SlideShare a Scribd company logo
1 of 84
Visual pathway Presenter: Dr.NIKHIL PANPALIA
GUIDE: Dr. K.R.NAIK
INTRODUCTION
• Visual processing poses an enormous
computational challenge for the brain, which
has evolved highly organized and efficient
neural systems to meet these demands.
• In primates, approximately 55% of the cortex
is specialized for visual processing (compared
to 3% for auditory processing and 11% for
somatosensory processing) (Felleman and
Van Essen, 1991).
• These structures include
the eye, optic nerves,
chiasm, tracts, lateral
geniculate nucleus (LGN)
of the thalamus,
radiations, striate cortex,
and extrastriate
association cortices.
EYE
• The corneal epithelium and stroma are transparent to permit
passage of light without distortion (Maurice, 1970).
• The ciliary muscles dynamically adjust the shape of the lens in
order to focus light optimally from varying distances upon the
retina (accommodation). The total amount of light reaching
the retina is controlled by regulation of the pupil aperture.
• Ultimately, the visual image becomes projected upside-down
and backwards on to the retina (Fishman, 1973).
RETINA
• When light reaches the retina, its energy is
converted by retinal photoreceptors into an
electrochemical signal that is then relayed by
neurons.
• To arrive at the photoreceptors, light must
first pass through transparent inner layers of
the neurosensory retina, comprised of the
nerve fiber layer, ganglion cells, amacrine
cells, and bipolar cells .
Top, high-resolution
optical coherence
tomography.
Middle, histological
section.
Bottom, schematic
depiction of retinal
layers.
FUNCTION OF EACH LAYER OF RETINA
• RETINAL PIGMENT EPITHELIAL LAYER
The RPE provides structural and metabolic
support for the photoreceptors, primarily
through the vital function of vitamin A
metabolism (Wald, 1933).
VITAMIN A METABOLISM TAKES PLACE
• Photoreceptors maintain the ability always to
produce a signal by ensuring a constant, buffered
supply of 11-cis-retinal.
• The spontaneous transformation of all-trans-
retinal back to 11-cis-retinal occurs over a very
slow half-life (of several minutes), so that the
store of 11-cis-retinal is always being replenished
and is available to transduce incoming light
signals.
• Humans possess four
photoreceptor types: three
cones and the rods.
• Under most conditions, our
vision is mediated by cones,
which operate over an
enormous range of intensities.
• Each type of cone
photoreceptor has a unique,
optimal response to specific
wavelengths of light – short
(blue), middle (green), or long
(red).
• Rods, on the other hand, are saturated at natural light
intensities and are incapable of discriminating colors; their
greater sensitivity to light renders them effective for night
vision (scotopic vision).
• The functional specializations of cones and rods arise from
variations in the structure of opsin, since the opsin
molecule tunes the light wavelengths at which the retinal
chromophore (11-cis-retinal) will alter its conformation and
initiate the biochemical response to light.
• Despite their functional differences, cones and rods utilize
the same 11-cis-retinal chromophore.
DISTRIBUTION OF RODS AND CONES
• The distribution of cones and
rods across the retina is highly
skewed and directly reflects
the specialized functions of the
fovea and retinal periphery
(Osterberg, 1935).
• The macula is located
temporal to the optic nerve
and is approximately 5.5 mm
in diameter.
• Within the macula is the fovea (diameter 1.5 mm) and
the foveola (0.35 mm). The fovea has up to 200 000
cones/mm2 (nearly 15-fold higher than in the
peripheral retina) so that it can provide excellent visual
acuity (Hirsch and Curcio, 1989).
• Progressively eccentric locations have much lower
concentrations of rods, and thus have decreasing
sensitivity.
• Rods are virtually absent in the fovea; rather, they are
the dominant photoreceptor in the periphery
© Stephen E. Palmer, 2002
Distribution of Rods and Cones
.
0
150,000
100,000
50,000
0
20 40 60 8020406080
Visual Angle (degrees from fovea)
Rods
Cones Cones
Rods
Fovea
Blind
Spot
#Receptors/mm2
Night Sky: why are there more stars off-center?
INNER NUCLEAR LAYER
• It consists of amacrine cells, horizontal cells
and bipolar cells which connect rods and
cones with Retinal ganglion cell layer.
Retinal Ganglion cell
• The excitatory “on” and “off” inputs to a
ganglion cell are arranged to form an
antagonistic center-surround receptive field
(Kuffler, 1953) .
• The action potential firing rate of an “on-
center” ganglion cell is highest when a light
stimulus is in the center of the receptive field,
with surrounding darkness.
• In contrast, the firing rate of “off-center” ganglion cells is
highest when a light stimulus is in the peripheral receptive
field, but not its center.
• With uniform illumination throughout a ganglion cell
receptive field, the summated center and surround
responses essentially cancel each other.
• However, when differential illumination (i.e., an edge of
light) occurs within the receptive field, the imbalance
between center and surround inputs allows the ganglion
cell to signal the local change in light intensity.
• There are three main types of ganglion cell,
each with specialized functions in the
detection of visual inputs
• Eighty percent of ganglion cells are midget
cells, 10% are parasol cells, and 10% are other
types.
• The different types of ganglion cells comprise
separate pathways that are named for their
targets in the LGN.
• Midget cells form the “P” (parvocellular)
pathway and parasol cells form the “M”
(magnocellular) pathway (Polyak, 1941;
Kaplan and Shapley, 1986; Hendry and
Yoshioka, 1994).
• In addition, small bistratified ganglion cells are
the most likely source of a more recently
identified “K” (koniocellular) pathway (Hendry
and Yoshioka, 1994).
• Midget ganglion cells have cone-opponent
receptive fields, allowing spectral selectivity
along the red–green or blue–yellow axes.
• These structural arrangements afford midget
ganglion cells the properties of an extremely
small receptive field, with specialization for
high spatial acuity, color vision, and fine
stereopsis (Livingstone and Hubel, 1988).
• At any given retinal eccentricity, parasol cells have a larger
receptive field and lower spatial resolution than midget
cells due to their broad dendritic arborization (Croner and
Kaplan, 1995).
• Parasol ganglion cells have spatially opponent center-
surround organization, allowing edge detection, but they
lack spectrally opponent organization; in essence, these
cells are color-blind.
• The anatomical features of parasol cells underlie their
specialization for low spatial resolution, motion detection,
and coarse stereopsis (Livingstone and Hubel, 1988).
• Foveal ganglion cells send axons
directly to the temporal aspect of
the optic disc in the papillomacular
bundle.
• The remaining temporal ganglion
cell nerve axons are arranged on
either side of the horizontal raphe
and form arcuate bundles that
course above and below the fovea,
and finally enter the superior and
inferior portions of the optic nerve.
• Finally, axons originating nasal to
the disc enter the nasal portion of
the optic nerve.
Optic disc
• The optic disc or optic nerve head is the point of exit
for ganglion cell axons leaving the eye. Because there are
no rods or conesoverlying the optic disc, it corresponds to a
small physiological blind spot in each eye.
• The ganglion cell axons form the optic nerve after they
leave the eye.
• The optic disc represents the beginning of the optic nerve
and is the point where the axons of retinal ganglion cells
come together.
• The optic disc is also the entry point for the major blood
vessels that supply the retina. The optic disc in a normal
human eye carries from 1 to 1.2 million neurons from the
eye towards the brain
Papilledema
Papilledema (or papilloedema) is optic disc swelling that is caused by
increased intracranial pressure. The swelling is usually bilateral and can occur over a
period of hours to weeks.
Optic nerve
• Each optic nerve is comprised of
approximately 1.2 million retinal ganglion cell
axons (in constrast to the acoustic nerve, for
example, which has only 31 000 axons)
(Bruesch and Arey, 1942).
• The intraocular segment of the optic nerve
head (the optic disc) is typically located 3–4
mm nasal to the fovea and is 1 mm thick.
• The optic nerve travels posteriorly through the lamina
cribrosa to exit the back of the globe, where it abruptly
increases in diameter from 3 to 4 mm.
• In order to accommodate the rotations of the globe,
the length of the intraorbital segment of the optic
nerve is typically between 25 and 30 mm in length, at
least 5 mm longer than the distance from the globe to
the orbital apex (Glaser and Sadun, 1990).
• Upon passing through the lamina cribrosa, the optic
nerve becomes invested with meninges and also
becomes myelinated.
• Upon exiting the orbit, the optic nerve enters
the optic canal, within the lesser wing of the
sphenoid bone, for approximately 6 mm.
• The intracanalicular optic nerve rises at a 45
angle and then exits the optic canal, where it
continues in its intracranial portion for
approximately 17 mm before reaching the
chiasma.
