The Neurology of the Visual System

Question 1

What are some of the landmarks in the vestibular system

Answer 1

Eye
Optic nerve (CNII)
Optic chiasm
Optic tracts
Lateral geniculate nucleus
Optic radiation 
Primary visual cortex

Question 2

Describe the pathway of the visual system

Answer 2

1. Optic nerve fibres consist of the axons of retinal ganglion nerve cells
2. Half of the fibres cross at the optic chiasm
3. The new fibre tracts are the optic tracts as they exit the optic chiasm
4. Fibres synapse in the lateral geniculate nucleus of the thalamus
5. 4th order neuron as the optic radiation
6. Relays signals to the primary visual cortex in the occipital lobe

Question 3

What is the different between a lesion anterior and posterior to the optic chiasm

Answer 3

Anterior to the optic chiasm - One eye affected

Posterior to optic chiasm - Both eyes affected

Question 4

What occurs in the eyes I there is a lesion behind the optic chiasm on the right and left sides

Answer 4

Right side - left homonymous hemianopia in both eyes (contralateral)

Left side - right homonymous hemianopia in both eyes (contralateral)

Question 5

What can bitemporal hemianopia be caused by

Answer 5

Typically caused by the enlargement of a pituitary gland tumour, which sits under the optic chiasma.

Question 6

What is homonymous hemianopia caused by

Answer 6

Caused by stroke

Question 7

Describe macular sparing homonymous hemianopia

Answer 7

Damage to primary visual cortex
Often due to stroke
Leads to contralateral homonymous hemianopia with macula sparing
Area representing the Macula receives dual blood supply from Posterior Cerebral Arteries from both sides = well protected

Question 8

Where is the primary visual cortex

Answer 8

In the occipital lobe along the calcarine sulcus

Question 9

What is the function of the primary visual cortex and its portions

Answer 9

Final destination of all visual information.

Superior portion - Upper portion of retina
Inferior portion - Lower portion of retina

Information from the macula takes up a larger segment of the cortex than any other part of the retina

Question 10

Describe the afferent pathway of the pupillary reflex

Answer 10

1. Pupil-specific retinal ganglion cells travel along the optic nerve
2. Exits at the posterior 1/3 of the optic tract
3. Synapses at the Pretectal nucleus in the brainstem
4. Afferents from each eye will synapse on the Edinger-westphal nucleus on both sides of the brainstem

Question 11

Describe the efferent pathway of the pupillary reflex

Answer 11

1. Leaves from the Edinger-westphal nucleus via the oculomotor nerve (CNIII)
2. Synapse at the ciliary ganglion
3. Short posterior ciliary nerve (from ganglion) will go to the pupillary sphincter (and cause constriction)

Question 12

What happens in the relative afferent pupillary defect and how is it tested for

Answer 12

Partial pupillary response is still present when the damaged eye is stimulated

Swinging torch test - alternating stimulation of right and left eye with the light.
Both pupils constrict when the light swings to the left undamaged side
Both pupils dilate when the light swings to the right damaged side

Question 13

Define duction

Answer 13

Eye movement in one eye

Question 14

Define vergence

Answer 14

Simultaneous movement of both eyes in the opposite direction

Question 15

Define convergence

Answer 15

Simultaneous adduction movement in both eyes while viewing a near object

Question 16

Define version

Answer 16

Simultaneous movement of both eyes in the same direction

Question 17

What movements are brought about by the rectus muscles

Answer 17

moves eye maximally in the ABDUCTED POSITION

Superior rectus: Moves the eye up.
Inferior rectus: Moves the eye down.
Lateral Rectus: Moves the eye toward the outside of the head
Medial Rectus: Moves the eye toward the middle of the head

Question 18

What movements are brought about by the oblique muscles

Answer 18

Moves the eye maximally in the ADDUCTED POSITION

Superior Oblique:
Passes under the Superior Rectus.
Travels through the trochlea
Depresses and abducts.

Inferior Oblique:
Passes over the Inferior Rectus.
Elevates and Abducts

Question 19

What muscles are supplied by the superior branch of the third cranial nerve

Answer 19

Superior Rectus – elevates eye

Lid Levator – raises eyelid

Question 20

Which muscles are supplied by the inferior branch of the third cranial nerve

Answer 20

Inferior Rectus – depresses eye
Medial Rectus – adducts eye
Inferior Oblique – elevates eye
Parasympathetic Nerve – constricts pupil

Question 21

Where is the eye in a third nerve palsy and why

Answer 21

Outwards (unopposed muscle tone from the lateral rectus, CN VI)
Downwards (unopposed muscle tone from the superior rectus, CN IV)

Question 22

What occurs in third nerve palsy other than eye movement

Answer 22

There is also ptosis/drooping of eyelid due to lack of innervation to the levator palpebrae superioris
Mydriasis (pupil widening) also occurs

Question 23

Describe what occurs in sixth nerve palsy

Answer 23

Eye is unable to move outwards and deviates inwards (lateral rectus innervation impaired
Diplopia (double-vision) possible

Question 24

Describe how you would test for individual movements of the extrinsic eye muscles

Answer 24

Lateral Rectus - Move finger LATERALLY
Medial Rectus - Move finger MEDIALLY
Superior Rectus - Move finger LATERALLY + UP
Inferior Rectus - Move finger LATERALLY + DOWN

Superior Oblique - Move finger MEDIALLY + DOWN

Inferior Oblique - Move finger MEDIALLY + UP