Optic Nerve Anatomy and relevant disorders Flashcards
What is the most common site for injury in traumatic optic neuropathies?
The point of attachment of the optic nerve to the dura in the optic canal
What percentage of axons cross over to the contralateral geniculate body?
53%, the rest stay ipsilateral
What is the ratio of the cup to the total area of the optic disc?
35%
what does a larger cup/disc ratio indicate?
The larger the cup, the higher the likelihood of glaucoma
How do you check for optic nerve dysfunction?
Visual acuity Visual fields (confrontational and formal) RAPD Colour vision Contrast sensitivity
Would a lesion behind the lateral geniculate body produce RAPD?
No, since the fibres have already corossed to both CNIII nuclei
Would a lesion on the optic tract cause RAPD?
Yes (53% of fibres cross, and 47 stay ipsilateral)
What conditions cause RAPD?
Most optic neuropathies, as well as defuse retinal dysfunction
What are the 3 elements used to evaluate the optic disc in fundoscopy?
BCC
Borders -> sharp
Cup (middle of the disc, surrounded by the rim)
Colour–> (normal is pink; pallor= usually pathologic)
How do drusens appear in the optic disc?
Drusens are small calcium deposits in the nerve that could make it look bumpy which could be mistaken for nonsharp edges
Define Papilledema. What causes it?
Swelling of the optic disc due to increased ICP
Usually bilateral
What could mistakenly show unilateral papilledema?
If one of the nerves is atrophic due to preexisting damage
The nerve would look pale due to loss of axons
Define axoplasmic statsis
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
What are the two possible mechanisms of papilledema?
Ischemia leading to optic nerve damage and swelling
Compression of the axons at the lamina cribrosa causing axonal swelling and damage
When would papilledema not be present despite increased ICP?
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
What is the clinical (symptomatic) difference between papilledema and other optic neuropathies?
in papilledema, vision is usually normal, unless the pressure is so high that fluid leaks into the macula
What is the difference between papilledema and optic disc swelling?
Papilledema is when the swelling is due to increased ICP
All other cases–> simply swelling
How does early disc swelling look?
Can’t see clear borders
Blood vessels look enlarged
What are the steps taken following discovery of papilledema?
Medical emergency
1- Neuroimaging–> MRI
2- LP- measure opening pressure and CSF comp (protein, glucose, WBC, TB/cryptococcal testing)
What are possible causes (general) of neurpathies?
VINDICATEM Vascular/ischemic inflammatory congenital metabolic toxic traumatic
What is the most common infectious optic neuropathies?
infectious is usually uncommon, but most common one is syphilis
What is the most common noninfectious optic neuropathies?
Optic neuritis due to demylintation
What could cause toxic/metabolic optic neuropathies?
Methanol
What is the most common optic neuropathy for patients under 50?
Demylinating optic neuropathy
What is the most common optic neuropathy for patients over 50?
Ischemic (arteritic - rare and none arteritic- more common)
How does demylinating optic neuropathy present?
Unilateral
1/3 optic disc swelling, 2/3 without
RAPD
pain with eye movements
What percentage of patients presenting with optic neuritis are diagnosed with MS?
50%
Is optic neuritis a good predictor of disability and prognosis with MS?
Yes. Usually good prognosis and low disability score
Does high dose IV steroids help with optic neuritis?
It increases the time of visual recovery but no overall effect on prognosis
How does non-arteritic ischemic optic neuropathy present?
Patients wake up with visual loss that respects the horizontal midline (altitudinal)
What age group is affected by arteritic ischemic optic neuropathy?
Older patients >70
What is a common cause of arteritic ischemic optic neuropathy?
Giant cell arteritis (Horton’s disease)
what are the symptoms of horton’s disease (giant cell arteritis)?
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)
How is giant cell arteritis treated?
high dose of steroids