• In the proximal third of the optic nerve the
positions of ganglion cell axons are rearranged.
• Macular ganglion cell axons which initially lie
temporally move to the nerve’s center.
• Peripheral temporal fibers become positioned
temporally, both superior and inferior to the
macular fibers.
• Finally, nasal fibers remain in the nasal portion of
the optic nerve.
RETINA
TEMPORAL NASAL
Srf
irf
saf
iaf
39
40
• Peripheral fibers 
deep in Retina
superficially in optic
nerve
• Fibers close to optic
nerve head
superficial in retina
central in optic nerve
OPTIC NERVE HEAD:
macula
Upper temporal
Lower temporal
Lower nasal
Upper nasal
41
In the Distal Region of optic nerve (just behind eye):
• In the Proximal Region of optic nerve(near
chiasma):
42
OPTIC CHIASMA
• The chiasm, which has a dumbbell shape when viewed
in coronal section, is the site of decussation for axons
from the optic nerve (Fig. 1.9).
• It lies in the subarachnoid space of the suprasellar
cistern, above the diaphragma sella and the pituitary
gland, inferior to the hypothalamus, and anterior to
the pituitary stalk (infundibulum).
• The chiasm is typically 10 mm above the pituitary,
which rests in the sella turcica within the sphenoid
bone
ANTERIORLY : Anterior
cerebral artery and
their communicating
artery
POSTERIORLY: Tuber
cinerium, Hypophyseal
stalk, Pituitary body,
mamillary body,
posterior perforated
substance
SUPERIORLY:3rd
ventricle
INFERIORLY: Pituitary
gland
LATERALLY:
Extracavernous part of
ICA & Anterior
perforated substance
44
OPTIC CHIASMA
46
Uncrossed temporal
fibers
Crossed Nasal fibers
47
Anterior
Knee of
Von-wille
Brand
Posterior
Knee of
Von-wille
Brand
OPTIC TRACT:
* Flattened cylindrical band that
travel posteriolaterally from
angle of chiasma
* Between tuber cinereum and
anterior perforated substance
upto lateral geniculate body.
* Each tract contains
uncrossed temporal
fibres and crossed nasal fibres .
48
OPTIC TRACT:
• Macular fibers (crossed
& uncrossed) occupy
dorsolateral aspect of
optic tract
• Upper peripheral fibers
(crossed &
uncrossed)medially
situated
• Lower peripheral
fibers laterally
situated
49
Fibers from optic tract:
50
Superior
Colliculus
Pretectal
nucleus
Dorsal
Lateral
geniculate
nucleus
SUPERIOR COLLICULUS
• The superior colliculi play a critical role
in generating orienting eye and head
movements to sudden visual (and other
sensory) stimuli. They are located in the
dorsal midbrain within the tectal plate.
• The superior colliculi are structurally
and functionally organized into
superficial and deep layers.
• The superficial layers solely process
visual information, with direct retinal
inputs comprising a visuotopic map of
the contralateral field (Cynader and
Berman, 1972)
• The deep layers of the colliculi receive
multimodal sensory inputs and help
mediate saccadic eye movements
through their efferent connections to
ocular motor systems.
PRETECTAL NUCLEAS
• A portion of the fibers in the optic tract subserve the
pupillary light reflex and synapse at the pretectal nuclei
in the midbrain.
• There is consensual innervation to both pretectal
nuclei, and each pretectal nucleus has dual
connections to each Edinger–Westphal nucleus.
• The Edinger–Westphal nuclei give rise to
parasympathetic efferent fibers which travel with the
oculomotor nerve and regulate pupillary size via
pupillary constrictors.
LATERAL GENICULATE BODY:
Elevation produced by
lateral geniculate
nucleus in which
most optic tract
fibers end
Axons of ganglion cells
of retina synapse
with dendrites of
LGB cells
3rd order neurons
begins
54
LATERAL GENICULATE BODY
Dorsal nucleus
Ventral nucleus (rudimentary)
6 laminae( alternating grey & white
matter)
Axons from the ipsilateral eye –
2, 3, 5
Axons from the contralateral eye - 1, 4,6
55
Lateral Geniculate Body:
56
• Large magnocellular neurons (M
cells) - 1 and 2 layer-Y ganglion
cells
perception of movement, gross
depth, and small differences in
brightness
• Small parvocellular neurons (P
cells)- 3,4,5,6 layer- X ganglion
cells
Colour perception, texture shape &
fine depth
• Koniocellular cells(K cells or
interlaminar cells)
Short-wavelength "blue" cones
LATERAL GENICULATE BODY:
57
Macular fibres - posterior
2/3 of LGB
Upper retinal fibres - medial
half of anterior 1/3 of LGB
Lower retinal fibres - lateral
half of anterior 1/3 of LGB
• The LGN is a critical relay station with dynamic control upon
the amount and nature of information that is transmitted
to visual cortex (Guillery and Sherman, 2002).
• In addition to retinal afferents, which may comprise only
5–10% of the synapses in the LGN (Van Horn et al., 2000),
the LGN also receives extensive modulating connections
from the thalamic reticular nucleus and layer 6 of the visual
cortex.
• The LGN thus provides a bottleneck to information flow,
filtering visual information for relevance to the present
behavioral state.
OPTIC RADIATIONS:
Geniculocalcarine pathway extend
from lateral geniculate body 
visual cortex
MEYERS LOOP(inferior retinal
fibers)-pass through temporal
lobe looping around inferior horn
of lateral ventricle
BARUMS LOOP(superior retinal
fibers)- directed posteriorly
through parietal lobe, occipital
lobe,internal capsule and relay
on visual cortex
59
OPTIC RADIATION:
60
Inferior
retinalower
part of optic
radiation
superior retina
upper part of
optic radiation
Visual Cortex:
Striate cortex Extrastriate cortex
61
•
VISUAL CORTEX(CORTICAL RETINA):
62
•Impulse from
corresponding 2 points
of retina meet
•Right visual
cortexreceive impulse
left half of visual field
•Left visual
cortexreceive impulse
from right half visual
field
MACULA posteriorly
PERIPHERAL RETINA anteriorly
UPPER RETINA above calcarine sulcus
LOWER RETINA below the calcarine sulcus
TWO STREAM HYPOTHESIS:
63
• Ventral
Ventral
Pathway(parvocellular)
temporal lobe
Dorsal
Pathway(magnocellular)
 parietal lobe
Recognistion &
indentification
Spatial
location
Visual
agnosia
Visual
neglec
t
Parvocellular
“what”
pathway
Magnocellular
“where”
pathway
LESIONS OF VISUAL PATHWAY
64
1) LESIONS OF OPTIC NERVE :
Causes:
1. Optic atrophy
2. Indirect optic neuropathy
3. Acute optic neuritis
4. Traumatic avulsion of optic nerve.
Characterised by:
Complete blindness in affected eye with loss of both
direct on ipsilateral & consensual light reflex on
contralateral side.
Near reflex is preserved.
Eg. Right optic nerve
involvement
65
2)CHIASMAL LESIONS:
66
Anterior
Chiasmal
lesions
Middle
Chiasmal
lesions
Posterior
Chiasmal
lesions
ANTERIOR CHIASMAL LESIONS:
67
• Affects the ipsilateral optic nerve fibers and
the contralateral inferonasal fibers
• Ipsilateral optic neuropathy manifested as a
central scotoma and a defect involving the
contralateral superotemporal fieldalso
known as a junctional scotoma
Abolition of direct light reflex on affected side
& consensual light reflex on contralateral side.
 Near reflex intact.
MIDDLE CHIASMAL LESIONS:
CENTRAL LESIONS OF CHIASMA (SAGITTAL)
Causes:
Suprasellar aneurysm
Tumors of pituitary gland
Craniopharyngioma
Suprasellar meningioma &
glioma of 3rd ventricle.
Third ventricular dilatation
due to obstructive hydrocephalus.
68
69
 Characterised by:
Bitemporal hemianopia
Paralysis of pupillary
reflex(usually lead to partial
descending optic atrophy)
LATERAL CHIASMAL LESIONS :
Causes:
Distension of 3rd ventricle causing pressure on each side
of optic chiasma
Atheroma of carotids & posterior communicating artery.
70
71
Characterised by :
Binasal hemianopia
Parallysis of pupillary reflex
(usually lead to partial descending optic atrophy)
POSTERIOR CHIASMAL SYNDROME
72
• macular fibers cross more posteriorly in the
chiasm
• paracentral bitemporal field loss
• Posterior lesions may also involve the optic
tract and cause a contralateral homonymous
hemianopia.
3)LESIONS OF OPTIC TRACT :
Causes:
1. Syphilitic meningitis/ Gumm
2. Tuberculous meningitis
3. Tumors of optic thalamus
4. Aneurysm of posterior
cerebral arteries.
73
74
Characterised by :
Incongruous homonymous hemianopia with C/L hemianopic
pupillary reaction( wernicke’s reaction)
These lesions usually lead to partial descending optic atrophy &
may be associated with C/L 3rd nerve paralysis(RAPD) &
ipsilateral hemiplegia
Wernickes pupil
4)LESIONS OF LATERAL GENICULATE BODY :
Leads to homonymous hemianopia with sparing
of pupillary reflexes & may end in partial optic
atrophy.
75
5)LESIONS OF OPTIC RADIATIONS :
Causes:
Vascular occlusion(Anterior choroidal artery,middle cerebral or
posterior cerebral artery)
Primary & secondary tumors
Trauma
Characterised by : No Optic Atrophy
Normal pupillary reactions
TOTAL OPTIC RADIATION
INVOLVEMENT
COMPLETE
HOMONYMOUS
HEMIANOPIA
( sometimes sparing
macula)
76
INFERIOR QUADRANTIC
HEMIANOPIA
Lesion of temporal lobe
(pie on sky)
SUPERIOR QUADRANTIC
HEMIANOPIA
77
Lesion of parietal lobe
(pie on floor)
6)LESIONS OF VISUAL CORTEX :
Congruous
homonymous
hemianopia(sparing
macula)
Occlusion of posterior
cerebral artery
supplying anterior part
of occipital cortex
Congruous
homonymous macular
defect
Head injury/gun shot
injury leading to
lesions of tip of
occipital cortex
78
Normal pupillary reactions and no optic atrophy
REFERENCES
• Clinical neuro-ophthalmology  Thomas
duane and Edward jaegar
• Neuroanatomy Carpenter
• Neuroanatomy Snells
• Thank you

