3. Special senses/ visual pathways, lesions Flashcards
Which visual field information crosses at the optical chiasma?
The left and right lateral (peripheral) visual field
Result of lesion in left superior temporal retina on vision?
e.g. AMD
Corresponding field defect in the left inferior nasal visual field
Result of lesion of right optic nerve on vision?
Total blindness of right eye (i.e. Right peripheral and left central vision lost)
result of chiasmal lesion on vision?
Bitemporal hemianopia
Result of lesion of the left optic tract (after the chiasma) on vision?
Right incongruous hemianopia
Very rare
Result of lesions of inferior optic radiations in temporal lobe on RHS?
Right homonymous superior quadrantanopia
What is hemianopia on vision?
hemianopia, the loss of the right or left half of the visual field in both eyes
What is quadrantanopia on vision?
Quadrantanopia refers to the loss of vision in one of the quarters of the visual field.
Result of involvement from upper left optic radiations on vision?
Right homonymous inferior quadrantanopia
Meaning of congruous?
In harmony (the same) so Incongruous is when two things are different
Result of lesion of the left hemisphere on vision?
Right homonymous hemianopia
What is AMD?
Age-related Macular Degeneration (AMD)
Leads to visual field loss which is specific to a part of the eye
Chiasm involved in creation of….
Stereovision
2 examples of chiasmal lesion?
Pituitary tumour
Craniopharyngioma
Why does chiasma result is loss of lateral vision?
Only effects the information that is crossing over
Journey of visual info from the world to visual cortex?
Field of vision Left or right retina Optic chiasma L or R Optic tract L or R Geniculate nucleus Optic radiations via Meyer's loop, dorsal bundle and central bundle Visual cortex
Result of lesion of Meyer’s loop?
A lesion in Meyer’s loop causes a contralateral homonymous superior quadrantanopia, sometimes termed a “pie-in-the-sky” defect (Fig. 8.4). Lesions of Meyer’s loop tend to spare fixation, as the fibers subserving the macula do not extend anteriorly.
Parietal damage leads to which type of quandrantopia?
Inferior
Why? Inferior visual field is seen by the top part of the retina. This information passes through parietal lobe when passing from geniculate nucleus to the visual cortex
Temporal damage leads to which type of quandrantopia?
Superior
Why? Superior visual field is seen by the bottom part of the retina. This information passes through temporal lobe when passing from geniculate nucleus to the visual cortex
Lesion of the left temporal lobe in a CVA leads to..
Hint: At meyers loop
Right superior quadrantanopia
What is PVL?
Peri-ventricular leucomalacia
A form of white-matter brain injury, characterized by the necrosis (more often coagulation) of white matter near the lateral ventricles.
What are the two streams of vision?
The “what” and the “where” streams
Children with spastic diplegia can have difficulty with tasks involving _____ field i.e. _____ lower ______________
Children with spastic diplegia can have difficulty with tasks involving lower field i.e. bilateral lower quandrantanopia
Relationship between cerebral palsy and PVL
Structural breakdown of the thalamus and it’s nuclei?
- Anterior nuclei
- Medial nuclei
- Lateral nuclei
- Lateral post nucleus
- Lateral dorsal nucleus
- Ventral anterior nucleus
- Ventral lateral nucleus
- Ventral posterior nucleus (VInt, V post-med, ventral posterolateral VPL) - Medial geniculate body
- Lateral geniculate body
LGN?
Lateral geniculate nucleus
Layers of the LGN?
6
Input and output of the LGN?
Input:
- Layers 2,3 and 5 receive ipsilateral eye info
- Layers 1,4 and 6 receive contralateral eye info
Output:
Layers 1 and 2 travel by the magnocellular pathways
Layers 3,4,5 and 6 travel by the parvocellular pathway
What is the line of gennari?
Myelinated fibres running from LGN (of the thalamus) to synapse in layer 4 of the striate cortex
Occipital lobe function?
• Relay staAon • Retinotopic map • Neural tuning is present • Specific populations of cells will respond to; 1. Colour 2. Spatial frequency 3. Orientation
Representation of the central __ degrees (shaded areas) in the visual field occupies about 40 % of the cortex.
representation of the central 5 degrees (shaded areas) in the visual field occupies about 40 % of the cortex.
Where is the “what system” found?
Temporal lobe
RHS- Faces and route finding
LHS- Words and shapes
Pathology of the “what system”?
Loss of face recognition; Prosopagnosia
Loss of route finding; Topographic Agnosia
Inability to read words; Alexia
Meaning of the following?
Alexia
Inability to read words;
Meaning of the following?
Topographic Agnosia
Loss of route finding
Meaning of the following?
Prosopagnosia
Loss of face recogniAon
Ebbinghaus Illusion?
The Ebbinghaus illusion - of different relative size perception, provides a way the eye and brain process visual information.
What is area V1?
The primary visual area (V1) of the cerebral cortex is the first stage of cortical processing of visual information. Area V1 contains a complete map of the visual field covered by the eyes. It receives its main visual input from the lateral geniculate nucleus of the thalamus (LGN), and sends its main output to subsequent cortical visual areas
