occipital lobe syndromes

1. Occipital Lobe Syndromes

2. CLASSIFICATION
• Visual field defects:-
Homonymous hemianopia
Blindsight
• Cortical blindness
• Visual anosognosia (Anton syndrome)
• Visual illusions (metamorphopsias)
• Visual hallucinations
• Occipital lobe epilepsy

3. Homonymous hemianopia
• It is hemianopia visual field
loss on the same side of
both eyes.
• Occurs because the right
half of the brain has visual
pathways for the left
hemifield of both eyes, and
the left half of the brain has
visual pathways for the right
hemifield of both eyes.
• When one of these
pathways is damaged, the
corresponding visual field is
lost.

4. Homonymous hemianopia
(homonymous hemianopia)
Homonymous hemianopia caused by lesion posterior to
the optic chiasm.
Vision is lost in ipsilateral nasal field & contralateral
temporal field.
2 types
 Complete
 Incomplete
Incomplete – 2 types
 Incongruous – differently shaped defect in both eyes
lesion site – anterior lesion
(optic tract, LGN)
 Congruous – similarly shape defect
lesion site – posterior (occipital lobe)
In complete hemianopia congruity can not be assessed
Homonymous hemianopia
Congruous
Incongruous

5. i[[[[[[[[[[[[[[[[[[[[]f

6. Lesions of visual cortex
Congruous
homonymous
hemianopia(sparing
macula)
Occlusion of posterior
cerebral artery
supplying anterior part
of occipital cortex
Congruous
homonymous macular
defect
Head injury/gun shot
injury leading to lesions
of tip of occipital
cortex+

7. Macular sparing
• Macular sparing is when the
central 5-10 degrees of the visual
field is unaffected in an otherwise
hemianopic defect. it is due to
 Separate blood supply
[Smith and Richardson (1996)].
They demonstrated two
interesting points:
• (i) in some individuals the
occipital pole of the visual cortex
is supplied by the middle cerebral
artery rather than the posterior
cereberal artery and
• (ii) in some patients, there is a
horizontal border at the macular
between the areas supplied by
the posterior temporal artery ( a
branch of the posterior cerebral
artery) and the area supplied by
the middle cerebral artery.
• Extent of macular
representation
The final theory to explain
macular sparing simply states
that the macular area has such a
large cortical representation that
in any incomplete lesion there is
a high probability that some of
the macular fibres will be left
intact.

8. Visual field defects
• Some visual perception is preserved in hemianopia field.
• OKN are usually spared in hemianopia of occipital origin.
• Coloured targets may be detected , achromatic one are not.
• Residual visual function –may be likely due to sparing of small
island of calcarine neurons.

9. CORTICAL BLINDNESS
• Due to B/L lesion of occipital lobe
• Total loss of vision in both eyes ,loss of reflex lid closure
to a bright light or threat
• Normal retina & ocular str., normal pupillary reflex and
maintenance of full extra ocular movements
• OKN –absent
• Alpha rhythm in EEG is lost
• Less complete lesion- variable perception

10. CORTICAL BLINDNESS (contd…)
ETIOLOGY :-
• Occlusion of PCA (Embolic or
thrombotic)
• Hypertensive/eclamptic/hypoxic
encephalopathy
• Schilder’s ds. & other
leucodystrophies
• CJD
• PML
• Cerebral infarction following cardiac
arrest
• B/L Glioma
TRANSITORY:-
• Head injury
• Migraine
• Antiphospholipid
syndrome
• Drugs:-IFN alpha,
cyclosporine

11. Anton–Babinski syndrome
(Visual anosognosia)
• Denial of blindness who cannot see.
• The lesion extend beyond the striate cortex to
involve visual association areas.
• Failing to accept being blind, the sufferer
dismisses evidence of his condition and
employs confabulation to fill in the missing
sensory input.
• Lesion is in visual association areas superior to
calcarine cortex.
Gabriel Anton