More Related Content

What's hot

Anatomy of lateral geniculate body and visual cortex
Anatomy of lateral geniculate body and visual cortexAnatomy of lateral geniculate body and visual cortex
Anatomy of lateral geniculate body and visual cortexRuturaj Sahoo
 
Accommodation of eye
Accommodation of eye Accommodation of eye
Accommodation of eye Rohit Rao
 
Light and dark adaptation chinnu
Light and dark adaptation chinnuLight and dark adaptation chinnu
Light and dark adaptation chinnuBidhuna Raj
 
Physiology of aqueous humor
Physiology of aqueous humorPhysiology of aqueous humor
Physiology of aqueous humorRohit Rao
 
Visual pathway
Visual pathwayVisual pathway
Visual pathwayLabeeb Pc
 
Physiology of Retina
Physiology of RetinaPhysiology of Retina
Physiology of RetinaNajara Thapa
 
Anatomy of visual pathway and its lesions.
Anatomy of visual pathway and its lesions.Anatomy of visual pathway and its lesions.
Anatomy of visual pathway and its lesions.Ruchi Pherwani
 
Light and Dark Adaptation
Light and Dark AdaptationLight and Dark Adaptation
Light and Dark AdaptationTrisruta Deb
 
Accommodation: Theories and Mechanism
Accommodation: Theories and MechanismAccommodation: Theories and Mechanism
Accommodation: Theories and MechanismGarima Poudel
 
Color vision : Physiology ,Defects, Detection, Diagnosis & Management
Color vision :  Physiology ,Defects, Detection, Diagnosis & ManagementColor vision :  Physiology ,Defects, Detection, Diagnosis & Management
Color vision : Physiology ,Defects, Detection, Diagnosis & ManagementAayush Chandan
 
Anatomy of crystalline lens by Dr. Aayush Tandon
Anatomy of crystalline lens by Dr. Aayush Tandon Anatomy of crystalline lens by Dr. Aayush Tandon
Anatomy of crystalline lens by Dr. Aayush Tandon Aayush Tandon
 
Physiology of vision
Physiology of visionPhysiology of vision
Physiology of visionBinny Tyagi
 
Anatomy and Lesions of Visual Pathways
Anatomy and Lesions of Visual Pathways Anatomy and Lesions of Visual Pathways
Anatomy and Lesions of Visual Pathways neurophq8
 

What's hot (20)

Anatomy of lateral geniculate body and visual cortex
Anatomy of lateral geniculate body and visual cortexAnatomy of lateral geniculate body and visual cortex
Anatomy of lateral geniculate body and visual cortex
 
Accommodation of eye
Accommodation of eye Accommodation of eye
Accommodation of eye
 
Visual Pathway - Ophthalmology - Eye
Visual Pathway - Ophthalmology - EyeVisual Pathway - Ophthalmology - Eye
Visual Pathway - Ophthalmology - Eye
 
Light and dark adaptation chinnu
Light and dark adaptation chinnuLight and dark adaptation chinnu
Light and dark adaptation chinnu
 
Physiology of aqueous humor
Physiology of aqueous humorPhysiology of aqueous humor
Physiology of aqueous humor
 
Visual pathway
Visual pathwayVisual pathway
Visual pathway
 
Retina
RetinaRetina
Retina
 
Physiology of Retina
Physiology of RetinaPhysiology of Retina
Physiology of Retina
 
Anatomy of visual pathway and its lesions.
Anatomy of visual pathway and its lesions.Anatomy of visual pathway and its lesions.
Anatomy of visual pathway and its lesions.
 
Eye movements
Eye movementsEye movements
Eye movements
 
Visual pathway
Visual pathwayVisual pathway
Visual pathway
 
Light and Dark Adaptation
Light and Dark AdaptationLight and Dark Adaptation
Light and Dark Adaptation
 
Visual pathway
Visual pathwayVisual pathway
Visual pathway
 
anatomy of retina
 anatomy of retina anatomy of retina
anatomy of retina
 
Accommodation: Theories and Mechanism
Accommodation: Theories and MechanismAccommodation: Theories and Mechanism
Accommodation: Theories and Mechanism
 
Color vision : Physiology ,Defects, Detection, Diagnosis & Management
Color vision :  Physiology ,Defects, Detection, Diagnosis & ManagementColor vision :  Physiology ,Defects, Detection, Diagnosis & Management
Color vision : Physiology ,Defects, Detection, Diagnosis & Management
 
Anatomy of crystalline lens by Dr. Aayush Tandon
Anatomy of crystalline lens by Dr. Aayush Tandon Anatomy of crystalline lens by Dr. Aayush Tandon
Anatomy of crystalline lens by Dr. Aayush Tandon
 
Physiology of vision
Physiology of visionPhysiology of vision
Physiology of vision
 
