OPTIC AND OCULOMOTOR NERVE ANATOMY, PHYSIOLOGY AND APPLIED

1. OPTIC NERVE AND
OCULOMOTOR NERVE
DR PRAVEEN K TRIPATHI

2. OVERVIEW OF OPTIC NERVE
• CNS Fibre Pathway Connecting Brain And retina
• The optic nerve carries about 1.2 million axons
that derive from the retinal ganglion cells
• 90% of fibers arise from macula.
• Not a true peripheral nerve but a tract of the
diencephalon.
• Contains myelinated axons.
• Invested by the dura and pia–arachnoid
membranes and lies within the subarachnoid
space.

3. General characteristics of CN II
• A special somatic afferent (SSA) nerve that
subserves vision and pupillary light reflexes.
• Enters the skull via the optic canal of the sphenoid
bone. has axons that continue via the optic chiasm
and optic tracts to the lateral geniculate body, a
thalamic relay nucleus that projects to the visual
cortex (area 17) of the occipital lobe.
• Contains fibers from the nasal retina that
decussate in the optic chiasm.
• Contains fibers from the temporal retina that
continue ipsilaterally through the optic chiasm.

4. The eye
• Objects in one lateral half of the visual field form
images on the nasal half of the ipsilateral retina
and the temporal half of the contralateral retina.
• The retina contains photoreceptors (rods and
cones), 1st-order sensory neurones (bipolar cells)
and second-order neurones (ganglion cells).
• The axons of retinal ganglion cells accumulate at
the optic disc (blind spot) and pass into the optic
nerve.

5. The retina

6. OPTIC DISC AND ASSOCIATED
STRUCTURES
•Bulk of the fibers in the optic nerve arise from the macula
•Nasal side form the papillomacular bundle
•Temporal hemimacula enter the disc as superior and inferior
arcades.

7. Anatomic consideration
• The optic nerve is about 50mm long and extends
from the eye to the optic chiasm.
• It is often described as consisting of four portions
 Intraocular portion (the optic disc, 1mm in
anterior-posterior length)
 Intraorbital portion (about 25mm long)
 Intracanalicular portion within the optic canal
(about 9mm long)
 Intracranial portion (about 16mm long)

8. Anatomic consideration
The intraocular segment
(a) is within the globe.
The intraorbital segment
(b) runs through the orbit
to the entrance of the
optic canal depicted by
the left-most blue dot.
The intracanalicular
segment (c) courses
between the two blue
dots.
The intracranial segment
(d) continues to its
junction with the optic
chiasm (blue bar).

9. Anatomic consideration

10. Optic Chiasma
The optic
chiasm, a
flattened
structure, is
situated about
10mm above
the pituitary
gland, which
rests in the sella
turcica of the
sphenoid bone

11. Optic Chiasma
normal chiasma overlies the diaphragma sellae

12. VARIATIONS IN OPTIC CHIASMA
• 5% chiasm overlies the anterior margin of the sella (prefixed chiasm)
• 12% it lies over the diaphragma sellae,
• 79% it is above the dorsum sellae, and in
•4% it projects behind the dorsum sellae (postfixed chiasm).

13. Variation in the length of the optic nerves alters the
relative position of the chiasm to the sellar structures

14. THE CHIASMA
• At, more than half of the fibers (those originating in
ganglion cells of the nasal retina) cross to reach the
contralateral optic tract.
• The ratio of crossed to uncrossed fibers is
approximately 53:47.
• Fibers from the inferior part of the nasal retina are
ventral in the chiasm and loop into the proximal
portion of the contralateral optic nerve (Wilbrand's
knee) before reaching the lateral aspect of the optic
tract .
• Those from the superior nasal retina remain dorsal
in the chiasm and become medial in the optic tract.

16. Projections of the visual fibers from
the upper and lower nasal quadrants
•Upper nasal quadrant
retinal fibers remain
superior and cross more
posteriorly in the chiasm.
•Lower nasal quadrant
retinal fibers remain
inferior, cross more
anteriorly in the chiasm,
loop anteriorly into the
terminal portion of the
contralateral optic nerve
(Wilbrand's knee), and
head into the optic tract.

17. Projections of the visual fibers from
the lower and upper arcades
Arcuate fibers
maintain their
relative superior or
inferior positions
as they pass
through the
chiasm.

