Neurology of the visual system

Question 1

Where does the visual pathway transmit a signal from and to?

Answer 1

From the eye to the optic chiasm

Question 2

Which cranial nerve is the optic nerve?

Answer 2

2

Question 3

What happens at the optic chiasm?

Answer 3

Half of the optic nerve fibres cross

Question 4

What do ganglion nerve fibres exit the optic chiasm as?

Answer 4

The optic tract

Question 5

Where do ganglion nerve fibres originate?

Answer 5

Retina

Question 6

Where do ganglion nerve fibres synapse with the next order neurone?

Answer 6

Lateral geniculate nucleus

Question 7

Where is the lateral geniculate nucleus?

Answer 7

In the thalamus

Question 8

What is the optic radiation?

Answer 8

4th order neurone that relays signals to the primary visual cortex in the occipital lobe for visual processing

Question 9

Where does the primary visual cortex (striate cortex) relay information to?

Answer 9

Extra striate cortex

Question 10

In the retina part of the visual pathway, what are the first order neurones?

Answer 10

Rod and cone retinal photoreceptors

Question 11

What are second order neurones?

Answer 11

Bipolar cells

Question 12

What are third order neurones?

Answer 12

Retinal ganglion cells

Question 13

What is the receptive field of a retinal neurone?

Answer 13

Retinal space within which incoming light can alter the firing pattern of a neurone

Question 14

Do rods or cones have bigger receptive fields?

Answer 14

Rods- high sensitivity

Question 15

Do rods or cones synapse less upon the same ganglion cells?

Answer 15

Cones- high visual acuity

Question 16

What is an on-centre ganglion cell?

Answer 16

It is stimulated by light falling on the centre of its receptive field and inhibited by light falling on the edge of its receptive field

Question 17

What is an off-centre ganglion cell?

Answer 17

It is inhibited by light on centre of receptive field and stimulated by light on edge

Question 18

What does this have an important role in?

Answer 18

Contrast sensitivity and enhanced edge detection

Question 19

What is the difference between lesions anterior or posterior to the optic chiasm?

Answer 19

Lesions anterior to the optic chasm affect one eye

Posterior affects both eyes

Question 20

Where do the 53% of fibres that cross at the optic chasm originate from?

Answer 20

Nasal retina

Question 21

What is it called where lesions lead to problems in both eyes?

Answer 21

Bitemporal hemianopia

Question 22

What are the two divisions of the optic radiation and where do they travel?

Answer 22

Upper division - through the parietal lobe (inferior visual quadrants)
Lower division- through the temporal lobe (superior visual quadrants)

Question 23

What is the Meyer’s loop formed from?

Answer 23

Lower division loops

Question 24

What will a Meyer’s loop lesion lead to?

Answer 24

Vision loss in one of the superior quadrants (superior homonymous quadrantopia)

Question 25

What is the most common cause of bitemporal hemianopia?

Answer 25

Enlargement of the pituitary gland which sits within the sella turcica beneath the optic chiasm

Question 26

Where is the primary visual cortex situated?

Answer 26

Along the calcarine sulcus within the occipital lobe

Question 27

What part of vision is PVC above the calcarine sulcus responsible for?

Answer 27

Inferior visual field

Question 28

What is the main cause of damage to the primary visual cortex?

Answer 28

Strokes

Question 29

What does the extrastriate cortex do?

Answer 29

Converts basic visual information to position and orientation

Question 30

How does the pupil regulate light input?

Answer 30

In light, the iris circular muscle contracts and there is constriction of the pupillary aperture which reduces light entering the eye and reduces the amount of photopigment bleaching which increases the depth of field

Question 31

Where do the retinal ganglion cells involved in the pupillary light reflex leave the optic tract and synapse?

Answer 31

They exit the posterior 1/3 before the lateral geniculate nucleus and synapse upon the dorsal brainstem- pretectal nucleus

Question 32

What happens at the Edinger-Westphal nucleus?

