Anatomy and visual field defects of optic nerve and chiasma

1. ANATOMY AND VISUAL
FIELD DEFECTS OF OPTIC
NERVE AND CHIASMA
Dr. Sadhwini M H

2. • VISUAL PATHWAY – refers to neural
network that extends from retina to visual
cortex.
• VISUAL FIELD - Each eye sees a part of the
visual space that defines its visual field. The
visual fields of both eyes overlap extensively
to create a binocular visual field. The total
visual field is the sum of the right and left
hemifields and consists of a binocular zone
and two
monocular zones.

3. PARTS OF VISUAL PATHWAY

4. EMBRYOLOGY
•Neural plate destined to form
prosencephalon
depresses to form optic sulcus
•Optic sulcus deepens and prosencephalon
bulge out to form optic vesicle
•Proximal part of optic vesicle becomes
constricted and enlongated to form optic
stalk
•Optic stalk – optic nerve
•Optic vesicle – eyeball
•Surface ectoderm destined to form lens
gets invaginated into optic cup
•A notch develops on ventral side of optic
stalk and cup – fetal fissure – permits entry
of blood vessels

5. Week of
Gestation
Developing events
4 Short optic stalk
5 Development of hyaloid vasculature and primitive retina
7 RGCs differentiate, optic nerve fibres begin to fill optic stalk and these af
ferent neaurons reach the chiasm
8 optic nerve vascularization starting to form, optic nerve head starting to
form
11 Vascular-connective septa invade the nerve
12 Pia mater, arachnoid, and dura mater distinguishable, glial
filaments appear
14 Subarachnoid spaces appears
15 Physiological cup starts to form
18 Vascularization of the optic nerve completed
23 Myelinization starts

6. OPTIC NERVE
• 2nd cranial nerve.
• 47-50 mm in length.
• Starts from optic disc & extends upto optic chias
ma
• Consists of axons originating from ganglion Cells t
hat pass out of lamina cribrosa
• Contains the afferent fibres of light reflex
• Fibres of optic nerve are very thin(2-10um in diam
eter)& are million in number
• Has 4 parts : intraocular (1mm)
intraorbital (30mm)
intracanalicular (6-9mm)
intracranial (10mm)

7. INTRAOCULAR PART
• About 1mm in size, 1.5mm in diameter, passe
s through sclera, choroid & finally appears in
eye as optic disc.
• Divided into 4 parts
– Surface nerve fibre layer
– Prelaminar region
– Lamina cribrosa
– Retrolaminar region

8. •SURFACE NERVE FIBRE LAYER
•Composed of axonal bundles from retina which
converge on optic disc
•Disc is covered by a thin layer of astrocytes, ILM which
is continuous
•PRELAMINAR REGION – just distal to optic nerve head
•Has neurons and significant increased quantity of
astroglial tissues
•Separated from choroid by Border tissue of Jacobie
•LAMINA CRIBROSA
•Fibrillar sieve like structure made of fenestrated sheets
of connective tissue lined by glial tissue
•Nerve fibres leave the eye through these fenestrations
•Separated from choroid by Border tissue of Elschnig
•RETROLAMINAR REGION
•Axons here acquire myelin sheath, supplied by
oligodendrocytes and doubles the nerve diametr to
3mm
•Optic nerve is analogous to white matter tracts of
brain. Hence susceptible to diseases of CNS tracts like
MS

9. INTRAORBITAL PART
• Extends from back of eyeball to optic foramina.
• Slightly sinuous & allows for eyemovements.
• Surrounded by all 3 layers of meninges & subarachnoi
d space
• The CRA & CRV enter the subarachnoid space to enter
the nerve on its inferomedial aspect, about 10mm fro
m eyeball.
• Near optic foramina, it is closely surronded by annulus
of zinn & the origin of four recti muscles. Some fibres
of superior & medial rectus are adherent to its sheath
– painful ocular movementa in retrobulbar neuritis

10. •Between the nerve & lateral rectus – ciliary
ganglion, division of occulomotor nerve, nasociliary
nerve, sympathetic nerve, abducent nerve.
•This close proximity of the structures around the
nerve accounts for the symptom complex of orbital
apex syndrome - proptosis, painful
ophthalmoplegia (3rd, 4th, 6th nerve palsy) and loss
of vision.
•Ophthalmic artery, superior ophthalmic vein and
the
nasociliary nerve cross the optic nerve superiorly
from the
lateral to the medial side.

