The document provides an overview of the anatomy and physiology of the visual pathways, beginning with the retina and optic nerve, then describing the optic chiasm, optic tracts, lateral geniculate bodies, optic radiations, visual cortex, and visual association areas. Key structures and functions are defined, including the types of retinal ganglion cells, pathways in the optic chiasm and lateral geniculate bodies, layers of the visual cortex, and the "what" and "where" pathways in visual processing.

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