applied anatomy of visual pathway

SEMINAR

APPLIED ANATOMY OF VISUAL PATHWAY

MOERATOR-Dr. SUJATA LAKHTAKIA

Dr. SYED IMRAN

INTRODUCTION

The afferent visual pathway which is responsible for mapping the external world into our consciousness begins with the anterior segment and via the retina, optic nerve, optic chiasm, optic radiations end in the visual cortex.

INTRODUCTION

Components of afferent visual pathway : Retina - Rods and Cones

Bipolar cells Ganglions cells Optic nerve (Ganglion cell axons) Optic chiasm Optic tracts Lateral geniculate body Optic radiations Visual cortex

INTRODUCTION

OPTIC NERVE The optic nerve is formed by the axons of the

ganglion cells .

It represents the second order neurons of the visual pathway.

80% of the fibers originate from the macular region which represents 90% of retinal ganglion cells.

There are 2.2 to 2.4 million fibers in the two optic nerves representing 42% of all fibers entering and leaving the cns.

OPTIC NERVE

The optic nerve is not really a nerve .it is actually a tract ( a part of cns).

Its axons are myelinated by oligodendrocytes and not schwan cells.

OPTIC NERVE

Humans have two types of retinal ganglion cell system. P cell system M cell system

OPTIC NERVE

P cell system : 90% of ganglion cellsSmall cells (small receptive fields)Small caliber axons (slow conduction)

Concentrated in macula Project in parvocellular

layer of LGN(3,4,5,6) Mediate spatial resolution and color perception

OPTIC NERVE

M cell system 10% of ganglion cellsLarge cells (large receptive field)Large caliber axons (fast conduction)

Concentrated in perepheral retina Project in magnocellular layers of LGN (1,2) Mediate motion detection

This explains in part the high sensitivity we have for light and motion detection (fast transmition) while color detection is slow.

OPTIC NERVE

Koniocellular pathway : Smallest ganglion cells (W cells in cat)

Very large receptive fieldsTerminate in the interlaminar

zone and superfical layer of LGN Functions not known

OPTIC NERVE

OPTIC NERVE

Divisions of optic nerve

Intraocular portion (in the globe)

Intraorbital portion ( in the muscle cone)Intracanalicular

portion ( in the optic canal)Intracranial portion

(in the cranial cavity)

OPTIC NERVE

Dimensions of optic nerve (in mm)

SEGMENT LENGTH DIAMETER

Intraocular 1.0 1.5 to 1.75

Intraorbital 25 3 to 4

Intracanalicular 4 to 10 3 to 4

Intracranial 10 4 to 7

OPTIC NERVE Intraocular portion

It is the shortest portion (1mm)

It extends from superficial nerve layer to the posterior margin of sclera

The nerve fibers are non myelinated

It can be divided into Superficial nerve fiber layerPre laminar region Laminar region

Retrolaminar region

OPTIC NERVE Superficial nerve fiber layer

It is made up of axons of ganglion cells

Nasal fibers

Temporal fibers

Papillomacular bundle

NERVE FIBRE LAYER ANALYSIS

Technique : Fundus examination(Green light) Confocal scanning technique OCT Scanning laser polarimetry

OPTIC NERVE

Prelaminar portion It extends from the surface of the optic disc

to the posterior margin of the choroid.

It can be further divided into -Pars retinalis -Pars choroidalis

OPTIC NERVE

Optic disc or Optic nerve head:

The optic nerve head is a 'plug-hole' down which over 1 million nerve fibers descend through a sieve-like sheath known as the lamina cribrosa

It is -Oval -Horizontally1.5mm -Vertically 1.75

mm

OPTIC NERVE

Arrangement of nerve fibers within the optic nerve head:

Peripheral retinal fibers – superficial

Central retinal fibers –deep

OPTIC NERVE

OPTIC NERVE Laminar portion (pars scleralis)

