Neurology of Vision Natesan Green

8/6/2019 Neurology of Vision Natesan Green

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NEUROLOGY OF VISION

NATESAN.D

SUBHRANSU



VISION¶the sense of sight, which¶the sense of sight, which

perceives the form, color, size,perceives the form, color, size,

movement, and distance of movement, and distance of

objects·objects·



THE VISUAL PATHWAY



OPTIC NERVE

� The axons of the ganglion cells

� Extends from the retina to optic chiasm.

� It is 5 cm long.

-Intraocular( 1 mm)

-Intraorbital( 25 mm)

-Intracanalicular( 9 mm)

- Intracranial(15 mm)



OPTIC CHIASM





WILBRAND·S KNEE

Wilbrand¶s knee



OPTIC TRACT

� 55% fibres are from contralateral nasal retina

� 45% fibres are from same side temporal retina

� The retinotopic organisation is well maintained, but with

change in orientation of the fibres.

� Incongruity of the visual field defect.





LATERAL GENICULATE BODY´the gateway to cortexµ

� The Subcortical thalamic relay nucleus of vision,starting the process of co-ordinating vision fromthe two eyes

� C-shaped 6 defined layers

� Layers 1, 2 receive from large M ganglion cellsMagnocellular division

� Layers 3,4,5 & 6 from small P ganglion cellsParvocellular division



LATERAL GENICULATE BODY

� Each layer receives input from one eye only- Layers 1,4,6 from contralateral eye

- Layers 2, 3,5 from ipsilateral eye

� Responses of neurons are similar to retinal GC(on-centre & off-centre organization)

� LGB also receives input from brain stem,reticular formation & feedback from cerebralcortex



OPTIC RADIATIONS

� Third order neuronal axons.

� Projection of LGB on to striate cortex.

� Two portions:

± Fibers from the inferior retina("Meyer's loop" or ́ Archambault's loopµ).

± Fibers from the superior retina

("Baum's tract")



PRIMARY VISUAL CORTEX(V1)(AREA 17)

� On medial aspect of each occipital lobe

� Its neurons arranged in the form of columns (1x1x2

mm) forming 6 distinct layers

� The input from the two eyes remain separated (Ocular

dominance columns)

� Fovea has broad presentation

� Its neurons (layers 2,3,4) project into areas 18 & 19

(association or secondary visual areas)



Visual area V2(prestriate cortex)

� the first region within the visual association area.� receives strong feeds from V1 (direct and via the

pulvinar)

� sends strong signals to V3, V4, and V5.

� also sends strong feedbacks to V1



OTHER ASSOCIATION AREAS

� V3- DORSAL V3 POSTERIOR PARIETALVENTRAL V3 INFERIOR TEMPORAL

� V4- (Part of ventral stream)

V2 POSTERIOR INFERIOR TEMPORAL

� V5 (MIDDLE TEMPORAL AREA )



VISUAL PROCESSING



VISIBLE SPECTRUM

370-730 nm

SCOTOPIC: 507 nm ,low light, rods (cones

unresponsive), 10-6 to

10Cd/m2

MESOPIC: mediumlight, rods and cones,

0.01 and 10Cd/m2

PHOTOPIC: 555 nm,

bright light , cones(rods saturate),

0.01 and 108Cd/m2



A BASIC CONNECTIVITY PATTERN OF

THE VISUAL PATHWAY

Photoreceptor Bipolar cell Ganglion

cell LBG Striate cortex



Photoreceptors release glutamate in darkness andexhibit graded hyperpolarizations in response to

different luminance levels

Hyperpolarization of photoreceptors results in

decreased glutamate release

PHOTOTRANSDUCTION



` Bipolar cells are of two

types:

´ONµ cells

´OFFµ cells

` Ganglion cells are of 3

types :

Parvocellular-X,Magnocellular-Y,

Koniocellular



BIPOLAR CELLS OFTHE RETINA

MECHANISMS FOR ¶ON· AND ¶OFF· RESPONSES

Bipolar cells exhibit graded

electrical potentials (i.e., NOT

action potentials)

