vision Flashcards
visual pathways: explain the visual pathways and how specific visual field defects can arise from lesions at different sites, and explain the basic processes of visual integration occurring at different levels of the visual pathway
what is the optic nerve
ganglion nerve fibres
what happens at the optic chiasm
half of nerve fibres cross
what is optical tract
ganglion nerve fibres exit as optic tract
what happens at lateral genticulate nucleus in thalamus
ganglion nerve fibres synapse onto optic radiation
what is the optic radiation
4th order neuron
where does optic radiation go
primary visual cortex (striate cortex) within occipital lobe
visual pathway anatomy diagram
slide 2
first order neurones in retina
rod and cone retinal photoreceptors
second order neurones in retina
retinal bipolar cells, which modulate signal
third order neurones in retina
retinal ganglion cells (optic nerve)
what do lesions anterior to optic chiasma affect
visual field in one eye only
what do lesions posterior to optic chiasma affect
visual field in both eyes
what fibres cross at optic chiasma
originating from nasal retina, responsible for temporal visual field
what fibres don’t cross at optic chiasma
originating from temporal retina, responsible for nasal visual field
diagram of crossing and uncrossing at optic chiasma
slide 4
what happens if lesion at optic chiasma
damaged crossed ganglion fibres from nasal retina in both eyes, causing temporal field deficit in both eyes (bitemporal hemianopia)
what happes if right sided lesion posterior to optic chiasma
left homonymous hemianopia in both eyes
what happes if left sided lesion posterior to optic chiasma
right homonymous hemianopia in both eyes
disorders of visual pathway diagram
slide 5
what typically causes a bitemporal hemianopia
enlargement of pituitary gland tumour
what typically causes homonymous hemianopia
stroke (cerebrovascular incident)
what typically is affected if superior or inferior field defect
eye problem e.g. glaucoma
what typically is affected if left or right field defect
neurological problem
type of vision defect if problem in occipital lobe (e.g. infarction)
macular sparing as part of central vision spared, unless massive occipital lobe trauma