Visual pathway
Visual pathwayVisual pathway
Visual pathway
 
Anatomy and Lesions of Visual Pathways
Anatomy and Lesions of Visual Pathways Anatomy and Lesions of Visual Pathways
Anatomy and Lesions of Visual Pathways
 

Similar to Visual pathway

Neuro-Ophthalmology_Dr. Bastola.pptx
Neuro-Ophthalmology_Dr. Bastola.pptxNeuro-Ophthalmology_Dr. Bastola.pptx
Neuro-Ophthalmology_Dr. Bastola.pptxDr. Pradeep Bastola
 
Physiology of the visual pathway & cerebral integration
Physiology of the visual pathway & cerebral integrationPhysiology of the visual pathway & cerebral integration
Physiology of the visual pathway & cerebral integrationHenok Samuel
 
Anatomy of pupillary pathways
Anatomy of pupillary pathwaysAnatomy of pupillary pathways
Anatomy of pupillary pathwaysHasika Ravula
 
Anatomy and Physiology of Optic Nerve Dr.PrabhatDevkota.pptx
Anatomy and Physiology of Optic Nerve Dr.PrabhatDevkota.pptxAnatomy and Physiology of Optic Nerve Dr.PrabhatDevkota.pptx
Anatomy and Physiology of Optic Nerve Dr.PrabhatDevkota.pptxDr. Prabhat Devkota, MD
 
Retina and visual tract
Retina and visual tractRetina and visual tract
Retina and visual tractMuhammad Saim
 
Optical coherence tomography in multiple sclerosis
Optical coherence tomography in multiple sclerosisOptical coherence tomography in multiple sclerosis
Optical coherence tomography in multiple sclerosisAhmed Mamdouh
 
Anatomy of optic nerve
Anatomy of optic nerveAnatomy of optic nerve
Anatomy of optic nerveSudheer Kumar
 
Eye optic nerve and visal pathway.pdf
Eye optic nerve and visal pathway.pdfEye optic nerve and visal pathway.pdf
Eye optic nerve and visal pathway.pdfssuser393009
 
Visual evoked potentials
Visual evoked potentialsVisual evoked potentials
Visual evoked potentialsDhaval Modi
 
Anatomy of oculomotor nerve
Anatomy of oculomotor nerveAnatomy of oculomotor nerve
Anatomy of oculomotor nervePankaj Sharma
 

Similar to Visual pathway (20)

Neuro-Ophthalmology_Dr. Bastola.pptx
Neuro-Ophthalmology_Dr. Bastola.pptxNeuro-Ophthalmology_Dr. Bastola.pptx
Neuro-Ophthalmology_Dr. Bastola.pptx
 
Physiology of the visual pathway & cerebral integration
Physiology of the visual pathway & cerebral integrationPhysiology of the visual pathway & cerebral integration
Physiology of the visual pathway & cerebral integration
 
Anatomy of pupillary pathways
Anatomy of pupillary pathwaysAnatomy of pupillary pathways
Anatomy of pupillary pathways
 
Anatomy and Physiology of Optic Nerve Dr.PrabhatDevkota.pptx
Anatomy and Physiology of Optic Nerve Dr.PrabhatDevkota.pptxAnatomy and Physiology of Optic Nerve Dr.PrabhatDevkota.pptx
Anatomy and Physiology of Optic Nerve Dr.PrabhatDevkota.pptx
 
anatomy of retina
anatomy of retinaanatomy of retina
anatomy of retina
 
Retina and visual tract
Retina and visual tractRetina and visual tract
Retina and visual tract
 
Optic AND OCULOMOTOR NERVE
Optic AND OCULOMOTOR  NERVEOptic AND OCULOMOTOR  NERVE
Optic AND OCULOMOTOR NERVE
 
Optical coherence tomography in multiple sclerosis
Optical coherence tomography in multiple sclerosisOptical coherence tomography in multiple sclerosis
Optical coherence tomography in multiple sclerosis
 
IIcranial nerve
IIcranial nerveIIcranial nerve
IIcranial nerve
 
Anatomy of optic nerve
Anatomy of optic nerveAnatomy of optic nerve
Anatomy of optic nerve
 
Eye optic nerve and visal pathway.pdf
Eye optic nerve and visal pathway.pdfEye optic nerve and visal pathway.pdf
Eye optic nerve and visal pathway.pdf
 
Photoreceptors
PhotoreceptorsPhotoreceptors
Photoreceptors
 
Retina & the vision
Retina & the visionRetina & the vision
Retina & the vision
 
Retina
RetinaRetina
Retina
 
Visual evoked potentials
Visual evoked potentialsVisual evoked potentials
Visual evoked potentials
 
Anatomy of oculomotor nerve
Anatomy of oculomotor nerveAnatomy of oculomotor nerve
Anatomy of oculomotor nerve
 
Vision1
Vision1Vision1
Vision1
 
Teath
TeathTeath
Teath
 
THE OPTIC NERVE
THE OPTIC NERVETHE OPTIC NERVE
THE OPTIC NERVE
 
PHYSIOLOGY OF RETINA.pptx
PHYSIOLOGY OF RETINA.pptxPHYSIOLOGY OF RETINA.pptx
PHYSIOLOGY OF RETINA.pptx
 

Recently uploaded

Transparency, Recognition and the role of eSealing - Ildiko Mazar and Koen No...
Transparency, Recognition and the role of eSealing - Ildiko Mazar and Koen No...Transparency, Recognition and the role of eSealing - Ildiko Mazar and Koen No...
Transparency, Recognition and the role of eSealing - Ildiko Mazar and Koen No...EADTU
 
HMCS Vancouver Pre-Deployment Brief - May 2024 (Web Version).pptx
HMCS Vancouver Pre-Deployment Brief - May 2024 (Web Version).pptxHMCS Vancouver Pre-Deployment Brief - May 2024 (Web Version).pptx
HMCS Vancouver Pre-Deployment Brief - May 2024 (Web Version).pptxmarlenawright1
 
NO1 Top Black Magic Specialist In Lahore Black magic In Pakistan Kala Ilam Ex...
NO1 Top Black Magic Specialist In Lahore Black magic In Pakistan Kala Ilam Ex...NO1 Top Black Magic Specialist In Lahore Black magic In Pakistan Kala Ilam Ex...
NO1 Top Black Magic Specialist In Lahore Black magic In Pakistan Kala Ilam Ex...Amil baba
 
UGC NET Paper 1 Unit 7 DATA INTERPRETATION.pdf
UGC NET Paper 1 Unit 7 DATA INTERPRETATION.pdfUGC NET Paper 1 Unit 7 DATA INTERPRETATION.pdf
UGC NET Paper 1 Unit 7 DATA INTERPRETATION.pdfNirmal Dwivedi
 
Ernest Hemingway's For Whom the Bell Tolls
Ernest Hemingway's For Whom the Bell TollsErnest Hemingway's For Whom the Bell Tolls
Ernest Hemingway's For Whom the Bell TollsPallavi Parmar
 
How to Manage Call for Tendor in Odoo 17
How to Manage Call for Tendor in Odoo 17How to Manage Call for Tendor in Odoo 17
How to Manage Call for Tendor in Odoo 17Celine George
 
HMCS Max Bernays Pre-Deployment Brief (May 2024).pptx
HMCS Max Bernays Pre-Deployment Brief (May 2024).pptxHMCS Max Bernays Pre-Deployment Brief (May 2024).pptx
HMCS Max Bernays Pre-Deployment Brief (May 2024).pptxEsquimalt MFRC
 
How to Add a Tool Tip to a Field in Odoo 17
How to Add a Tool Tip to a Field in Odoo 17How to Add a Tool Tip to a Field in Odoo 17
How to Add a Tool Tip to a Field in Odoo 17Celine George
 
Spellings Wk 4 and Wk 5 for Grade 4 at CAPS
Spellings Wk 4 and Wk 5 for Grade 4 at CAPSSpellings Wk 4 and Wk 5 for Grade 4 at CAPS
Spellings Wk 4 and Wk 5 for Grade 4 at CAPSAnaAcapella
 
