Neuro-ophthalmology Illustrated Chapter 11 – Abnormal Visual Perceptions: Hallucinations and Illusions 1

Questions: 1. What is the difference between hallucination and illusion?
2. Are isolated visual hallucinations common in psychiatric disorders?
3. Are psychiatric hallucinations associated with altered mental status or focal neurologic signs?
4. Are phosphenes seen in patients with optic neuropathies?
5. What is the Pulfrich phenomenon?
6. In what conditions is the Pulfrich phenomenon seen?
7. What is the Charles Bonnet syndrome?
8. Can encephalopathies or focal cerebral lesions cause hallucinations and illusions?
9. Can confusion and dementia cause visual hallucinations and illusions?
10. Is Lewy body dementia commonly associated with visual hallucinations or illusions?n
11. Which dementias may be associated with paranoid hallucinations and illusions?
12. Can the drugs that are used to treat Parkinson disease cause hallucinations?

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Questions with answers:
1. What is the difference between hallucination and illusion?
Hallucination refers to the perception of a stimulus when in reality, none is present.  An Illusion refers to the misperception of a stimulus that is present in the external environment.

2. Are isolated visual hallucinations common in psychiatric disorders?
No, many psychiatric illnesses have visual illusions and hallucinations, which are not usually isolated but are associated with other perceptive abnormalities (usually auditory).

3. Are hallucinations associated with altered mental status or focal neurologic signs?
No, hallucinations are not associated with altered mental status or focal neurologic signs.

4. Are phosphenes seen in patients with optic neuropathies?
Yes, phosphenes are sometimes reported by patients with optic neuropathies. They are sometimes triggered by a noise or moving the eye.

5. What is the Pulfrich phenomenon?
It is the perception of an elliptical movement when observing a pendulum swinging in one plane. It is a stereo-illusion related to the difference in conduction delay between the two eyes in the optic nerves.

6. In what conditions is the Pulfrich phenomenon seen?
Unilateral or asymmetric optic neuropathies. 

7. What is the Charles Bonnet syndrome?
The Charles Bonnet syndrome is characterized by visual hallucinations associated with poor vision in each eye, such as that in advanced 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.

8. Can encephalopathies or focal cerebral lesions cause hallucinations and illusions?
Yes, a variety of encephalopathies or focal cerebral lesions can cause hallucinations and illusions. They occur in awake or drowsy patients, who often are not aware that these are hallucinations and they may become frightened. These symptoms are most often visual and tactile, whereas psychiatric hallucinations most often are auditory. 

9. Can confusion and dementia cause visual hallucinations and illusions?
Yes, confusion and dementia can cause visual hallucinations and illusions.

10. Is Lewy body dementia commonly associated with visual hallucinations or illusions?
Yes, Lewy body dementia is commonly associated with visual hallucinations.

11. Which dementias may be associated with paranoid hallucinations and illusions?
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.

12. Can the drugs that are used to treat Parkinson disease cause hallucinations?
Yes, the drugs used to treat Parkinson disease can cause hallucinations.

The information below is from Neuro-ophthalmology Illustrated-2nd Edition. Biousse V and Newman NJ. 2012. Thieme

11 Abnormal Visual Perceptions: Hallucinations and Illusions
Abnormal visual perceptions are common in psychiatric disorders, ophthalmic disorders, and neurologic diseases, and can be due to numerous drugs and toxins.
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.

11.1 Psychiatric Disorders
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.

11.2 Ophthalmic Disorders
11.2.1 Optical Causes
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).

11.2.2 Retinal Disorders (Maculopathies)
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).

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 the multiple evanescent white dot syndrome, may cause simple white flashing lights.

11.2.3 Optic Nerve Disease
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 stereo illusion related to the difference in conduction delay between the two eyes.

11.2.4 Charles Bonnet Syndrome
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.

11.3 Neurologic Disorders
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.

11.3.1 Confusion and Dementia
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.

Reference: 1. Neuro-ophthalmology Illustrated-2nd Edition. Biousse V and Newman NJ. 2012. Thieme

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