VISION - Visual Pathway Flashcards
What defect produces a junctional scotoma defect?
Defect in optic nerve near optic chiasm at wilbrands knee –> nasal fibres decussate and bend upwards towards opposte optic and get affected
What field is produced with a central optic chiasm defect?
Leads to bitemporal hemianopia (both nasal fibres are affected)
Bitemporal hemianoic paralysis of the pupillary response
What is the visual pathway? (7)
- Retina
- Optic nerve
- Optic chiasm
- Optic tract
- Lateral geniculate body
- Optic radiations
- Visual cortex
What are the causes of a central optic chiasm lesion (5)
- Craniopharyngioma
- Pituitary tumor
- Suprasellar aneurysm
- Supresellar meningioma
- Third ventricular dilatation due to hydrocephalus
What happens following an optic tract lesion to the fibres? What visual defect?
uncrossed temporal fibres lead to nasal defect in ipsilateral eye and crossed nasal fibres lead to temporal defect in opposite eye - homonymous hemianopia
Can cause a third nerve palsy and ipsilateral hemiplegia
What is the outcome of a lateral optic chiasm defect
Affects temporal fibres of optic chiasm –> nasal defect
Binasal hemianopia
Binasal hemianopic paralysis of pupillary reflex
What are the main causes of optic tract lesions? (5)
- Thalamus tumours
- Syphilitic meningitis
- TB
- Posterior cerebral artery aneurysm
- Superior cerebellar artery aneurysm
What visual defect is produced with a lateral geniculate body lesions? Pupillary response is present or absent?
Homonymous hemianopia with sparing of pupillary reflex as the pupillary fibres have already left the optic tract at the superior colliculus
What visual defect is produced from a lesion in Meyer’s loop (inferior retinal fibres in optic radiation travelling in temporal lobe)
Homonymous superior temporal quadrantinopia (pie in the sky)
What visual field defect is produced from a lesion in superior retinal fibres from optic radiations?
Homonymous inferior temporal quadrantinopia (pie in the floor)
–> fibres pass through parietal lobe
What is the blood supply of the visual cortex?
Posterior cerebral artery
Middle cerebral artery
What visual field lesion is seen in a visual cortex lesion (PCA /MCA stroke)
Congruous Homonymous hemianopia with macular sparing (macular spared as receives dual supply from PCA or MCA)
What conditions can affect the first order neurons in the sympathetic pathway in Horner’s syndrome (hypothalamus to spinal centre of budge)
- CVA
- Lateral medullary syndrome
- Multiple sclerosis
- Neurological disorders and infections
What conditions can affect the second order (preganglionic neurons) from ciliospinal centre of budge to superior cervical ganglion in sympahetic pathway (Horner’s syndrome)
Any disease affecting mediastinum and neck
1. Apex lung lesions - Pancoast
2. Subclavian artery injury
3. Brachial plexus injury
4. Mediastinal lymphadenopathy
5. Dental abscess involving mandibular region
What diseases can affect the third order (Superior cervical ganglion to long ciliary nerves) in Horner’s syndrome
- Carotid cavernous fistula
- Carotid artery dissection/aneurysm
- Raeder paratrigeminal system
- Herpes zoster infection
- Temporal arteritis
- Cluster headaches or migraines
What is the reason for partial ptosis or reverse/inverse ptosis in Horner’s syndrome?
- Symphathetic chain supplies superior tarsal plate, responsible for partial elevation of eyelid
- Sympathetic chain supplies lower eyelid - lesions leads to upward movement of lower eyelid
What happens to the pupil in Horner’s syndrome?
Smaller than other side
Pupillary and accomodation reflex is intact as they are not reliant on sympathetic nerve supply
Right sided visual field is present in which side of the visual pathway?
Left side (contralateral)
Nasal fields go on which side of the retina? Nasal or temporal?
temporal
Nasal fibres carry which visual field? nasal or temporal?
temporal.
Which fibres dessucate in the optic chiasm?
The NASAL fibres.
Which fibres are carried in the optic tract?
- Uncrossed (ipislateral) temporal fibres carrying nasal visual field information
- crossed (contralateral) nasal fibres carrying temporal visual field information
Where is the optic chiasm located?
Superior -
Inferior
Anterior -
Lateral -
superior: lamina terminalis (anterior wall/recess of third ventricle)
inferior: pituitary gland / diaphragma sellae
anterior: anterior cerebral arteries and anterior communicating artery
lateral: internal carotid and cavernous sinus
How big is the optic chiasm?
12mm x 8mm
Where do the fibres from the LGN go to?
What is the difference in route between the superior and inferior visual field fibres from LGN?
Optic radiations into the calcarine fissure in visual cortex (area 17)
- superior visual field: inferior horn of lateral ventricle (MEYER’S LOOP) and travel towards calcarine fissure –> carry impulses from superior visual field.
- inferior visual field: travel in parietal lobe and enter into calcarine fissure of visual cortex (BAUM’S LOOP)
What are the components of the visual cortex?
- Primary visual cortex (Broadmann’s area number 17)
- Secondary visual cortex
- Ventral stream (inferotemporal area)
- Dorsal stream (Posterior partial area)
What is the ventral stream responsible for?
WHAT? of the object - shape, colour
Whatis the dorsal stream responsible for?
The WHERE of the object
What is the order of neurons in the visual pathway?
