Visual System Pathways

Question 1

What happens are the optic chiasm?

Answer 1

Half of the nerve fibres cross here

Question 2

What happens at the Optic tract?

Answer 2

Ganglion nerve fibres exit as optic tract

Question 3

What happens at the lateral geniculate nucleus?

Answer 3

Ganglion nerve fibres synapse at this place

Question 4

What is the optic radiation?

Answer 4

4th Order neuron

Question 5

What is the primary visual cortex found?

Answer 5

Within occipital lobe

Question 6

What is the primary visual cortex also called?

Answer 6

Striate cortes

Question 7

What are the 2nd order neurons called?

Answer 7

Retinal bipolar cells, come after the first order photoreceptors

Question 8

What are the 3rd order neurons?

Answer 8

Retinal ganglion cells (includes optic nerve, decussation, tract, destination)

Question 9

If a lesion affects the area anterior to the optic chiasma what does this to the visual field?

Answer 9

Affects one eye only

Question 10

If a lesion is posterior to the optic chiasma what does this do to the visual field?

Answer 10

affects both eyes

Question 11

What are the crossed fibres at the optic chiasma responsible for?

Answer 11

The temporal visual field

these fibres originate from the nasal retina

Question 12

What are the uncrossed fibres responsible for?

Answer 12

Responsible for the nasal visual field

These fibres originate from the temporal retina

Question 13

How does a lesion at the optic chiasma present as?

Answer 13

Temporal field deficit in both eyes = bitemporal hemianopia

• damages crossed fibres from the nasal retina in both eyes

Question 14

How does a lesion posterior optic chiasma present?

Answer 14

Right sided lesion :left homonymous hemianopia in both eyes

Life sided lesion : right homonymous hemianopia in both eyes

Question 15

What are the causes of bitemporal hemianopia?

Answer 15

• Typically caused by enlargement of Pituitary Gland Tumour

- Pituitary Gland sits under Optic Chiasma

Question 16

What are the causes of homonymous hemianopia?

Answer 16

Stroke (Cerebrovascular Accident)

Question 17

What causes Homonymous hemianopia with macula sparing?

Answer 17

Damage to primary visual cortex itself

Often due to stroke

Question 18

Why is the macula spared?

Answer 18

Area representing macular recieves dual blood supply from posterior cerebral from both right and left arteries

Question 19

What does pupil constriction do?

Answer 19

in light :

decreases spherical aberrations and glare

Increases depth of field

reduced bleaching of photo pigments

pupillary constriction mediated by parasympathetic nerve

Question 20

What does pupil dilation do?

Answer 20

increased light sensitivity in the dark by allowing in more light

mediated by sympathetic nerve

Question 21

Describe the afferent pathway of pupillary reflex? (3)

Answer 21

Rod and cone receptors synapse in bipolar cells which synapse on retinal ganglion cells

Pupil specific ganglion cells exit at posterior 1/3rd of optic tract before entering lateral geniculate nucleus

Afferent pathway from both eye synapse on edinger-westphal nuceli on both sides in brainstem

Question 22

How does the efferent pathway in the pupillary reflex work? (3)

Answer 22

Edinger-westphal nucleus –> occulomotor nerve efferent

Synapses at ciliary ganglion

Short posterior ciliary nerve –> pupillary sphincter

Question 23

What is direct light reflex?

Answer 23

Refers to constriction of pupil from light stimulated eye

Question 24

WHat is consensual light reflex?

Answer 24

Constriction of pupil from fellow eye

• due to afferent pathway on either side alone stimualting efferent pathways on both sides

Question 25

What may cause right afferent defect?

How will this present?

Answer 25

Damage to optic nerve

reflex test : no pupil constriction in both eyes when right is stimulated

normal pupil constriction in both eyes when left eye is stimulated

Question 26

What may cayse right efferent defect?

Answer 26

Damage to Right 3rd Nerve

No right pupil constriction whether right or left eye is stimulated with light

Left pupil constricts whether right or left eye is stimulated with light

Question 27

What is unilateral afferent defect?

Answer 27

Difference response pending on which eye is stimulated

Question 28

What is Unilateral efferent defect?

Answer 28

Same unequal response between left and right eye irrespective which eye is stimulated

Question 29

What is the swinging torch test?

Answer 29

Elicited by the swinging torch test – alternating stimulation of right and left eye with light

Question 30

How does swinging torch test show relative afferent pupillary defect?

Answer 30

Partial pupillary response still present when the damaged eye is stimulated

Both Pupils constrict when light swings to left undamaged side

Both Pupils paradoxically dilate when light swings to the right damaged side