ND - Perceptual Disorders as a Higher Level Dysfunction - Week 9 Flashcards
Define visual illusion.
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.
Define hallucination.
An experience involving the apparent perception of something that is not present
Are most visual distortions due to eye disease positive or negative?
Negative
List 2 reasons why patients can experience positive visual phenomena. What senses can it affect (3)? Give two examples.
Due to abnormal retinal/cortical processing
Can affect auditory, olfactory, and visual senses
Flashes
-due to vitreo-retinal traction
-due to elevated IOP
What is an illusion?
Distortion or misinterpretation of a visual input
In what state do illusions occur?
Awake people with eyes open
Do illusions involve unusual or normal neural processing?
Either
What are pathological illusions due to?
Aberrant image processing
Give two ocular causes for pathological illusions and give three examples.
Optical
-aniseikonia caused by astigmatism
-anismometropia
Retinal
-due to vitreo-retinal traction
Give two examples of cortical pathological illusions.
Palinopsia
Alice in Wonderland syndrome
List three ways to differentiate an ocular vs cortical cause of pathological illusions.
One eye (retinal) vs one hemifield
If homonymous, then cortical
Higher order distortions give complex perceptual illusions (shape, depth etc)
What is palinopsia? What is it known as in normal conditions? What about in disease conditions?
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
What are four characteristics of palinopsia?
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)
Are standard after-images positive or negative?
Negative
Dysfunction in what region is associated with palinopsia?
Brain/cortical dysfunction or pathology
Individuals with what two conditions can experience palinopsia?
Migraine sufferers
Visual snow
What are stop-motion action pictures? What is it due to? What percentage of indivduals does it affect (which kind of individuals specifically)?
Trailing after ingestion of hallucinogens (serotonin receptor excitotoxicity)
Affectd ~10% of people with migraine
What is alice in wonderland syndrome and how long can it last? How long does it last typically?
Distortion/illusion that lasts between minutes to days in prone people. Typical duration is ~20 minutes.
What is the most prominent symptom of alice in wonderland syndrome?
Altered body image, which is disturbing
List four characteristics of alice in wonderland syndrome.
Sensory distortions, especially touch and hearing
Altered body image
Change in size of inanimate objects
List 4 diseases associated with alice in wonderland syndrome.
Migraine
Epilepsy
Cerebral lesions
Schizophrenia
What are two forms of aura that can occur with alice in wonderland syndrome?
Gross magnification of hands/face
Body as taller after enlarging feet
Do visual hallucinations require vision? Can they be seen with eyes closed?
Vision not needed, can be seen with eyes closed
What causes hallucinations (2)? What does this mean?
Aberrant inhibition or overexcitation of the brain - doesnt require visual input
List three categorisations for visual hallucinations and give two major causes for each.
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
List two syndrome types for hallucinations that arise subsequent to vision loss, and give an example for each.
Cortical syndromes
-posterior cortical atrophy
Ocular syndromes
-charles bonnet syndrome
What is a cause of posterior cortical atrophy and what is it considered a variant of?
Lesion of the primary visual cortex, visual pathway, midbrain, or thalamus
Considered a variant of alzhiemers disease
What impairment does posterior cortical atrophy result in (2)?
Spatial and percentual impairment?
In what percentage of posterior cortical atrophy cases do hallucinations occur? What is needed for this to occur (2)?
25%
Requires damage across multiple sites or to a network of interconnecting structures
Activation of what brain region are related to hallucinations? Explain how this occurs with loss of vision exactly.
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
What kind of hallucinations are present in charles-bonnet syndrome? Is cognition intact? What is this syndrome produced by?
Hallucinations caused by binocular eye diseases, where cognition is intact
Produced by any disease resulting in bilateral visiond loss
List 2 typical casues of charles-bonnet syndrome.
Bilateral AMD
Bilateral glaucoma
What is the timing and frequency of CBS like?
Can vary widely
How long can CBS hallucinations last?
Usually several minutes, but can be seconds or hours
What is a problem with diagnosing CBS (aside from it being a diagnosis by exclusion)?
High rate of patient non-reporting of visual hallucinations to care providers due to feal or psychotic labelling
What is the mainstay of CBS management? List three additional treatment options.
Mainstay is patient reassurance and education on cause
Can also improve visual function, increased social interaction, and improved lighting
What does anton-babinski syndrome occur in conjunction with? Is this syndrome common or rare?
Very rare
Occurs in conjunction with a sudden bilateral occipital dysfunction
What is the visual status of someone with anton-babinski syndrome? How do these individuals behave when interacting with someone?
Patient is blind, but behave and talk as though they can see
What is visual sno?
Continuous appearance of visual static
List the diagnostic criteria for visual snow (4).
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
Is visual snow easy to diagnose? Explain.
Often misdiagnosed due to lack of objective signs
