Visual Pathway Flashcards
centrocecal
includes fixation and the blind spot
scotomas
Island defect surrounded by “seeing field”
what is the optic chiasm surrounded by
circle of willis
nerve fiber bundle defect
nasal step
-Defects on the horizontal midline nasally >15 degrees away from central fixation
how many optic nerve fibers
1-2.2 million
optic chiasm relations
- Posterior + inferior to the anterior cerebral + communicating arteries
- Medial to the internal carotid arteries
- Inferior to the third ventricle
- Superior to the pituitary gland
striate connections
hypothalamus
circadian rhythm
what is the diameter of the intraorbital portion of the nerve
diameter: 3mm
pupils and optic tract
pupils affected if lesion is in the anterior 2/3 of the tract
where is the first place that a single lesion will affect both eyes
optic chiasm
nasal fibers cross the midline
optic radiation blood supply
middle radiations
deep optic branch of the middle cerebral artery
where does myelination occur
only in he postlaminar region
vertical organization
- ocular dominance columns
- columns for stimulus orientation
- -responds to the direction of light
visual association areas names and functions
Brodmann areas 18, 19 now referred to as V2, V3, V4, V5
Functions as storage for visual patterns and recall
bitemporal hemianopia most common cause
pituitary gland adenoma
primary visual cortex blood supply
Calcarine branch of the posterior cerebral artery
superior network blood supply to optic chiasm
- Anterior communicating artery
- Anterior cerebral artery
LGN retinotopic representation
A given point in the visual field projects to a specific location in the LGN
Fibers from corresponding points in both retinas terminate in neighboring areas of adjacent LGN layers
meyers loop
- part of inferior retina (temporal)
- must pass through the temporal lobe by looping around the inferior horn of the lateral ventricle.
optic chiasm
superior nasal fibers
cross to the contralateral, medial optic tract
-posterior knees of wilbrand
what does the calcarine fissure intersect
intersects the parietooccipital sulcus
what is the lamina cribosa
network of scleral fibers where the optic nerve exits the eye
To nucleus of the optic tract
Optokinetic nystagmus (OKN)
superior field is imagined in
inferior retina
inferior nasal fibers
cross to the contralateral, lateral optic tract
-anterior knees of wilbrand
function of visual cortex
- Process visual information
- Integration of binocular information
optic tract lesions
right VF
left VF
- right vf carried in left optic tract
- left vf carried in right optic tract
Paracentral scotoma
Does not affect fixation
Hemianopia or Hemianopsia
- homonymous defect extends past the 180th meridian
- involves half the visual field
- respects the vertical midline
retinotopic representation visual cortex
Adjacent fibers in the LGN project to adjacent areas in the visual cortex
temporal field imagined in
nasal retina
optic chiasm
macular fibers
Macular fibers stay in the middle
- Temporal fibers
- Nasal fibers
- —Cross to contralateral eye
temporal wedge
a small defect temporal to the blind spot
pericentral ring
Does not affect fixation
Makes an annular pattern
synapse 3
LGN nucleus
axons –> optic radiations
synapse 1
photoreceptor cell
list the parts of the ON longest to shortest
intraorbital > intracranial > intracanalicular > intraocular
homonymous
- eye in both eyes
- nasal in one eye, temporal in other
- respects the vertical midline
LGN relations
- Medial to the internal capsule
- Lateral to the medial geniculate nucleus
- Medial to the inferior horn of the lateral ventricle
anterior junction syndrome
- compression of the optic nerve at its junction with the chiasm
- central defect in ipsilateral eye
- pie in the sky in the contralateral eye
optic disc fibers
Nasal fibers Temporal fibers Superior fibers Inferior fibers Macular fibers
physiological blind spot
15 degrees temporal to fixation
a right homonymous hemianopsia lesion
left side
optic radiation blood supply
posterior radiations
calcarine branch of the posterior cerebral artery
ganglion cell
axons (optic nerve) –> optic chiasm –> optic tract
optic radiations fibers
superior fibers –> parietal lobe
inferior fibers –> temporal lobe
synapse 2
bipolar cell
post-chiasmal VF
binocular
post laminar blood supply
Ophthalmic artery
Central retinal artery,
Pial vessels
optic chiasm
superior temporal fibers
exit to the medial optic tract
binasal hemianopia and chiasm
involves both lateral sides of the chiasm
magnocellular layers process..
