Introduction
Primary Optic Disc Atrophy has 5 major causes:
- Retrobulbar optic neuritis
- Compression
- Trauma
- Toxin or malnutrition
- Hereditary
Optic neuritis is the most common cause of primary optic disc atrophy, and can either be in the form of retrobulbar optic neuritis, papillitis or neuroretinitis, all of which can eventually cause secondary optic atrophy.
- It is the inflammation of the optic nerve, and leads to acute to sub-acute monocular vision loss
- Primarily affects young adults (20-50s) and primarily females
- Could be due to demyelination such as from multiple sclerosis, infectious such as from cat-scratch disease, or idiopathic
- Largely unilateral, presenting with vision loss that ranges from mild to light perception
- Decreased CV/CS, RAPD
- Periocular pain also with eye movements
- VF loss is very variable, and almost 50% are diffuse
Retrobulbar Optic Neuritis has demyelination as the most common cause, and is typically caused by multiple sclerosis. It is an autoimmune inflammatory demyelinating disease that affects white matter in the CNS
- MS has a 51% chance of developing in patients with >3 lesions, 37% chance if 1-2 lesions and 16% if no lesions.
Compressive neuropathy involves direct compression through ischaemic damage or mechanical compression. Damages external transport and transmission.
- Most susceptible area to damage is where the optic nerve passes through the bony structure, such as canal or apex.
- Could be due to neoplasia such as meningioma, vascular origin such as carotid cavernous fistula, or others like TED.
Hereditary causes include LHON and Dominant Optic Atrophy
- Both have preferential loss of papillomacular bundle
- Both are typically bilateral, with an initially hyperaemic appearance
- Both present with central or ceco-central scotomas.
Toxic/Nutritional
- Exposure to toxic stimulus or nutritional deficiency
- Typically during war or periods of famine. Lots of vitamin B12 deficiencies, folic acid and copper being implicated.
- Can also be caused by injection or inhalation of toxic substances, such as ethambutol, methanol, excess tobacco or alcohol
Direct Trauma
- Penetrating injury, bone fragments, orbital haemorrhages or haematomas
- Also through mechanical compression, though that is usually considered compressive
Indirect Trauma
- Caused by transmitted shock from blunt trauma
- Such as motor vehicle accident, falls and assaults
- Blunt force transmission causes shearing damage
- Appearance of ONH depends on location and type of injury, though usually develops a week after
Dead Giveaways
Retrobulbar Optic Neuritis
on MRI, will reveal. multiple plaques in gray and white matter of the brain and spinal chord
MS also leads to other neurological symptoms such as sensory loss, muscle weakness and poor balance.
Visual recovery is rapid, and >90% recover to 6/9 or better. Visual recovery is much faster with IV steroids, but outcomes are unchanged.
This does however lead to a relative temporal disc pallor, due to excessive thinning
Neuromyelitis Optica (NMO)
The associated optic neuritis is often very severe, and more likely bilateral with poor visual outcomes.
Also affects optic chiasm due to bilateral nature, leading to temporal homonymous hemianopia and significant RNFL loss
Toxic Aetiology:
Continuous exposure causes preferential loss of papillomacular bundle, which causes it to discolour
diagnostic features
Clinical Features:
Flat chalky discoloured disc with distinct edge margins
Minimal gliosis (enlargement of glial cells)
Reduction in surface capillaries + attenuation of peripheral vessels
OCT imaging reveals loss of RNFL
Occasional colour loss, RAPD, VF loss
Optic Neuritis Feature:
Can present with Uhthoff's Phenomenon, where vision is worse with rising temperatures, such as after exercise or shower, especially for patients with multiple sclerosis
Can present with Pulfrich's Phenomenon, where there is altered perception of direction of moving objects