18. Optic Tract
• The optic tract emerges from the optic chiasma
and passes posterolaterally around the cerebral
peduncle.
• Most of the fibers now terminate by synapsing
with nerve cells in the lateral geniculate body,
which is a small projection from the posterior
part of the thalamus.
• A few of the fibers pass to the pretectal nucleus
and the superior colliculus of the midbrain and
are concerned with light reflexes

20. Thalamocortical pathways

21. Optic Radiation
• The fibers of the optic radiation are the axons of
the nerve cells of the lateral geniculate body.
• The tract passes posteriorly through the
retrolenticular part of the internal capsule and
terminates in the visual cortex (area 17).
• Area 17 occupies the upper and lower lips of the
calcarine sulcus on the medial surface of the
cerebral hemisphere.
• The visual association cortex (areas 18 and 19) is
responsible for recognition of objects and
perception of color.

22. Visual (striate) cortex (area 17)
• located on the banks of the calcarine sulcus.
• receives retinal input via the ipsilateral LGB.
• receives its blood supply from the calcarine artery, a
branch of the posterior cerebral artery;
• anastomosis with the middle cerebral artery may be
substantial (macular sparing).
• lesions result in a contralateral homonymous
hemianopia with macular sparing. Bilateral
• Destruction of both cunei results in a lower altitudinal
hemianopia, and bilateral destruction of the lingual gyri
results in an upper altitudinal hemianopia.

23. Retinotopic organization of the visual cortex
includes
1. Posterior third of the visual cortex
receives macular input (central vision).
2. Intermediate area of the visual cortex
receives paramacular input (peripheral input).
3. Anterior area of the visual cortex receives
monocular input.

24. The central visual
pathway

25. The central visual pathway
■ At the optic chiasm, axons from the nasal halves of the two
retinae decussate and pass into the contralateral optic tract.
■ The optic tract contains axons that carry information relating to
the contralateral half of the field of vision.
■ Optic tract fibres end in the lateral geniculate nucleus of the
thalamus.
■ Third-order visual fibres from the lateral geniculat e nucleus pass
through the retrolenticular part of the internal capsule and the
visual radiations to terminate in the primary visual cortex.
■ The primary visual cortex is located above and below the
calcarine sulcus of the occipital lobe.
■ The rest of the occipital lobe constitutes the visual association
area

26. PUPILLARY LIGHT PATHWAY

27. Clinical evaluation
• Visual acuity
• Color vision
• Visual field
• Pupillary evaluation
• Fundus examination

28. Clinical correlations: CN II
• When it is transected, ipsilateral blindness
and loss of direct pupillary light reflex result;
regeneration of the optic nerve does not
occur.
• When subjected to increased intracranial
pressure (e.g., tumor), papilledema, a choked
optic disk results.
• When it is constricted, optic atrophy (i.e.,
axonal degeneration) results.

29. •Junctional scotomas
occur with compression
of the anterior angle of
the chiasm (sphenoid
meningioma).
•Bitemporal hemianopia
results from compression
of the body of the
chiasm from below (e.g.,
because of pituitary
adenoma, sellar
meningioma).
•Compression of the
posterior chiasm and
its decussating nasal
fibers may cause central
bitemporal hemianopic
scotomas (e.g., because
of hydrocephalus,
pinealoma,
craniopharyngioma).

30. •The macular fibers decussate
as a separate compact bundle
•inferior retinal (superior visual
field [VF]) fibers cross
inferiorly, and superior retinal
(inferior VF) fibers superiorly.
•Masses impinging from below
(e.g., pituitary adenoma) tend
to cause early defects in the
superior temporal fi elds;
masses impinging from above
(e.g., craniopharyngioma) tend
to cause early defects in the
inferior temporal fi elds.

31. Compressive Chiasmal Syndromes
• Chiasmal glioma
• Craniopharyngioma
• Dysgerminoma
• Meningioma
• Optic chiasm diastasis from pituitary tumor
• Pituitary apoplexy
• Pituitary tumor (especially pituitary adenoma)
• Suprasellar aneurysm

33. Papilledema showing blurred disc and
tortuous vessels

34. OCULOMOTOR NERVE

35. GENERAL CONSIDERATION
• A purely motor nerve that moves the eye, constricts the
pupil, accommodates, and converges.
• exits the brainstem from the interpeduncular fossa of the
midbrain, passes through the lateral wall of the cavernous
sinus, and enters the orbit via the superior orbital fissure.
Cranial nerve III innervates
• the medial rectus,
• superior rectus,
• inferior rectus, and inferior oblique muscles,
• pupillary sphincter and the levator palpebrae that
elevates the upper eyelid.

