Class_02_Vision Flashcards
Week 2
Retina
Contains many photosensitive cells at the back of the eye
- produce electrical activity when stimulated
Optic nerve
- Receive electrical signal from retina
- Transfer them to occipital lobe
Adaption
- The light has to pass through lots of other cells first
- They adapt to anything that stays still and then They stop firing
Fovea
This is the only part of the retina which allows high-definition vision
- can only see things in detail that are focused on the fovea
Macula
a larger area than the fovea and contains other parts, not just the fovea
- used interchangeably with fovea
Blind Spot
- Where the axons all meet to leave the retina
- forming the optic nerve
- no light receptors
- blind in that part
- very rarely aware of that blind spot
Rod Cells
- Only sensitive to intensity of light
- sensitive to low levels of light
- monochrome
Cone Cells
- Sensitive to particular wavelengths of light
- RGB
- require more stimulation than rod cells
Visual Pathway
Retina -> Optic nerves -> Optic chiasm -> Optic tracts -> Lateral geniculate nucleus (LGN) of Thalamus -> Visual cortex
Optic Chiasm
Carrying the information from the retina
- split up optic nerves
- some staying on the same side of the body
- some crossing over to the opposite side
Left Visual Field of Both Eyes
Right retina -> Optic nerves -> Optic Chiasm -> Right optic tract -> Right lateral geniculate nucleus (LGN) of Thalamus => Right visual cortex
Right Visual Field of Both Eyes
Left retina -> Optic nerves -> Optic Chiasm -> Left optic tract -> Left lateral geniculate nucleus (LGN) of Thalamus => Left visual cortex
Optic Radiations
3 different routes that projections take from the LGN to the primary visual cortex
- Meyer’s loop
- Central bundle
- Dorsal bundle
Meyer’s loop
Upper visual field travel through
the temporal lobe
Central Bundle
Middle visual field travel through
the parietal lobe
Dorsal Bundle
Lower visual field travel through
the parietal lobe
The most serious brain damage causing visual field loss
- Damage all of the radiations on one side of the brain
- Damage the primary visual cortex in the occipital lobe
Hemianopia
A half blind
- a substantial loss of vision for the RIGHT visual field (of each eye)
- damage to the LEFT hemisphere optic radiations
- damage to the LEFT primary visual cortex
- Vice versa: LEFT visual field from RIGHT parts of the brain
Quadrantanopia
Quarter blind
- loss of vision for an upper/lower part of visual field (seen from either eye)
- damage to one of optic radiation
Upper Left Quadrantanopia
loss of vision to the upper left visual field (seen from either eye)
- damage to right hemisphere Meyer’s loop
Homonymous Hemianopia
same hemianopia for both eyes
Macula Sparing
with hemianopia
- maintain vision within the part of the visual field supplied by information from the macula of the retina
- receiving blood supply from both the posterior cerebral artery
and the middle cerebral artery
scotoma
smaller visual field losses often occur, so that an area of visual field much smaller than a quadrant
- will shrink with recovery
- human all have a scotoma in each eye, caused by the blind spot
Superior Colliculi
Receive projections from the retina
- attention
- eye movements towards things that we see
Visual Field Check
2 finger signal at each eye quadrant
Case Bryan Kolb
Left homonymous hemianopia
- Right primary visual cortex damage
Event Awareness
Accurately guess about things
presented to their blind fields
Case G.Y.
Right homonymous hemianopia with macular sparing
- Left occipital lobe damage
- able to describe the direction of lights moving within blind hemifield
- Reason: processing some visual information in earlier stages in subcortical regions
- LGN and visual areas of thalamus is still intact
Blindsight
- cortically blind
- can perform visual tasks
- no visual consciousness
Circadian Rhythms
- sleep-wake cycle
- changes in immunity responses
- body temperature and appetite
Suprachiasmatic Nucleus
Receiving light information from the retina or ipRGCs
- Allow the circadian rhythms
Intrinsically Photosensitive Retinal Ganglion Cells (ipRGCs)
Special light sensitive neuron
- not rod or cone cell
Circadian rhythms implications for cognitive assessment
Attention and working memory appear to be most efficient in the afternoon
- neurodegenerative disease caused cognitive disorders
Color blindness
- proteins that produce sensitivity to light are on the X chromosome
- color blindness is relatively rare in women
Ishihara Test
Color blindness test
- numbers in plates
Cerebral Achromatopsia
Damage to the ventral occipital cortex
- can be unilateral brain damage
- one side color, one side color blinded
quadrant visual field achromatopsia
Developmental Dyslexia
- Phonological processing impairments
- Visual processing problems
- have LGN that are smaller
-> affect magnocellular regions
Dyslexia Assessment
Reading aloud or repeating pseudowords
- e.g. ‘polatile’ or ‘dovine’
- rely on phonological skills
Magnocellular
‘Big cells’
- ganglion cell that carry information from the retina to the lateral geniculate nucleus (LGN), via the optic nerve
- small LGN -> affect magnocellular -> dyslexia
- dorsal visual stream
- connect the LGN to the primary visual cortex to the parietal lobe
Dorsal Visual Stream
Retina -> primary visual cortex -> parietal lobe
- convey information used for attention, and motion, and timing
Magnocellular System Input
Red and green cone cells in the retina
Treatment for dyslexia
- Yellow filter glasses
-> stimulate magnocellular system - Blue filter glasses
-> stimulate ipRGCs -> suprachiasmatic nucleus -> circadian rhythms
- blue color of sky in daytime