horizontal organization
motion and low spatial frequency
intraocular nerve prelaminar
fascicles: sheaths of astrocytes bundle ~1000 fibers per fascicle
what surrounds the postlaminar region
EOMS
visual pathway order
retina –> ON –> optic chiasm –> optic tract –> LGN –> optic radiations –> striate cortex
blood supply to the ON
prelaminar and laminar
peripapillary choroidal network, unfenestrated
what is optic tract
-flattened. cylindrical band of ganglion fibers from the optic chiasm to the LGN
what are the functions of the LGN
some visual processing
- Ensures the most important information is sent to the visual cortex
- Has a pathway to the visual cortex and other cortical areas
- Has a pathway from the visual cortex
optic radiation blood supply
anterior radiations
anterior choroidal artery
what % of fibers from the optic tract go to the LGN
90%
frontal eye fields
Voluntary and reflexive binocular eye movements
synapse 4
visual cortex nucleus
retinal nerve fiber layer (RNFL)
- group of ganglion cells
- arcuate scotoma or nasal step
- horizontal midline typically respected
where is the LGN located
on the dorsolateral portion of the pulvinar thalamus
optic tract blood supply
- anterior choroidal
- middle cerebral
arcuate scotoma
Complete or incomplete/partial
Double arcuate
optic chiasm
inferior temporal fibers
exit to the lateral optic tract
optic nerve fibers
- Distal from the chiasm
- Proximal to the chiasm
- –Macular fibers move to the center
LGN vf loss
homonymous loss
posterior lesion
congruent
marginal tissue (of Elschnig)
connective tissue continuous with the sclera
other names for primary visual cortex
striate cortex, brodmann area 17, v1
where do retinal axons terminate
LGN
anterior lesion
incongruent
what is the function of glial tissue (ON)
separates the nerve from the retina, choroid, sclera
primary visual cortex location
- medial portion of the occipital lobe
- line of Gennari runs near the calcarine fissure
intraocular nerve laminar
within the lamina cribosa
what part of the ON is the post laminar
intraorbital
Each layer receives information from only one eye at the LGN
2,3,5 ipsilateral
1,4,6 contralateral
10% of fibers from optic tract go where
pretectal area,
superior colliculus
hypothalamas
central or centrocecal defect ON
(+) APD, afferent pupillary defect
LGN blood supply
- Anterior choroidal artery
- Posterior choroidal artery
optic tract fibers
Ipsilateral temporal fibers and contralateral nasal fibers are now grouped
-macular fibers are in the middle
pre-chiasmal VF
monocular
optic tract relations
- Lateral to cerebral peduncle
- Parallel to the posterior cerebral artery
- Inferior to the globus pallidus
cecal
enlarged blind spot
optic radiation fibers
fibers fan out passing through the parietal and temporal lobes
congruency and chiasm
incongruent- closer to chiasm
congruent- further from the chiasm
what is affected first with compression to ON
macular fibers
altitudinal
-Upper or lower half of the field affected
-Respects the horizontal midline
Unilateral
Bilateral
meyers loop lesion
a lesion in the temporal lobe that results in damage to Meyer’s loop causes a characteristic loss of vision in a superior quadrant (quadrantanopia or “pie in the sky” defect.)
bilateral altudinal
Damage to the upper or lower calcarine fissure of both eyes
temporal crescent
- Portion of the peripheral field without a counterpart in the nasal field of the other eye
- Located very _anterior__ in the visual cortex
inferior network blood supply to optic chiasm
- Posterior communicating artery
- Posterior cerebral artery
- Internal carotid artery
optic radiation relations
-lateral to the inferior horn of the lateral ventricles
what bigger structure of the brain is the LGN apart of
thalamus
what bone does the ON go through
lesser wing of the sphenoid bone
optic radiations vf loss
likely a quadranopsia
intermediary tissue (of kuhnt)
glial tissue separating the retina
what are the 6 layers of the LGN
layers 1-2 = magnocellular layer
Layer 3-6 = parvocellular layer
koniocellular dispersed around
meyers loop carry info from
carry information from the superior part of the visual field
visual cortex fibers
superior fibers –> cuneus gyrus
inferior fibers –> lingual gyrus
macular fibers run more posterior
intraorbital: postlaminar
fascicles acquire a connective tissue sheath and become myelinated by oligodendrocytes
post-chiasmal lesions
damage affects the contralateral field
-vertical midline respected
border tissue (of jacoby)
glial tissue separating the choroid
what is the horizontal diameter of ONH
1.5mm (1500 um)
pituitary gland location
located inferior to the optic chiasm
blood supply to intracranial
Ophthalmic artery
Anterior cerebral artery
Anterior communicating artery
Internal carotid artery
what sheaths are attached to the optic nerve
EOM
MR and SR
anatomical location
- inferior to the olfactory tract
- inferior to anterior cerebral artery
- superior + medial to the ICA
- lateral to the sphenoid body
retinal nerve fiber layer
- ganglion cell axons
- papillomacular bundle
- horizontal raphe
cuneus lingual
cuneus- upper
lingual- lower
parvocellular layers process..
horizontal organization
color and high spatial frequency
visual cortex vf loss
- congruent homonymous hemianopia
- VA usually not affected
right side of VF imagined in
nasal retina in right eye
temporal retina in the left eye
heteronymous
fields of both eyes show on opposite sides
- bitemporal
- binasal
striate connections
superior colliculus
fixation and saccades
