Visual Field Defects

Question 1

What does the visual pathway encompass?

Answer 1

1) Retina
2) Optic nerve
3) Optic chiasm
4) Optic radiations
5) Visual centre of occipital lobe

Question 2

What are the 2 types of photoreceptors?

Answer 2

Rods & cones

Question 3

Where are photoreceptors located?

Answer 3

In the retina

Question 4

Role of photoreceptors?

Answer 4

Stimulated by photons of light entering 1) the eye.

2) Light-sensitive surface membrane proteins (e.g. rhodopsin) of these cells are stimulated to propagate second messenger responses which convert light energy into electrical signals.

3) The photoreceptors synapse with retinal bipolar cells, which in turn transmit these signals to retinal ganglion cells.

Question 5

What converges to form the optic nerve?

Answer 5

Retinal ganglion cells

Question 6

How does the optic nerve exit the eye?

Answer 6

Through a defect in the lamina cribrosa of the sclera

Question 7

Why may the optic nerve be considered an extension of the forebrain?

Answer 7

It is covered by the meninges of the CNS

Question 8

Pathway of optic nerve?

Answer 8

1) Exits the eye through a defect in the lamina cribrosa of the sclera.

2) Travels through the bony orbit and into the middle cranial fossa through the optic canal

3) Once inside skull, travels along the floor of the middle cranial fossa, through the medial aspect of the cavernous sinus.

4) L & R optic nerves converge at optic chiasm

Question 9

Where is the optic canal found?

Answer 9

Defect in the lesser wing of the sphenoid

Question 10

Where is the optic chiasm located?

Answer 10

directly above the sella turcica of the sphenoid bone

Question 11

What projects down directly behind the optic chiasm?

Answer 11

Pituitary gland

Question 12

What happens at the optic chiasm?

Answer 12

Fibres from the nasal aspect of each retina cross over to the contralateral optic tract, while fibres from the temporal retina remain on their respective sides.

Question 13

Where do the optic tracts extend from?

Answer 13

The chiasm to the thalamus

Question 14

What happens to the optic tracts at the thalamus?

Answer 14

Sensory afferent nerves from eye synpase with the 2nd order sensory neurones at the lateral geniculate nucleus (LGN) in the thalamus.

Question 15

Where is the visual cortex?

Answer 15

Calcarine sulcus of occipital lobe

Question 16

Describe visual pathway from LGN to visual cortex

Answer 16

Sensory nerves radiate (as optic radiations) dorsally to the calcarine sulcus of the occipital lobe.

Optic radiations loop either through the parietal lobe or through the temporal lobe (Meyer’s loop).

Question 17

What do radiations travelling through the parietal lobe correspond to?

Answer 17

Upper half of retina/lower visual field

Question 18

What do radiations travelling through Meyer’s loop in the temporal lobe correspond to?

Answer 18

Bottom half of the retina/upper visual field.

Question 19

Where is Meyer’s loop?

Answer 19

Temporal lobe

Question 20

where do the optic radiations terminate?

Answer 20

Calcerine sulcus of occipital lobe

Question 21

Blood supply of optic nerve?

Answer 21

Ophthalmic artery

Question 22

Blood supply of optic tract & optic radiations?

Answer 22

Middle cerebral artery

Question 23

What visual field defect will pre-chiasmal lesions (optic nerve lesions) result in?

Answer 23

Ipsilateral monocular visual field defect (i.e. total visual loss in one eye)

Question 24

What visual field defect will post-chiasmal lesions (optic nerve lesions) result in?

Answer 24

homonymous visual field defects of the contralateral side

Question 25

Visual field defect caused by lesions to optic radiations?

Answer 25

Homonymous contralateral quadrantanopia

Question 26

Describe visual field defect caused by lesion to Meyer’s loop

Answer 26

a homonymous upper quadrantanopia (“pie in the sky”),

Question 27

Describe visual field defect caused by lesion to optic radiation in the parietal lobe

Answer 27

lower quadrantanopia (“pie on the floor”).

Question 28

Describe visual field defect in lesions affecting the calcarine sulcus of the occupital lobe

Answer 28

Tend to cause homonymous hemianopia with sparing of the macula.

Question 29

Why is the macula spared in lesions affecting the calcarine sulcus of the occipital lobe?

Answer 29

Due to the dual blood supply to the anterior portion of the visual centre (PCA & MCA)

Question 30

Give the site of lesion in an ipsilateral monocular blindness

Answer 30

Optic nerve

Question 31

Give some examples of optic nerve lesions

Answer 31

• optic neuritis
• amaurosis fugax
• optic atrophy
• retrobulbar optic neuropathy
• trauma

Question 32

Give the site of lesion in a bitemporal hemianopia

Answer 32

Optic chiasm (central)

Question 33

Give 2 causes of bitemporal hemianopia

Answer 33

1) pituitary adenoma
2) suprasellar aneurysm

Question 34

Give the site of lesion in an ipsilateral monocular nasal hemianopia

Answer 34

Optic chiasm lesion (lateral)

Question 35

Give 2 causes of an ipsilateral monocular nasal hemianopia

Answer 35

1) Distension of 3rd ventricle

2) Internal carotid/posterior communicating artery atheroma

Question 36

Give the site of lesion in a contralateral homonymous hemianopia

Answer 36

Optic tract lesion

Question 37

Give 2 causes of an optic tract lesion

Answer 37

1) MCA stroke

2) Tumours

Question 38

Give the site of lesion in a contralateral homonymous quadrantanopia

Answer 38

Optic radiation

Question 39

Give 3 causes of an optic radiation lesion

Answer 39

1) MCA stroke
2) Tumour
3) Trauma

Question 40

Give the site of lesion in a contralateral homonymous hemianopia with macular sparing

Answer 40

Occipital cortex

Question 41

Give 2 causes of an occipital cortex lesion

Answer 41

1) PCA stroke
2) Trauma

Question 42

In bitemporal hemianopia, what does it indicate if upper quadrant defect > lower quadrant?

Answer 42

Inferior chiasmal compression –> commonly pituitary tumour

Question 43

In bitemporal hemianopia, what does it indicate if lower quadrant defect > upper quadrant?

Answer 43

Superior chiasmal comperssion –> commonly a craniopharyngioma

Question 44

A 48 year old man attends the GP surgery with headaches. He has noticed that his hands have become larger, and his facial features have coarsened.

More recently, his vision has deteriorated.
He has an upper temporal defect in both visual fields.

Damage to which structure is the most likely source of his visual problems?

Answer 44

Optic chiasm (due to bitemporal visual field defect)

This indicates compression of the optic chiasm, particularly from an inferior approach.