36. Anatomy

37. Anatomy
• The third nerve nuclear complex extends
rostrocaudally for about 5 mm near the midline
in the midbrain at the level of the superior
colliculus (SC) .
• It lies ventral to the Sylvian aqueduct, separated
from it by the periaqueductal gray (PAG) matter,
and dorsal to the two medial longitudinal
fasciculi.
• One unpaired and four paired rostrocaudal
columns can be distinguished in the oculomotor
nuclear complex.

38. Anatomy
• The unpaired column, shared by the right and left nuclei, is
in the most dorsal location and contains the visceral nuclei
(Edinger-Westphal nucleus) rostrally and the subnucleus for
the levator palpebrae (LP) superioris caudally.
• The Edinger-Westphal nucleus mediates pupillary
constriction.
• Of the four paired subnuclei, the most medial innervates
the SR muscle.
• This is the only portion of the oculomotor nucleus that
sends its axons to the opposite eye.
• Decussating fibers actually traverse the contralateral
subnucleus for the SR.

40. oculomotor nerve in relation to the
major arteries at the base of the brain.
• An aneurysm
arising from
the posterior
communicating
artery is
compressing
and distorting
the nerve.

41. 7 types of 3rd cn palsies
1. nuclear IIIrd nerve palsies
2. fascicular syndromes of the IIIrd nerve
3. uncal herneation syndrome of IIIrd nerve
4. posterior communicating artery aneurysm
5. cavernous sinus syndrome of IIIrd nerve
6. orbital syndrome of the IIIrd nerve
7. pupil-sparing, isolated IIIrd nerve palsies

42. 2) fascicular syndromes of the IIIrd
nerve
• IIIrd nerve + superior cerebellar peduncle =
Nothnagel’s syndrome
• IIIrd nerve + red nucleus = Benedikt’s
syndrome
• IIIrd nerve + cerebral peduncle = Weber’s
syndrome
• IIIrd nerve + superior cerebellar peduncle +
red nucleus = Claude’s syndrome

43. 3) uncal herniation syndrome of IIIrd
nerve
• IIIrd passes along free edge of tentorium
cerebelli
• with expanding supratentorial mass lesions,
the uncal portion of the undersurface of the
temporal lobe may compress the IIIrd nerve
• Pupil is usually involved early and
predominantly-HUTCHINSON PUPIL
• Generally ipsilateral 3rd cn palsy but
sometimes contralateral (false localizing)

44. 4) posterior communicating artery
aneurysm
-most common cause of
• painful, non-traumatic, IIIrd nerve palsy
• 3rd cn passes between posterior cerebral
artery and superior cerebellar artery parallel
to posterior communicating artery
• PUPIL RULE-complete isolated 3rd cn palsy
with pupil sparing is never due to aneurysm

45. 5) cavernous sinus syndrome of IIIrd
nerve
• involvement of III +/- IV +/- VI nerves +/-
oculosympathetics
• may give rise to primary misdirection
syndromes of the IIIrd nerve
• Aberrant Regeneration of the IIIrd Nerve =
misdirection syndrome = acquired
• oculomotor synkinesis

46. Coronal section through the optic
chiasm and cavernous sinuses
The chiasm is
flanked laterally by
the supraclinoid
segments of the
carotid arteries and
inferolaterally by
the cavernous
sinuses through
which pass the
oculomotor
nerves and first two
divisions of the
trigeminal nerve

47. 7) pupil-sparing, isolated
IIIrd nerve palsies
• small caliber, poorly myelinated
parasympathetic fibers tend to locate to the
superonasal portion of the peripheral IIIrd
nerve
• 80% of diabetic IIIrd nerve palsies are pupil
sparing
• 95% of compressive IIIrd nerve palsies have
pupil involvement

48. MLF SYNDROME

50. A right ptosis and miosis in Horner ’ s
syndrome

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