12. Blindsight:-
– Pt. with no ability to discriminate
patterns in the hemianopic field,
nonetheless could still reach
accurately and look at a moving
light in blind field.
– Flashing lights & moving objects
can sometime be seen even
without patient’s full awareness
(Weiskrantz & colleagues)
– Attributed to preserved function
of retinocollicular or
geniculoprestriate cortical
connections

13. Visual illusions (metamorphopsias)
• Distortion of form, size,
movement or color.
• Anatomic correlation is
imprecise.
• Reported with lesions
confined to occipital lobes.
• More frequently caused by
occipitoparietal or
occipitotemporal lesions, right
hemisphere involving more
than left.
Amsler grid

14. Visual illusions contd..
Different forms of illusions:-
• PHOSPHENES – flashes of light.
• METACHROMATOPSIA – colour changes into entirely
different colour
• ALLESTHESIA – displacement of real object, person
from its true geographic location
• PALLINOPSIA – persistence/reccurence of image after
the stimulus has been removed
• METAMORPHOPSIA – distortion of shape
• MICROPSIA – object appear small, lilliputian vision
• MACROPSIA – magnification of object

15. Visual illusions contd…
Different forms of illusions:-
• TELEOPSIA – object appear distant.
• POLYOPIA – seeing single target as multiple
• ENTOMOPIA – multiple copies of same image in a grid
like pattern
• SCINTILLATION – subjective sensation of sparks,
flickering, or flashes of light
• UNFORMED – images not recognized as person or
object
• FORMED – images of person or object

16. Visual hallucinations
SIMPLE/Elementary
(unformed) visual
hallucination:-
 points, stars, flames,
flashes, wheels,
circles and triangles,
may be
stationary/moving.
Lesion #Occipital
lobes
Coloured in SEIZURE
Simplest black & white
moving scintillation
MIGRAINE

17. Complex Visual Hallucinations
Complex Hallucinations
• Complex
hallucinations may
feature images of
people, faces,
birds, animals or
scenery.
• Lesion in
Temporal or
frontal lobes

18. Visual hallucinations
contd….• With hemianopia, visual hallucinations appear in the
defective field or move from intact field toward
hemianopic field.
• Also can occur during recovery from cortical blindness.
• Charles Bonnet syndrome:-
Complex visual hallucination in elderly
Preservation of insight and other cognitive abilities
Almost always have poor vision
Visual hallucinations in blindness .

19. OCCIPITAL LOBE EPILEPSY
Characteristics:-
 Elementary visual hallucination:-
 flashing or steady spots or simple geomatric forms either
coloured or achromatic
 When lateralised – contralateral to side of lesion
 Stationary or move across the visual field
 Ictal amaurosis:-
 second most common symptom
 Blindness may limited to one visual field but often B/L
If spread outside occipital lobe
– Somatosensory aura
– Complex visual or auditory hallucination
 Aura of eye movement sensation without detectable eye
movement.
 Forced blinking or eye lid flutter at the beginning of seizure
are objective evidence of occipital lobe origin.

20. OCCIPITAL LOBE EPILEPSY
Idiopathic occipital epilepsy:-
Gastaut type:-
• Age of onset is b/w 3 to 16 yrs of age.
• Characteristics:-visual hallucinations, ictal blindness,
phosphenes & tonic deviation of eyes.
• Seizure type- Hemiclonic, CPS, GTCS
• Duration usually <1 min
• Behavioral &autonomic features(eg:-vomitting) are
unusual
• Seizures resolves within 2 to 5 yrs in 50-60% of pt

21. OCCIPITAL LOBE EPILEPSY
• Panayiotopoulos syndrome:-
• Age of onset 3 to 6yrs (upto 14yrs)
• Characteristic :-
• Esp nocturnal
• Tonic deviation of the eyes
• Autonomic and behavioral features common
• e.g:- sweating, vomiting, pallor and irritability
• Best classified as autonomic rather than occipital
epilepsy
• Prognosis is good with remission in 1 to 2yrs
• Treatment with AED is usually unnecessary .