It is enclosed in the scleral canal Scleral canal is 0.5mm long

Lamina cribrosa It is a sieve like connective tissue

meshwork integrated with the scleraIt has 10 connective

tissue plates with 200 to 300 pores They transmit

axonal bundles

OPTIC NERVE

Retrolaminar portion Just posterior to pars scleralis

Fibers get myelinated by oligodendrocytes causing a doubling of the thickness of the nerve to 3mm

Nerve gets surrounded by menengial sheaths

OPTIC NERVE

Intra orbital portion It extends from the back of the eye to the optic canal

It runs backwards and medially

25 to 30 mm long 3 to 4 mm thick

This length is far more than the distance between the back of globe and optic canal which is 18mm

OPTIC NERVE

For this reason the nerve is slack or S shaped in primary position

It allows eye movements without stretching

OPTIC NERVE

Annulus of zinn It is a tough fibrous sheath Located at the orbital apexGives origin to the four recti

Because superior and medial recti partly originate from the nerve sheath itself inflammatory optic neuropathy may be associated with pain on ocular movements

OPTIC NERVE

Intracanalicular portionOptic canal is -8 to 10 mm long

-5 to 7 mm wide It runs superiorly and

medially The optic nerve

passes through the canal accompanied by opthalmic artery (inferiorly ) and sympathetic nerves

OPTIC NERVE

The nerve inside the canal is immobile and fixed

This makes it highly vulnerable to injury by blunt trauma

Optic nerve edema in this area can produce compartment syndrome further causing nerve damage

OPTIC NERVE

Intracranial portion Its length varies from 5 to 16 mm Average 10mm Diameter 4.5mmIt is not covered by menenges It is related bellow and temporally to the

anterior loop of internal carotid artery

The anterior cerebral artery crosses over the nerve

It terminates in the chiasm

OPTIC NERVE

At its intracranial exit the optic nerve passes under a fold of dura ( Falciform ligament ) that may impinge on the nerve, especially if it is elevated by lesion of sphenoid or sella.

OPTIC CHIASM

OPTIC CHIASM

It is a junction at which the two optic nerves join to allow hemidecussation of nasal fibers to opposite optic tracts and the direct passage of temporal fibers to the ipsilateral optic tracts.

Thus, all visual information from the right visual space is transmitted to left cerebral cortex and vice versa.

OPTIC CHIASM It is 12 х 8 х 4mm in size

Situated 10mm above the pituitary and seperated from it by the suprasellar cistern

It is related-- laterally to the supraclinoid segment of carotid arteries

-- inferolaterally to the cavernouss sinuses

It has an inclination of 45˚to the horizontal

OPTIC CHIASM

1.Optic nerve 2.Optic chiasma 3.Optic tract 4.Tuber cinereum 5.Mamillary bodies 6.Anterior perforated substance 7.Olfactory trigone 8.Pons 9.Uncus

Upper nasal fibers

Macular fibers

Lower nasal

Anterior clenoid

Pituitary

Third ventricle

Craniopharangioma

Chiasm

Posterior clenoid

Dorsum sellae

Diphragma sellae

OPTIC CHIASM Chiasmal nerve pathways

Lower nasal :Pass low and anterior More vulnerable to damage by pituitary lesion

Wilibrands knee : Some inferonasal fibers loop forwards into the contralateral optic nerve

It may be affected in lesions of the terminal part of optic nerve

OPTIC CHIASM

Upper nasal : Pass high and posteriorlly They are involved in lesions above the chiasm

