1. Innervation of the Eye and Orbit Part 1: The Optic Nerve and
Innervation of the Eye and Orbit Part 1: The Optic Nerve and its Projections
VS111

2. A sensory organ with complex mobility
Performing the basic neurological exam of the eye isn’t difficult, but to accurately diagnose a problem requires knowledge of the wiring and connections that underlie the observable behaviors.
There are a lot of terms, anatomy and pathways you’ll need to know.

3. Organization Optic Nerve - pathways, lesions.
Cranial Nerves - who’s on first.
Parasympathetic & Sympathetic.
Nerve Damage, Growth and Development.

4. Background: Neurons What is a nerve cell? Anatomy of a cell. (Fig 5.1)
What is their job and how to they do it?
Anatomy of a cell. (Fig 5.1)
Gather information (synaptic input)
encode information
Deliver information (Fig 5.2)

5. Different morphologies for different specialization of nerve function.

6. Nerve Action Membrane potential Excitability Receptor potential
Synapses
Inhibition
Action potentials

7. Synapses are communication sites

8. Synapses: Cell to cell connections: Know Electrical vs
Synapses: Cell to cell connections: Know Electrical vs. Chemical Synapses
Fig 5-1

9. Lecture 1 Optic Nerve and Optic Pathways
Parsing out the pathways.
Central Destinations.
Lesions and Visual Fields.
Remember the goal is to get all this information out to the brain for processing The shortest route (along the interior surface of a sphere) is an arc directly to exits sign. But in the interest of optical clarity the fovea is considered a “no fly” or no fiber zone.

10. Optic Nerve (sensory output)
Forming the nerve - GANGLION Cells(5.3)
Economy of movement or flow
Geographical segregation
Organizing the flow of information
Step 1: Nasal/Temporal
Visual Fields
Left Brain Right Right Brain (5.5)

11. Forming the nerve - GANGLION Cells(5.3)
Temporal fibers coalesce at the chiasm

12. Visual Fields (5.4 draw on board)
Nasal field = temporal retina
Temporal (lateral) field = ??
Superior field (sky) = inferior retina
E.g.: mouse or rabbit blue cone density
Inferior field (earth) = ??

13. Primary Optic Pathway is to the LGN and on to striate cortex
Contralateral visual field
Through ipsilateral eye’s nasal retina,
And contralateral eye’s temporal retina

14. Decussation at the Chiasm
Information sorting begins here (Fig. 5.5)
Partial cross-over of ganglion cell fibers organizes the visual world into left vs. right visual fields
Temporal - tight (short- non crossing)
Nasal - meandering (crosses over)

15. Decussation follows a pattern related to the visual fields.
Fig 5-5 draw on overhead

16. Lesions of the Optic Pathway
Optic nerve => one entire eye (5.12)
Split chiasm => loss of crossing fibers (nasal retina=temporal visual fields)
Optic tract =>Loss of contralateral visual field
Partial chiasm - unpredictable due to meandering fibers (5.13)

17. Visual field deficits predict location of the lesions

18. Projections of the optic nerve (5.7)
Lateral Geniculate Nucleas (main relay to cortex)
Superior Colliculus (eye movement)
Pretectal Nuclei (pupillary light reflex)
Accessory optic system
Biological clock (suprachiasmatic n.)

19. Brainstem and Midbrain (Fig5-7)

20. Lateral Geniculate Nuclei - paired structure.
90% of G-cell projection (fig )
Distinctly layered structure (6 layers - monkey)
Layer specific to eye (1,4,6 contralateral)
Layers 2,3,5 ispsilateral eye
Retinotopic mapping

21. Lateral Geniculate nucleas is part of the thalamus- a paired structure, important for relaying information to cortex

22. The Big Picture

23. LGN is a layered structure

24. Retino-topic mapping An exaggeration of the foveal input Fig 5.9
Central 5° of visual field (3% of retina) covers 50% of LGN and visual cortex.

25. Multiple maps overlie one another in the layers of LGN
Retinotopicmaps overlie, meaning that common points in visual fields stack in the layers.
Layer 1,4,6 contralateral
Layer 2,3,5 ipsilateral

26. LGN - organization Summary
Left LGN - right visual field
From left eye temporal retina
Right eye nasal retina
Retinotopic mapping (6 -copies)
Layer 1 & 2 Magnocellular (large cells)
Layers 3-6 parvocellular
Maps are in-register in layers 5.10
2,3,5 ipsilateral
1,4,6 contralateral

27. Superior colliculus Largest axon bundle for non-visual projections
Axon collaterals create retinotopic map
Contralateral visual field (diagram on board)
Binocular-non-segregated input
Under-represented fovea
Input from many sites (eye movement - related)

28. Projections to superior colliculi
From left eye
From right eye
In this experiment a the left optic nerve was cut or crushed, and then, after time the tissues were fixed and labeled for degenerating axons. X
Left eye
ipsilateral visual field has no blind spot
Fig 5-11

29. Pretectal nuclei - Grab bag of 5 nuclei receiving G-cell inputs
Olivary (projects to Edinger-Westphal nuclei) and involve in pupillary light reflex
Nucleus of the optic tract - eye movement controls
Anterior, posterior and medial pretectal nuclei (specific functions unknown).

30. Accessory Optic System
Three pairs of nuclei receive small inputs from ganglion cells
Output to vestibular nuclei and cerebellum
Thought to be involved in coordinating head/eye movements

31. Suprachiasmatic Nucleus
Part of the hypothalamic pathway
Degeneration studies show direct input from the retina
Thought to be part of circadian clock (jet lag. S.A.D.)

32. Summary Optic Nerve LGN SCN, AON, Sup Coll, Pretectal Formation
Crossing at chiasm
Projections
LGN
Visual field segregation
Contra - ipsi-lateral eye separation
Functional G-cell type separation
Parvo and magno pathways
SCN, AON, Sup Coll, Pretectal