Download MBBS (Bachelor of Medicine, Bachelor of Surgery) Human Anatomy ppt lectures Topic 42 Visual Pathway Notes. - anatomy ppt free download human anatomy ppt lectures, medicine notes ppt, anatomy handwritten notes pdf, mbbs 1st year anatomy notes pdf download, best anatomy notes pdf, human anatomy notes pdf, anatomy easy notes pdf, anatomy notes online, anatomy short notes, Anatomy ppt, Powerpoint Presentations and lecture notes.
Visual pathway
Visual pathway consists of a series of cells & synapses that
carry visual information from environment to brain for
processing.
Components : Retina Optic nerve Optic chiasma
Optic tract
Lateral geniculate body
Geniculostriate tract
Optic radiation
to visual sensory area
occipital lobe 17,18 &19
Visual field & retinal quadrant:
? One eye is closed.
? Area seen by open eye constitutes visual field of that
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
eye of that side.
? For convenience visual field is divided into right & left
halves.
Optic nerve, optic chiasma & Optic tract
? Optic nerve is made up of axons from ganglion cells of
retina
? Fibers of optic nerve arising from four quadrants of
retina maintain same relative position with in nerve.
? Fibers of nasal half of each retina enter optic tract of
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
corresponding side.
? Finally they are relayed into area 17, 18 & 19 of occipital
cortex.
Lateral geniculate body
? Part of metathalamus
? Grey matter in 6 layers
? Fibers from same side of
end in lamina 2, 3, & 5.
? Fibers from opposite side
of eye end in 1, 4 & 6.
? Macular fiber end in central
& posterior part of body &
this area is relatively large
Geniculocalcarine tract & visual cortex
? Fibers arising from
lateral geniculate body
form geniculocalcarine
tract or optic radiation.
? These fiber pass through
retrolentiform part of
internal capsule.
? Radiation end in visual
areas of cerebral cortex
(Area 17, 18 & 19)
? Cortex Occipital ?
17,18 & 19
receives impulses
from retinal
halves of same
side ( from
opposite halves of
field of vision)
? Cortical area of
macula is much
larger than that for
peripheral area.
Visual Functional areas
? Primary visual area: 17 occipital pole ? visual
perception
? Visual association area- 18 & 19 ? parastriate
cortex ,
? Area -18 ? linear stimuli &
? Area-19 ?angular stimuli.
? Higher visual association area- 39 ? angular
gyrus of parietal lobe ? comprehension of
various signs & symbols of language by vision.
Visual area....
? Visual Association area- 18 & 19 - correlation of
past and present visual experiences , assess distance
,speed, and orientation in 3d space.
? Lesion- Visual agnosia ? person is unable to identify
an object or a person seen in past.
Eyes & retina:
Fovea: central fixation
point of each eye -
region of retina with
highest visual acuity.
Macula: oval region
approximately 3-5 mm
that surrounds fovea,
also has high visual
acuity.
Eyes & retina:
Eyes & retina:
Optic disc: region where axons leaving retina
gather to form Optic nerve.
Photoreceptors are absent over optic disc >>
creates small blind spot located 15 lateral
and inferior to central fixation point of each
eye.
Photoreceptors:
Rods: more numerous than
cons-20:1, have poor spatial
& temporal resolution of
visual stimuli, do not detect
colors >> vision in low level
lighting conditions.
Cons: less numerous, much
more highly represented in
fovea >> have high spatial &
temporal resolution >> they
detect colors.
Optic nerve, chiasma and tract:
Visual processing pathways:
Dorsal Pathway:
Project to parieto-
occipital ass.
Cortex.
Ventral Pathway:
Project to occipito-
temporal ass.
Cortex.
Positive phenomenon:
? Light flashes >> retinal detachment.
? Rainbow-colored halos around objects >> acute
glaucoma.
? Migraine: visual blurring, scotoma that have
scintillating appearance or consist of jagged
alternating light and dark zigzag lines (fortification
scotoma).
? Pulsating colored lights/moving geometric shapes
>> occipital seizures.
Describe the visual field defect ?
Junctional scotoma: lesion at junction of
optic nerve and chiasm
Describe visual field defect ?
Bitemporal Homonymous Hemianopia
Describe visual field defect ?
Describe visual field defect ?
Left sector sparing homonymous hemianopia >> lesion at
LGN.
Describe visual field defect ?
Right superior quadrantanopia >>
temoporal lobe lesion
Describe visual field defect ?
Left inferior quadrantanopia >> parietal
lobe lesion
Describe visual field defect ?
Left homonymous hemianopia with
macular sparing
Macular sparing:
Watershed area with respect to blood
supply.
The `macular' visual cortex is supplied
by terminal branches of posterior &
middle cerebral arteries.
Visual cortex subserving the
midperipheral & peripheral field is
supplied only by the PCA. The area is
supplied by a more proximal `not
terminal' vessel.
Optic disc drusen: globules of
Retinitis Pigmentosa
mucoproteins and
mucopolysaccharides that
progressively calcify in the optic
disc.
Describe the visual field defect ?
Left incongruous homonymous hemianopia
Describe visual field defect ?
Right congruous homonymous hemianopia
Describe visual field defect ?
Enlarged Blind Spot
This post was last modified on 05 April 2022