Macular fibers : decussate throughout the chiasm

LESIONS OF OPTIC CHIASM Anterior Chiasmal Lesions

Damage to ipsilateral optic nerve and Knee of Wilibrand

RE LE

Rt Anterior Chiasmal lesion

LE RE

HM

CF

Decussating fibersare most vulnerable

VISUAL FIELD DEFECTS IN PITUITARY ADENOMAS

VISUAL FIELD CHANGES IN CRANIOPHARANGIOMA

LE RE

HM

CF

Posterior crossing fibers most vulnerable

Meningioma LE RE

Junctional scotoma

Tuberculum Sellameningioma

Olfactory groove meningioma

Sphenoid ridge meningioma

OPTIC CHIASM

Anatomical variations : Variations in the length of optic nerve alters the relative position of the chiasm to the sellar structures

Central –80%

Prefixed--10%

Postfixed –10%

CENTRAL 80%

PREFIXED 10% POSTFIXED 10%

OPTIC TRACTS

OPTIC TRACTS

Each optic tract contains ipsilateral temporal and contralateral nasal fibers

They wind round the cerebral peduncle of the rostral midbrain and each divide into

Lateral root

Medial root

OPTIC TRACTS

Lateral root :Large ( 90%)

Concerned with conscious visual functions

Terminates in Lateral geniculate body

Medial root :Small ( 10%)

Not concerned with conscious visual functions

Contains six groups of fibers

OPTIC TRACTS

Termination of medial root fibers : -Superior Colliculus -three groups Visual grasp reflex Automatic scanning of images

Visual association pathways -Pretectal nucleus

Pupilary light reflex

OPTIC TRACTS

-Parvocellular reticular formation Arousal function in response to light

-Suprachiasmatic nucleus of hypothalamus It is called Retinoypothalamic tract

Photoperiod regulation Beneficial effect of sunshine on mood

OPTIC TRACTS

Arrangement of Fibers : Fibers from superior retina remain

superiorly while those from inferior remain inferiorly Fibers from corresponding parts of the retina do not pair This explains the incongruous nature of visual field defects seen in optic tract lesions Magnocellular axons dominate the periphery while Parvocellular dominate the center

OPTIC TRACTS

As temporal visual is 1.5 times the size of nasal field

The contralateral nasal retina supplies more axons (55% ) than the temporal retina of ipsilateral (45% ) eye

This is the reason for monocular temporal

crescent ( 60 to 90˚) in contralateral visual field caused by damage to the most anteromedial part of occipital cortex

OPTIC TRACTS

Lesions of optic tract cause incongruous homonymous hemianopia contralateral to the affected optic tract

RE LE

Rt Optic tract lesion

LATERAL GENICULATE NUCLEUS


It is a synaptic zone (relay center ) for higher visual projections

Located in the posteroinferior part of thalamus

It is divided into six layers by medulated nerve fibers

Numbered 1 to 6 from below upwards

Arranged in a dome shaped pattern

In the early 1960s, David Hubel and Torsten Wiesel (who won the Nobel Prize for Medicine in 1981) were the first to use microelectrodes to explore the receptive fields of the neurons in the lateral geniculate nucleus and the visual cortex


Magnocellular fibers layer 1,2 Parvocellular fibers layer 3,4,5,6 Koniocellular fibers interlaminar zone

superficial layers Contralateral axons layer1,4,6 Ipsilateral axons layer 2,3,5


In LGN the retinal representation rotates to almost 90˚

Superior fibers move superomediallyInferior fibers move inferolaterally Macular fibers move superolaterally


The LGN also receives inputs from cortex, reticular formation, occulomotar center, superior colliculus and pretectal nucleus

The visual impulses are modified in accordance to the impulses from these centers and relayed to the visual cortex


Lesions of Lateral geniculate nucleus cause incongruous homonymous hemianopia contralateral to the to the affected optic tract

RE LE

Rt Optic tract lesion

OPTIC RADIATION

OPTIC RADIATIONS

Also called Geniculocalcarine tracts

These consists of nerve fiber bundles whose cell bodies lie in the LGN

They terminate in the visual cortex

OPTIC RADIATIONS

Along the radiations the fibers from corresponding retinal elements lie progressively closer together

This is the reason why lesions in posterior radiations cause more congruous hemianopia than anterior

