Lecture 23 - vision 2 Flashcards
How are fibres located?
Fibres representing one half of the field of view cross over to the opposite side of the brain
what type of order do fibres retain in the optic nerve and throughout the visual system?
retinotopic order
what do optic nerve fibres enter?
the LGN
whats LGN ?
Lateral geniculate nucleus
How many layers does the LGN have?
6
what are the layers of the LGN?
2 magnocellular layers and
4 parvocellular layers
how does the LGN receive input form the eye ?
Alternating layers receive input from alternate eyes
what layers of the LGN are ipsilateral?
5 3 2
what layers of the LGN are contralateral?
6 4 1
where d nerve fibres form the LGN go?
to the visual cortex
where do nerve fibres from the LGN synapse?
layer IV of the cortex
what is the arrangement of the Cortex ?
each eye contributes to both sides but remain segregated to some degree in primary cortex
How is the visual cortex arranged?
in columns
Adjacent columns represent alternate eyes
what do simple cells respond too?
Simple cells respond to bars of light of one orientation
what kind of regions do simple cells have?
on-off regions
facts about complex cells
- orientation selective
- do not have simple on-off fields
- usually binocular
Neurones with the same orientation selectivity are arranged in ______
columns
Adjacent orientation columns within an ocular dominance column show what?
a gradual shift in orientation across the full range
what do you find between ocular dominance columns?
blobs
what are blobs?
patches of colour sensitive neurones
what are blobs and modules arranged into?
modules
what do modules contain?
complete representation of the colour, motion and orientation of a point in the visual field observed using both eyes
How many channels can the pathway from the retina to cortex be split into ?
atleast two main channels
what happens at the p- channel?
retinal ganglion cells have small receptive fields and analyse detailed form and colour
what happens at the m-channel?
retinal ganglion cells have large receptive fields and probably detect motion and large scale detail
how many pathways are there in the primary visual cortex?
2
what does the dorsal pathway in the higher visual centres subserve?
subserves spatial vision
what does the ventral pathway in the higher visual centres subserve?
subserves colour and object vision
where can visual disorders occur?
anywhere in the visual pathway
name a neural deficit?
Colour blindness, caused by loss of one type of cone
whats optic neuropathy?
A Neural deficit, specific to retina; blood vessel damage and regrowth
what does glaucoma cause?
Causes thinning of the nerve fibre layer in the retina and gradually results in loss of vision
what does untreated glaucoma eventually lead too?
lead to blindness
whats a risk factor for glaucoma?
a family history of glaucoma, increasing age and prolonged steroid use.
whats AMD?
Age related macula degeneration
whats the most commonest cause of registered blindness?
Age related macula degeneration
who does AMD affect?
65 years
does peripheral vision remain unaltered with AMD ?
yes
what does AMD produce?
Produces blurry vision, wavy or distorted lines or a central blind spot.
what are the risk factors of AMD?
Risk factors include increasing age, female gender and smoking. The disease may have a genetic component.
what is diabetic retinopathy?
Deterioration of the tight junctions of a blood vessel wall causing blockage, exudates hemorrhages and micro aneurysms.
Name a common eye disease?
Superior temporal branch retinal vein occlusion
what is Superior temporal branch retinal vein occlusion
?
blockage of a retinal vein ?
what are predisposing factors of Superior temporal branch retinal vein occlusion
?
- Increasing age
- Systemic hypertension
- Raised Intra ocular pressure and long sighted spectacle corrections.
what is Presbyopia ?
when Ages of 40-45 showing difficulties with reading.
what are some symptoms of Presbyopia?
holding reading material further from the eyes and blurry distance vision immediately after reading.
why does Presbyopia happen?
the lens becoming inelastic making focusing on near objects difficult
How can Presbyopia be rectified?
Rectified by the use of bifocals, varifocals, separate reading spectacles or contact lenses.
what is cataracts?
Any opacity of the lens.
May present as gradual blurring of the vision, seeing double in one eye or increased sensitivity to glare.
when is cataracts more common?
common with increasing age. Excessive unprotected exposure to UV light, smoking, poor nutrition and prolonged steroid.
How can cataracts be treated?
Cataracts can be removed surgically by replacing the lens with a clear plastic lens implant.
