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Skorin/Page 1 of 4
Leonid Skorin, Jr., OD, DO, FAAO, FAOCO
Albert Lea Medical Center
Mayo Health System
404 West Fountain St.
Albert Lea, MN 56007
Phone: (507) 373-8214
e-mail: [email protected]
VISUAL ILLUSIONS OR HALLUCINATIONS
I.
Negative Visual Phenomena
A. Decreased visual acuity
B. Scotoma – Isolated area of absent vision in the visual field surrounded by an
area of normal vision
C. Visual field defect – Characteristic pattern corresponding to lesion location
along visual pathway
II.
Positive Visual Phenomena
A. Illusion
1. misperceptions of viewed objects
2. mistaking a rope for a snake
3. polka dots on a dress seen as insects
B. Hallucination
1. sensory perception of things not there
2. subjective experience without objective stimuli
3. persist with eye closure
C. Pseudohallucination
1. patient knows it is not real
2. Charles Bonnet Syndrome
D. Both occur from disturbances of neural visual pathway
E. Illusions – May also be caused by optical abnormalities
F. Hallucinations – Always neural events
III.
Entopic Phenomena
A. Produced by eyes’ own structures
B. Halos around lights
1. lens fibers act as a diffraction grating
2. corneal edema
C. Floaters
1. muscae volitantes – “flitting flies.” Small floating spots composed
of debris in vitreous humor viewed against a bright background
2. Scheerer’s phenomenon – leukocytes flowing through parafoveal
blood vessels
3. Shafer’s sign (tobacco dust) – pigment granules floating in anterior
vitreous- indicative of retinal break or tear
D. Phospenes – flashes of light
1. retinal stimulation
2. prolonged accommodation
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3. quick eye movement
4. digitally pressing the eye
5. Moore’s lighting streaks – unformed vertical streaks appear in
peripheral field and mostly affect elderly patients
IV.
Illusions
A. Multiple Images – Monocular
1. ocular media aberration
a. corneal edema, myopic astigmatism, cataract
2. pinhole eliminates accessory image by reducing scattered light
B. Altered Size Or Shape
1. refractive correction problem
a. aniseikonia – image size from an object is focused larger on
one retina than on the other
b. power, axis, base curve – often glasses problem
2. macular disease
a. metamorphopsia – distorted vision due to displacement of
visual receptor cells of the retina
b. Amsler grid
C. Altered Color
1. brunescence
a. yellowish brown tint
b. cataract
2. cyanopsia
a. blue discoloration
b. recent cataract surgery
3. erythropsia
a. reddish cast to vision
b. hyphema, vitreal hemorrhage
D. Decreased Brightness
1. optic neuropathy
a. afferent pupillary defect
b. decreased color vision
2. dense hyphema or vitreous hemorrhage
E. Altered Motion
1. Pulfrich stereo-illusion
a. optic neuropathy
b. unequal conduction rates between optic nerves
c. pendulum swinging in a single plane is misperceived as
swinging in an elliptical plane
d. counterclockwise rotation if the right optic nerve affected;
clockwise rotation if the left optic nerve is affected
V.
Binocular Hemifield Illusions
A. Etiology
1. occipitoparietotemporal lesion
2. vertebrobasilar TIA
3. rarely migraine
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B. Altered Shape
1. cerebral metamorphopsia – elongations of forms along one plane
with overlapping of one object onto another
2. illusory spread – visual scene is displaced and distorted
3. disappear spontaneously within days or weeks
4. may be episodic or persistent
C. Altered Position
1. visual allesthesia – previously viewed object displaced into opposite
hemifield
2. cerebral diplopia – object viewed in intact hemifield displaced into
defective hemifield
3. cerebral polyopia for stationary objects – multiple vision
D. Palinopsia
1. visual perseveration in time – image is played back before patient’s
eyes
2. occurs in blind or reduced acuity hemifield
3. image persists for just a few minutes
4. usually resolve spontaneously
VI.
Hallucinations
A. Unformed (Simple, Elementary)
1. photopsias – dots, spots, sparks, streaks, wavy lines
2. chromatopsias – environment uniformly tinted a single color
3. geometric patterns – fortification spectrum or teichopsia
B. Formed (Complex)
1. metamorphopsia
2. macropsia, micropsia – changes in size
3. telopsia – objects perceived as being further away
4. mosaic vision – fracture of image into facets
5. macro-, microsomatognosia – perception that a part of the body is
disproportionately large or small
6. Alice in Wonderland phenomena – distortion of body image
VII.
Charles Bonnet Syndrome
A. Swiss philosopher described phenomenon in 1760
1. 89-year-old grandfather developed complex visual hallucinations
after bilateral cataract surgery
2. Cognitively intact, he knew his visions were “fictions” of the brain
3. Charles Bonnet experienced similar visual hallucinations in his later
life
B. Charles Bonnet Syndrome
1. mean age of incidence 75 – 80 years old
2. impaired vision – 20/60 or worse in better eye
3. most common ocular pathology – macular degeneration
4. images are recurrent and complex
5. duration: seconds to hours
6. episodes: days to years, variable frequency
7. nonfrightening, patient retains insight
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C. Image Content
1. people, animals, places
2. B&W, color, static, dynamic
3. autoscopia – images of themselves
D. Triggers and Stoppers
1. triggers
a. fatigue
b. stress
c. low level of illumination
d. general sensory reduction
e. social isolation
2. Stoppers
a. closing or opening the eyes
b. blinking
c. turning on light
d. looking for distraction
e. hitting the hallucination
f. shouting at the hallucination
E. Theories
1. release theory
a. sensory deprivation leads to release of subconscious
perceptions – engrams
b. phantom vision like phantom limb
c. correct patients vision – stops hallucinations
2. irritative theory
a. spontaneous electrical discharge from visual cortex
b. no activity on neuroimaging to substantiate this theory
3. neuromatrix theory
a. network of neurons imparts a pattern – neuro-signature
b. changes in sensory input modulates output of neuromatrix
F. Treatment
1. correct ocular pathology
2. optical
3. pharmacological
a. anti-convulsants
b. neuroleptics
4. keep patients socially involved
G. Case
1. 100-year-old female
2. hand motion vision both eyes
3. end-stage glaucoma and CRVO
4. saw 3 young children, well-dressed, cute
5. smaller boy hopping next to 2 girls
6. occasionally saw herself walking with children
7. felt they were there to protect and watch over her