3 - Visual Pathways Flashcards
how many rods and cones does the retina contain?
rods - 100 million
cones - 6 million
what are the 3 roles of rods?
- vision in low lighting
- peripheral vision
- low resolution
what are the 3 roles of cones?
- detailed vision
- colour vision
- brighter light
the retina projects to four subcortical regions in the brain - what are they?
- lateral geniculate nucleus - primary visual pathway
- superior colliculus
- hypothalamus
- pretectum
what is the course of the fibres in meyer’s loop?
fibres from inferior retina travel through the temporal lobe
the straight fibres of the optic radiation contain fibres from which part of the retina?
superior retina
the straight fibres of the optic radiation travel through which lobe of the brain?
parietal
meyer’s loop fibres travel through what lobe of the brain?
temporal
meyer’s loop contains fibres from which part of the retina?
inferior retina
the looped part of the optic radiation is called what?
meyer’s loop
where is the optic disc in relation to the fovea?
nasal
what is the optic disc?
a blind spot in temporal visual field at about 15 degrees eccentricity
list a retinal cause of a visual field defect:
- vascular - retinal artery occlusion
- retinal detachment
- macular lesion - central defect
list an optic nerve cause of a visual field defect:
- glaucoma
- optic neuritis
- optic atrophy
- optic nerve compression
list a lesion at the chiasm that could cause a visual field defect
tumour - esp pituitary
list a lesion after the chiasm that could cause a visual field defect
- stroke
- tumour
list an occipital cortex cause of visual field defects
- stroke
- trauma
visual field abnrmalities that do not cross the midline are of what origin?
retinal
macular degeneration causes what sort of visual field defect?
central visual field defect
a superonasal retinal detachment in the left eye will cause what visual field defect?
inferotemporal visual field defect
a pituitary tumour most often results in what type of visual field defect?
bitemporal hemianopia
homonymous hemianopias (retrochiasmal lesions) are named after what?
the eye that has the temporal vision loss
what are the two theories of macular sparing?
- macular takes up large area of visual cortex - massive infarct would be needed to completely wipe it out
- area of the visual cortex that involves the macular vision has 2 diff blood supplies - both would need to be blocked
if there is superior visual field loss, what optic radiations are affected?
optic radiations in Meyer’s loop
if there is inferior visual field loss, what optic radiations are affected?
optic radiations in parietal lobe
what does the acronym “PITS” refer to in homonymous quadrantanopia?
Parietal lesions cause an
Inferior defect
Temporal lesions cause a
Superior defect