Play hard learn harder: The Serious Business of Play
Play hard learn harder:  The Serious Business of PlayPlay hard learn harder:  The Serious Business of Play
Play hard learn harder: The Serious Business of PlayPooky Knightsmith
 
Observing-Correct-Grammar-in-Making-Definitions.pptx
Observing-Correct-Grammar-in-Making-Definitions.pptxObserving-Correct-Grammar-in-Making-Definitions.pptx
Observing-Correct-Grammar-in-Making-Definitions.pptxAdelaideRefugio
 
Jamworks pilot and AI at Jisc (20/03/2024)
Jamworks pilot and AI at Jisc (20/03/2024)Jamworks pilot and AI at Jisc (20/03/2024)
Jamworks pilot and AI at Jisc (20/03/2024)Jisc
 
Details on CBSE Compartment Exam.pptx1111
Details on CBSE Compartment Exam.pptx1111Details on CBSE Compartment Exam.pptx1111
Details on CBSE Compartment Exam.pptx1111GangaMaiya1
 
FSB Advising Checklist - Orientation 2024
FSB Advising Checklist - Orientation 2024FSB Advising Checklist - Orientation 2024
FSB Advising Checklist - Orientation 2024Elizabeth Walsh
 
What is 3 Way Matching Process in Odoo 17.pptx
What is 3 Way Matching Process in Odoo 17.pptxWhat is 3 Way Matching Process in Odoo 17.pptx
What is 3 Way Matching Process in Odoo 17.pptxCeline George
 
21st_Century_Skills_Framework_Final_Presentation_2.pptx
21st_Century_Skills_Framework_Final_Presentation_2.pptx21st_Century_Skills_Framework_Final_Presentation_2.pptx
21st_Century_Skills_Framework_Final_Presentation_2.pptxJoelynRubio1
 
Understanding Accommodations and Modifications
Understanding  Accommodations and ModificationsUnderstanding  Accommodations and Modifications
Understanding Accommodations and ModificationsMJDuyan
 
Introduction to TechSoup’s Digital Marketing Services and Use Cases
Introduction to TechSoup’s Digital Marketing  Services and Use CasesIntroduction to TechSoup’s Digital Marketing  Services and Use Cases
Introduction to TechSoup’s Digital Marketing Services and Use CasesTechSoup
 
Personalisation of Education by AI and Big Data - Lourdes Guàrdia
Personalisation of Education by AI and Big Data - Lourdes GuàrdiaPersonalisation of Education by AI and Big Data - Lourdes Guàrdia
Personalisation of Education by AI and Big Data - Lourdes GuàrdiaEADTU
 
80 ĐỀ THI THỬ TUYỂN SINH TIẾNG ANH VÀO 10 SỞ GD – ĐT THÀNH PHỐ HỒ CHÍ MINH NĂ...
80 ĐỀ THI THỬ TUYỂN SINH TIẾNG ANH VÀO 10 SỞ GD – ĐT THÀNH PHỐ HỒ CHÍ MINH NĂ...80 ĐỀ THI THỬ TUYỂN SINH TIẾNG ANH VÀO 10 SỞ GD – ĐT THÀNH PHỐ HỒ CHÍ MINH NĂ...
80 ĐỀ THI THỬ TUYỂN SINH TIẾNG ANH VÀO 10 SỞ GD – ĐT THÀNH PHỐ HỒ CHÍ MINH NĂ...Nguyen Thanh Tu Collection
 

Recently uploaded (20)

Transparency, Recognition and the role of eSealing - Ildiko Mazar and Koen No...
Transparency, Recognition and the role of eSealing - Ildiko Mazar and Koen No...Transparency, Recognition and the role of eSealing - Ildiko Mazar and Koen No...
Transparency, Recognition and the role of eSealing - Ildiko Mazar and Koen No...
 
HMCS Vancouver Pre-Deployment Brief - May 2024 (Web Version).pptx
HMCS Vancouver Pre-Deployment Brief - May 2024 (Web Version).pptxHMCS Vancouver Pre-Deployment Brief - May 2024 (Web Version).pptx
HMCS Vancouver Pre-Deployment Brief - May 2024 (Web Version).pptx
 
NO1 Top Black Magic Specialist In Lahore Black magic In Pakistan Kala Ilam Ex...
NO1 Top Black Magic Specialist In Lahore Black magic In Pakistan Kala Ilam Ex...NO1 Top Black Magic Specialist In Lahore Black magic In Pakistan Kala Ilam Ex...
NO1 Top Black Magic Specialist In Lahore Black magic In Pakistan Kala Ilam Ex...
 
UGC NET Paper 1 Unit 7 DATA INTERPRETATION.pdf
UGC NET Paper 1 Unit 7 DATA INTERPRETATION.pdfUGC NET Paper 1 Unit 7 DATA INTERPRETATION.pdf
UGC NET Paper 1 Unit 7 DATA INTERPRETATION.pdf
 
Ernest Hemingway's For Whom the Bell Tolls
Ernest Hemingway's For Whom the Bell TollsErnest Hemingway's For Whom the Bell Tolls
Ernest Hemingway's For Whom the Bell Tolls
 
How to Manage Call for Tendor in Odoo 17
How to Manage Call for Tendor in Odoo 17How to Manage Call for Tendor in Odoo 17
How to Manage Call for Tendor in Odoo 17
 
HMCS Max Bernays Pre-Deployment Brief (May 2024).pptx
HMCS Max Bernays Pre-Deployment Brief (May 2024).pptxHMCS Max Bernays Pre-Deployment Brief (May 2024).pptx
HMCS Max Bernays Pre-Deployment Brief (May 2024).pptx
 
How to Add a Tool Tip to a Field in Odoo 17
How to Add a Tool Tip to a Field in Odoo 17How to Add a Tool Tip to a Field in Odoo 17
How to Add a Tool Tip to a Field in Odoo 17
 
Spellings Wk 4 and Wk 5 for Grade 4 at CAPS
Spellings Wk 4 and Wk 5 for Grade 4 at CAPSSpellings Wk 4 and Wk 5 for Grade 4 at CAPS
Spellings Wk 4 and Wk 5 for Grade 4 at CAPS
 
Play hard learn harder: The Serious Business of Play
Play hard learn harder:  The Serious Business of PlayPlay hard learn harder:  The Serious Business of Play
Play hard learn harder: The Serious Business of Play
 
Observing-Correct-Grammar-in-Making-Definitions.pptx
Observing-Correct-Grammar-in-Making-Definitions.pptxObserving-Correct-Grammar-in-Making-Definitions.pptx
Observing-Correct-Grammar-in-Making-Definitions.pptx
 
Jamworks pilot and AI at Jisc (20/03/2024)
Jamworks pilot and AI at Jisc (20/03/2024)Jamworks pilot and AI at Jisc (20/03/2024)
Jamworks pilot and AI at Jisc (20/03/2024)
 
Details on CBSE Compartment Exam.pptx1111
Details on CBSE Compartment Exam.pptx1111Details on CBSE Compartment Exam.pptx1111
Details on CBSE Compartment Exam.pptx1111
 
FSB Advising Checklist - Orientation 2024
FSB Advising Checklist - Orientation 2024FSB Advising Checklist - Orientation 2024
FSB Advising Checklist - Orientation 2024
 
What is 3 Way Matching Process in Odoo 17.pptx
What is 3 Way Matching Process in Odoo 17.pptxWhat is 3 Way Matching Process in Odoo 17.pptx
What is 3 Way Matching Process in Odoo 17.pptx
 
21st_Century_Skills_Framework_Final_Presentation_2.pptx
21st_Century_Skills_Framework_Final_Presentation_2.pptx21st_Century_Skills_Framework_Final_Presentation_2.pptx
21st_Century_Skills_Framework_Final_Presentation_2.pptx
 
Understanding Accommodations and Modifications
Understanding  Accommodations and ModificationsUnderstanding  Accommodations and Modifications
Understanding Accommodations and Modifications
 
