Visual System (Pathways)

Question 1

Which nerve connects the eye brain?

Answer 1

Optic nerve (II)

Question 2

Which fibres comprise the optic nerve?

Answer 2

Myelinated ganglion nerve fibres

Question 3

Where are the cell bodies of the optic nerve located?

Answer 3

The cell bodies reside within the retina

Question 4

Where do the optic nerves from both eyes converge?

Answer 4

At the optic chiasm, anterio-superior of the brainstem

Question 5

What happens at the optic chiasm?

Answer 5

Approximately half of the ganglion nerve fibres contralaterally exit along the optic tract.

Question 6

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

Answer 6

At the Lateral geniculate nucleus

Question 7

Where is the lateral geniculate nucleus?

Answer 7

It is a relay centre situated within the thalamus

Question 8

What forms the fourth order neurones?

Answer 8

Optic radiation

Question 9

What is optic radiation?

Answer 9

Relays signals from the lateral geniculate ganglion to the primary visual cortex within the occipital lobe for lower visual processing

Question 10

Where is the primary visual cortex?

Answer 10

Within the occipital lobe

Question 11

What is the striate cortex?

Answer 11

Primary visual cortex

Question 12

Which region is responsible for further high visual processing besides the primary visual cortex?

Answer 12

The extra-striate cortex.

Question 13

What are the first order neurones within the visual pathway?

Answer 13

The Rod and Cone photoreceptor cells

Question 14

What are the second order neurones within the visual pathway?

Answer 14

The retinal bipolar cells.

Question 15

What are the third order neurones within the visual pathway?

Answer 15

Retinal ganglion cells

Optic nerve

Question 16

What happens to the retinal ganglion cell fibres at the optic chiasm?

Answer 16

Partial decussation at optic chiasm- 53% of ganglion fibres cross the midline into contralateral optic tracts.

Question 17

Where do retinal ganglion fibres terminate?

Answer 17

Within the lateral geniculate ganglion

Question 18

A lesion occurring anterior to the optic chiasm will affect which visual fields?

Answer 18

Affect visual field in one eye only

Question 19

A lesion occuring posterior to the optic chiasm will affect the visual field in which eyes?

Answer 19

Both eyes

Question 20

Where do contralateral optic fibres originate from?

Answer 20

From nasal retina, responsible for the temporal half of the visual field in each eye

Question 21

Where do the uncontrolled fibres predominantly originate from?

Answer 21

Originate from the temporal retina

Question 22

What are temporal retinal fibres responsible for?

Answer 22

Responsible for nasal half of the visual field in each eye.

Question 23

A lesion to the optic chiasm will result in damage to white fibres?

Answer 23

Predominantly damaging decussation contralateral retinal ganglion fibres

Question 24

Which type of visual field deficit arises from a lesion to the optic chiasm?

Answer 24

Temporal field deficit in both eyes, considered to be bitemporal hemianopia.

Question 25

What type of visual field deficit arises from a right-side posterior to the optic chiasm lesion (optic tract, radiation or visual cortex)?

Answer 25

Left homonymous hemianopia in both eyes.

Question 26

What visual field defect occurs in a left sided lesion to the posterior optic chiasm?

Answer 26

Right homonymous hemianopia in both eyes.

Question 27

What is monocular blindness?

Answer 27

Loss of vision in a single eye due to damage to retinal ganglion nerve fibres anterior to the optic chiasm.

Question 28

What is the common cause of bitemporal hemianopia?

Answer 28

Enlargement of the pituitary gland (adenoma) Considering the pituitary gland resides within the sella turcica, beneath the optic chiasm --> Adenoma causes optic nerve compression

Question 29

What is the common of homonymous hemianopia?

Answer 29

Stroke (CVA)

Question 30

Which structure is affected in patients with homonymous hemianopia with macular sparing?

Answer 30

Damage to the primary visual cortex, caused due to a stroke. --> This contralateral homonymous hemianopia

Question 31

Why is macula central vision spared in homonymous hemianopia?

Answer 31

Receives dual blood supply from both right and left posterior cerebral arteries.

Question 32

What is the function of the pupil?

Answer 32

Regulates light input to the eye like a camera aperture.

Question 33

When light intensities increase, wha tis the pupillary response?

Answer 33

Constrictions to decrease spherical abberations and flare Increases depth of field -- near response triad. Reduced bleaching of photopigments Mediated by oculomotor nerve

Question 34

Which cranial nerve mediates the pupillary constriction?

Answer 34

Parasympathetic oculomotor nerve (CNIII).

Question 35

When light intensities decrease, what is the pupillary response?

Answer 35

Increases light sensitivity in the dark my allowing more light into the eye, facilitated by pupillary dilatation.

Question 36

Which nerve mediates the pupillary dilatation?

Answer 36

Sympathetic oculomotor nerve

Question 37

Which muscles cause pupillary constriction?

Answer 37

Circular sphincter pupillae muscles

Question 38

Which muscles cause pupillary dilatation?

Answer 38

Radial dilator pupillae

Question 39

Where do the pupil-specific ganglion cells exit out of the optic tract?

Answer 39

The posterior third of the optic tract before entering the lateral geniculate nucleus

Question 40

Where do afferent pathways from each eye synapse within the brainstem?

Answer 40

Synapses on the Edinger-Westphal Nuclei on both sides of the brainstem

Question 41

Which brainstem nucleus is involved within the pupillary reflex?

Answer 41

Edinger-Westphal nuclei

Question 42

Which cranial nerve synapses with the Edinger-Westhphal nuclei in the efferent pathway?

Answer 42

Oculomotor nerve

Question 43

Where does the oculomotor nerve synapse within the efferent pathway during the pupillary reflex?

Answer 43

Ciliary ganglion

Question 44

Which nerve directly innervates the pupillary sphincter muscles?

Answer 44

The short posterior ciliary nerve

Question 45

What is a direct light reflex?

Answer 45

Constriction of the pupil of the light stimulated eye

Question 46

What is a consensual light reflex?

Answer 46

Constriction of pupil of the other eye

Question 47

What is the effect of right afferent pupillary pathway damage? (Damage to the right optic nerve)

Answer 47

Stimulation of the right eye will elicit weak No pupillary constriction in both eyes. However stimulation of the left eye will elicit normal pupillary responses in both eyes.

Question 48

What is the effect is the right efferent pathway is damaged?

Answer 48

There will be no pupil constriction in the right eye, irrespective of stimulation

Question 49

What is a unilateral afferent defect?

Answer 49

Difference responses pending on which eye is stimulated

Question 50

What is a unilateral efferent defect?

Answer 50

Produces the same unequal responses between left and right eye, regardless whether which eye is stimulated.

Question 51

Which clinical test can be conducted to test pupillary defects?

Answer 51

Swinging torch test

Question 52

What is the relative afferent pupillary defect?

Answer 52

Partial pupillary response still present when the damaged eye is stimulated Elicited by the swinging torch test – alternating stimulation of right and left eye with light Both Pupils constrict when light swings to left undamaged side Both Pupils paradoxically dilate when light swings to the right damaged side