Abduction issues are often as a result of an issue with which muscle and which nerve?
For which reasons may the abducens nerve fail to fucntion correctly?
- Microvascular causes
- Raised ICP
Why does raised ICP cause the abducens nerve to often fail?
It is compressed onto the petrous tip of the temporal bone
How will a fourth nerve palsy present?
Reduced depression in adduction
With which nerve palsy will a head tilt often be seen and why?
Attempted correction of double vision
What are the causes for a 4th nerve palsy?
- Congenital (most common)
How does a 3rd nerve palsy present?
Eye down and out
What are the causes for a 3rd nerve palsy?
- Aneurysm (often life threatening)
- Multiple sclerosis
Which vessel is often affected by aneurysm in a 3rd nerve palsy?
Posterior communicating artery
The following clinical signs are indicative of what?
- Pain in the back of the head
- Large pupil
Posterior communicating artery aneurysm
(causing a third nerve palsy)
What causes homonymous hemionopia?
Damage to temporal nerve fibres from one eye and nasal fibres from the other eye
(this happens after the optic chiasm)
What can can cause optic nerve defects?
- Ischaemic optic neuropathy
- Optic neuritis
What is internuclear ophthalmoplegia?
The affected eye cannot abduct
The other eye abducts but with nystagmus
What can cause internuclear ophthalmoplegia?
- Vascular causes
- Many others
How quickly is vision lost with optic neuritis?
What may be the cause for an visual field defect originating at the optic chiasm?
- Pituitary tumour
Which type of defect will a optic chiasm problem induce?
Bi-temporal field defect
What are the main causes for visual field defects originating in the optic tracts and radiations?
- Vascular abnormalities
Which type of visual field defects are associated with the optic tracts and radiations?
What are the main causes for a visual field defect originating in the occipital cortex?
- Vascular disease
How do visual field defects originating in the occipital cortex differ from those which originate in the optic tract/radiations?
Macula is spared