They release neurotransmitter(glutamate) in proportion to the

level of depolarization as opposed

to the rate of action potentials

¶OFF· BIPOLAR

¶ON· BIPOLAR

0 mV

-40 mV

0 mV

-40 mV

LIGHT ON

LIGHT ON



0 mV

-40 mV

light on

LGN

µOFF¶ bipolar (glutamate depolarizes)

0 mV

-40 mV

light on

photoreceptor

0mV

-40 mV

light on

µON¶ ganglionµOFF¶ ganglion

light onlight on

A LIGHT SPOT IN AN

OTHERWISE DARK

FIELD:

µON¶ bipolar (glutamate hyperpolarizes)



0 mV

-40 mV

light off

LGN

0 mV

-40 mV

light off

photoreceptor

0mV

-40 mV

light off

µON¶ ganglionµOFF¶ ganglion

light off light off

A DARK SPOT IN AN

THERWISE ILLUMINATED

FIELD:

µOFF¶ bipolar (glutamate depolarizes)

µON¶ bipolar (glutamate hyperpolarizes)



GANGLION CELL OUTPUT OF THE RETINA

PARVOCELLULAR-

(X)

MAGNOCELLULAR(Y)

KONIOCELLULAR

SURROUND

INHIBITION

YES YES NO

COLOROPPONENCY

YES NO YES

RECEPTIVE FIELDSIZE

SMALL LARGE --------

RESOLUTION HIGH LOW ---------

RESPONSE TOLIGHT

SUSTAINED TRANSIENT ---------

LOW-CONTRAST,

MOVING STIMULI

POOR

RESPONSE

STRONG

RESPONSE

--------

PERCENT OFGANGLION CELL

POPULATION

80% 10% 10%



PARVOCELLULAR

LAYERS

MAGNOCELLULA

LAYERS

KONIOCELLULAR

LAYERS

THE LGB: LAYERING CORRESPONDS TO TYPE

OF GANGLION CELL



Neurons in the Cerebral Cortex

Simple CellsNeurons with fixed excitatory & inhibitory zones in theirreceptive fields

Found only in the Primary Visual Cortex (V1)

Complex Cells

Receive input from a combination of Simple Cells

Have receptive fields that respond to particular orientationsof light but cannot be mapped into fixed excitatory &inhibitory zones

Located in V1 and V2End-stopped (Hyper-complex) Cells

Strongly resemble complex cells but have an inhibitory area atone end of its bar-shaped receptive field



PRIMARY VISUAL CORTEX (AREA 17 / V1)

CORTICAL COLUMNS

OCULAR DOMINANCE

COLUMNORIENTATION

COLUMNS





ORIENTATION

COLUMNS

OF

THE STRIATE

CORTEX



COLUMNS AND BLOBS



COLOUR

Theories of colour vision:` TrichromaticTheory

` Opponent-process Theory

` RetinexeTheory (The Land Effect)



�Horopter

�Panum's

Fusional

Area

�Retinal

disparity

Stereopsis ² the ability to appreciate depth



-Damage to IT (TE + TEO) impairs object identification

(but only via visual information)

-Damage to parietal cortex (MT, MST, 7a, VIP, LIP) impairs visuospatial

abilities(e.g., reaching to an object)

¶ WHAT· (TEMPORAL) AND ¶ WHERE·

(PARIETAL) PATHWAYS



DISORDERS OF OBJECT RECOGNITION

Visual AgnosiaThe inability to recognize objects

despite otherwise normal vision

Prosopagnosia

The inability to recognize faces

without an overall loss of vision

or memory

The Fusiform Gyrus in the

Inferior Temporal Cortex is

specialized for face recognition

Identifying car models, bird

species



MOTION DETECTION

Medial Temporal Cortex

Middle Temporal Cortex &

Medial Superior Temporal Cortex

important in motion detection

Involved in distinguishing

between moving objects

& head changes

Damage to Medial Temporal

Cortex results in motionblindness



THANK YOU

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Neurology of Vision Natesan Green