LGN

Inferior fibers

Myers loop

Superior fibers

Lateral ventricle(Posterior cornu )

Visual cortex

LESIONS OF OPTIC RADIATIONS

Temporal Lobe (Myers loop) : Conralateral superior wedge shaped incongruous homonymous

hemianopia (Pie in the sky defect ) sparing the central vision


Parietal lobe : Conralateral inferior wedge shaped incongruous homonymous

hemianopia sparing the central vision


Main radiations : Complete homonymous hemianopia on

contralateral side

VISUAL CORTEX

VISUAL CORTEX

It can be divided into 1.Primary visual area ( V1, Area 17, striate cortex )

2. Secondary visual areas -Area V2 ( Area 18 , Parastriate cortex) -Area 19 (Peristriate cortex) -Area V3a and Area V3 -Area V4 -Area V5 ( MT ) -Area V6

VISUAL CORTEX

To date, researchers have discovered nearly 30 different cortical areas that contribute to visual perception

VISUAL CORTEX

Primary visual cortex ( Area 17 ) -Also called striate cortex because of

prominent white bands of fibers –the stria of Gennari

-Located within the depths of calcarine sulcus

-Envelops the posterior pole upto 1.5 cm

- Measures 20 to 45 sqcm

VISUAL CORTEX

Projection of fibers -Superior retinal Upper lip of calcarine

quadrants sulcus

-Inferior retinal Lower lip of calcarine quadrants sulcus

-Macular fibers Posterior most portion of cortex

VISUAL CORTEX 50 to 60 % of visual cortex responds to central

10˚of retina and 80% of the cortex to central 30˚ of retina

VISUAL CORTEXHitologically it has 4 different layers Layer 4 is most cellular Called the internal granular layer Optic radiations mainly terminate this layer The predominant cell type not being pyramidal but

small stelate It is further subdivided into 4a,4b and 4cMagnocellular inputs 4c alphaParvocellular inputs 4c beta

VISUAL CORTEX

The cells of Lamina 2,3 Secondary

visual cortex

Lamina 5 Superior

colliculus Lamina 6 LGN

VISUAL CORTEX

Secondary visual areas : Nonstriate cortex They are Visual association areas

They lie above and bellow the Area 17 and extend into the lateral surfaces of the cortex

They show the usual six layers but layer 4 is less extensive

They receive inputs from area 17, thalamus, basal ganglia, and other areas of cortex

VISUAL CORTEX

There connections mainly fallow Dorsal and Ventral pathways

Dorsal outputs (Magnocellular ) V5 in parietal cortex Stereopsis and movement detection

Ventral output (Parvocellular ) to V4 in inferotemporal cortex

Analysis of color and form

VISUAL CORTEX

Area V2 : Parastriate cortex or Area 18Located adjacent to Area 17

Connected to V1, V3 of same side and V1 and V2 of opposite

Also connects to other areas of cortex and mid brain

It is a site of integration of information

VISUAL CORTEX

Area V3 andV3a : In lunate and parietooccipital sulciThey are sensitive to motion and

direction Area V4 :

Located in lingual and fusciform gyrus Sensitive to color

Area V5 : Located anterior and lateral to area V4Highly sensitive to speed and direction

of moving stimulus

LESIONS OF OPTIC RADIATIONS AND VISUAL CORTEX

Anterior visual cortex dysfunction Caused by PCA occlusion

Contralateral Congruous homonymous hemianopia With Macular sparing

Macular Cortex lesion Severe hypotension Contralateral Homonymous

hemianopia involving only the Fixation region

Contralateral Monocular temporal crescent is seen in lesions of the most anteromedial part of the visual cortex

