Optic Disc Flashcards
It is useful to consider the causes of optic nerve damage anatomically. Which four areas?
- Within the globe
- Within the nerve and sheath
- Outside the nerve, but in the orbit
- Intracranial nerve (pre-chiasmal, chiasmal, post-chiasmal)
What are four appearances which are possible when examining the optic nerve?
- No abnormality
- Optic disc swelling: a non-specific term which includes papilloedema.
- Optic atrophy: an optic nerve which has lost substance, seen as a pale disc
- Optic disc cupping: a characteristic of a specific disease entity (glaucoma)
What is true papilloedema, and it is the result of impairment of what?
True papilloedema is a swollen optic nerve head due to raised intracranial pressure.
It is the result of impairment of normal axoplasmic flow.
Disc swelling without raised ICP may be due to impairment of axoplasmic flow (as occurs in ischaemic and compressive states), oedema or infiltrate. Papilloedema requires early neuroimaging.
Name three ways in which one can consider the clinical features of optic nerve damage.
- Features of optic nerve dysfunction
- Features of underlying disease
- Associated findings
What is the primary function of the optic nerve?
Vision, including visual acuity, peripheral vision and colour.
Most disease processes cause loss of acuity, usually at an early stage. However, papilloedema causes late loss of acuity. Early, transient visual obscuration (blurring) is common.
What is the characteristic field defect in optic nerve dysfunction?
Many types of field defect can occur, but a characteristic defect is a central or centrocaecal scotoma (a centrocoecal scotoma is a central scotoma which extends to include the blind spot).
The altitudinal defect is typical of ischaemia at the optic nerve head, the arcuate scotoma occurs in glaucoma, the bitemporal hemianopia is caused by chiasmal disease and a homonymous hemianopia may be due to optic tract disease.
What colour defects are typical of optic nerve dysfunction?
Red-green defects are typical of optic nerve dysfunction, so a bright red target, looking for desaturation (greyness) should be used.
Most tests of colour vision such as Ishihara plates have been designed to detect inherited rather than acquired deficiencies, but are nevertheless useful.
What features on clinical examination should be included when assessing optic nerve dysfunction?
- Visual acuity
- Confrontational testing (field defects)
- Formal perimetry (for monitoring disease progression and Rx)
- Colour vision
- Pupil testing (likely to be helpful in unilateral disease only). Swinging flashlight test may reveal an RAPD.
What four features should be elicited during history and examination, when considering the features of underlying disease in optic nerve disease?
- Raised ICP
- Ischaemia (associated with atherosclerosis, diabetes, giant cell arteritis).
- Systemic hypertension
- Thyroid disease
The pt with multiple sclerosis may have what finding of their optic nerve?
A pale disc (optic atrophy).
However, in acute retrobulbar optic neuritis, the nerve head is normal.
Pts with MS may not have a definite hx of previous visual disturbance.
A drug history is important in investigating optic nerve disease, why?
Also, how could ethambutol affect the optic nerve?
Hx important as many drugs are associated with benign intracranial hypertension.
Ethambutol (and some others) may cause optic atrophy.
Name two causes of intraocular inflammation which may lead to optic disc swelling and late atrophy.
- Sarcoidosis
2. Syphilis
Name three associated features of optic nerve disease.
- Sixth nerve palsy: convergent squint with abduction weakness, from raised ICP. This is a non-localising sign, meaning that the disease is not directly affecting the nerve, but indirectly causing it to be stretched or compressed.
- Proptosis: indicates orbital disease.
- Flame-shaped retinal haemorrhages: characteristic of retinal vein occlusion.
What is pseudopapilloedema?
A non-pathologically swollen optic nerve.
Optic nerve head drusen (hyaline bodies) is included, perhaps mistakenly since it may cause progressive field loss.
What is the most common cause of pseudopapilloedema?
Hypermetropia (long-sightedness).