- Rod’s and Cones (1st Order)
- Bipolar Cells (2nd Order)
- Ganglion cells (3rd Order)
- LGB (4th Order)
What is the role of the pulvinar nucleus?
visual attention and motor integration
What is the role of the suprachiasmatic nucleus?
circadium rhythm
What is the role of the pretectal nucleus?
pupillary light reflex —-> some fibres break off before reaching LGN and synapse at pretectal nucleus –> pass to edinger westphal nucleus on ipsilateral and contralateral sides –> parasympathetic fibres to CG –> postganglionic fibres travel in short ciliary nerves to constrictor pupillae
What is the role of the superior colliculus? (5)
- visual grasp reflex
- automatic scanning of images
- visual attention
- co-ordination of head/eye movements - vertical
- auditory/visual association pathways.
What is are the two routes of the optic nerve after the optic chiasm? What are the other 4 pathways?
LATERAL ROOT:
optic tracts —-> lateral geniculate body —-> optic radiation —> terminate at Brodmann area 17 of visual cortex
MEDIAL ROOT:
some fibres bypass LGB (10%) and contribute to unconcscious stimuli and terminate in either:
1) pretectal nucleus (pupillary light reflex)
2) superior colliculus (regulaton of saccadic eye movements)
3) parvocellular reticular formation (arousal)
4) retinohypothalamic tract - photoperiod regulation
What is are the two routes of the optic nerve after the optic chiasm?
optic tracts —-> lateral geniculate body —-> optic radiation —> terminate at Brodmann area 17 of visual cortex
some fibres bypass LGB and terminate in either:
1) pretectal nucleus (pupillary light reflex)
2) superior colliculus (regulaton of saccadic eye movements)
Where is inferior visual field information carried in the optic tract?
superior retinal fibres - branch around parietal lobe into visual cortex.
Where is superior visual field information carried in optic tract?
inferior retinal fibers branch around temporal lobe (meyer’s loop)
How many layers are there in the LGN?
6
What causes an inferior bitemporal hemianopia?
What causes a superior bitemporal hemianopia?
Inferior –> superior chiasmal lesion –> craniopharyngioma, suprasellar/olfactory groove meningioma
Superior –> inferior chiasmal lesion –> pituitary adenoma
What are the layers of optic radiations?
1, 4, 6 - contralateral fibres synapse
2, 3, 5 - ipsilateral fibres synapse
What is the function of 1-2 layers of the LGN? Via which pathway?
Magnocellular pathway - concerned with detection of movement.
Transmits peripheral retinal information.
What type of retinal information is relayed in layers 3-6 of the LGN? Via which pathway?
information from fovea (colour vision and colour acuity) transmitted by parvocellular pathway
What are optic radiations? Where do their cell bodies lie? Where do they terminate?
Nerve fibre bundles whos cell bodies lie in the LGN and terminate in striate visual cortex (area 17)
macula information passes directly or widely in optic radiations?
peripheral information is transmitted directly or widely in optic radiations?
macula - directly
peripheral - widely.
Where does macula information enter the visual cortex?
Where does peripheral information enter the visual cortex?
macula - posterior 1/3rd of visual cortex
peripheral - anteriorly.
How many layers are there in the visual cortex?
6
What is the function of layer 2 of the visual cortex?
contains cells which synapse with contralateral visual cortex via corpus callosum. Projects to secondary visual cortex.
What is the functon of layer 4 (thickest layer) of the visual cortex?
receives efferents from LGN and contains stellate cells. It contains fibres from the macula.
What is the function of layer 5 of the visual cortex?
Relays information to the superior colliculus which connects to MLF which allows ocular movements to be co-ordinated with flashes of light.
What is the function of layer 6 of the visual cortex?
relays information to the LGN (feed-forward) and contains mostly pyramidal cells.
Whats the difference between magnocellular vs parvocellular fibres? 1. Velocity, 2. Type, 3. Location, 4. Length of response.
- Velocity - Magno fast, parvo slow
- Type - Magno - light detection fibres ;
Parvo - foveal/parafoveal and spatial discrimination fibres - Location - Magno - Layers 1 & 2 of LGN
- Parvo - Layers 3-6 of LGN - Length of response - Magno - transient, Parvo - sustained
What patterns are elicited when there is a lesion at the junction of optic nervea nd chiasm?
- Junctional scotoma of Traquair
- Monocular temporal field defect (nasal fibres)
- Monocular nasal field defect (temporal fibres) - Junctional scotoma
- Lesion causing ipsilateral optic neruopathy and contralateral superotemporal field defect
Lateral medullary syndrome caused by occlusion to what artery?
PICA.
Where do these laminae project to
- Laminae 2 and 3
- Laminae 5
- Laminae 6.
- Laminae 2 and 3 - secondary visual areas
- Laminae 5 - superior colliculus
- Laminae 6 - lateral geniculate nucleus
Rod and cone diagram
What visual field defect would an anterior communicating artery aneurysm cause?
Bitemporal lower quadrantinopia –> likely to compress upper part of optic chiasm.
What artery supplies
1. Optic tracts
2. LGN
3. Optic radiations
4. visual cortex
Optic tracts - anterior choroidal and posterior communicating, also MCA
LGN - anterior choroidal (ICA) and posterior choroidal (PCA)
Optic radiations - MCA, PCA
Visual cortex - posterior cerebral, MCA near occipital lobe for macula sparing strokes.