Introduction to TechSoup’s Digital Marketing Services and Use Cases
Introduction to TechSoup’s Digital Marketing  Services and Use CasesIntroduction to TechSoup’s Digital Marketing  Services and Use Cases
Introduction to TechSoup’s Digital Marketing Services and Use Cases
 
Personalisation of Education by AI and Big Data - Lourdes Guàrdia
Personalisation of Education by AI and Big Data - Lourdes GuàrdiaPersonalisation of Education by AI and Big Data - Lourdes Guàrdia
Personalisation of Education by AI and Big Data - Lourdes Guàrdia
 
80 ĐỀ THI THỬ TUYỂN SINH TIẾNG ANH VÀO 10 SỞ GD – ĐT THÀNH PHỐ HỒ CHÍ MINH NĂ...
80 ĐỀ THI THỬ TUYỂN SINH TIẾNG ANH VÀO 10 SỞ GD – ĐT THÀNH PHỐ HỒ CHÍ MINH NĂ...80 ĐỀ THI THỬ TUYỂN SINH TIẾNG ANH VÀO 10 SỞ GD – ĐT THÀNH PHỐ HỒ CHÍ MINH NĂ...
80 ĐỀ THI THỬ TUYỂN SINH TIẾNG ANH VÀO 10 SỞ GD – ĐT THÀNH PHỐ HỒ CHÍ MINH NĂ...
 