11. INTRACANALICULAR PART
•5-7mm
•Limited space for expanion
•Most frequently affected in
traumatic optic neuropathies
•Ophthalmic Artery crosses
the nerve inferiorly from
medial to lateral side in
dural sheath.
Sphenoid & posterior
ethmoidal sinuses lie medial
to
it & seperated by thin bony
lamina, this relation
accounts for retrobulbar
neuritis following infection
of sinusitis

12. INTRACRANIAL PART
• About 10mm
• Lies above cavernous sinus &
convergeswith its fellow to fo
rm chiasma.
• Ensheathed in pia mater.
• Internal carotid artery runs b
elow then lateral to it & give
s off ophthalmic artery below
it.
• Superiorly, related to anterior
perforated substance, medial
root of olfactory tract, anteri
or cerebral artery

13. OPTIC CHIASMA
• Dorsoventrally flattened structure
• Results from cross over of 2 opti
c nerves
• Lies in suprasellar subarachnoid
cistern
• Ensheathed by pia & surrounded
by CSF
• Anteroposterior – 8mm
• Horixontal – 15mm
• Height – 4mm

14. •RELATIONS OF CHIASMA
•Anterior - anterior cerebral
arteries & its
communicating arteries.
•Posterior- tuber cinereum,
infundibulum ,pitutary
body ,posterior perforated
substance.
•Superior- third ventricle.
•Inferior- hypophysis
•Lateral- extra cavernous
part of internal carotid
artery& anterior
perforated substance.

15. Anatomical variations in position of
chiasma
CENTRAL : lies directly
over sella, expanding
pituitary tumor
involves chiasma first
PREFIXED : lies more
anteriorly over
tuberculum
sellae, pituitary tumor
involves optic tract
first
POSTFIXED : lies
more posterior over
Dorsum sellae,pituitary
tumor damage optic
nerve first

16. ARRANGEMENT OF FIBRES IN
RETINA
SAF
IAF
PMB
SRF
IRF

17. ARRANGEMENT OF FIBRES IN
OPTIC NERVE HEAD
•Peripheral fibers - deep
in Retina - superficially in
optic
nerve
•Fibers close to optic
nerve head – superficial
in retina - central in
optic nerve

18. ARRANGEMENT OF FIBRES IN
DISTAL REGION OF OPTIC NERVE
MACULA
SRF
SAF
IRF
IAF

19. ARRANGEMENT OF FIBRES IN
PROXIMAL REGION OF OPTIC NERVE

20. ARRANGEMENT OF FIBRES IN
OPTIC CHIASMA

21. Blood supply of Optic Nerve
• Peripapillary choroidal vesselsPrelaminar
• Posterior choroidal vessels
Lamina
cribrosa
• Centrifugal branches from central retinal
artery
• Centripetal branches from pial vessels
Retrolaminar
INTRAOCULAR PART

22. INTRAORBITAL PART
• Derived from 6 branches of ICA :
ophthalmic, long & short posterior ciliary
artery.
• Lacrimal artery.
• Central artery of retina.
PERIAXIAL
SYSTEM OF
VESSELS
• Intraneural b/o central retinal artery.
• Central collateral b/o central retinal
artery.
• Central artery of optic nerve
AXIAL SYSTEM
OF VESSELS

23. •Intracanalicular part :
periaxial system of vessels.
•Intracranial part : Pial
system of vessels

24. VENOUS DRAINAGE
• Central retinal veinONH
• Peripheral pial plexus
• Central retinal vein
ORBITAL
PART
• Pial plexus which ends in anterior
cerebral & basal vein
INTRACRANI
AL PART

25. BLOOD SUPPLY OF OPTIC
CHIASMA
• B/o anterior cerebral & anterior
communicating arterySUPERIOR
ASPECT
• B/o internal carotid artery,
posterior communicating artery
,anterior superior hypophyseal
artery
INFERIOR
ASPECT

