Neuroanatomy of vision Flashcards
what is the visual field
overall field of vision when both inputs from both orbits are combined
what is the mechanism of vision
light enters the eyes and lands on the temporal or nasal portions of the retina
signals from the retina transmitted via the optic nerve (CN II)
decussation at the optic chiasm
on each side fibres from the nasal portion of the retina cross over
fibres from the contralateral visual field combine to travel up the optic tract to the lateral geniculate body
fibres from the upper and lower visual fields separate to reach occipital cortical areas in the optic radiation
where is the lesion in monocular blindness
optic nerve of affected eye
where is the lesion in bitemporal hemianopia
optic chiasm
where is the lesion in right homonymous hemianopia
left optic tract
(vice-versa for left HH)
where is the lesion in right superior homonymous quadrantanopia
lower fibres in left temporal lobe (optic radiation)
(again vice-versa in left SHQ)
where is the lesion in inferior homonymous quadrantanopia
upper fibres in left anterior parietal lobe (optic radiation)
(again vice-versa in left IHQ)
where is the lesion in right homonymous hemianopia with macular sparing
both the lower fibres in the left temporal lobe and the upper fibres in the left anterior parietal lobe (optic radiation)
(vice-versa in left)
describe the features of the optic nerve
travels alongside retinal vessels within the optic sheath to reach and innervate the retina
enters the eye at the optic disc (blind spot)
myelinated tract of the CNS, rather than a peripheral nerve
encased in the meninges like the rest of the brain
what are the two major layers of the retina
neurosensory retina
retinal pigment epithelium
describe the features of the neurosensory retina
photoreceptors - specialised neurons for phototransduction
rod cells - more sensitive, decreased acuity, no colour
cone cells - less sensitive, increased acuity, red-green colour
ganglion - blue colour, circadian rhythm, pupillary light reflex
describe the features of the retinal pigment epithelium
maintain overlying neurosensory layer
absorbing scattered light
blood/eye barrier
describe the primary visual cortex
located in occipital lobe
receives direct visual signalling input originating from the contralateral side
what are the higher visual centres
dorsal stream - posterior parietal cortex, ‘where/how’ pathway, integrates vision with motor/sensation
ventral stream - inferior temporal cortex, ‘what’ pathway, form recognition, object representation, visual memory
what is visual agnosia
inability to visually recognise pbjects
lesions of occipital and/or temporal lobes