22. OCCIPITAL LOBE EPILEPSY
Idiopathic photosensitive occipital epilepsy:-
• Age of onset 5 to 17 yrs
• Trigger agent:- watching TV, playing video games
• Semiology:-starts with moving colorful spots in
peripheral visual field f/b head and eye version
with visual blurring, nausea, vomiting, sharp pain
in head or orbit & unresponsiveness
• Cognition, neurological examination and brain
imaging are normal
• Need distinction from IGE with photosensitivity.

23. OCCIPITAL LOBE EPILEPSY
EEG finding :-
• Interictal
Gastaut type & Panaiyotopoulos syn:-
• Runs of high amplitude 2 to 3 Hz sharp & slow
wave complexes in post quadrants.
Idiopathic photosensitive occipital epilepsy:-
• B/l synchronous/asynchronous occiptal spikes &
spike-wave complexes.
• Photic stimulation may induce an occipital
photoparoxysmal response & generalized
discharge.

24. OCCIPITAL LOBE EPILEPSY
Ictal EEG:-
• Gastaut type:- prominent occipital discharge
• Panayiotopoulos syndrome:- posterior
slowing
• Photosensitive epilepsy:- occipital
epileptiform activity which may shift from one
side to other.

25. OCCIPITAL LOBE EPILEPSY
Symptomatic form of ocipital epilepsy:-
• Following conditions associated with
prominent occipital discharges:-
Lafora’s disease
Mitochondrial disorders
Malformations of occipital cortical
development
Occipital epilepsy with b/l occipital
calcifications
Celiac disease

26. SUMMARY
Effects of unilateral disease, either
right or left
• Contralateral (congruent) homonymous
hemianopia, which may be central (splitting the
macula) or peripheral; also homonymous
hemiachromatopsia
• Elementary (unformed) hallucinations—usually
because of irritative lesions

27. Effects of left
occipital disease :
• Left homonymous
hemianopia
• With more extensive
lesions, visual illusions
(metamorphopsias) and
hallucinations (more
frequent with right-sided
than left-sided lesions)
• Visual object agnosia
• Effects of right
occipital disease :
• Left homonymous
hemianopia
• With more extensive
lesions, visual illusions
(metamorphopsias) and
hallucinations (more
frequent with right-sided
than left-sided lesions)
• Loss of topographic
memory and visual
orientation

28. Bilateral occipital disease
• Cortical blindness (pupils reactive)
• Anton syndrome (visual anosognosia, denial of
cortical blindness)
• Loss of perception of color (achromatopsia)
• Prosopagnosia (bilateral temporooccipital including
fusiform gyrus), simultanagnosia (parietooccipital)
• Balint syndrome (bilateral dorsal [high]
parietooccipital

29. THANKS
A beautiful, fascinating
and educational book of
optical illusions and eye
tricks, created by experts,
Eye Tricks takes the reader
on a journey around the
brain, teaching why we
see the way we do, and
even how we think!

30. Occipital Lobe Syndromes

31. VISUAL AGNOSIA
• Impairment of ability to recognise objects visually in the
absence of loss of visual acuity and general intellectual
functions that would account for it .
• Two factor in object recognition
– Act of conscious perception of sensory impression
(perception)
– The act of linking the content of perception with
previously encoded percept thus acquiring meaning
(association)

32. VISUAL AGNOSIA
• Not able to name and function of
seen object ( neither by spoken,
written words nor by gesture).
• Visual acuity intact and not
aphasic.
• Can identify object by palpation,
smell or sound i.e if presented in
other sensory modality.
• Usually a/w alexia,
homonymous hemianopia and
prosopagnosia.
• Lesion usually bilateral.
One highly intelligent patient described by
Oliver Sacks, when asked to identify a flower,
described it as 'a convoluted red form, with a
linear green attachment' but only recognised
it as a rose when allowed to smell it

33. Visual Agnosia
Neurophysiology
• “What” pathway (located in the temporal lobe)
 Perceive allocentric space (where objects are located with respect
to other objects)
 Visual perception-to-meaning processing
 Object processing
 Categories of knowledge about objects
• “Where” pathway (located in the parietal lobe)
 Perception of egocentric space (where objects are with respect to
the perceiver’s position)
 Perception-to-spatial location processing
 Conscious Space processing
 ‘Where’ and ‘How’

