Neurology, ophthalmology, optic pathway anatomy, and lesions

1. OPTIC PATHWAY AND
LESIONS
UMA CHIDIEBERE JOHN

2. • Beginning in the retina, the visual pathway continues
• through the optic nerves,
• optic chiasm,
• and optic tracts to synapse in
• the lateral geniculate nucleus (LGN).
• From the LGN, it extends through
• the temporal and parietal lobes
• to terminate in the occipital lobes

3. • A healthy disc is normally pink to
orange in color, with well
delineated margins and a small
cup to disc ratio (<0.3)
3

4. Why the normal disc is pink?
• Thickness and the
cytoarchitecture of fiber bundles
passing between glial columns
containing capillaries
4

5. • The retina is a thin, multilayered tissue sheet containing
three developmentally distinct, interconnected cell groups
that form signal processing networks:
• • Class 1 :: sensory neuroepithelium (SNE) ::
photoreceptors and BCs
• • Class 2 :: multipolar neurons :: GCs, ACs, and axonal cells
(AxCs)
• • Class 3 :: gliaform neurons :: horizontal cells (HCs)

6. Receptors:
1. Rods
2. Cones
Neurons:
1. First order: bipolar cells
2. Second order: ganglion cells
3. Third order: LGB
Visuo-striate area (17):
Both walls of calcarine sulcus
involving Cuneus and lingual
gyrus

7. Components of the visual pathway
A. Optic nerve
B. Optic chiasma
C. Optic tracts
D. Lateral geniculate bodies
E. Optic radiations
F. Visual cortex

8. VISUAL PATHWAY

9. Visual
Pathway

10. Optic chisam
• Floor of the third ventricle.
• 5-10 mm above the diphragma sella and the hypophysis cerebri.
• 12mm wide, 8mm A-P , 4 mm thick.
• Important relations: 3rd ventricle, hypothalmus, pituitary stalk, sella,
dorsum sellam anterior and posterior clinoid processes, cavernous
sinus.
• Nasal fibers cross ; temporal fibers do not (53:47).
• Wilband’s knee.

11. 1. OPTIC
NERVE
(STUMP)
2. 0PTIC
CHIASMA
3. OPTIC
TRACTS

12. Visual
Pathway
Optic chiasma:
1. Junction of the floor and
the anterior wall of the
third ventricle
2. Rests on the diaphragma
sellae
3. Wilbrand’s loop

13. 13

14. OPTIC TRACTS
• Cylindrical bundle of nerve
fibres.
• Run outwards & backwards
from posterolateral aspect of
optic chiasma ,between tuber
cinereum & anterior
perforated substance to unite
with cerebral peduncle.
• Fibres from temporal half of
retina of same eye & nasal half
of opposite eye.
• Posteriorly each ends in
Lateral Geniculate Body.

15. Visual
Pathway
Optic tracts:
1. Medial root
Gudden’s commisure
2. Lateral root
a. LGB
b. Superior colliculus &
pre-tectal nucleus
c. Supra-chiasmatic
nucleus

16. Visual
Pathway
Lateral geniculate body:
1. Part of meta-thalamus
2. Connected to superior
colliculus via superior
brachium
3. Cells arranged in six layers

17. OPTIC RADIATIONS (Geniculo-Calcarine
Pathway)
• From LGB to the occipital cortex.
• Pass forwards then laterally through the area of
wernicke as optic peduncles.
• Anterior to lateral ventricle ,traversing the
retrolenticular part of internal capsule,medial to
auditory tract.
• Its fibres then spread out fanwise to form medullary
optic lamina.
• Inferior fibres subserve upper visual fields & sweep
anteroinferiorly in meyer’s loop & temporal lobe to
visual cortex.
• Superior fibres subserve inferior visual field proceed
posteriorly through parietal lobe to visual cortex.

18. Visual
Pathway
Optic radiation:
1. From LGB to striate area
of visual cortex (17)
2. Passes through the retro-
Lentiform part internal
capsule
3. Meyer’s loop

19. Primary Visual Cortex????
• Area 17
• located in the occipital
lobe in the calcarine
fissure region extending
to the pole
• large representation in
visual cortex for the
macula (region for
highest visual acuity)
• receives the primary
visual input
19

20. primary VISUAL CORTEX
• FROM THE LATERAL GENICULATE NUCLEUS, THE FIBRES PASS BY THE
OPTIC RADIATIONS TO THE PRIMARY VISUAL CORTEX.
• IT IS LOCATED IN THE CALCARINE FISSURE AREA OF THE MEDIAL
OCCIPITAL LOBE. (BRODMANN’S AREA 17 OR V1)

21. Secondary Visual Areas
• visual association cortex (area
18, 19)
• responsible for analyzing the
visual information
• area for 3 dimensional
position, gross form, and
motion
• area for color analysis
21

22. Retinal Projections to Subcortical
Regions
• suprachiasmatic nucleus of the
hypothalamus
• control of circadian rhythms??
• pretectal nuclei
• pupillary light reflex
• accommodation of the lens
• superior colliculus
• rapid directional movement of both eyes
22

23. The Autonomic Nerves to the Eyes
23

24. The Autonomic Nerves to the
Eyes
• The eye is innervated by both parasympathetic and
sympathetic neurons.
• Parasympathetic fibers arise in the Edinger-Westphal
nucleus, pass in the 3rd cranial nerve to the ciliary
ganglion.
• Postganglionic fibers excite the ciliary muscle and sphincter
of the iris.
• Sympathetic fibers originate in the intermediolateral horn
cells of the superior cervical ganglion.
• Postganglionic fibers spread along the corotid artery and
eventually innervate the radial fibers of the iris.
24

