Visual fields Flashcards
What is the visual field?
The entire area that can be seen by a patient without movement of their head and with their eyes fixed on one point
What happens to the image of the visual field on the retina?
image is inverted upside down and flipped left-to-right
How is each visual field divided?
4 quadrants:
upper temporal
lower temporal
upper nasal
lower nasal
Outline the visual pathway
- 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
- The two optic nerves converge to form the optic chiasm on the base of the brain
- 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
- 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
- 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
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?
optic canal
The two optic nerves converge to form what?
the optic chaism
Where is the optic chiasm located?
directly above the sella turcica of the sphenoid bone
What happens at the optic chiasm?
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
The optic tracts then diverge away from the optic chiasm and pass round the cerebral peduncle to terminate mainly where?
lateral geniculate nucleus (within the lateral geniculate body of the thalamus)
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?
terminate at the pretectal area of the superior colliculus and are involved in the mediation of the pupillary light reflex
From the lateral geniculate nucleus, third-order thalamocortical neurones project through the retrolenticular part of the internal capsule and form what?
the optic radiation
Where does the optic radiation terminate?
the primary visual cortex of the occipital lobe
Where is the primary visual cortex predominantly located?
On the medial surface of the hemisphere in the region above and below the calcarine sulcus
What is the area surrounding the primary visual cortex called?
rest of the occipital lobe constitutes the visual association cortex - concerned with the interpretation of visual images, recognition, depth perception and colour vision
The optic radiations can loop through two regions - what are they?
parietal lobe or temporal lobe (Meyer’s loop)
Radiations travelling through the parietal love correspond to what?
upper half of the retina, lower visual field
Radiations travelling through Meyer’s loop in the temporal lobe correspond to what?
lower half of the retina, upper visual field
What visual field defect occurs if there is a lesion at the level of the optic nerve?
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
What visual field defect occurs if there is a lesion at the optic chiasm?
bitemporal hemianopia - loss of the upper and lower temporal visual field in both eyes
What visual defect occurs if there is a lesion in the optic tract?
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
What is the general rule to remember with lesions in the visual pathway?
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
Enlargement of the pituitary gland will commonly cause what visual field defect?
bilateral hemianopia - pituitary gland sits in the sella turcica so when it becomes enlarged it presses on the optic chiasm
What visual field defect occurs if there are lesions to the optic radiations?
homonymous contralateral quadrantanopia
Lesions affecting Meyer’s loop will result in what visual field defect?
upper quadrantanopia
Lesions affecting the optic radiations going to the parietal lobe will cause what?
lower quadrantanopia
What visual field defect is caused by lesions affecting the calcarine sulcus?
homonymous hemianopia with sparing of the macula
