W4 VF representations in V1

what is the line of decussation

divides nasal and temporal retina

% of ganglion cells in the macular and fovea

66-75%

describe pathway of axons arising from GC in nasal superior and inferior retinal quadrants to the nerve head

direct

describe pathway of axons arising from GC temporally to the macula

arcuate course around fovea centralis

describe pathway of axons arising from GC in the fovea and macula to the nerve head

directly

aka papillomacular bundle

how do ganglion cell axons preserve topography / maps

peripheral axons from superior, nasal, inferior and temporal quadrants enter ONH peripherally

central axons enter more centrally

what is present below the optic chiasm

pit gland

what is present above the optic chiasm

hypothalamus

3rd ventricle

what is present laterally to the optic chiasm

Internal carotid artery

cavernous sinus

what is the cavernous sinus

network of small arteries and veins that sit behind the orbit

what do the arteries around the optic chiasm form

circle of willis

where does the orbital nerve receive blood from

ophthalmic artery

where does the canalicular nerve receive blood from

short branches from anterior cerebral and anterior communicating arteries

where does the cranial nerve & chiasm receive blood from

short branches from posterior cerebral and posterior communicating arteries

what can compression of the chiasm at the midline be caused by

pituitary tumour (adenoma)

raised pressure in the 3rd ventricle

what can compression in the chiasm at the midline cause

bi-temporal hemi anopsia

what can compression of temporal axons be caused by

ICA outpocketing due to an aneurysm

cavernous sinus expansion due to thrombosis

where is the VF loss if a pituitary adenoma initially compresses axons from nasal inferior retina

superior temporal VF

where do nasal axons from the opposite eye terminate in the LGN

layers 1,4,6

where do temporal axons from the same eye terminate in the LGN

layers 2,3,5

what is the function of the LGN

organise retinal inputs from 2 eyes into alt maps of the opposite hemi-field

where does the LGN relay info to

V1

on the same side of the brain via axons that arise from the LGN in each layer

where do the axons from the LGN first travel to

posterior limb of internal capsule

THEN

optic radiations to area V1

what does the medial half of the LGN represent

lower visual quadrant of VF

what does the lateral half of the LGN represent

upper visual quadrant of VF

where do the optic radiations from the medial half of LGN go

upper bank of calcarine sulcus

where do the optic radiations from the lateral half of LGN go

lower bank of calcarine sulcus

what is 'Meyer's loop' and why is formed

inferior horn of the lateral ventricle causes an obstruction

axons from lateral half of LGN have to travel anteriorly then loop around to join the optic radiations

what is the blood supply for axons in 1st part of radiations after the internal capsule

middle cerebral artery

what is the blood supply for axons in the last part of radiations under the occipital lobe

posterior cerebral artery

what is the blood supply for calcarine sulcus upper and lower banks

calcarine artery

what is the blood supply for occipital pole

dual supply of calcarine artery and terminal branch of MCA?

what does damage at the optic nerve cause

blindness in visual field

one eye damaged

what does damage at the midline / chiasm cause

nasal axons destroyed

bi-temporal hemi-anopsia

what does damage of the optic tract cause

lose one half of the vision field

what does damage at meyer's loop cause

upper quadrant anopsia