25. Control of Pupillary Diameter
• miosis: decreasing of pupillary
aperture due to stimulation of
parasympathetic nerves that excite
the pupillary sphincter muscle
• mydriasis: dilation of pupillary
aperture due to stimulation of
sympathetic nerves that excite the
radial fibers of the iris
25

26. Fig.
16.07
26

27. Visual reflexes
• Light reflex or pupillary
reflex:
When light is shown to one
eye, normally the pupils of
both eyes constrict.
- Direct light reflex:
The constriction of pupils
upon which light is shown is
called direct light reflex.
- Indirect or consensual:
The constriction of pupil on
the other eye even though
no light is shown

29. Pathways of direct and indirect light reflexes
(v.imp.)
29

30. Pupillary light reflex
Direct
Consensual

31. Accommodation

32. ACCCOMODATION REFLEX
• When the eyes are focussed
from a distant to near
object, three reactions take
place
• 1. Constriction of pupils
• 2. thickening of lens due to
contraction of ciliary
muscles
• 3. Convergence of both eye
balls
These three reactions
together constitute
Accommodation or near
reflex

33. Accommodation
reflex

34. LESIONS OF THE VISUAL PATHWAY

35. Optic nerve lesions (A,B)
Causes : Optic atrophy, traumatic avulsion, acute optic neuritis etc.
1.Distal optic nerve lesion (A)
• Complete blindness of affected side
• Abolition of direct light reflex on affected side
• Accommodation reflex intact

36. 2. Proximal optic nerve lesion (B)
• Blindness on affected side
• Contralateral hemianopia
• Abolition of direct light reflex on affected side
• Accommodation reflex intact

37. Chiasmal lesions (C,D)
1.Central chiasmal lesion (C)
• Bitemporal hemianopia
• Bitemporal hemianopic paralysis of pupillary reflexes
2.Lateral chiasmal lesion (D)
• Binasal hemianopia
• Binasal hemianopic paralysis of pupillary reflexes

38. Causes :
I. Intrinsic causes – Lesions which produce thickening of
chiasma. Eg. Gliomas, multiple sclerosis
II. Extrinsic causes – Compressive lesions. Eg. Pitutary
adenoma, meningioma
III. Other causes – Include metabolic, toxic and
inflammatory syndromes. Eg. Lymphoid hypophysitis,
sarcoidosis

39. Optic tract lesions (E)
Causes :
I. Intrinsic causes – Demyelinating diseases and infarction.
II. Extrinsic causes – Compressive lesions. Eg. Pitutary adenomas, tumours of
optic thalamus
III. Other causes – syphilitic meningitis, tubercular meningitis

40. Optic tract lesions
• Incongruous homonymous hemianopia
• Contralateral hemianopic pupillary responses (Wernicke’s
reaction)
• Optic disc changes – Descending type of partial optic
atrophy is produced characterized by temporal pallor on
the side of the lesion and bow tie atrophy on the
contralateral side.
• Visual acuity is intact

41. Pitutary adenoma
• Visual fields ; bitemporal hemianopia,junctional
scotoma,
bitemporal hemianopic scotoma
• Colour vision; early red deficit
• Visual acuity tends to reduce
• Optic disc- bow tie atrophy rarely papilloedema
• Extraocular movements: cranial nerve palsies,see
saw nystagmus,spasm nutans.

42. Lateral geniculate nucleus lesions(E)
• Incongruous homonymous hemianopia
• Pupillary reflexes are normal as the fibres go to pretectal nucleus and
not the LGN
• Optic disc pallor may occur due to partial descending atrophy

43. Lesions of optic radiations (F,G)
Common lesions include :
• Vascular occlusions
• Tumours
• Trauma
• Temporal lobectomy for seizures

44. Lesions of optic radiations
• Superior quadrantic hemianopia(F) – Pie in the sky lesions.
It is explained by the fact that inferior fibres of optic
radiations contain fibres from ipsilateral lower temporal
retina and contralateral lower nasal retina.(part of optic
radiations in temporal lobe)
• Inferior quadrantic hemianopia(G) – Pie on the floor
lesions. This is the same as above. Difference being the
superior fibres are affected. (part of optic radiations in
parietal lobe)

45. • Complete homonymous hemianopia(H) – produced when
all fibres of optic radiations are involved sometimes sparing
the macular fibres as they lie centrally.
• Pupillary reflexes are spared
• Optic disc atrophy does not occur

46. Visual cortex lesions (I,J,K)
• Congruous homonymous hemianopia – macular field of vision is
spared. It is a feature of occlusion of posterior cerebral artery.
• Congruous homonymous macular defects – occurs in lesions at the tip
of occipital cortex following head injuries or gun shot injuries

47. • Bilateral homonymous macular defects – presenting like
bilateral central scotoma occur in bilateral lesions of
occipital cortex
• Pupillary light reflexes are normal
• Optic atrophy doesn’t occur.
Other manifestations of occipital lobe lesions include :
• Cortical blindness
• Dyschromatopsia

48. • Visual hallucinations
• Palinopsia – Persistent perception of visual image
• Visual anesthesia – transposition of visual stimulus from
one hemifield to another
• Polyopsia – multiple images of single object which do not
disappear on closing the eye.