9 - Opth - Visual fields and Optic nerve Flashcards
describe the visual pathway (pre-chiasm)
light projected onto retina in reversed manner
APs transmitted by retinal rod, cone and ganglion cells
Fibres leave eye at optic disc in optic nerve - to chiasm
describe visual pathway (chiasm to occipital cortex)
Nasal retinal fibres decussate and join temporal fibres from other eye – form each optic tract
(tract = ipsilateral temporal retina + contralateral nasal retina fibres)
These fibres synapse at each lateral geniculate body (except those that control pup reflexes)
Fibres then reach occipital cortex
describe the visual pathway once fibres leave the lateral geniculate nuclei - including diff between path of upper and lower fibres
Lateral geniculate nucleus > parietal and temporal lobes > optic radiation > occipital (visual) cortex)
UPPER retinal fibres (lower fields) – through parietal lobes – upper occipital cortex
LOWER retinal fibres (upper fields) – through temporal lobes – lower occipital cortex
Field loss corresponds to lesion on…
OPPOSITE side of brain
Pre-chiasmal lesions …
do not respect vertical midline (mononuclear field loss)
Chiasmal/Post-chiasmal lesions …
always respect the vertical midline (hemi/quadrantanopia)
Where is the lesion?
paracentral scotoma
Retinal lesions eg AMD, DR, Glaucoma
Where is the lesion?
Mononuclear field loss (whole eye visual loss)
Complete optic nerve lesion
Where is the lesion?
Bitemporal hemianopia
Chiasm lesion
Where is the lesion?
Homonymous hemianopia
optic tract lesion
Where is the lesion?
Right Superior Homonymous quadrantanopia
left temporal lesion
bc sup vision hits lower retinal fibres which travel through temporal lobe
Where is the lesion?
Right Inferior Homonymous quadrantanopia
left parietal lobe
bc inf vision hits superior retinal fibres which travel through parietal lobe
Where is the lesion?Homonymous hemianopia with macular sparing
optic radiation or occipital cortex
macular cortex at occipital pole supplied by different blood supply)
Where is the lesion?
Homonymous hemianopia - hemiscotoma (half macula vision gone)
occipital pole (macular cortex) lesion
