Optic neuropathies Flashcards
how long is the intraocular portion of the optic nerve?
- The intraorbital
- Intracannalicular
- Intracranial
- 1mm in length
- 25 mm
- 9mm
- 16mm
what are the 3 clinical pearls about the optic nerve?
- Longer than orbital length (stretch)
- Attached to dura in optic canal (site of injury)
- 2 nerves form the chiasm - pathology there is chiasmopathy, optic neuropathy or both
What is a disorder that preferentially affects ganglion cells?
Glaucoma - will respect horizontal midline
What is the cup of the optic nerve composed of?
Dead tissue
What part of the eye is mostly responsible for central visual acuity?
The maccula/fovea
If you have a lesion of the right optic tract what defects do you expect?
- RAPD in the left eye
2. Heminiopia
Vast majority of optic neuropathies are…
Asymmetric
What is the function of the RAPD?
Compares the amount of light perceived by each optic nerve
What disease is RAPD present in?
- Most optic neuropathies
ALWAYS IN OPTIC NEURITIS - Diseases producing diffuse retinal dysfunction
A lesion in the optic tract is enough to produce a RAPD why?
There is a 6% difference in the proportion of fibers that cross behind the chiasm
Will patient with cataracts have a RAPD?
Never!
How do you evaluate an optic nerve clinically?
Borders (are they sharp)
color (pink is normal, pallor is pathologic)
cup (yellow hole in the middle)
are there hemorrhages?
What are Drusen
Small calcium deposits in the nerve
What is Pepilledema?
Swelling of the optic nerve due to increased ICP, and swelling is BILATERAL
What is the general flow chart from increased ICP to optic nerve swelling?
–> narrower spaces for CSF circulation, CSF excess around the optic nerve
Papilledema is swelling of which portion of the optic nerve?
VISIBLE portion - secondary to increased ICP
In papilledema is swelling often uni or bilateral?
bilateral
When might papilledema appear unilateral?
If one of the nerves is atrophic
What is the mechanism for papilledema?
Axoplasmic stasis - slowing axoplasmic flow at lamina cribrosa - transmitted along meningeal sheaths IN SUBARACHNOID SPACE
What is the difference between papilledema and other optic neuropathies?
Central vision is NORMAL
When does central vision fail?
when nerve swells and fluid accummulates around the nerve seeps into the maccula
If disc swelling is chronic how will the disc appear?
Axons die, whitish color, cup disappears
What is the first step in diagnosing papilledema?
MRI
If MRI for suspected papilledema is normal what do you do?
Do a lumbar puncture and assess opening pressure and measure CSF composition -
what is the most common inflammatory - infectious cause of optic neuropathy?
Syphillis, TB, viruses, fungi
what is the most common inflammatory - non- infectious cause of optic neuropathy?
Demyelinating optic neuritis, sarcoid,
Most common causes of optic neuropathies for patients under 50
Demyelinating neuropathies - usually UNIlateral visual loss, RAPD and pain on eye movement
Most common causes of optic neuropathies for patients OVER 50
Ischemic - non arteritic (more common) and arteritic (rarer can lead to bilateral blindness)
In patients under 50 with demyelinating neuropathies what proportion have optic nerve head swelling?
1/3 with variable swelling,
2/3 with normal appearing nerve
describe the visual loss in non-arteritic ischemic optic neuropathies
Altitudinal - respects horizontal midline due to hypo-perfusion of the optic nerve head
What age group does giant cell arteritis affect?
Older patients over 70
What are common systemic symptoms of giant cell arteritis ?
- Jaw claudications
- Headache
- scalp tenderness
- wt loss
- shoulder pain and fatigue
Which two inflammatory markers are high in giant cell arteritis?
ESR and CRP
