1. Anatomy and Physiology
of the Visual pathways
Raed Behbehani , MD, ABO

2. Outline

3. The optic nerve
 1.2 Milllion RGC axons.
 Different types of RGC (parvocellular,
magnocellular).
 Parvocellular : high spatial resolution, color
vision, fine stereopsis.
 Magnocellular : low spatial resolution, motion,
gorss stereopsis.
 Parvocellulae layer 4c-alpha
 Magnocellular layer 4c beta.

4. RGC axons
http://www.city.ac.uk

5. Optic Nerve
 Lamina cribrosa provides structural support.
 Lamia cribrosa: Type I,III,V,VI with intersposed
elastic fibers.
 Ophthalmic artery short PCA (segmental)
 Watershed area (PCA anastomoses are scant).
 Circle of Zinn-Haller.

6. ONH Blood Supply

7. Optic Nerve Cross Section
http://neuromedia.neurobio.ucla.edu

8. Intracanalicular Optic Nerve
 Within the two bases of the LWS.
 Medial wall of canal forms lateral wall of
sphenoid sinus (can be absent !).
 Within canal : meninges, ophthalmic artery and
sympathetic plexus.
 10 mm length.
 Tight space !
 Internal carotid artery.

10. Intra-orbital Optic Nerve
 Myelination (oligodendrocytes).
 20-30 mm Long.
 Axons: mylein and glial cell (metabolic support
at the nodes of Ranvier).

11. Optic nerve (Intracranial)
 Leaves the cranial end of the optic canal (medially,
backwards, upwards).
 4-15 m (depending on the position of chiasm).
 Upward 45 degree-angle.
 Anterior cerebral and anterior comunicating artery lie
superior.

12. Physiology of the Optic Nerve
 Axoplasmic transport : clearance of expired
organelles, structural maintainance, and energy
requirements.
 Interruption of axoplasmic transport : ischemia,
compression, inflammation.
 Orthograde axonal transport : away from the cell
body LGN.
 Retrograde axonal transport : toward cell body.

13. Physiology of the Optic Nerve
 Orthograde  fast and slow speeds.
 Proteins, transmitters transported in smooth
surface vesicles at 400 mm/day (5 hours to
LGB).
 Elements of cytoskeleton (microtubules,
neurofilaments) dependant on actin, kinesin and
dynein.
 Mitochondria moving in both orthograde and
retrograde fashion.

14. Chiasm

15. Chiasm

16. 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.

17. Chiasm

18. Chiasm

19. Chiasm

20. Chiasm
 90% of chiasmal fibers have macular origin
(superior and posterior portions of chiasm).
 Supraclinoid portions of carotid artery lie lateral
to chiasm.

21. Wilbrand’s knee

22. Optic tracts
 Travel around the cerebral peduncles at dorsal
midbrain.
 Divides into lateral root LGN , and a smaller
medial root pretectal area (pupillary light
reflex).

23. Lateral Geniculate Bodies
 Part of the thalamus.
 Hilum, medial and lateral horn.
 Six laminae (layers 1-6), crossed fibers1,4,6 ,
uncrossed fibers 2,3,5.
medial
lateral

24. LGN
 Upper quadrant medial aspect of LGN,
Lower quadrant lateral aspect of LGN.
 Macular fibers central wedge of LGN.
 Layers 1,2: magnocellular. (motion)
 Layers 3-6: Parvocellular. (color)

25. Optic radiations
 Nerve fibers bundles with cell bodies in the
LGN.
 Loop of Meyers (around temporal and inferior
horn of LV).
 Inferior fascicle.
 Superior fascicle.

26. Optic radiations
 Inferior fascicle anterior pole of temporal
lobe lower calcarine cortex.
 Superior fascicle parietal lobe upper
calacrine cortex.

27. Visual cortex
 Upper bank and lower bank (Calcarine fissure).
 LGN input into layer 4 (Stria of Gennari ).
 Inferior visual filed (upper bank) , Superior
visual field (lower bank).

28. Visual cortex
-Maculr projections represented by
50%-60% of the area of the calcarine
cortex.
-Occipital tip is for foveal vision.
-Anterior striate cortex (8%-10%) is
monocularly innervated (temporal
crecsent of contralateral eye).

29. Visual association areas

30. Visual association areas
 Ventral stream (occipitotemporal) : “what”
pathway i.e. object recognition , continuation of
the parvocellular pathway.
 V4- color perception (lingual,fusiform gyri)
 Dorsal stream (occipitoparietal): “where”
pathway i.e. spatial orientation , continuation of
magnocellular pathway.
 V5-motion perception.

31. Higher visual functions

32. Problem 1
 72 year old with progressive vision loss over the
last 2 years.
 Visual acuity: 20/20 , 20/40

33. Problem 1

34. Problem 2
 A 55 year old patient with sudden, pain less
vision loss in her left eye.
 Visual acuity : OD-20/200 OS-20/25
 Color vision : OD- Nil OS-8/8

35. Problem 2

36. Problem 2

37. Problem 2

38. Problem 3