Neuroanatomy of vision Flashcards

1
Q

what is the visual field

A

overall field of vision when both inputs from both orbits are combined

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2
Q

what is the mechanism of vision

A

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

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3
Q

where is the lesion in monocular blindness

A

optic nerve of affected eye

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4
Q

where is the lesion in bitemporal hemianopia

A

optic chiasm

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5
Q

where is the lesion in right homonymous hemianopia

A

left optic tract
(vice-versa for left HH)

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6
Q

where is the lesion in right superior homonymous quadrantanopia

A

lower fibres in left temporal lobe (optic radiation)
(again vice-versa in left SHQ)

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7
Q

where is the lesion in inferior homonymous quadrantanopia

A

upper fibres in left anterior parietal lobe (optic radiation)
(again vice-versa in left IHQ)

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8
Q

where is the lesion in right homonymous hemianopia with macular sparing

A

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)

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9
Q

describe the features of the optic nerve

A

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

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10
Q

what are the two major layers of the retina

A

neurosensory retina
retinal pigment epithelium

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11
Q

describe the features of the neurosensory retina

A

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

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12
Q

describe the features of the retinal pigment epithelium

A

maintain overlying neurosensory layer
absorbing scattered light
blood/eye barrier

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13
Q

describe the primary visual cortex

A

located in occipital lobe
receives direct visual signalling input originating from the contralateral side

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14
Q

what are the higher visual centres

A

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

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15
Q

what is visual agnosia

A

inability to visually recognise pbjects
lesions of occipital and/or temporal lobes

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16
Q

what are the subtypes of visual agnosia

A

prosopagnosia - unable to recognise even familiar faces
associative visual agnosia - unable to name things visually

17
Q

what are conjugate eye movements important fot

A

stable vision
failure can lead to diplopia (double vision)

18
Q

what are the extraocular muscles

A

recti muscles - superior and inferior rectus, medial and lateral rectus
oblique muscles - inferior and superior oblique
levator palpebrae superiororis

19
Q

what are the movements of the recti muscles

A

superior - elevates
inferior - depresses
medial - adducts
lateral - abducts

20
Q

what are the movements of the oblique muscles

A

inferior elevates
superior - depresses

21
Q

what is the movement of levator palpebrae superioris

A

raises the upper eyelid

22
Q

how is coordination of eye movements controlled

A

important for stable vision
controlled within brainstem
inputs come from visual cortex, cerebellum, vestibular nuclei, superior colliculus

23
Q

what are the outputs for coordinated eye movements

A

horizontal and vertical gaze centres in pons and midbrain coordinate output to cranial nerve nuclei bilaterally, resulting in conjugate eye contact
connected by medial longitudinal fasciculus

24
Q

what can cause dysconjugate ocular movements

A

internuclear ophthalmoplegia - lesion in the medial longitudinal fasciculus