Optic Nerve

Question 1

What are the two parts of the optic nerve?

Answer 1

Orbital part and intracranial part

Question 2

What are the optic nerve fibers composed of?

Answer 2

Axons of the cells in the ganglionic layer of the retina

Question 3

Where do the optic nerve fibers exit the eye?

Answer 3

Through the lamina cribrosa

Question 4

Are the optic nerve fibers myelinated within the eyeball?

Answer 4

No, they are nonmyelinated within the eyeball

Question 5

What forms the myelin sheaths of the optic nerve fibers posterior to the disc?

Answer 5

Oligodendrocytes

Question 6

How many myelinated axons make up the optic nerve?

Answer 6

About 1,200,000

Question 7

What is the typical diameter of the majority of optic nerve axons? What is the range of diamteres for the larger optic nerve axons?

Answer 7

1micron
2 to 10microns (around 8% axons)

Question 8

How long is the optic nerve?

Answer 8

About 4 cm
(runs backwards and medially through oribtal cavity, passess through optic canal nd joins optic chiasma)

Question 9

What three meningeal sheaths surround the optic nerve?

Answer 9

• Dura (fibrous)
• Arachnoid (delicate)
• Pia (vascular)

All fuse with sclera

Question 10

What does the pia mater do for the optic nerve?

Answer 10

Closely invests the optic nerve and sends septa into its substance

Question 11

What happens to the lamina cribrosa during abnormal cerebrospinal fluid pressure?

Answer 11

It bulges inward, producing a convex disc. This is because subarachnoid space of brain continues around optic nerve to back of eye)

Question 12

Where does the central artery and vein enter the optic nerve?

Answer 12

About 12 mm posterior to the eyeball

Question 13

What condition can compress the vein in the optic nerve?

Answer 13

Disorders of raised cerebrospinal fluid pressure

Question 14

What clinical sign is caused by retinal venous engorgement?

Answer 14

Papilledema

Question 15

What arterial branches supply the optic nerve in the orbital cavity vs at optic disc?

Answer 15

Posterior ciliary arteries iin orbital cavity
central artery of the retina at optic disc

The optic nerve receives its arterial supply from these arteries, which provide essential blood flow.

Question 16

What is the source of arterial reinforcement for the optic nerve?

Answer 16

Partial arterial circle of Haller-Zinn

This circle is derived from the short posterior ciliary arteries behind the lamina cribrosa.

Question 17

Where does the venous drainage of the optic nerve occur?

Answer 17

Central vein of the retina

This vein is responsible for draining the blood from the optic nerve.

Question 18

What happens to the axons of the optic nerve as they pass through the lamina cribrosa?

Answer 18

They become myelinated and white

In the retina, the axons are unmyelinated and transparent.

Question 19

Why is the optic nerve unable to regenerate?

Answer 19

It does not possess Schwann cells

Schwann cells are essential for the regeneration of most peripheral nerves.

Question 20

What condition can cause a perineuritis in the optic nerve?

Answer 20

Meningitis

Inflammation of the meninges can spread to the areas around the optic nerve.

Question 21

What effect does a rise in cerebrospinal fluid pressure have on the optic disc?

Answer 21

Causes bulging of the optic disc and papilledema

This is a critical indicator of increased intracranial pressure.

Question 22

What is the normal appearance of the optic disc?

Answer 22

Normal posterior bowing

This should not be confused with pathologic bowing, which can occur in conditions like glaucoma.

Question 23

Fill in the blank: The optic nerve is an anterior extension of the _______.

Answer 23

white matter of the brain

This highlights the optic nerve’s connection to the central nervous system.

Question 24

What is the optic disc?

Answer 24

The optic disc is the area where the optic nerve exits the eye and does not possess the cells of Müller.

Question 25

Why does the optic disc swell in papilledema?

Answer 25

The optic disc swells in papilledema because it lacks Müller cells that hold nerve fibers together.

Question 26

What happens to the surrounding retina in individuals with papilledema?

Answer 26

The surrounding retina remains flat in individuals with papilledema.

Question 27

What is a crescent of choroid at the optic disc?

Answer 27

A crescent of pigmented choroid that can be seen when the retina does not reach the edge of the optic disc.

Question 28

What can be seen if the choroid and retina do not reach the optic disc?

Answer 28

A white scleral crescent can be seen.