Visual field defects (N)

Question 1

Describe the order of the visual pathway from eye to visual cortex (for understanding purposes).

Answer 1

• eye (neurons in retina)
• optic nerve - ganglion nerve fibres
• optic chiasm - optic nerves from both eyes converge, 53% decussate to form contralateral optic tract
• optic tract - ganglion nerve fibres continuation
• lateral geniculate nucleus - relay centre within thalamus, where ganglion nerve fibres synapse
• optic radiation - 4th order neuron, relay signal from lateral geniculate ganglion to primary visual cortex

Question 2

Which eyes control which visual fields?

Answer 2

For each eye, respective nasal retinas responsible for temporal fields and vice versa

L temporal retina = L nasal field
L nasal retina = L temporal field
R temporal retina = R nasal field
R nasal retina = R temporal field

Question 3

What happens at the optic chiasm?

Answer 3

• partial decussation - 53% of ganglion fibres cross
• crossed fibres originate from nasal retina = responsible for temporal visual field
• uncrossed fibres originate from temporal retina = responsible for nasal visual field

Question 4

What does a lesion to the optic nerve cause?

Answer 4

No light perception in that eye –> monocular vision loss

Question 5

What does a lesion to the optic chiasm cause?

Answer 5

Bitemporal hemianopia

Question 6

What does a lesion to the optic tract cause?

Answer 6

Contralateral homonymous hemianopia

Incongruous = same side affected on both sides, different degree of hemianopia

Question 7

What does a lesion to the lateral geniculate nucleus cause?

Answer 7

• contralateral homonymous sectoranopia OR
• incongruous right homonymous hemianopia

Question 8

What does a lesion to the temporal lobe cause visually?

Answer 8

Contralateral homonymous upper quadrant defect (pie in the sky)

Question 9

What does a lesion to the parietal lobe cause visually?

Answer 9

Contralateral homonymous defect, denser inferiorly

Question 10

What does a lesion to the occipital lobe cause visually?

Answer 10

• upper bank - contralateral homonymous lower quadranopsia + macular sparing
• lower bank - contralateral homonymous upper quadranopsia + macular sparing

Question 11

What does a lesion to the right occipital lobe cause visually?

Answer 11

Contralateral homonymous hemianopia + macular sparing

Question 12

What are the different types of homonymous hemianopia?

Answer 12

• incongruous defects - lesion of optic tract
• congruous defects - lesion of optic radiation or occipital lobe/cortex
• macular sparing - lesion of occipital lobe/cortex
• will be on same side of paresis (contralateral)

Question 13

What is a homonymous quadrantanopia?

Answer 13

Loss of vision in part of visual field (less than half)

Inferior and superior refer to the quadrantanopia itself

Question 14

What are the different types of homonymous quadrantanopia?

Answer 14

• superior - lesion of the inferior optic radiations in the temporal lobe (Meyer’s loop)
• inferior - lesion of the superior optic radiations in the parietal lobe
• mnemonic = PITS (Parietal-Inferior, Temporal-Superior)

Question 15

What mnemonic helps us remember the types of homonymous quadrantanopia?

Answer 15

PITS (Parietal-Inferior, Temporal-Superior)

Question 16

What are the different types of bitemporal hemianopia?

Answer 16

• lesion of optic chiasm
• upper quadrant defect > lower quadrant defect = inferior chiasmal compression, commonly a pituitary tumour
• lower quadrant defect > upper quadrant defect = superior chiasmal compression, commonly a craniopharyngioma