Answer 32

The afferent pathway from each eye synapses there on both sides of the brainstem

Question 33

What provides the efferent pathway of the pupillary reflex?

Answer 33

Parasympathetic nerve that originates at the Edinger-Westphal nucleus and synapses at the ciliary ganglion with the short posterior ciliary nerve which then directly innervates the iris pupillary sphincter

Question 34

Will light in the left eye stimulate the pupillary reflex in the right eye?

Answer 34

Yes- both eyes

Question 35

What is an example of an afferent deficit?

Answer 35

Damage to the optic nerve

Question 36

What happens in an afferent deficit?

Answer 36

No constriction in either eye when affected eye is stimulated but normal constriction in both eyes when unaffected eye is stimulated

Question 37

What happens in an efferent deficit?

Answer 37

There is no constriction in affected eye when either eye is stimulated and the unaffected eye constricts both times

Question 38

How do you test for a relative afferent pupillary deficit>

Answer 38

Swinging torch test

Question 39

What is duction?

Answer 39

Movement in one eye

Question 40

What is version?

Answer 40

Simultaneous movement of both eyes in same direction

Question 41

What is vergeance?

Answer 41

Simultaneous movement of eyes in opposite directions

Question 42

What is convergence?

Answer 42

Simultaneous adduction movement of both eyes when viewing a near object

Question 43

What is a saccade?

Answer 43

Short fast burst

Question 44

What is smooth pursuit?

Answer 44

Sustained slow movement

Question 45

What are the six extra-ocular muscles?

Answer 45

``` Superior rectus Inferior rectus Superior oblique Inferior oblique Lateral rectus Medial rectus ```

Question 46

Which muscle does the trochlear nerve innervate?

Answer 46

Superior oblique

Question 47

Which muscle does the abducens innervate?

Answer 47

Lateral rectus

Question 48

Which muscles does the oculomotor innervate

Answer 48

Inferior oblique, superior rectus, inferior rectus and medial rectus

Question 49

Where do all the rectus muscles originate from?

Answer 49

Common tendinous ring behind the eye at the orbital apex

Question 50

Where do the rectus muscles insert?

Answer 50

Sclera of the anterior globe- they pull the eye backwards

Question 51

In relation to rectus muscles, which direction do the obliques rotate the eye?

Answer 51

The opposite direction

Question 52

What effect does the superior rectus have on the eye?

Answer 52

It elevates the eye when in an abducted position

Question 53

What effect does the superior oblique have on the eye?

Answer 53

It depresses the eye when in an adducted position

Question 54

In 3rd nerve palsy what are the only two eye muscles that are working?

Answer 54

Lateral rectus and superior oblique

Question 55

What does this mean happens to the eye in 3rd nerve palsy?

Answer 55

The eye moves down and out

Question 56

What else do you get in 3rd nerve palsy?

Answer 56

Ptosis (drooping eyelid) because the oculomotor also innervates lid levator. There is also pupil dilation due to loss of parasympathetic innervation from oculomotor

Question 57

What muscle is no longer innervated in 6th nerve palsy?

Answer 57

Lateral rectus

Question 58

What does this means happens to the eye in 6th nerve palsy?

Answer 58

A deficit in abduction of the affected eye

Question 59

What is Hering's law?

Answer 59

There is equal innate innervation to both muscles from both eyes involved in conjugate or pair movements

Question 60

What does the medial longitudinal fasciculatus do?

Answer 60

It acts as a link synchronising the 6th nerve nucleus on the right side and third nerve nucleus on left side so when the eyes looks to the left, both eyes move at the same time

Question 61

In what condition is Hering's law violated?

Answer 61

Internuclear opthalmoplegia

Question 62

What is Sherrington's law of reciprocal innervation?

Answer 62

Agonist muscles contract whilst antagonist muscles relax

Question 63

In what condition is Sherrington's law violated?

Answer 63

Duane's syndrome

Question 64

What is Duane's syndrome?

Answer 64

Congenital absence of abducens- both medial and lateral rectus are innervated by oculomotor now so both agonist and antagonist contract at same time