processing.
Components : Retina Optic nerve Optic chiasma
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Optic tract
Lateral geniculate body
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Geniculostriate tractOptic radiation
to visual sensory area
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occipital lobe 17,18 &19
Visual field & retinal quadrant:
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? One eye is closed.
? Area seen by open eye constitutes visual field of that
eye.
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? Visual field of the two eye overlap to a great extent.
? On either side there is a small area which is seen only by
eye of that side.
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? For convenience visual field is divided into right & left
halves.
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Optic nerve, optic chiasma & Optic tract
? Optic nerve is made up of axons from ganglion cells of
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retina? Fibers of optic nerve arising from four quadrants of
retina maintain same relative position with in nerve.
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? Fibers of nasal half of each retina enter optic tract of
opposite side after crossing in chiasma.
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? Fibers from temporal half enter optic tract of same side.? Optic tract carries these fibers to lateral geniculate body of
corresponding side.
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? Finally they are relayed into area 17, 18 & 19 of occipitalcortex.
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Lateral geniculate body? Part of metathalamus
? Grey matter in 6 layers
? Fibers from same side of
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end in lamina 2, 3, & 5.
? Fibers from opposite side
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of eye end in 1, 4 & 6.? Macular fiber end in central
& posterior part of body &
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this area is relatively largeGeniculocalcarine tract & visual cortex
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? Fibers arising fromlateral geniculate body
form geniculocalcarine
tract or optic radiation.
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? These fiber pass through
retrolentiform part of
internal capsule.
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? Radiation end in visual
areas of cerebral cortex
(Area 17, 18 & 19)
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? Cortex Occipital ?
17,18 & 19
receives impulses
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from retinalhalves of same
side ( from
opposite halves of
field of vision)
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? Cortical area of
macula is much
larger than that for
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peripheral area.Visual Functional areas
? Primary visual area: 17 occipital pole ? visual
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perception? Visual association area- 18 & 19 ? parastriate
cortex ,
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? Area -18 ? linear stimuli &
? Area-19 ?angular stimuli.
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? Higher visual association area- 39 ? angulargyrus of parietal lobe ? comprehension of
various signs & symbols of language by vision.
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Visual area....? Visual Association area- 18 & 19 - correlation of
past and present visual experiences , assess distance
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,speed, and orientation in 3d space.? Lesion- Visual agnosia ? person is unable to identify
an object or a person seen in past.
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Eyes & retina:
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Fovea: central fixationpoint of each eye -
region of retina with
highest visual acuity.
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Macula: oval regionapproximately 3-5 mm
that surrounds fovea,
also has high visual
acuity.
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Eyes & retina:
Eyes & retina:
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Optic disc: region where axons leaving retina
gather to form Optic nerve.
Photoreceptors are absent over optic disc >>
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creates small blind spot located 15 lateraland inferior to central fixation point of each
eye.
Photoreceptors:
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Rods: more numerous than
cons-20:1, have poor spatial
& temporal resolution of
visual stimuli, do not detect
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colors >> vision in low levellighting conditions.
Cons: less numerous, much
more highly represented in
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fovea >> have high spatial &temporal resolution >> they
detect colors.
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Optic nerve, chiasma and tract:
Visual processing pathways:
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Dorsal Pathway:
Project to parieto-
occipital ass.
Cortex.
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Ventral Pathway:
Project to occipito-
temporal ass.
Cortex.
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Positive phenomenon:
? Light flashes >> retinal detachment.
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? Rainbow-colored halos around objects >> acute
glaucoma.
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? Migraine: visual blurring, scotoma that havescintillating appearance or consist of jagged
alternating light and dark zigzag lines (fortification
scotoma).
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? Pulsating colored lights/moving geometric shapes
>> occipital seizures.
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Describe the visual field defect ?Junctional scotoma: lesion at junction of
optic nerve and chiasm
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Describe visual field defect ?
Bitemporal Homonymous Hemianopia
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Describe visual field defect ?
Describe visual field defect ?
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Left sector sparing homonymous hemianopia >> lesion at
LGN.
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Describe visual field defect ?Right superior quadrantanopia >>
temoporal lobe lesion
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Describe visual field defect ?
Left inferior quadrantanopia >> parietal
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lobe lesion
Describe visual field defect ?
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Left homonymous hemianopia withmacular sparing
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Macular sparing:Watershed area with respect to blood
supply.
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The `macular' visual cortex is suppliedby terminal branches of posterior &
middle cerebral arteries.
Visual cortex subserving the
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midperipheral & peripheral field issupplied only by the PCA. The area is
supplied by a more proximal `not
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terminal' vessel.Optic disc drusen: globules of
Retinitis Pigmentosa
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mucoproteins and
mucopolysaccharides that
progressively calcify in the optic
disc.
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Describe the visual field defect ?
Left incongruous homonymous hemianopia
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Describe visual field defect ?
Right congruous homonymous hemianopia
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Describe visual field defect ?
Enlarged Blind Spot
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