BLOOD SUPPLY

BLOOD SUPPLY The blood supply of optic nerve varies from

segment to segment

The central retinal artery :Branch of ophtalmic artery It enters the optic nerve 10-12mm

behind the globeIt divides into superior and inferior

arcades

BLOOD SUPPLY Intraocular Optic nerve

Nerve fiber layer Central retinal artery

Prelaminar Nerve Short post ciliary Recurrent choroidal

arteries Laminar Nerve Short post cillary arteries

Branches from circle of Haller and Zinn Retrolaminar Nerve Pial

Short post cillary arteries

BLOOD SUPPLY

Intraorbital Part : Proximally Pial vascular network

Branches of Opthalmic artery

Distally Intraneural branches of CRA

Most anteriorly Post cillary arteries

BLOOD SUPPLY Intracanalicular part Opthalmic artery

Intracranial part Internal carotid arter Opthalmic artery

OPTIC CHIASM Sup hypophysial artery Internal carotid artery

Post communicating artery Ant cerebral artery Ant communicating artery

BLOOD SUPPLY

OPTIC TRACT Ant chorotdal artery (br of ICA)

LATERAL GENACULATE NUCLEUS Ant choroidal artery Posterolateral choroidal

artery ( br of PCA)

BLOOD SUPPLY

OPTIC RADIATIONSCommencement Ant choroidal

arteries Posterior fibers Lateral striate (deep optic) branches of PCA

VISUAL CORTEX Penetrating branches of Cortical arteries

mainly Calcarine and parieto-occipital branches of PCA

Anastamosis between MCA and calcarine artery

REFERENCES

• Ophthalmology, 2nd edition : Yanoff & Duker• Clinical Neuroophthalmology :Walsh & Hoyt΄s• American academy of ophthalmology :Basic and

clinical science course• Clinical Ophthalmology : Kanski• Parson’s basic diseases of the eye : Radhika

Tandon, Ramanjeet Sihota ; 20th edition• Clinical Ophthalmology : A.K. Khurana ; 3rd

edition• Anatomy and Physiology of Eye: A.K. Khurana 2nd

ed.

Thank You…

DEVELOPMENT OF OPTIC NERVE

DEVELOPMENT OF OPTIC NERVE It develops from the optic stalk that connects the

optic vesicle and fore brain The optic stalk is Fluid

filled tube Lined by Neuroectoderm

It has two separate regions Distal crescent shaped invaginated segment

(choroidal fissure)Proximal non invaginated circular

segment


At the 6th week (17mm stage) nerve fibers begin to grow and the embryonic cleft begins to close


This results in a double layer of neuroectoderm with obliteration of the fluid filled cavity

The invagination process leads to incorporation of hyaloid vessels and surrounding mesenchyme


The ganglion cell axons run through the inner neuroectodermal layer towards the brain

At about the end of 6th week, optic nerve fibers penetrate the under surface of forebrain, in 7th week optic chiasm is formed, and at 9thweek optic tracts are formed.

The outer neuroectodermal layer differentiate into peripheral glial mantle and glial components of lamina cribrosa


Initially there is increase in the number of axons10 to 12 wks – 1.9 million

16th wk - 3.7 million

Later attrition of axons occur 33rd wk - 1.1 million

Myelination Begins in the LGN – 5th month of gestation Reaches Chiasm - 6 to 7th month of gestationLamina cribrosa – Term

APPLIED ANATOMY

CONGENITAL ANOMALIES

Prepapillary loop : vascular loop extending from the disc margin into vitreous cavity


Bergmeister papilla : This cone shaped mass of tissue derived

from the retinal cells is present at the presumptive optic disc during fetal life

It involutes during development The degree of atrophy

determines the depth of physiological cup -Complete atrophy –

Deep cup -Moderate atrophy –Shallow cup -Minimal atrophy --Substantial glial elements present on cup called persistent Bergmeister papilla


Medulated nerve fibersSeen in 0.3 to 0.6 % population

Whitish patch with feathery margins usually adjoining the disc margins


Tilted disc :This occurs due to oblique entry of

optic nerve into the globe

CONGENITAL ANOMALIES Optic disc pits :

Herniation of dysplastic retina into the nerve substance

Round to oval grey white depression in the disc usually temporally

CONGENITAL ANOMALIES Optic nerve hypoplegia

Decreased number of axons with normal mesodermal components Small pale disc with surrounding double ring sign


Megalopapilla : Large optic disc (>2mm)with large CD ratio


Optic disc Coloboma : An inferior segmental form of optic nerve hypoplasia.