26. VENOUS DRAINAGE OF CHIASMA
• Superior chiasmal vein
drains into anterior
cerebral vein
SUPERIOR
ASPECT
• Pre-infundibular vein
draining into basilar vein
INFERIOR
ASPECT

27. LESIONS OF VISUAL
PATHWAY

28. LESIONS OF OPTIC NERVE
• Characterised by : complete
blindness in affected eye wit
h loss of both direct on i/l
& concensual light reflex on
c/l side.
• Causes : optic atrophy, indir
ect optic neuropathy, acute
optic neuritis, traumatic avul
sion of optic nerve.

29. ARCUATE
CENTRAL

30. ALTITUDINAL

31. HEMIFIELD SLIDE PHENOMENON

32. •U/L or Binasal Hemianopias :
•No connection with blind spot
•Respects vertical midline
•Caused by damage to lateral aspect of optic nerve fibres
•Pituitary adenoma compressing lateral aspect of nerve
•Intracranial tumors between optic nerve pushing them
laterally
•Primary hydrocephalus

33. CHIASMAL LESIONS
• Unilateral or Bilateral.
• Junctional scotoma.
• Bitemporal defect.
• Homonymous defects

34. CAUSES OF CHIASMAL SYNDROME
• Pituitary adenoma
• Suprasellar meningiomas
• Supraclinoid internal carotid artery aneurysms
• Craniopharyngiomas
• Optic nerve gliomas
• Uncommon : Optic nerve or chiasmal neuritis,
Pachymeningitis , Trauma ,Inflammatory (e.g.,sa
rcoidosis)

35. LESIONS OF PROXIMAL PART OF 1 OPTIC N
ERVE AND ANTERIOR ANGLE OF CHIASMA
• Lesion at the angle – Traquair’s junctiona
l scotoma – i/l monoocular visual loss &
c/l defect in ST area

36. •Small lesion damaging only
crossing fibres of homolateral eye
– monoocular temporal field defect
respecting midline.
•Only macular crossed fibres of 1
eye damaged – monoocular
temporal field defect, but
scotomatous and located
temporally
•Only Wilbrands knee involved –
c/l superior temporal field defect

37. LESIONS OF BODY OF
CHIASM
• BITEMPORAL field defct – quandrantic/hemian
opic
• If lesion compresses chiasm from below – typic
al bitemporal fiel defect

38. •Pituitary adenoma – field defects are typical
•Peripheral fibres are initially affected, usually
commence in outer upper quadrants of both
eyes
•Right eye – clockwise direction
•Left eye – anticlockwise direction
•Defects may be unequal in both eyes – so one
eye may be almost blind

39. LESIONS OF POSTERIOR ANGLE OF
CHIASM
• 90% of chiasmal fibers have macular orig
in (superior and posterior portions of chi
asm) – bitemporal hemianopic scotomas
•Posterior lesions may
also involve the optic
tract and cause a
contralateral
homonymous
hemianopia

40. LESIONS OF LATERAL ASPECT OF
CHIASM
• Binasal hemianopia - rarely
• Distension of 3rd ventricle causing pressure on each si
de of optic chiasma
• Atheroma of carotids & posterior communicating arter
y.
• Various tumors, pressure from supraclinoid portion of I
CA – damage both uncrossed temporal fibres of i/l eye
and crossed nasal fibres of c/l eye – c/l homonymous
hemianopic defect

41. •If lesion extends from optic
nerve or optic tract to chiasm –
blind eye is always on the side of
the lesion
•If chiasmal lesion extends to
optic nerve or tract – blind eye is
always on the side of extension

42. BAND ATROPHY

43. REFERENCES
• Walsh and Hoyt’s clinical neuroophthalm
ology – 5th edition
• A.k.Khurana Anatomy and physiology of
the eye- 3rd edition
• Yanoff & Duker ophthalmology – 4th editi
on
• Postgraduate ophthalmology – zia chaud
huri
• Wolff’s anatomy of eye -8th edition