Visual Fields Flashcards
What is a field defect?
A loss of vision in a part of an individual’s vision
Name the 7 parts of the visual pathway?
Retina Optic nerve Optic chiasm Optic tract (continuation of the optic nerve) Lateral geniculate nucleus Optic radiation Optic cortex
How are the lesions described?
Their effect on the visual field, not the part of the retina affected
What information crosses the optic chiasm - temporal or nasal retina?
What happens where this pathology of the optic chiasm?
Nasal retina
Chiasm compression affects info at the nasal retina, which leads to bitemporal hemianopia, as temporal visual fields falls on the nasal retina.
Q’s to ask about visual fields:
Is the defect unilateral or bilateral?
Does the defect have sharp boundaries or blurred?
Central scotoma:
What may happen to the macula that could cause this? - 2
Cause linked to MS
Other causes
Macular degeneration
Macular oedema
Optic neuritis (including MS)
Methanol
Glaucoma
Alcohol or tobacco amblyopia
Optic nerve:
What will damage to the optic nerve cause?
What type of pupillary reflex will be absent?
What type of pupillary reflex is not affected?
Complete blindness in one eye
Direct pupillary reflex - optic nerve damage
Consensual pupillary reflex - CN 3 still intact - signal from opposite eye
Bitemporal hemianopia:
What is it?
What is damaged?
What may cause this? - 1
Why are the reflexes still intact?
Loss of vision on the outside halves of vision
Optic chiasm
Pituitary tumour
Temporal info is still able to pass through the visual pathway
Binasal hemianopia - It is VERY RARE:
What is it?
What may cause it?
Loss of vision on the inside halves of vision
Ischaemic optic neuropathy
Glaucoma
Homonymous hemianopia:
Where is the lesion?
Why?
What cause this?
Optic tract
Temporal - ipsi - therefore nasal visual field lost
Nasal - contra - therefore temporal visual field lost
Stroke or tumour between the optic chiasm and occipital cortex
Contralateral homonymous hemianopia:
Where is the lesion? - 2
Do the radiations transmit nasal information from the ipsi/contralateral side?
Do the radiations transmit temporal information from the ipsi/contralateral side?
In the optic radiations
Can also be in the visual cortex
Ipsilateral - nasal visual field
Contralateral - temporal visual field
What is important to remember about quadrantopia’s?
Where is the lesion for SUPERIOR contralateral homonymous quandrantopia? - 2
Where is the lesion for INFERIOR contralateral homonymous quandrantopia? - 2
What mneumonic can be used to remember the above?
The lesion is opposite to the defect - LESIONS IN RADIATIONS
Inferior occipital cortex or temporal lobe = Lateral fibres (Meyers loop)
Superior occipital cortex or parietal lobe = Medial fibres
PITS
Visual cortex:
What would damage to the left primary visual cortex cause?
What about the pupillary reflexes?
Why is the macula usually spared in a vascular cause?
Right contralateral homonymous hemianopia with macular sparing - remember always opposite like in optic tracts
Pupillary reflexes intact
In most, there is usually an anatomises between the posterior and middle cerebral arteries
What would cause homonymous central scotoma?
Lesion of the occipital lobe rather than the primary visual cortex
Tests:
What are amsler grids?
Detects distortion in central vision (e.g. macular disease)
