The Retina and Central Visual Pathways

Question 1

What are the important layers of the retina?

Answer 1

• Choroid
• Pigemented layer
• Neural layer

Question 2

What cells are contained within the neural layer of the retina?

Answer 2

• Photoreceptor cells
• Bipolar cells
• Horizontal cells

Question 3

What does the pigemented layer of the retina contain?

Answer 3

Melanin

Question 4

What are the functions of the pigemented layer of the retina?

Answer 4

• Reduces refraction of light
• Acts as an anchor for photoreceptor cells

Question 5

Why is it important that the pigmented layer of the retina reduces the refraction of light?

Answer 5

Prevents the light from being too bright

Question 6

What are the types of photoreceptor cells?

Answer 6

• Rod cells
• Cone cells

Question 7

What are rod cells good for?

Answer 7

• Black and white
• Low levels of light

Question 8

What are cone cells good for?

Answer 8

• Colour vision
• Higher acuity vision

Question 9

What is the function of horizontal cells?

Answer 9

They are inhibitory cells that are employed so you don’t get too many conflicting messages from photoreceptors

Question 10

Which part of the retina is responsible for central vision?

Answer 10

The macula lutea

Question 11

What is found within the macula?

Answer 11

The fovea centralis

Question 12

What is significant about the fovea centralis?

Answer 12

It has the highest concentration of cone cells, and therefore allows you to see details when looking straight ahead

Question 13

How can the retina be visualised?

Answer 13

Fundoscopy

Question 14

What can fundoscopies be useful to visualise?

Answer 14

• Retinopathies
• Vascular occlusions
• Macula
• Optic disc

Question 15

What retinopathy can be caused by vascular occlusions?

Answer 15

Amaurosis fungax

Question 16

What is amaurosis fugax?

Answer 16

A usually transient condition characterised by a ‘curtain coming down’ over vision

Question 17

What optic disc pathology can be seen on fundoscopy?

Answer 17

Swelling of the optic disc, called papilloedema

Question 18

What is papillodema a sign of?

Answer 18

Raised ICP

Question 19

Other than fundoscopy, what investigations can be done on the eye?

Answer 19

Optical coherence tomography

Question 20

Which fibres of the optic nerve run ipsilaterally?

Answer 20

The temporal fibres

Question 21

Which fibres of the optic nerve decussate at the optic chiasm?

Answer 21

The nasal fibres

Question 22

Where do the optic tracts run?

Answer 22

From the optic chiasm to the lateral geniculate nucleus

Question 23

What happens to the optic radiations?

Answer 23

They split into superior and inferior portions, and run into the primary visual cortex

Question 24

What field of vision are the nasal fibres responsible for?

Answer 24

The temporal

Question 25

What field of vision are the temporal fibres responsible for?

Answer 25

The nasal

Question 26

What is the clinical relevance of knowing the pathway of the optic nerve?

Answer 26

Becasue lesions at any point in the pathway will correspond to a pattern of visual loss, and so the pattern of loss can localise the lesion

Question 27

What are visual fields named based on?

Answer 27

The area of visual loss, *not the site of the lesion*

Question 28

What does a visual loss that is unilateral and ipsilateral suggest?

Answer 28

The damage has occured before the optic chiasm

Question 29

What does a bilateral visual loss suggest?

Answer 29

The damage occurs at or after the optic chiasm

Question 30

What does a visual loss that is bilateral and contralateral suggest?

Answer 30

The damage occurs after the optic chiasm

Question 31

What is monocular blindness?

Answer 31

Blindness in one eye

Question 32

What is monocular blindness caused by?

Answer 32

A lesion of the optic nerve

Question 33

Give two examples of things that might cause a lesion of the optic nerve in children

Answer 33

* Optic nerve glioma * Retinoblastoma

Question 34

Give an example of a condition that can cause an optic nerve lesion in adults

Answer 34

Meningiomas

Question 35

What is bitemporal hemianopia?

Answer 35

A loss of vision in both temporal fields, *also known as tunnel vision*

Question 36

What causes bitemporal hemianopia?

Answer 36

A lesion at the optic chiasm, *therefore affecting both nasal fibres and so loss of both temporal fields*

Question 37

What can cause a lesion at the optic chiasm?

Answer 37

Pathology of the pituitary gland or anterior communicating artery

Question 38

What causes a left homonomous hemianopia?

Answer 38

A loss of the right temporal and left nasal fibres due to a lesion of the right optic tract

Question 39

What can cause a lesion of the optic tract?

Answer 39

* Stroke * Neoplasia * Trauma

Question 40

What causes a right homonomous hemianopia?

Answer 40

Loss of the left temporal and right nasal fibres, caused by a lesion of the left optic tract

Question 41

What is the blood supply of the occipital lobe?

Answer 41

* Posterior cerebral artery * Occipital part of the middle cerebral artery *Has a dual blood supply*

Question 42

What happens in a stroke affecting the posterior cerebral artery?

Answer 42

Most of the occipital lobe will be lost, however the middle cerebral artery supplies the occipital pole, which represents the macula. Therefore, macula function will be spared

Question 43

Describe the pathway of the light reflex

Answer 43

1. The light stimulates the afferent nerve - CN II 2. The nerve synpases in the pretectal area, which gives rise to neurones supplying the Edinger-Westphal nuclei bilaterally 3. The pre-ganglionic parasympathetic fibres and then post-ganglionic parasympathetic fibres of both oculomotor nerves are stimulated to cause direct and consenual pupillary constriction

Question 44

What is the accomodation reflex required for?

Answer 44

Near vision

Question 45

What aspects does the accommodation reflex consist of?

Answer 45

* Convergence * Pupillary constriction * Change in convexity of the lens to increase its refractive power

Question 46

What muscle is responsible for convergence in the accomodation reflex?

Answer 46

Medial rectus

Question 47

What muscle is responsible for pupillary constriction in the accomodation reflex?

Answer 47

Constrictor pupillae

Question 48

What muscle is responsible for the change in convexity of the lens to increase the refractive power in the accomodation reflex?

Answer 48

The ciliary muscle

Question 49

Why must the cerebral cortex be involved in the accomodation reflex?

Answer 49

Because it is related to image analysis

Question 50

What is the result of the accomodation reflex involving the cerebral cortex on the pathway it must take?

Answer 50

The visual pathway goes via the lateral geniculate nucleus to the visual cortex

Question 51

Where does the accomodation reflex pathway go from the visual cortex?

Answer 51

It is common with the light reflex pathway, via the Edinger-Westphal nucleus