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