementia with Lewy bodies, or Alzheimer’s disease Observation of normal phenomena or ocular pathologyĪccompanying auditory or tactile hallucinations This chapter details the various categories, but first the history, examination, and diagnostic and therapeutic considerations in patients with hallucinations and illusions are reviewed.ĭistinguishing Feature(s) of Visual Hallucinations or Illusions These are summarized in Table 12.1, which also describes distinguishing features of each. The causes of visual hallucinations and illusions can be grouped into several major categories: migraine, release phenomena (in the setting of impaired vision), entoptic (ocular) phenomena, alcohol and drug-related, seizures, neurodegenerative disease, central nervous system lesions, psychiatric disease, and narcolepsy. Visual hallucinations and illusions are generally positive phenomena, in contrast to visual loss, which is a negative phenomenon. In contrast, illusions are misinterpretations of a true sensory stimulus. Visual hallucinations can be classified as unformed/simple (e.g., dots, flashes, zig-zags) or formed/complex (actual objects or people).

Hallucinations are defined as perceptions that occur in the absence of a corresponding external sensory stimulus. Visual hallucinations and illusions comprise some of the most vivid and sometimes bizarre symptoms in neuro-ophthalmology.

Entoptic phenomena quotes