The document discusses higher visual dysfunction and disorders that can result from damage to different parts of the visual pathway and visual processing streams in the brain. It describes how visual information is processed from the eyes to the primary visual cortex and then into two streams - the ventral "what" stream for object recognition and the dorsal "where" stream for spatial processing. It then provides details on four specific disorders: visual agnosia (failure to recognize objects), achromatopsia (loss of color vision), pure alexia (impaired reading ability despite normal writing), and prosopagnosia (inability to recognize faces). Each disorder is caused by damage to different regions of the visual system and results in unique symptoms and challenges for

1. By Ahmed Koriesh
HIGHER VISUAL
DYSFUNCTION

2. Visual Pathway:
• Visual information leaving the eyes in the optic nerve converges at
the chiasm where the fibres partially decussate.
• The optic tract sends most of its fibres to the lateral geniculate
nucleus (LGN) of the thalamus.
• The remaining fibres pass to the superior colliculus (involved in
directing eye movements).
• The optic radiations, fanning into the parietal and temporal lobes,
carry information from the LGN to the primary visual area, also
known as V1 or 'the striate cortex'

3. Visual Pathway:
• The concept of 'streams' of vision flowing out from V1 allows us to
group and understand some of the individual components of higher
visual function
• The ventral (temporal) stream is also referred to as the 'what'
stream, being concerned with object and face recognition as well as
reading and colour.
• The dorsal (parietal), or 'where' stream, encompasses visual motion
and detects and collates multiple items in a scene.

5. •Ventral (temporal or 'what') stream disorders:
• Visual agnosia
• Achromatopsia
• Pure alexia
• Prosopagnosia

6. Visual agnosia
• Failure to recognize objects by the visual modality alone
• apperceptive agnosia
• Severe deficit
• lack the basic perception required to draw a copy of it
• Most of these patients have widespread brain lesions, specially CO poisoning .
• associative agnosia
• Milder deficits
• They know that they are looking at something distinct and can copy it line-by-
line but cannot recognize it
• Selective lesion of secondary visual areas

7. Achromatopsia
• Complete or partial loss of colour vision
• Bilateral damage (most often a stroke) to a relatively small region of
the cortex (the inferior surface of the temporal–occipital regions)
• A unilateral lesion causing hemiachromatopsia often remains
unnoticed, unless the patient is directly tested
• Usually associated with a superior quadrantanopia and frequently
there is prosopagnosia and alexia.
• Diagnosed by Ishihara plates
• My shirts all look dirty… I have no idea what tie to wear… I can tell peas and bananas
only by their size and shape. An omelette, however, looks like a piece of meat and when
I open a jar I never know if I will find jam or pickles in it!

8. .

9. Pure alexia
• Acquired disorder of reading
• Results from infarction within the vascular territory of the left
posterior cerebral artery.
• Patients cannot read numbers, letters, map signs or symbols
• The most striking feature of pure alexia, however, is the
dissociation between the impaired reading and the normal writing
ability.

10. Prosopagnosia
• Inability to recognize familiar faces
• Inability to experience a feeling of familiarity when viewing a
known face
• Prosopagnosics often employ other methods to recognize people
('I memorize hair, jewellery and favorite clothes. I recognize gaits,
tics and voices')
• Associated with right occipito temporal lesions
• Commonly associated with left homonymous quadrantanopia

11. Thank you