34. Ventral Stream – “WHAT ?”
• Striate cortex to inferior temporal lobe
• Activated by static images
• Provides info about what an object is
Dorsal Stream – “WHERE ?”
• Striate cortex to posterior parietal lobe
• Activated by moving objects
• Provides info about where an object is
Visual Perception (Higher visual pathways)
• Helps in visual recognition of objects,
faces & perception of colour
• Lesions produces impaired pattern
recognition & learning, producing
-Visual object agnosia
-Prosopagnosia
-Alexia
-Colour agnosia
-Ventral simultanagnosia
• Lesion produces—disorders of
spatial temporal analysis &
disturbances of visually guided eye &
hand control
-Balint syndrome
-Hemi neglect syndrome
-Dorsal simultanagnosia

35. “Object centered”
a mental
representation of
what whole object
looks like
Basic 2D description, gives
information about the fundamental
elements such as contours, edges,
lengths and position
“Viewer-centred” picture from
viewers standpoint , adds texture,
figure-ground discrimination
and depth from cues of shading
Semantic interpretation
Object
Primal sketch
2 ½ D sketch
3-D model Object
Recognition unit
Give
meaning
to stimulus
Marr’s computational theory of
visual processing

36. Object
Initial Representation
Viewer-centered representation
Object-centered
representation
Object
recognition units
Semantic
Processing
Name Retrieval
Spoken name
Modern model of visual processing

37. VISUAL AGNOSIA
• There are two categories:-
APPERCEPTIVE AGONOSIA:-
Difficulty in assembling the pieces or features of
object together into a meaningful whole
ASSOCIATIVE AGONOSIA:-
Can perceive a whole object but have difficulty
naming or assigning a label to it.

38. Apperceptive Visual Agnosia
• Defect in early stage of visual processing, preventing a
correct perception of the stimulus being formed.
• Can pick out features of an object correctly, such as
lines, angles, colors, or movements but fail to appreciate
the whole object.
• Object is not seen in a meaningful way.
• Common Causes:- Stroke, anoxia & carbon monoxide
poisoning.
• Often associated with diffuse, posterior lesions or stage
of recovery from complete cortical blindness.

39. Associative Visual Agnosia
• Patient can perceive objects presented visually but
cannot interpret, understand or assign meaning to the
object, face or word.
• Primary sensory & early visual processing are
preserved.
• More common than apperceptive visual agnosia
• Usually result of b/l damage to the inferior temporo-
occipital junction and subjacent white matter.

40. • Copying a drawing
– Apperceptive
agnosia
• Cannot copy the
drawing
• Cannot identify it
–
– Associative agnosia
• Can copy the
drawing
• Cannot identify it

41. Apperceptive Associative

42. Simultagnosia
• Term first used by Wolpert in 1924
• Defined as inability to grasp the scene of the multiple
components of a total visual scene despite retained ability
to identify individual detail.
• Inability to report all the items and relations in a complex
visual display despite unrestricted head & eye movements
• Describe the picture in a piecemeal manner.
 Two types-
 Dorsal simultanagnosia
 Ventral simultanagnosia

43. DORSAL SIMULTANAGNOSIA
• Perception is limited to a single object without
awareness of the presence of other stimuli. Thus, being
able to see only one object at a time
• Patient may collide with various objects in a room being
unaware of them. Additionally, objects in motion appear
more difficult to perceive
• Appear blind to observers
• Lesion in B/L junction at parieto-occipital lobe.