Visual pathway

  • 1. Visual pathway Presenter: Dr.NIKHIL PANPALIA GUIDE: Dr. K.R.NAIK
  • 2.
  • 3. INTRODUCTION • Visual processing poses an enormous computational challenge for the brain, which has evolved highly organized and efficient neural systems to meet these demands. • In primates, approximately 55% of the cortex is specialized for visual processing (compared to 3% for auditory processing and 11% for somatosensory processing) (Felleman and Van Essen, 1991).
  • 4. • These structures include the eye, optic nerves, chiasm, tracts, lateral geniculate nucleus (LGN) of the thalamus, radiations, striate cortex, and extrastriate association cortices.
  • 5. EYE • The corneal epithelium and stroma are transparent to permit passage of light without distortion (Maurice, 1970). • The ciliary muscles dynamically adjust the shape of the lens in order to focus light optimally from varying distances upon the retina (accommodation). The total amount of light reaching the retina is controlled by regulation of the pupil aperture. • Ultimately, the visual image becomes projected upside-down and backwards on to the retina (Fishman, 1973).
  • 6. RETINA • When light reaches the retina, its energy is converted by retinal photoreceptors into an electrochemical signal that is then relayed by neurons. • To arrive at the photoreceptors, light must first pass through transparent inner layers of the neurosensory retina, comprised of the nerve fiber layer, ganglion cells, amacrine cells, and bipolar cells .
  • 7. Top, high-resolution optical coherence tomography. Middle, histological section. Bottom, schematic depiction of retinal layers.
  • 8. FUNCTION OF EACH LAYER OF RETINA • RETINAL PIGMENT EPITHELIAL LAYER The RPE provides structural and metabolic support for the photoreceptors, primarily through the vital function of vitamin A metabolism (Wald, 1933).
  • 9. VITAMIN A METABOLISM TAKES PLACE
  • 10. • Photoreceptors maintain the ability always to produce a signal by ensuring a constant, buffered supply of 11-cis-retinal. • The spontaneous transformation of all-trans- retinal back to 11-cis-retinal occurs over a very slow half-life (of several minutes), so that the store of 11-cis-retinal is always being replenished and is available to transduce incoming light signals.
  • 11. • Humans possess four photoreceptor types: three cones and the rods. • Under most conditions, our vision is mediated by cones, which operate over an enormous range of intensities. • Each type of cone photoreceptor has a unique, optimal response to specific wavelengths of light – short (blue), middle (green), or long (red).
  • 12. • Rods, on the other hand, are saturated at natural light intensities and are incapable of discriminating colors; their greater sensitivity to light renders them effective for night vision (scotopic vision). • The functional specializations of cones and rods arise from variations in the structure of opsin, since the opsin molecule tunes the light wavelengths at which the retinal chromophore (11-cis-retinal) will alter its conformation and initiate the biochemical response to light. • Despite their functional differences, cones and rods utilize the same 11-cis-retinal chromophore.
  • 13. DISTRIBUTION OF RODS AND CONES • The distribution of cones and rods across the retina is highly skewed and directly reflects the specialized functions of the fovea and retinal periphery (Osterberg, 1935). • The macula is located temporal to the optic nerve and is approximately 5.5 mm in diameter.
  • 14. • Within the macula is the fovea (diameter 1.5 mm) and the foveola (0.35 mm). The fovea has up to 200 000 cones/mm2 (nearly 15-fold higher than in the peripheral retina) so that it can provide excellent visual acuity (Hirsch and Curcio, 1989). • Progressively eccentric locations have much lower concentrations of rods, and thus have decreasing sensitivity. • Rods are virtually absent in the fovea; rather, they are the dominant photoreceptor in the periphery
  • 15.
  • 16. © Stephen E. Palmer, 2002 Distribution of Rods and Cones . 0 150,000 100,000 50,000 0 20 40 60 8020406080 Visual Angle (degrees from fovea) Rods Cones Cones Rods Fovea Blind Spot #Receptors/mm2 Night Sky: why are there more stars off-center?
  • 17. INNER NUCLEAR LAYER • It consists of amacrine cells, horizontal cells and bipolar cells which connect rods and cones with Retinal ganglion cell layer.
  • 18. Retinal Ganglion cell • The excitatory “on” and “off” inputs to a ganglion cell are arranged to form an antagonistic center-surround receptive field (Kuffler, 1953) . • The action potential firing rate of an “on- center” ganglion cell is highest when a light stimulus is in the center of the receptive field, with surrounding darkness.
  • 19. • In contrast, the firing rate of “off-center” ganglion cells is highest when a light stimulus is in the peripheral receptive field, but not its center. • With uniform illumination throughout a ganglion cell receptive field, the summated center and surround responses essentially cancel each other. • However, when differential illumination (i.e., an edge of light) occurs within the receptive field, the imbalance between center and surround inputs allows the ganglion cell to signal the local change in light intensity.
  • 20.
  • 21. • There are three main types of ganglion cell, each with specialized functions in the detection of visual inputs • Eighty percent of ganglion cells are midget cells, 10% are parasol cells, and 10% are other types. • The different types of ganglion cells comprise separate pathways that are named for their targets in the LGN.
  • 22. • Midget cells form the “P” (parvocellular) pathway and parasol cells form the “M” (magnocellular) pathway (Polyak, 1941; Kaplan and Shapley, 1986; Hendry and Yoshioka, 1994). • In addition, small bistratified ganglion cells are the most likely source of a more recently identified “K” (koniocellular) pathway (Hendry and Yoshioka, 1994).
  • 23. • Midget ganglion cells have cone-opponent receptive fields, allowing spectral selectivity along the red–green or blue–yellow axes. • These structural arrangements afford midget ganglion cells the properties of an extremely small receptive field, with specialization for high spatial acuity, color vision, and fine stereopsis (Livingstone and Hubel, 1988).
  • 24. • At any given retinal eccentricity, parasol cells have a larger receptive field and lower spatial resolution than midget cells due to their broad dendritic arborization (Croner and Kaplan, 1995). • Parasol ganglion cells have spatially opponent center- surround organization, allowing edge detection, but they lack spectrally opponent organization; in essence, these cells are color-blind. • The anatomical features of parasol cells underlie their specialization for low spatial resolution, motion detection, and coarse stereopsis (Livingstone and Hubel, 1988).
  • 25.
  • 26. • Foveal ganglion cells send axons directly to the temporal aspect of the optic disc in the papillomacular bundle. • The remaining temporal ganglion cell nerve axons are arranged on either side of the horizontal raphe and form arcuate bundles that course above and below the fovea, and finally enter the superior and inferior portions of the optic nerve. • Finally, axons originating nasal to the disc enter the nasal portion of the optic nerve.
  • 27.
  • 28.
  • 29.
  • 30.
  • 32. • The optic disc or optic nerve head is the point of exit for ganglion cell axons leaving the eye. Because there are no rods or conesoverlying the optic disc, it corresponds to a small physiological blind spot in each eye. • The ganglion cell axons form the optic nerve after they leave the eye. • The optic disc represents the beginning of the optic nerve and is the point where the axons of retinal ganglion cells come together. • The optic disc is also the entry point for the major blood vessels that supply the retina. The optic disc in a normal human eye carries from 1 to 1.2 million neurons from the eye towards the brain
  • 33. Papilledema Papilledema (or papilloedema) is optic disc swelling that is caused by increased intracranial pressure. The swelling is usually bilateral and can occur over a period of hours to weeks.
  • 34.
  • 35. Optic nerve • Each optic nerve is comprised of approximately 1.2 million retinal ganglion cell axons (in constrast to the acoustic nerve, for example, which has only 31 000 axons) (Bruesch and Arey, 1942). • The intraocular segment of the optic nerve head (the optic disc) is typically located 3–4 mm nasal to the fovea and is 1 mm thick.
  • 36. • The optic nerve travels posteriorly through the lamina cribrosa to exit the back of the globe, where it abruptly increases in diameter from 3 to 4 mm. • In order to accommodate the rotations of the globe, the length of the intraorbital segment of the optic nerve is typically between 25 and 30 mm in length, at least 5 mm longer than the distance from the globe to the orbital apex (Glaser and Sadun, 1990). • Upon passing through the lamina cribrosa, the optic nerve becomes invested with meninges and also becomes myelinated.
  • 37. • Upon exiting the orbit, the optic nerve enters the optic canal, within the lesser wing of the sphenoid bone, for approximately 6 mm. • The intracanalicular optic nerve rises at a 45 angle and then exits the optic canal, where it continues in its intracranial portion for approximately 17 mm before reaching the chiasma.
  • 38. • In the proximal third of the optic nerve the positions of ganglion cell axons are rearranged. • Macular ganglion cell axons which initially lie temporally move to the nerve’s center. • Peripheral temporal fibers become positioned temporally, both superior and inferior to the macular fibers. • Finally, nasal fibers remain in the nasal portion of the optic nerve.
  • 40. 40 • Peripheral fibers  deep in Retina superficially in optic nerve • Fibers close to optic nerve head superficial in retina central in optic nerve OPTIC NERVE HEAD:
  • 41. macula Upper temporal Lower temporal Lower nasal Upper nasal 41 In the Distal Region of optic nerve (just behind eye):
  • 42. • In the Proximal Region of optic nerve(near chiasma): 42
  • 43. OPTIC CHIASMA • The chiasm, which has a dumbbell shape when viewed in coronal section, is the site of decussation for axons from the optic nerve (Fig. 1.9). • It lies in the subarachnoid space of the suprasellar cistern, above the diaphragma sella and the pituitary gland, inferior to the hypothalamus, and anterior to the pituitary stalk (infundibulum). • The chiasm is typically 10 mm above the pituitary, which rests in the sella turcica within the sphenoid bone
  • 44. ANTERIORLY : Anterior cerebral artery and their communicating artery POSTERIORLY: Tuber cinerium, Hypophyseal stalk, Pituitary body, mamillary body, posterior perforated substance SUPERIORLY:3rd ventricle INFERIORLY: Pituitary gland LATERALLY: Extracavernous part of ICA & Anterior perforated substance 44
  • 45.
  • 48. OPTIC TRACT: * Flattened cylindrical band that travel posteriolaterally from angle of chiasma * Between tuber cinereum and anterior perforated substance upto lateral geniculate body. * Each tract contains uncrossed temporal fibres and crossed nasal fibres . 48
  • 49. OPTIC TRACT: • Macular fibers (crossed & uncrossed) occupy dorsolateral aspect of optic tract • Upper peripheral fibers (crossed & uncrossed)medially situated • Lower peripheral fibers laterally situated 49
  • 50. Fibers from optic tract: 50 Superior Colliculus Pretectal nucleus Dorsal Lateral geniculate nucleus
  • 51. SUPERIOR COLLICULUS • The superior colliculi play a critical role in generating orienting eye and head movements to sudden visual (and other sensory) stimuli. They are located in the dorsal midbrain within the tectal plate. • The superior colliculi are structurally and functionally organized into superficial and deep layers. • The superficial layers solely process visual information, with direct retinal inputs comprising a visuotopic map of the contralateral field (Cynader and Berman, 1972) • The deep layers of the colliculi receive multimodal sensory inputs and help mediate saccadic eye movements through their efferent connections to ocular motor systems.
  • 52. PRETECTAL NUCLEAS • A portion of the fibers in the optic tract subserve the pupillary light reflex and synapse at the pretectal nuclei in the midbrain. • There is consensual innervation to both pretectal nuclei, and each pretectal nucleus has dual connections to each Edinger–Westphal nucleus. • The Edinger–Westphal nuclei give rise to parasympathetic efferent fibers which travel with the oculomotor nerve and regulate pupillary size via pupillary constrictors.
  • 53.
  • 54. LATERAL GENICULATE BODY: Elevation produced by lateral geniculate nucleus in which most optic tract fibers end Axons of ganglion cells of retina synapse with dendrites of LGB cells 3rd order neurons begins 54
  • 55. LATERAL GENICULATE BODY Dorsal nucleus Ventral nucleus (rudimentary) 6 laminae( alternating grey & white matter) Axons from the ipsilateral eye – 2, 3, 5 Axons from the contralateral eye - 1, 4,6 55
  • 56. Lateral Geniculate Body: 56 • Large magnocellular neurons (M cells) - 1 and 2 layer-Y ganglion cells perception of movement, gross depth, and small differences in brightness • Small parvocellular neurons (P cells)- 3,4,5,6 layer- X ganglion cells Colour perception, texture shape & fine depth • Koniocellular cells(K cells or interlaminar cells) Short-wavelength "blue" cones
  • 57. LATERAL GENICULATE BODY: 57 Macular fibres - posterior 2/3 of LGB Upper retinal fibres - medial half of anterior 1/3 of LGB Lower retinal fibres - lateral half of anterior 1/3 of LGB
  • 58. • The LGN is a critical relay station with dynamic control upon the amount and nature of information that is transmitted to visual cortex (Guillery and Sherman, 2002). • In addition to retinal afferents, which may comprise only 5–10% of the synapses in the LGN (Van Horn et al., 2000), the LGN also receives extensive modulating connections from the thalamic reticular nucleus and layer 6 of the visual cortex. • The LGN thus provides a bottleneck to information flow, filtering visual information for relevance to the present behavioral state.
  • 59. OPTIC RADIATIONS: Geniculocalcarine pathway extend from lateral geniculate body  visual cortex MEYERS LOOP(inferior retinal fibers)-pass through temporal lobe looping around inferior horn of lateral ventricle BARUMS LOOP(superior retinal fibers)- directed posteriorly through parietal lobe, occipital lobe,internal capsule and relay on visual cortex 59
  • 60. OPTIC RADIATION: 60 Inferior retinalower part of optic radiation superior retina upper part of optic radiation
  • 61. Visual Cortex: Striate cortex Extrastriate cortex 61 •
  • 62. VISUAL CORTEX(CORTICAL RETINA): 62 •Impulse from corresponding 2 points of retina meet •Right visual cortexreceive impulse left half of visual field •Left visual cortexreceive impulse from right half visual field MACULA posteriorly PERIPHERAL RETINA anteriorly UPPER RETINA above calcarine sulcus LOWER RETINA below the calcarine sulcus
  • 63. TWO STREAM HYPOTHESIS: 63 • Ventral Ventral Pathway(parvocellular) temporal lobe Dorsal Pathway(magnocellular)  parietal lobe Recognistion & indentification Spatial location Visual agnosia Visual neglec t Parvocellular “what” pathway Magnocellular “where” pathway
  • 64. LESIONS OF VISUAL PATHWAY 64
  • 65. 1) LESIONS OF OPTIC NERVE : Causes: 1. Optic atrophy 2. Indirect optic neuropathy 3. Acute optic neuritis 4. Traumatic avulsion of optic nerve. Characterised by: Complete blindness in affected eye with loss of both direct on ipsilateral & consensual light reflex on contralateral side. Near reflex is preserved. Eg. Right optic nerve involvement 65
  • 67. ANTERIOR CHIASMAL LESIONS: 67 • Affects the ipsilateral optic nerve fibers and the contralateral inferonasal fibers • Ipsilateral optic neuropathy manifested as a central scotoma and a defect involving the contralateral superotemporal fieldalso known as a junctional scotoma Abolition of direct light reflex on affected side & consensual light reflex on contralateral side.  Near reflex intact.
  • 68. MIDDLE CHIASMAL LESIONS: CENTRAL LESIONS OF CHIASMA (SAGITTAL) Causes: Suprasellar aneurysm Tumors of pituitary gland Craniopharyngioma Suprasellar meningioma & glioma of 3rd ventricle. Third ventricular dilatation due to obstructive hydrocephalus. 68
  • 69. 69  Characterised by: Bitemporal hemianopia Paralysis of pupillary reflex(usually lead to partial descending optic atrophy)
  • 70. LATERAL CHIASMAL LESIONS : Causes: Distension of 3rd ventricle causing pressure on each side of optic chiasma Atheroma of carotids & posterior communicating artery. 70
  • 71. 71 Characterised by : Binasal hemianopia Parallysis of pupillary reflex (usually lead to partial descending optic atrophy)
  • 72. POSTERIOR CHIASMAL SYNDROME 72 • macular fibers cross more posteriorly in the chiasm • paracentral bitemporal field loss • Posterior lesions may also involve the optic tract and cause a contralateral homonymous hemianopia.
  • 73. 3)LESIONS OF OPTIC TRACT : Causes: 1. Syphilitic meningitis/ Gumm 2. Tuberculous meningitis 3. Tumors of optic thalamus 4. Aneurysm of posterior cerebral arteries. 73
  • 74. 74 Characterised by : Incongruous homonymous hemianopia with C/L hemianopic pupillary reaction( wernicke’s reaction) These lesions usually lead to partial descending optic atrophy & may be associated with C/L 3rd nerve paralysis(RAPD) & ipsilateral hemiplegia Wernickes pupil
  • 75. 4)LESIONS OF LATERAL GENICULATE BODY : Leads to homonymous hemianopia with sparing of pupillary reflexes & may end in partial optic atrophy. 75
  • 76. 5)LESIONS OF OPTIC RADIATIONS : Causes: Vascular occlusion(Anterior choroidal artery,middle cerebral or posterior cerebral artery) Primary & secondary tumors Trauma Characterised by : No Optic Atrophy Normal pupillary reactions TOTAL OPTIC RADIATION INVOLVEMENT COMPLETE HOMONYMOUS HEMIANOPIA ( sometimes sparing macula) 76
  • 77. INFERIOR QUADRANTIC HEMIANOPIA Lesion of temporal lobe (pie on sky) SUPERIOR QUADRANTIC HEMIANOPIA 77 Lesion of parietal lobe (pie on floor)
  • 78. 6)LESIONS OF VISUAL CORTEX : Congruous homonymous hemianopia(sparing macula) Occlusion of posterior cerebral artery supplying anterior part of occipital cortex Congruous homonymous macular defect Head injury/gun shot injury leading to lesions of tip of occipital cortex 78 Normal pupillary reactions and no optic atrophy
  • 79.
  • 80.
  • 81.
  • 82. REFERENCES • Clinical neuro-ophthalmology  Thomas duane and Edward jaegar • Neuroanatomy Carpenter • Neuroanatomy Snells
  • 83.

