Optic Nerve Anatomy and relevant disorders

Question 1

What is the most common site for injury in traumatic optic neuropathies?

Answer 1

The point of attachment of the optic nerve to the dura in the optic canal

Question 2

What percentage of axons cross over to the contralateral geniculate body?

Answer 2

53%, the rest stay ipsilateral

Question 3

What is the ratio of the cup to the total area of the optic disc?

Answer 3

35%

Question 4

what does a larger cup/disc ratio indicate?

Answer 4

The larger the cup, the higher the likelihood of glaucoma

Question 5

How do you check for optic nerve dysfunction?

Answer 5

Visual acuity
Visual fields (confrontational and formal)
RAPD
Colour vision
Contrast sensitivity

Question 6

Would a lesion behind the lateral geniculate body produce RAPD?

Answer 6

No, since the fibres have already corossed to both CNIII nuclei

Question 7

Would a lesion on the optic tract cause RAPD?

Answer 7

Yes (53% of fibres cross, and 47 stay ipsilateral)

Question 8

What conditions cause RAPD?

Answer 8

Most optic neuropathies, as well as defuse retinal dysfunction

Question 9

What are the 3 elements used to evaluate the optic disc in fundoscopy?

Answer 9

BCC
Borders -> sharp
Cup (middle of the disc, surrounded by the rim)
Colour–> (normal is pink; pallor= usually pathologic)

Question 10

How do drusens appear in the optic disc?

Answer 10

Drusens are small calcium deposits in the nerve that could make it look bumpy which could be mistaken for nonsharp edges

Question 11

Define Papilledema. What causes it?

Answer 11

Swelling of the optic disc due to increased ICP

Usually bilateral

Question 12

What could mistakenly show unilateral papilledema?

Answer 12

If one of the nerves is atrophic due to preexisting damage

The nerve would look pale due to loss of axons

Question 13

Define axoplasmic statsis

Answer 13

Stoppage of slow axoplasmic flow at the lamina cribrosa due to increase ICP that is transmitted to the optic nerve along the meningeal sheaths in the subarachnoid space

Question 14

What are the two possible mechanisms of papilledema?

Answer 14

Ischemia leading to optic nerve damage and swelling

Compression of the axons at the lamina cribrosa causing axonal swelling and damage

Question 15

When would papilledema not be present despite increased ICP?

Answer 15

in 2% of the population, there is decreased subarachnoid space surrounding the optic nerve, and the pia would be directly adjacent to it–> no papilledema visible

Question 16

What is the clinical (symptomatic) difference between papilledema and other optic neuropathies?

Answer 16

in papilledema, vision is usually normal, unless the pressure is so high that fluid leaks into the macula

Question 17

What is the difference between papilledema and optic disc swelling?

Answer 17

Papilledema is when the swelling is due to increased ICP

All other cases–> simply swelling

Question 18

How does early disc swelling look?

Answer 18

Can’t see clear borders

Blood vessels look enlarged

Question 19

What are the steps taken following discovery of papilledema?

Answer 19

Medical emergency
1- Neuroimaging–> MRI
2- LP- measure opening pressure and CSF comp (protein, glucose, WBC, TB/cryptococcal testing)

Question 20

What are possible causes (general) of neurpathies?

Answer 20

VINDICATEM
Vascular/ischemic 
inflammatory 
congenital
metabolic
toxic
traumatic

Question 21

What is the most common infectious optic neuropathies?

Answer 21

infectious is usually uncommon, but most common one is syphilis

Question 22

What is the most common noninfectious optic neuropathies?

Answer 22

Optic neuritis due to demylintation

Question 23

What could cause toxic/metabolic optic neuropathies?

Answer 23

Methanol

Question 24

What is the most common optic neuropathy for patients under 50?

Answer 24

Demylinating optic neuropathy

Question 25

What is the most common optic neuropathy for patients over 50?

Answer 25

Ischemic (arteritic - rare and none arteritic- more common)

Question 26

How does demylinating optic neuropathy present?

Answer 26

Unilateral
1/3 optic disc swelling, 2/3 without
RAPD
pain with eye movements

Question 27

What percentage of patients presenting with optic neuritis are diagnosed with MS?

Answer 27

50%

Question 28

Is optic neuritis a good predictor of disability and prognosis with MS?

Answer 28

Yes. Usually good prognosis and low disability score

Question 29

Does high dose IV steroids help with optic neuritis?

Answer 29

It increases the time of visual recovery but no overall effect on prognosis

Question 30

How does non-arteritic ischemic optic neuropathy present?

Answer 30

Patients wake up with visual loss that respects the horizontal midline (altitudinal)

Question 31

What age group is affected by arteritic ischemic optic neuropathy?

Answer 31

Older patients >70

Question 32

What is a common cause of arteritic ischemic optic neuropathy?

Answer 32

Giant cell arteritis (Horton’s disease)

Question 33

what are the symptoms of horton’s disease (giant cell arteritis)?

Answer 33

Jaw claudications (ischemia to facial/zygomatic?)
headache
scalp tenderness (ischemia to CN V)
Weight loss
Fever
Shoulder pain
Fatigue 
Visual loss in one eye which if not treated could spread to the other eye
High ESR and CRP (inflammatory markers)

Question 34

How is giant cell arteritis treated?

Answer 34

high dose of steroids