4. Retina And Central Visual Pathways

Question 1

What are the layers of the retina?

Answer 1

Pigmented layer
Photoreceptor cells
Horizontal cells
Bipolar cells

Question 2

What is the role of the pigmented layer?

Answer 2

Acts as main site of absorption of light

Helps anchor photoreceptor cells

Question 3

What is the role of photoreceptor cells?

Answer 3

Rods - Black and white

Cones - colour, high detail

Question 4

What is the role of horizontal cells?

Answer 4

Lateral inhibition - help narrow down signals that are being sent

Question 5

What is the role of bipolar cells?

Answer 5

Connect photoreceptor cells to axons of ganglion cells to optic nerve

Question 6

Describe the visual pathway from the eyes

Answer 6

1. Optic nerve leaves each eye from superior and inferior temporal fibres and superior and inferior nasal fibres
2. They then join at the optic chasm, nasal fibres decussate, temporal fibres remain ipsilateral
3. Optic tracts formed, from optic chasm to lateral geniculate nucleus
4. Optic radiations formed, from lateral geniculate nucleus to primary visual cortex (occipital lobe)

Question 7

What are the 2 routes to get to the primary visual cortex?

Answer 7

Superior optic radiations - through parietal lobe (continuation of superior quadrant fibres)
Inferior optic radiations - through temporal lobe (continuation of inferior quadrant fibres)

Question 8

What do visual fields relate to?

Answer 8

Peripheral vision

Question 9

What is responsible for our temporal field of vision?

Answer 9

Nasal retinal fibres

Question 10

What is responsible for our nasal field of vision?

Answer 10

Temporal retinal fibres

Question 11

What happens if there is an optic nerve lesion?

Answer 11

Monocular blindness

Both nasal and temporal visual fields are lost on ipsilateral side

Question 12

What happens if there is an optic chiasm lesion in the centre?

Answer 12

Bitemporal hemianopia

Both temporal visual fields are lost

Question 13

What can cause optic chiasm lesion?

Answer 13

Pituitary tumour

Question 14

What is homonomous hemianopia?

Answer 14

Lesion in optic tract

Ipsilateral nasal visual field and contralateral temporal visual field are lost

Question 15

What is responsible for our inferior quadrant field of vision?

Answer 15

Superior radiations

Question 16

What is responsible for our superior quadrant field of vision?

Answer 16

Inferior radiations

Question 17

What is a homonomous inferior quadrantanopia?

Answer 17

Lesion of superior optic radiation (parietal lobe)

• Loss of inferior nasal visual field on ipsilateral side
• Loss of inferior temporal visual field on contralateral side

Question 18

What is homonomous superior quadrantanopia?

Answer 18

Lesion of inferior optic radiation (temporal lobe)

• loss of superior nasal visual field on ipsilateral side
• loss of superior temporal visual field on contralateral side

Question 19

What are the 3 aspects of the accommodation reflex?

Answer 19

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

Question 20

Why does he accommodation reflex follow the visual pathway via the lateral geniculate nucleus to the visual cortex?

Answer 20

Cerebral cortex must be involved because it is relating to image analysis