Visual fields

Question 1

What is the visual field?

Answer 1

The entire area that can be seen by a patient without movement of their head and with their eyes fixed on one point

Question 2

What happens to the image of the visual field on the retina?

Answer 2

image is inverted upside down and flipped left-to-right

Question 3

How is each visual field divided?

Answer 3

4 quadrants:
upper temporal
lower temporal
upper nasal
lower nasal

Question 4

Outline the visual pathway

Answer 4

1. Axons of the retinal ganglion cells assemble at the optic disc and pass into the optic nerve, which enters the cranial cavity via the optic canal
2. The two optic nerves converge to form the optic chiasm on the base of the brain
3. In the chiasm, the axons from the nasal halves of the two retinae decussate and pass into the contralateral optic tract but those from the temporal hemiretinae remain ipsilateral
4. Optic tracts diverge away from the chiasm and pass round the cerebral peduncle to terminate mainly in the lateral geniculate nucleus (within the lateral geniculate body) of the thalamus
5. From the lateral geniculate nucleus, third-order thalamocortical neurones project through the retrolenticular part of the internal capsule and form the optic radiation, which terminates in the primary visual cortex of the occipital lobe

Question 5

The axons of the retinal ganglion cells assemble at the optic disc and pass into the optic nerve, which enters the cranial cavity via what?

Answer 5

optic canal

Question 6

The two optic nerves converge to form what?

Answer 6

the optic chaism

Question 7

Where is the optic chiasm located?

Answer 7

directly above the sella turcica of the sphenoid bone

Question 8

What happens at the optic chiasm?

Answer 8

Axons derived from the nasal halves of the retinae decussate to the contralateral optic tract whilst those from the temporal hemiretinae remain on the ipsilateral side

Question 9

The optic tracts then diverge away from the optic chiasm and pass round the cerebral peduncle to terminate mainly where?

Answer 9

lateral geniculate nucleus (within the lateral geniculate body of the thalamus)

Question 10

A small number of fibres leave the optic nerve before reaching the lateral geniculate nucleus and terminate where instead? What are these fibres involved in?

Answer 10

terminate at the pretectal area of the superior colliculus and are involved in the mediation of the pupillary light reflex

Question 11

From the lateral geniculate nucleus, third-order thalamocortical neurones project through the retrolenticular part of the internal capsule and form what?

Answer 11

the optic radiation

Question 12

Where does the optic radiation terminate?

Answer 12

the primary visual cortex of the occipital lobe

Question 13

Where is the primary visual cortex predominantly located?

Answer 13

On the medial surface of the hemisphere in the region above and below the calcarine sulcus

Question 14

What is the area surrounding the primary visual cortex called?

Answer 14

rest of the occipital lobe constitutes the visual association cortex - concerned with the interpretation of visual images, recognition, depth perception and colour vision

Question 15

The optic radiations can loop through two regions - what are they?

Answer 15

parietal lobe or temporal lobe (Meyer’s loop)

Question 16

Radiations travelling through the parietal love correspond to what?

Answer 16

upper half of the retina, lower visual field

Question 17

Radiations travelling through Meyer’s loop in the temporal lobe correspond to what?

Answer 17

lower half of the retina, upper visual field

Question 18

What visual field defect occurs if there is a lesion at the level of the optic nerve?

Answer 18

total visual loss in the eye in which the optic nerve is damaged
eg - lesion in the right optic nerve = total right eye visual loss

Question 19

What visual field defect occurs if there is a lesion at the optic chiasm?

Answer 19

bitemporal hemianopia - loss of the upper and lower temporal visual field in both eyes

Question 20

What visual defect occurs if there is a lesion in the optic tract?

Answer 20

homonymous hemianopia - visual loss on the same side of the visual field in both eyes
if the lesion is on the left it will cause right homonymous hemianopia and vice verse

Question 21

What is the general rule to remember with lesions in the visual pathway?

Answer 21

pre-chiasmal lesions will result in ipsilateral monocular visual field defects
post-chiasmal lesions will result in homonymous visual field defects of the contralateral side

Question 22

Enlargement of the pituitary gland will commonly cause what visual field defect?

Answer 22

bilateral hemianopia - pituitary gland sits in the sella turcica so when it becomes enlarged it presses on the optic chiasm

Question 23

What visual field defect occurs if there are lesions to the optic radiations?

Answer 23

homonymous contralateral quadrantanopia

Question 24

Lesions affecting Meyer’s loop will result in what visual field defect?

Answer 24

upper quadrantanopia

Question 25

Lesions affecting the optic radiations going to the parietal lobe will cause what?

Answer 25

lower quadrantanopia

Question 26

What visual field defect is caused by lesions affecting the calcarine sulcus?

Answer 26

homonymous hemianopia with sparing of the macula