44. Patients suffering from Simultanagnosia and Balint’s syndrome will only
report the features they are presently looking at but will not be able to
understand the contents of the scene.
Simultanagnosia

45. VENTRAL SIMULTANAGNOSIA
• Patients are able to see several objects at once, but their
recognition of objects is limited to one object at a time.
• Slowed visual processing speed causing difficulty in
simultaneously recognizing the individual parts of a
multipart object
• capable of navigating through a room without bumping
into furniture
• Don’t appear blind to observer
• Site of lesion—left inf. temporooccipital cortex

46. Ventral simultanagnosia
“Mixed figures” used in the assessment of ventral simultanagnosia

47. Prosopagnosia
Greek: "prosopon" = "face", "agnosia" = "not knowing"
• A case of a prosopagnosia
is "Dr. P." in Oliver Sacks'
1985 book The Man Who
Mistook His Wife for a
Hat, though this is more
properly considered to be
one of a more general
visual agnosia.
• Although Dr. P. could not
recognize his wife from
her face, he was able to
recognize her by her
voice.

48. Prosopagnosia
• Inability to recognize familiar faces or to learn and recognize
new faces
• They can identify facial parts, recognize a face as a face but
cannot recognize the person
• Semantic knowledge about people is intact (Can retrieve
history of familiar persons when their name/other details
are provided verbally)
• They can identify familiar people by nonvisual or nonfacial
visual cues
• Prosopagnosia may occur in isolation suggesting that there
are specific areas of the brain that process visual information
pertaining to face recognition.

49. Prosopagnosia
• Many are also impaired in distinguishing specific types of
objects in a class (discriminating apple from a mango, a
maruti car from a santro)
• Eventhough patients have difficulty in identification,
usually they recognize the category of the visual object
eg., fruit,car or bird. (vs patients with visual agnosia who
fail to recognize the object category to which they
belong)
• They may identify facial expression& emotion, sex, and
age correctly, depending on the extent & location of the
lesion
• In severe cases, the patient may not even recognize his
own face

50. Prosopagnosia-Neurophysiology
• For face recognition, there are 2 stages beyond perception:
Recognition units :
Store the abstract representations of familiar faces derived
from our previous experience
Their activation by the perceptual processing raises a feeling of
familiarity, although not yet permitting identification
Occurs mainly in visual association areas of right hemisphere
Identity nodes:
 Subsector of the semantic store that provides the information
concerning the biography and relationship between the
observer & familiar persons and allows their identification.
Then only the name of face can be retrieved
 Carried out by left inferomedial temporal lobe

51. Prosopagnosia
Tests:
 Matching pictures of unknown faces
 Asking the patient to describe a given face verbally or to recognize familiar
faces or faces of well-known politicians /celebrities
Lesions site:
B/L mesial occipito-temporal region & subjacent white matter involving the
fusiform gyrus
Causes:
 Stroke (PCA infarct)
 Trauma, tumors, abscess, surgical resection
 Viral encephalitis, migraine, hypoxia, FTD etc

52. Patients with damage to the amygdala have
difficulties in recognizing emotion from facial
expression

53. Associative visual
Agnosia related
syndromes

54. Category specific Agnosia
• Impaired recognition of objects within a certain
categories
- living ,nonliving,
- metals, fruits, and musical instruments
• Warrington and Shallice (1984) reported a patient
who following an acute lesion to the left temporal
lobe had a selective deficit when asked to name
pictures from just one semantic category – living
things
• By contrast he was able to name non-living objects
very well including those with low frequency
names such as ‘accordion’

55. Movement agnosia, motion blindness or akinetopsia
A patient is unable to perceive motion, while all other
perceptual capabilities are intact.
He can still read books and see colors, but cannot discern
which direction something is moving, or how fast it is.
 Everyday actions, such as crossing a street ,are extremely
difficult since she cannot judge how fast a car is approaching
Lesion site: B/L medial-temporal area
Motion Agnosia

56.  Difficulty in naming visually presented objects
 Convey their recognition by pantomiming or describing
their use
 Can name stimuli presented in modalities other than
vision
 Some consider it as distinct entity from associative
agnosia, others consider it part of the later
 Most commonly due to a left occipital lesion
Optic aphasia