Disc appears enlarged with a sharply demarcated glistening white bowl shaped excavation.

Inferior rim thinner ; only remaining neural tissue lies superiorly in a C shaped / Moon shaped crescent. neural tissue lies superiorly in a C shaped / Moon shaped crescent

OPTIC DISC DRUSENS

BURRIED EXPOSED


MORNING GLORY SYNDROME – this is unilateral congenital anomaly, with enlarged and excavated disc with annular pigmented retinal tissue around it.

PAPILLEDEMA

Optic disc edema, usually bilateral resulting from raised ICP.

Purely hydrostatic, non-inflammatory phenomenon,

Pathophysiology; blockage of axoplasmic transport along with edema and vascular congestion.

EARLY

CHRONIC

FULLY DEVELOPED

OPTIC NEURITIS Optic neuritis: Inflammatory, infective or

demyelinating process affecting the optic nerve.

Classified as PapillitsNeuroretinitis Retrobulbar neuritis

PAPILLITIS NEURO RETINITIS

OPTIC ATROPHY

Condition of the disc following degeneration of the optic nerve.

Primary Optic Atrophy:

Lesions affecting the visual pathway from the retrolaminar portion of the optic nerve to the LGB.

No ophthalmoscopic evidences of previous local inflammation

OPTIC ATROPHY

Secondary or Postneuritic optic atrophy:Follows an injury or direct pressure

affecting the visual nerve fibers in any part from lamina cribrosa to LGB, preceded by swelling of optic nerve head.

PRMARY

Pale Flat discDistinct margins

POSTNEURITIC

Dirty grey disc Indistinct margins

REFERENCES

OPTIC NERVE

Meningial sheaths are supplied by sensory nerves, which account

in part for the pain experienced by patients

with inflammatory optic nerve diseases

OPTIC NERVE

Microglia

They are immune derived cells

Protect the optic nerve from infections

Apoptosis of ganglion cells which occur in various diseases and during development is modulated by these cells

OPTIC NERVE

Oligodendrocytes These are specialized glial cells

Provide myelination to axons

In up to 0.6% myelination may extend to the peripapillary retinal nerve fiber layer

OPTIC NERVE

Meningial sheaths Pia materArachnoid materDura mater

Pia materIt is the inner most layer

It sends numerous septa into the nerve dividing the nerve axons into bundles

These septa continue throughout the nerve and end just before the chiasm

OPTIC NERVE

Dura mater Anteriorly it fuses to the outer layer of sclera

Posteriorly it splits at the orbital opening, majority continuing around the optic nerve and a thin portion blending with the periostium around the optic canal

This completely immobilizes the nerve Blunt trauma to brow area may transmit forces

to this area causing tear between dural sheath and its attachment .This leads to interruption of blood vessels and severe nerve damage

OPTIC NERVE Arachnoid mater It is connected to the pia across the

subarachnoid space by vascular trabeculae

The subarachnoid space ends anteriorly at the lamina cribrosa and posteriorly it is continious with the subarachnoid space of the brain

The central retinal vessels cross the subarachnoid space and are therefore vulnerable particularly the vein in case

of raised ICT

OPTIC NERVE

Astrocytes These are specialized glial cells They have extensive neurofibrilary processes spread among nerve fibers Functions :

Formation Forms blood brain barrier Provide nutrition and support to axons

When axons are lost they proliferate and fill the empty space

applied anatomy of visual pathway

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