In this chapter, the term hallucination refers to perception of a stimulus when, in reality, none is present, for example, when a patient with delirium tremens describes seeing bugs and snakes on the bedroom walls. The term illusion refers to misperception of a stimulus that is present in the external environment, for example, when an elderly individual interprets a chair in a poorly lit room as a person. Hallucinations are common in psychotic syndromes. They are most often complex and auditory. Isolated visual hallucinations are uncommon in psychiatric disorders. Pearls Primary psychiatric illnesses often cause visual illusions and hallucinations, which are usually associated with other perceptive abnormalities (usually auditory); they are not associated with altered mental status or focal neurologic signs. Optical causes of abnormal visual perceptions include alterations in the tear film (dry eyes and abnormalities in blinking), and irregularities in the cornea (keratoconus and corneal scarring) or the lens (cataract). Entoptic phenomena are visual experiences caused by ocular structures (e.g., floaters). Retinal disorders or maculopathies can produce visual hallucinations. Metamorphopsias from macular disorders are best detected by the Amsler grid test. Macular edema produces micropsia (increased separation of retinal photoreceptors), and epiretinal membrane produces macropsia (when the photoreceptors are pushed together) (▶ Fig. 11.1). Fig. 11.1 Epiretinal membrane in the right eye responsible for decreased visual acuity and severe distortion of vision. Note the whitish membrane that pulls on the retina (arrows). Vitreoretinal traction is responsible for phosphenes (flashing lights). These are more apparent in a dark environment. Floaters (posterior vitreous detachment and vitreous debris) are most noticeable against a uniformly illuminated background. Outer retinal diseases, such as cancer-associated retinopathy, acute zonal occult outer retinopathy, and multiple evanescent white dot syndrome, may cause simple white flashing lights. Phosphenes are sometimes reported by patients with optic neuropathies. They are sometimes triggered by noise or moving the eye. Pulfrich phenomenon, or the perception of an elliptical movement when observing a pendulum swinging in one plane, occurs in patients with unilateral or asymmetric optic neuropathies. It is a stereoillusion related to the difference in conduction delay between the two eyes. Charles Bonnet syndrome is characterized by visual hallucinations associated with poor vision, such as in macular degeneration. Simple and complex visual hallucinations are present in up to 10% of patients with severe binocular visual loss, presumably because the normal visual cortex has been “released” from anterior visual pathway input. This syndrome is more common in the elderly. The hallucinations are not stereotyped and involve vivid scenes of animals, flowers, and people. They may be episodic or continuous and are more common in the evening and when patients have their eyes open. Once patients are reassured, they often tolerate these hallucinations well, but treatment is usually unsuccessful. A variety of encephalopathies or focal cerebral lesions can cause hallucinations and illusions. These symptoms are most often visual and tactile, whereas psychiatric hallucinations are most often auditory. They occur in awake or drowsy patients, who often are not aware that these are hallucinations and may become frightened. Confusion and dementia can cause visual hallucinations and illusions. Delirium tremens is associated with very frightening, well-formed visual hallucinations, including bugs, monsters, and snakes. Lewy body dementia is commonly associated with visual hallucinations. Other dementias, such as Alzheimer disease, Pick disease, human immunodeficiency virus (HIV) dementia, Huntington chorea, Creutzfeldt–Jakob disease, and multi-infarct dementia, may be associated with paranoid hallucinations and illusions. Drugs used to treat Parkinson disease can also cause hallucinations. Numerous visual phenomena occur during the visual aura of migraine (▶ Table 11.1). These visual phenomena are often positive and therefore can be described as hallucinations. Characteristics Migraine with visual aura Occipital seizures Visual phenomena Positive and negative Positive and negative Color Bright, scintillating, black and white Colorful Description Simple, but with stereotyped progression from center to periphery; experienced in both eyes; often in a hemifield Often simple (sparkles, pinwheel, bubbles, circles); experienced in both eyes; often in a hemifield Duration 10 to 30 minutes (up to 1 hour) A few seconds Recurrence Yes, often change sides, various patterns Yes, often daily, stereotyped for each patient, same side Associated symptoms Migrainous headache after aura Often isolated, or with other epileptic symptoms Examination Normal between attacks May have visual field defect Migrainous visual phenomena usually last between 10 and 30 minutes and progress over time (migrainous march) (see Chapter ▶ 6, ▶ Fig. 6.1). They may be associated with other neurologic symptoms, such as ipsilateral tingling and speech impairment, and are classically followed by migrainous headaches. Migraineurs are aware that the images they see are not real. Positive or negative visual phenomena are present in both eyes, either in the entire eye or in one hemifield. Phenomena include phosphenes, which are usually bright or white, and scintillating scotoma, described as progressively enlarging bright scotoma with sharp edges (▶ Fig. 11.2). Distortion of images with micropsia and macropsia (Alice in Wonderland syndrome) or tilting of objects can also occur. Fig. 11.2 Scintillating scotoma with zig-zag pattern highly suggestive of migraine.
11.1 Psychiatric Disorders
11.2 Ophthalmic Disorders
11.2.1 Optical Causes
11.2.2 Retinal Disorders (Maculopathies)
11.2.3 Optic Nerve Disease
11.2.4 Charles Bonnet Syndrome
11.3 Neurologic Disorders
11.3.1 Confusion and Dementia
11.3.2 Migraine
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