The Retina + The Central Visual Pathway

Question 1

What are the layers of the eye?

Answer 1

Sclera - tough + continuous with dural sheath of optic nerve
Choroid - pigmented vascular layer
Retina - neural layer

Question 2

Role of the pigmented layer of the retina

Answer 2

• main site of absorption of light
• prevents light from ‘bouncing around’ in eyeball causing glare
• anchors the photoreceptor cells

Question 3

What are the 2 different types of photoreceptors?

Answer 3

Rods
Cones

Question 4

Function of rods

Answer 4

Black and white vision

Question 5

Function of cones

Answer 5

Coloured vision
High acuity vision
Central vision at macula

Question 6

Role of bipolar cells in retina

Answer 6

Act to connect photoreceptor cells to axons

Question 7

Role of horizontal cells in retina

Answer 7

Lateral inhibition
inhibits photoreceptors cells on either side of photoreceptor receiving impulses

Question 8

What is amaruosis fugax?

Answer 8

• due to occulsion of central retinal artery (branches from Opthalamic artery)
• Presentation of ‘curtain coming down over vision’

Question 9

What is amaurosis fugax a symptom of?

Answer 9

Stroke
Occlusion of central retinal artery

Question 10

A patient tells you they fell like a ‘curtain is falling over their vision, what is the most likely cause?

Answer 10

Amaurosis fugax
Occlusion of central retinal artery
Symptom of stroke

Question 11

What is the layout of the retina in fundoscopy?

Answer 11

Macula sits lateral to optic disc
Central retinal artery + vein can be seen

Question 12

Examples of conditions that can be detected by fundoscopy

Answer 12

• hypertensive retinopathy
• diabetic retinopathy
• macular degeneration
• papilloedma
• vascular occlusions

Question 13

What can be used to view the layers of the retina?

Answer 13

Optical coherence tomography

Question 14

Why is the macula the point of highest visual acuity?

Answer 14

Highest concentration of cones

Question 15

What are the parts of the retina?
What are they called?

Answer 15

medial retina - nasal
lateral retina - temporal
superior + inferior

Question 16

What are the parts of the visual pathway?

Answer 16

• optic nerve
• optic chiasm
• optic tract
• lateral geniculate nucleus
• superior optic radiation via parietal lobe + inferior optic radiation via temporal love
• primary visual cortex

Question 17

Difference between fibres in the optic nerve + tract

Answer 17

• optic nerve: only fibres from ipsilateral eye
• optic tract: fibres from both eyes | contralateral nasal fibres | ipsilateral temporal fibres

Question 18

Outline the visual pathway

Answer 18

• optic nerve consists of ipsilateral nasal and temporal fibres
• at the optic chiasm nasal fibres decussate
• optic tract consists of contralateral nasal + ipsilateral temporal fibres
• lateral geniculate nucleus
• superior optic radiation takes superior quadrant fibres to primary visual cortex via parietal lobe
• inferior optic radiation takes inferior quadrant fibres to primary visual cortex via temporal lobe

Question 19

What are the two routes to the primary visual cortex from the lateral geniculate nucleus?

Answer 19

• superior optic radiation via parietal lobe | superior quadrant fibres
• inferior optic radiation via temporal lobe | inferior quadrant fibres

Question 20

What field of vision are nasal fibres responsible for?

Answer 20

Temporal field of vision

Question 21

What field of vision are temporal fibres responsible for?

Answer 21

Nasal field of vision

Question 22

List 5 types of visual loss

Answer 22

• monocular blindness
• bitemporal hemianopia
• homonomous hemianopia
• homonomous inferior quadrantanopia
• homonomous superior quadrantanopia

Question 23

What type of visual loss does damage to the optic nerve cause?

Answer 23

Monocular blindness
- Loss of vision in one eye
- Contains fibres from ipsilateral side

Question 24

What type of visual loss does damage to the optic chiasm cause?

Answer 24

Bitemporal haeminaopia
- Loss of both temporal visual fields
- Due to nasal fibres on both sides affected

Question 25

What type of visual loss does damage to the optic tract cause?

Answer 25

Homonomous hemianopia
- loss of ipsilateral nasal visual field + contralateral temporal visual field
- i.e. left side of both eyes or right side of both eyes

Question 26

What do the inferior retinal fibres detect?

Answer 26

Superior quadrant field of vision

Question 27

What do the superior retinal fibres detect?

Answer 27

Inferior quadrant field of vision

Question 28

What type of visual loss does damage to the superior optic radiation cause?

Answer 28

Homonomous inferior quadrantanopia
- Loss of ipsilateral inferior nasal visual field
- Loss of contralateral inferior temporal visual field

Question 29

What type of visual loss does damage to the inferior optic radiation cause?

Answer 29

Homonomous superior quadrantanopia
- Loss of ipsilateral superior nasal visual field
- Loss of contralateral superior temporal visual field

Question 30

What type of visual loss does damage to the both optic radiation or the lateral geniculate nucleus cause?

Answer 30

Homonomous hemianopia
- like lesion in optic tract
- loss of ipsilateral nasal visual field
- loss of contralateral temporal visual field

Question 31

You see a patient with albinism who complains that he is unable to see well in bright sunlight. Why is this?

Answer 31

• Albinism causes reduced pigmentation in eyes > iris translucent
• This allows excessive light to enter the eyes
• causing sensitivity to bright sunlight > photophobia

Question 32

A patient suffers from homonymous hemianopia caused by a stroke.
How might we determine whether the lesion is in the optic tract or the visual cortex?

Answer 32

• optic tract lesion is not macula sparing
• visual cortex lesion is macula spaing - because it has a dual blood supply