Session 4 - Central Visual Pathways

Question 1

What are the two layers of the retina?

Answer 1

Pigmented layer (retinal pigmented epithelium)
Neural layer

Question 2

What layer covers the retinal pigmented epithelium (RPE)?

Answer 2

Choroid

Question 3

What pigment is found in the RPE?

Answer 3

Melanin

Question 4

Why do albinos struggle to see in bright light?

Answer 4

They have no melanin in their retinal pigmented epithelium. This means less light is absorbed in the retina and more is reflected, making it difficult for albinos to see in bright light.

Question 5

What are the two types of photoreceptor cells?

Answer 5

Rods and cones

Question 6

What is the function of rod cells?

Answer 6

Receptor cells for black and white vision, low level lighting.

Question 7

What is the function of cone cells?

Answer 7

Receptor cells for colour vision, high definition

Question 8

Other than rod and cone cells, what other cell types are present in the retina?

Answer 8

Bipolar cells
Horizontal cells
Amacrine cells
Ganglion cells

Question 9

Which area of the retina has the highest concentration of cone cells, and therefore the greatest ability for definition?

Answer 9

Fovea

Question 10

Raised intracranial pressure can result in what condition seen on fundoscopy?

Answer 10

Papilloedema

Question 11

What structures should be visible in a normal fundoscopy?

Answer 11

Optic disc
Fovea
Macula
Central retinal artery and vein 
Retinal arterioles and venules

Question 12

What conditions can be visible on fundoscopy?

Answer 12

Retinopathies 
Vascular occlusions
- branch of central retinal artery 
- amaurosis fugax
Papilloedema

Question 13

Which fibres decussate and which run ipsilateral?

Answer 13

Nasal fibres decussate

Temporal fibres run ipsilateral

Question 14

Which fibres are responsible for relaying the nasal fields of vision and which relay the temporal fields?

Answer 14

Nasal fibres relay the temporal fields

Temporal fibres relay the nasal fields

Question 15

Where do the nasal fibres decussate?

Answer 15

Optic chiasm

Question 16

Where do the optic tracts run from and to?

Answer 16

From the optic chiasm to the lateral geniculate nucleus.

Question 17

Superior optic radiations are responsible for which field of vision?

Answer 17

Inferior field of vision

Question 18

Inferior optic radiations are responsible for which field of vision?

Answer 18

Superior filed of vision

Question 19

Which lobes of the brain do the optic radiations project into?

Answer 19

Superior radiations project into the parietal lobe

Inferior radiations project into the temporal lobe

Question 20

Where is the primary visual cortex located?

Answer 20

Occipital lobe

Question 21

How are visual field defects named?

Answer 21

Named based on the area of visual loss rather than the site of the lesion.

Question 22

Lesions before the optic chiasm produce what signs relative to the lesion?

Answer 22

Signs are unilateral and ipsilateral

Question 23

What is monocular blindness and what lesion causes it?

Answer 23

Complete loss of either the left or right visual field. Lesion of optic nerve on ipsilateral side.
E.g. lesion of right optic nerve causes right monocular blindness

Question 24

Give examples of conditions that can cause monocular blindness.

Answer 24

Optic nerve glioma or retinoblastoma (children)

Optic sheath meningiomas (middle aged)

Question 25

What is bitemporal hemianopia, what lesion causes it?

Answer 25

Tunnel vision.

Lesion at the optic chiasm affecting both nasal fibres resulting in the loss of both temporal fields.

Question 26

What is left hemianopia, what lesion causes it?

Answer 26

Lesion of the right optic tract affecting the right temporal and left nasal fibres, resulting in loss of the right nasal and left temporal fields.

Question 27

What is right hemianopia, what lesion causes it?

Answer 27

Lesion of the left optic tract affecting the left temporal and right nasal fibres, resulting in the loss of the left nasal and right temporal fields.

Question 28

What are the possible causes of hemianopia?

Answer 28

Vascular causes are the most common (e.g. stroke)

Also neoplasia and trauma

Question 29

What lesions cause quadrantanopias?

Answer 29

Lesions of the superior or inferior optic radiations

Question 30

The occipital lobe is supplied by which two arteries?

Answer 30

Posterior cerebral artery

Middle cerebral artery (occipital pole)

Question 31

Why does macular sparing occur in a stroke affecting the posterior cerebral artery?

Answer 31

In a stroke affecting the posterior cerebral artery, most of the occipital lobe will be affected. However, the middle cerebral artery’s supply to the occipital lobe will still be intact. The middle cerebral artery supplies the macula therefore macular function (central vision) will be spared.

Question 32

Describe the light reflex.

Answer 32

Light simulates the optic nerve (CN II) - afferent
Synapses in the pretectal area - gives rise to neurones supplying Edinger-Westphal nuclei bilaterally
Both oculomotor nerves (CN III) are stimulated to cause direct and consensual pupillary constriction - parasympathetic fibres

Question 33

What are the three aspects of the accommodation reflex?

Answer 33

Convergence (medial rectus)
Pupillary constriction (constrictor pupillae)
Convexity of the lens to increase refractive power (ciliary muscle)

Question 34

What is the function of the medial longitudinal fasciculus?

Answer 34

Links the three main nerves controlling eye movement (oculomotor, trochlear, abducens) to allow coordination of eye movements.