ND - Perceptual Disorders as a Higher Level Dysfunction - Week 9

Question 1

Define visual illusion.

Answer 1

Describes visual images that are not the same as the physical reality of the stimulus.
There is an alteration of the interpretation of the physical stimulus.

Question 2

Define hallucination.

Answer 2

An experience involving the apparent perception of something that is not present

Question 3

Are most visual distortions due to eye disease positive or negative?

Answer 3

Negative

Question 4

List 2 reasons why patients can experience positive visual phenomena. What senses can it affect (3)? Give two examples.

Answer 4

Due to abnormal retinal/cortical processing
Can affect auditory, olfactory, and visual senses
Flashes
-due to vitreo-retinal traction
-due to elevated IOP

Question 5

What is an illusion?

Answer 5

Distortion or misinterpretation of a visual input

Question 6

In what state do illusions occur?

Answer 6

Awake people with eyes open

Question 7

Do illusions involve unusual or normal neural processing?

Answer 7

Either

Question 8

What are pathological illusions due to?

Answer 8

Aberrant image processing

Question 9

Give two ocular causes for pathological illusions and give three examples.

Answer 9

Optical
-aniseikonia caused by astigmatism
-anismometropia
Retinal
-due to vitreo-retinal traction

Question 10

Give two examples of cortical pathological illusions.

Answer 10

Palinopsia

Alice in Wonderland syndrome

Question 11

List three ways to differentiate an ocular vs cortical cause of pathological illusions.

Answer 11

One eye (retinal) vs one hemifield
If homonymous, then cortical
Higher order distortions give complex perceptual illusions (shape, depth etc)

Question 12

What is palinopsia? What is it known as in normal conditions? What about in disease conditions?

Answer 12

Propensity for an ìmâgé to persist even after the stimulus has left
In normal conditions it is known as an after-image
In disease conditions, it is exaggerated and called palinopsia

Question 13

What are four characteristics of palinopsia?

Answer 13

Increased duration of the afterimage (tracer - blur)
Reduced amount of time to form an after-image
Positive after-images become noticeable with routine eye movements
Negative after-images also possible (inverted colours)

Question 14

Are standard after-images positive or negative?

Answer 14

Negative

Question 15

Dysfunction in what region is associated with palinopsia?

Answer 15

Brain/cortical dysfunction or pathology

Question 16

Individuals with what two conditions can experience palinopsia?

Answer 16

Migraine sufferers

Visual snow

Question 17

What are stop-motion action pictures? What is it due to? What percentage of indivduals does it affect (which kind of individuals specifically)?

Answer 17

Trailing after ingestion of hallucinogens (serotonin receptor excitotoxicity)
Affectd ~10% of people with migraine

Question 18

What is alice in wonderland syndrome and how long can it last? How long does it last typically?

Answer 18

Distortion/illusion that lasts between minutes to days in prone people. Typical duration is ~20 minutes.

Question 19

What is the most prominent symptom of alice in wonderland syndrome?

Answer 19

Altered body image, which is disturbing

Question 20

List four characteristics of alice in wonderland syndrome.

Answer 20

Sensory distortions, especially touch and hearing
Altered body image
Change in size of inanimate objects

Question 21

List 4 diseases associated with alice in wonderland syndrome.

Answer 21

Migraine
Epilepsy
Cerebral lesions
Schizophrenia

Question 22

What are two forms of aura that can occur with alice in wonderland syndrome?

Answer 22

Gross magnification of hands/face

Body as taller after enlarging feet

Question 23

Do visual hallucinations require vision? Can they be seen with eyes closed?

Answer 23

Vision not needed, can be seen with eyes closed

Question 24

What causes hallucinations (2)? What does this mean?

Answer 24

Aberrant inhibition or overexcitation of the brain - doesnt require visual input

Question 25

List three categorisations for visual hallucinations and give two major causes for each.

Answer 25

Hallucinations that are isolated findings
-drug induced
-subsequent to vision loss
Hallucinations associated with sleep/trance
-trance-like
-sleep induced
Hallucinations as part of specific pathology
-dementia
psychoses

Question 26

List two syndrome types for hallucinations that arise subsequent to vision loss, and give an example for each.

Answer 26

Cortical syndromes
-posterior cortical atrophy
Ocular syndromes
-charles bonnet syndrome

Question 27

What is a cause of posterior cortical atrophy and what is it considered a variant of?

Answer 27

Lesion of the primary visual cortex, visual pathway, midbrain, or thalamus
Considered a variant of alzhiemers disease

Question 28

What impairment does posterior cortical atrophy result in (2)?

Answer 28

Spatial and percentual impairment?

Question 29

In what percentage of posterior cortical atrophy cases do hallucinations occur? What is needed for this to occur (2)?

Answer 29

25%

Requires damage across multiple sites or to a network of interconnecting structures

Question 30

Activation of what brain region are related to hallucinations? Explain how this occurs with loss of vision exactly.

Answer 30

Cortical activation in the lateral infero-temporal cortex
Lack of stimulation of visual areas due to loss of vision or a cortical lesion leads to reduced inhibition of the lateral infero-temporal cortex by these areas, giving spontaneous activation of IT neurons, resulting in hallucinations

Question 31

What kind of hallucinations are present in charles-bonnet syndrome? Is cognition intact? What is this syndrome produced by?

Answer 31

Hallucinations caused by binocular eye diseases, where cognition is intact
Produced by any disease resulting in bilateral visiond loss

Question 32

List 2 typical casues of charles-bonnet syndrome.

Answer 32

Bilateral AMD

Bilateral glaucoma

Question 33

What is the timing and frequency of CBS like?

Answer 33

Can vary widely

Question 34

How long can CBS hallucinations last?

Answer 34

Usually several minutes, but can be seconds or hours

Question 35

What is a problem with diagnosing CBS (aside from it being a diagnosis by exclusion)?

Answer 35

High rate of patient non-reporting of visual hallucinations to care providers due to feal or psychotic labelling

Question 36

What is the mainstay of CBS management? List three additional treatment options.

Answer 36

Mainstay is patient reassurance and education on cause

Can also improve visual function, increased social interaction, and improved lighting

Question 37

What does anton-babinski syndrome occur in conjunction with? Is this syndrome common or rare?

Answer 37

Very rare

Occurs in conjunction with a sudden bilateral occipital dysfunction

Question 38

What is the visual status of someone with anton-babinski syndrome? How do these individuals behave when interacting with someone?

Answer 38

Patient is blind, but behave and talk as though they can see

Question 39

What is visual sno?

Answer 39

Continuous appearance of visual static

Question 40

List the diagnostic criteria for visual snow (4).

Answer 40

Dynamic visual snow for more than 3 months
At least two additional visual symptoms of palinopsia, entopic phenomena, photophobia, or nytalopia
Symptoms not consistent with typical migraine visual aura
Symptoms not better explained by any other disorder or psychotic drug intake

Question 41

Is visual snow easy to diagnose? Explain.

Answer 41

Often misdiagnosed due to lack of objective signs