57. Mirror Agnosia
• Mirror agnosia is the inability to differentiate between
real and reflected objects, to mentally rotate objects, and
to perform line orientation tasks
• Patients cannot correct their behavior even after they
have been shown the real location of the object; they
always believe the object to be behind or in the mirror
itself and reach for it accordingly
• Lesions of either parietal lobe near the posterior angular
gyrus/superior temporal gyrus (the temporo-parieto-
occipital) junction

58. Pure alexia
 Alexia without agraphia / Pure word blindness
 A perceptual disorder causing impairment in reading words
and letters
 Patient can write to dictation but is unable to read back what
has been written
 The patient can copy words and letters and in the act of
copying the words or tracing out the letters may recognize the
word or letter
Lesion site:
 Damage to pathways conveying
visual inputs from both hemispheres
to the dominant angular gyrus
 Combined lesions of dominant
medial occipital region &
inferior fibers of splenium
of corpus callosum

59. Color Agnosia
 Naming & recognition of colors may be selectively
impaired
 Colour matching & other aspects of colour perception are
normal (as tested by Holmgrens colour sorting test)
 Can’t point to the colour named by the examiner
 Perform well in verbal-verbal tasks (e.g. “tell me the colour
of the sky?”)
 Lesion is commonly in inferomesial aspect of the occipital
& temporal lobes of dominant hemisphere

60. Color Agnosia
• Tests for a colour agnosia
showing patients
incorrectly coloured
objects.
• A patient who identifies an
inappropriately coloured
object as correct as to
colour, may have colour
agnosia.
• For example, a blue
banana may seem quite
normal to a colour agnosic

61. Assessment of visual agnosia
• First step :- establish the preservation of adequate elementary
visual abilities—acuity, visual fields, colour vision
• Then assess for..
Object recognition—recognition & naming tested
Colour —recognition & naming
Face recognition—persons, photographs
Picture recognition—for simultanagnosia
Matching & Copying - to differentiate between apperceptive
& associative agnosias

62. Assessment of visual agnosia
Test items Visual
agnosia
Optic aphasia Anomia Semantic
dementia
Visual naming Impaired Impaired, able
to pantomime,
circumloculate
Impaired, able
to pantomime,
circumloculate
Impaired
Tactile naming Normal Normal Impaired Impaired
Naming of
verbally
described
objects
Normal Normal Impaired Impaired
Object or
picture sorting
by semantic
category
Fails Normal Normal Fails
Error type Visual Semantic Paraphasic Semantic

63. Balint’s Syndrome
• Clinical triad described by Balint :-
– Optic Ataxia-- visually difficult to reach for objects;
may see, recognize object, but movement is usually
misdirected
– Psychic paralysis of gaze--difficulty in visual scanning;
not able to maintain fixation on an object - eyes will
begin to wander to another object
– Simultanagnosia - (can only “see” one object at a
time) not able to perceive more than one object at a
time
• Bilateral occipital-parietal lesions

64. Optic Ataxia
 Inability to perform coordinated voluntary
movements in order to reach for an object.
 Kinematics of reaching is altered
 More prominent in periphery of extrapersonal
space
 A visuomotor problem, can reach out
properly in response to tactile/auditory cues
 Damage to the dorsal stream at unilateral or
bilateral parieto-occipital junction (Karnath)
 Unilat lesions: failure of reach to
contralateral side with either hand

65. Prerequisites for a diagnosis of Optic
Ataxia (Garcin)
• A normal visual field
• Objects can be seen, recognised and named
even in the field where the visuomotor
deficits occur
• No defect in binocular stereopsis
• Normal proprioceptive function
• No intrinsic motor, oculomotor or cerebellar
deficit

66. Optic Ataxia

67. Oculomotor apraxia – Psychic paralysis
of gaze
 An inability to move the eyes voluntarily to points in
the visual field.
 Difficulty in visual scanning as in reading a book or
appreciating a painting. Failure of disengagement of
fixation (?)
 Reflexive movements may be spared.
 Eye movements towards auditory or somatosensory
stimuli spared.
 Usually co-occurs with visuospatial deficits

68. Ocular apraxia