Editor's Notes

  1. Photoreceptors use a highly efficient mechanism to convert a photon of light into an electrochemical neural signal (Fig. 1.3). As a consequence, the photoreceptor cell reduces its neurotransmitter output in response to the absorption of light. The process is self-limited: the membrane complex transducin catalyzes GTP back to GDP, ceasing stimulation of the PDE enzyme. cGMP levels therefore rise, the inward sodium current is restored, the membrane potential increases, and tonic neurotransmitter release is restored.
  2. Peripheral part lie deep in retina but occupy most peripheral(superficial part) of optic nerve Fibers close to optic nerve headlie superficial in retina and occupy central(deep) part of optic nerve
  3. Same as retina i.e.upper temporal and lower temporal are situated in temporal half of optic nerve separated from each other by wedge shaped area of papillomacular bundle. Upper and lower nasal are situated in nasal side.
  4. Upper and Lower temporal situated on the temporal side separated by macular fibres . Upper and Lower nasal situated on the nasal side.
  5. Upper Nasal fibres involved first by lesions coming from above eg . Craniopharyngiomas Lower nasal fibres first affected in tumours of pituitary gland  upper temporal field defects. Ipsilateral blindness is associated with contralateral field defects.
  6. Function : 1)relay station 2) to gate the transmission of signals Large magnicellular neurons (M cells) - 1 and 2 –receive input from Y ganglion cells of retina(10% seen in periphearl retina) Motion detection transmitts only black and white information Small parvicellular neurons (P cells) - 3,4,5,6 layers-receive input from X ganglion cells of retina Colour perception –texture shape fine depth vision
  7. The fibres of optic radiation spread out fanwise to form medullary optic lamina The inferior fibres of optic radiation subserve upper visual field & the superior fibres subserve lower visual field . Ends in a extensive area of thin occipital cortex in which is a distinctive white stripe , striae of Gennari visible to naked eyehence the name areastriate
  8. Fibres from inferior retina (Meyer’s loops) Pass through temporal lobe looping around the inferior horn of lateral ventricleInformation from the superior part of visual fieldLoss of vision in superior quadrant ( quadrantanopia or ‘pie in sky defect) Fibres from superior retina (Baum’s loop) Parietal lobe occipital lobe internal capsule visual cortex Information from the inferior part of visual field. Vascular lesion of internal capsulehemiplegia & homonymous hemianopia
  9. VISUOSENSORY AREA:Medial aspect of the occipital lobe around and in the calcarine sulcus, with extension into cuneus and lingual gyrus variably into lateral aspect of occipital pole limited by sulcus lunateus (Brodmann area 17 or V1) VISUOPSYCHIC AREA:peristriate area 18 &19 V1- primary visual area V2- greater part of area 18 V3- narrow stripe over anterior part of area 18 V4- within area 19 V5- posterior end of superior temporal gyrus
  10. Called cortical retina since true copy of retinal image is formed here. Only in visual cortex impulse originating from corresponding point of two retina meet. Right visual cortexreceive impulse from temporal half of right retina & nasal half of left retina(left half visual field) Left visual cortexreceive impulse from temperal half of left retina & nasal half of right retina & (right half visual field)
  11. Ventral system(pavocellular):Recognition/identification, Long term stored representations,inputMainly foveal or parafoveal Dorsal system(magnocellular):spatial location, Only very short-term storage, Across retina
  12. LESIONS OF PARIETAL LOBE (involving superior fibres of optic radiations)INFERIOR QUADRANTIC HEMIANOPIA( PIE ON THE FLOOR) LESIONS OF TEMPORAL LOBE (involving inferior fibres of optic radiations)SUPERIOR QUADRANTIC HEMIANOPIA( PIE ON THE ROOF) Pupillary reactions are normal as fibres of light reflex leave the optic tracts to synapse in the superior colliculi. Lesions of optic radiations do not produce optic atrophy as the 1st order neurons (optic nerve fibres) synapse in LGB.
  13. Macular sparing can also occur due to double vascularisation of occipital lobe by middle and posterior cerebral artery & due to b/l macular representation