BS - Optic Nerve - Week 7

Question 1

How long is the optic nerve?

Answer 1

5-6cm

Question 2

What percentage of the information conveyed by the optic nerve goes where?

Answer 2

LGN - 90%

Superior colliculus - 10%

Question 3

Consider the optic nerve. What does the pia mater cover?

Answer 3

Covers individual optic nerve axons, as well as the optic nerve.

Question 4

The sclera partially infiltrates the optic nerve. Consider the portion that does not infiltrate. What does this form?

Answer 4

The dura mater of the brain.

Question 5

Define the prelaminar optic nerve, and how optic nerve axons are arranged here. What cells are found here?

Answer 5

The optic nerve anterior to the lamina cribrosa.

2000 axons are arranged per channel here. Astrocytes surround the channels.

Question 6

Define the retrolaminar optic nerve, and what happens here to the optic nerves.
What cells are present here, and in what arrangement?

Answer 6

Posterior to the lamina cribrosa. Optic nerve axons are myelinated here.
Oligodendrocytes and astrocytes are found here in bundles.

Question 7

What purpose do astrocytes have at the pre/retrolaminar regions of the optic nerve?

Answer 7

They separate bundles of nerve fibres, they dont bind axons together.
They have repair and protection functions.

Question 8

What forms the blood retina barrier?

Answer 8

Astrocytes

Question 9

How are pores on the lamina cribrosa arranged.

Answer 9

Larger pores are found at the superior and inferior regions of the optic nerve.

Question 10

Specifically at what point do the axons become myelinated?

Answer 10

Posterior limit of the lamina cribrosa.

Question 11

What is the typical diameter of the optic disc?

Answer 11

1.5-2mm

Question 12

Is the optic disc completely flat?

Answer 12

No, the edges are slightly raised.

Question 13

What appearance does the optic cup have?

Answer 13

White/pale appearance.

Lamina cribrosa can sometimes be seen.

Question 14

When checking the optic disc for health, what is an important indicator?

Answer 14

The proportion of the cup-disc ratio.

Question 15

What is a typical cup:disc ratio?

Answer 15

<0.4 is normal, 0.3 is the median

Question 16

Define the horizontal raphe.

Answer 16

The midpoint on the retina where the nasal radial and temporal radial nerve fibres meet.

Question 17

Explain why higher diameter pores are found in certain regions of the lamina cribrosa.

Answer 17

More are found in the superior/inferior regions because the nerve fibres travel radially towards the optic disc, and so they meet chiefly at the superior and inferior end.

Question 18

Describe the nerve fibre arrangement distal to the optic chiasm.

Answer 18

Macula fibres occupy at least half of the nerve cross section, with ~12.5% each for superior temporal/nasal, and inferior temporal/nasal fibres.

Question 19

Describe the nerve fibre arrangement proximal to the optic chiasm.

Answer 19

Left eye
Macula fibres are located in the middle of the cross section.
Top right and left are occupied by superior temporal and nasal fibres respectively.
Bottom right and left are occupied by the inferior temporal and nasal fibres respectively.

Question 20

How do temporal fibres exit the optic chiasm?

Answer 20

Ipsilateral side.

Question 21

How do superior and inferior nasal fibres exit the optic chiasm?

Answer 21

Inferior - some loop at the anterior knee of Wilbrand

Superior - some loop at the posterior knee of Wilbrand

Question 22

What supplies blood to the inner retina?

Answer 22

Central retinal artery

Question 23

What structures does the posterior ciliary artery supply blood to?

Answer 23

Choroid and retrolaminar optic nerve

Question 24

What is the Circle of Zinn-Haller.

Answer 24

Rich blood vessel network formed by the posterior ciliary artery, supplying the choroid and retrolaminar optic nerve.

Question 25

What supplies blood to the nerve surface (2)?

Answer 25

Branches from the central retinal artery, and small branches from the choroid.

Question 26

What supplies blood to the prelamina and lamina cribrosa (2)?

Answer 26

Circle of Zinn-Haller and small branches from the central retinal artery.

Question 27

What supplies blood to the retrolamina (2)?

Answer 27

Branches from pial blood supply, and small branches of the central retinal artery.

Question 28

What happens to the neuroretinal rim and axons in glaucoma?

Answer 28

Axonal loss | Neuroretinal rim loss

Question 29

Define the scleral crescent, and what occurs here, and why its there.

Answer 29

Crescent-shaped area on the neuroretinal rim where there is no overlying retina. Pigment from the RPE beneath can be seen. Is phsiologic, high myopia.

Question 30

Define the ISNT rule.

Answer 30

Describes the order of neuron fibre density from highest to lowest: Inferior>superior>nasal>temporal

Question 31

What happens to the cup:disc ratio in glaucoma?

Answer 31

Increases.

Question 32

Where does axonal loss present first initally in glaucoma?

Answer 32

Inferior region.

Question 33

What happens to the appearance of the lamina cribrosa with glaucoma? What appearance do the pores have, and which direction to the central retinal vessels shift?

Answer 33

Lamina visibility increases. Pores are more like slits than circles. Vessels shift nasally.

Question 34

Name the three dietary carotenoids that contribute to macular pigments.

Answer 34

Lutein Zeaxanthin Meso-zeaxanthin

Question 35

What purpose do macular pigments have (3)?

Answer 35

- Pre-receptoral absorption of blue light - Reduces chromatic abberation and light scatter - Antioxidant capacity

Question 36

Where are macular pigments concentrated?

Answer 36

Central retina along the axons of cone receptors.

Question 37

Why do nerve fibres segregate the way they do post-optic chiasm?

Answer 37

Possibly to protect the macular fibres in the event of trauma.