Pathways of the Visual System

Question 1

Describe the order of the visual pathway

Answer 1

Eye
Optic nerve
Optic chiasm
Optic tract
Lateral geniculate nucleus
Optic radiation- 4th order neuron 
Primary visual cortex

Question 2

What happens to fibres at the optic chiasm?

Answer 2

53% of them cross over

Question 3

What synapses at the lateral geniculate nucleus?

Answer 3

The ganglion nerve fibres

Question 4

Where is the primary visual cortex found?

Answer 4

Within the occipital lobe

Question 5

In the retina what are the 1st order neurons?

Answer 5

Rod and cone retinal photoreceptors

Question 6

In the retina what are the 2nd order neurons?

Answer 6

Retinal bipolar cells

Question 7

In the retina what are the 3rd order neurons?

Answer 7

Retinal ganglion cells

Question 8

What will lesions anterior to the optic chiasm affect?

Answer 8

The visual field of one eye

Question 9

What will lesions posterior to the optic chiasm affect?

Answer 9

The visual field of both eyes
Right sided lesion – Left Homonymous Hemianopia in Both Eyes
Left sided lesion – Right Homonymous Hemianopia in Both Eyes

Question 10

What visual field are crossed fibres responsible for?

Answer 10

The temporal visual field

Question 11

What visual field are uncrossed fibres responsible for?

Answer 11

The nasal visual field

Question 12

Where do crossed fibres originate from?

Answer 12

The nasal retina

Question 13

Where do uncrossed fibres originate from?

Answer 13

The temporal retina

Question 14

What will a lesion at the optic chiasm affect?

Answer 14

Both visual field, it will cause a bitemporal hemianopia

Question 15

What is a homonymous hemianopia?

Answer 15

The patient sees only the left or right visual field in BOTH eyes

Question 16

What is a bitemporal hemianopia?

Answer 16

Loss of peripheral visual field in BOTH eyes

Question 17

What is a quadrantanopia?

Answer 17

Loss of visual field in one quadrant of both eyes

Question 18

What is macular sparring?

Answer 18

When there is loss of visual field eg left visual field of both eyes BUT the very centre of the visual field is preserved

Question 19

What is the most common cause of bitemporal hemianopia?

Answer 19

Compression of the optic chiasm due to pituitary enlargement

Question 20

What is the most common cause of homonymous hemianopia?

Answer 20

Stroke/ cerebrovascular accident

Question 21

When does homonymous hemianopia with macular sparring occour?

Answer 21

If there is damage to the primary visual cortex

Often due to stroke

Question 22

What does the pupil regulate?

Answer 22

How much light is let into the eye

Question 23

What happens to the pupil when its exposed to light?

Answer 23

It constricts

Question 24

What does constriction of the pupil do?

Answer 24

Decreases glare
Increases depth of field
Reduces bleaching of photo pigments

Question 25

What nerve carries out constriction of the pupil?

Answer 25

Parasympathetic nerve (CN III)

Question 26

What muscles contract to cause pupil constriction?

Answer 26

Circular muscles

Question 27

What happens to the pupil in the dark?

Answer 27

It dilates

Question 28

What does dilation of the pupil achieve?

Answer 28

Allows increased sensitivity to light by allowing more light into the eye

Question 29

What nerve carries out dilation of the pupil?

Answer 29

Sympathetic nerve

Question 30

What muscles contract to allow dilation of the pupil?

Answer 30

Radial muscles

Question 31

Describe the afferent pathway starting at rod and cone photoreceptors

Answer 31

Rod and cone photoreceptors synapse on bipolar cells
These synapse on retinal ganglion cells
Ganglion cells exit at posterior third of optic tract before entering lateral geniculate nucleus
Afferent pathway from each eye synapses on Edinger-Westphal nuclei on both sides of the brainstem

Question 32

Describe the efferent pathway starting at the Edinger Westphal nucleus

Answer 32

Edinger Westphal nucleus goes to oculomotor nerve efferent
Synapses at the ciliary ganglion
Short posterior ciliary nerve goes to pupillary sphincter

Question 33

What are the 2 pupillary reflexes?

Answer 33

Direct and consensual

A normal reflex will illicit both

Question 34

What is the direct pupillary reflex?

Answer 34

Constriction of the pupil in the eye that is stimulated by light

Question 35

What is the consensual pupillary reflex?

Answer 35

Constriction of the pupil in the other eye (not the one that is stimulated by light)

Question 36

If there is a right afferent defect, how will the pupillary reflex be affected?

Answer 36

No constriction in either pupil when light is shone in the right eye
Constriction in both pupils when light is shone in the left eye

Question 37

If there is a right efferent defect, how will the pupillary reflex be affected?

Answer 37

No constriction in the right pupil when either eye is stimulated
Constriction in the left eye when either pupil is stimulated

Question 38

If there is a unilateral afferent defect, how will the pupillary reflex be affected?

Answer 38

When light is shone into the damaged eye, both eyes will not constrict
When light is shone into the undamaged eye, both eyes will constrict

Question 39

If there is a unilateral efferent defect, how will the pupillary reflex be affected?

Answer 39

Whichever eye is damaged will not constrict when either eye is stimulated
The undamaged eye will constrict when either eye is stimulated

Question 40

Which test is used to check the afferent and efferent eye pathways?

Answer 40

The swinging torch test- alter stimulation of right and left eye with light
Dilation of both pupils when light is shone on damaged eye

Question 41

Where do 3rd order neurons travel after retinal ganglion cells?

Answer 41

Optic nerve
Partial decussation at optic chiasm
Optic tract
Lateral geniculate nucleus in thalamus
Visual cortex

Question 42

What percentage of ganglion fibres cross at the optic chiasm?

Answer 42

53%