Visual System - Pathways

Question 1

The visual pathway transmits signals from where to where?

Answer 1

eye

visual cortex

Question 2

List visual pathway landmarks.

Answer 2

eye, optic nerve, optic chiasm, optic tract,
lateral geniculate nucleus – Ganglion nerve fibres synapse at Lateral Geniculate Nucleus in thalamus, optic radiation – 4th order neuron, primary visual cortex or Striate Cortes – within the Occipital Lobe

Question 3

First order neurons made up of?

Answer 3

rod and cone retinal photoreceptors

Question 4

Second order neurons made up of?

Answer 4

retinal bipolar cells

Question 5

Third order neurons made up of?

Answer 5

retinal ganglion cells

Question 6

53% of ganglion fibres decussate at what location?

Answer 6

optic chiasm

Question 7

How do lesions anterior to the optic chiasm affect the visual field?

Answer 7

only one eye affected

Question 8

How do lesions posterior to the optic chiasm affect the visual field?

Answer 8

both eyes affected

Question 9

Crossed fibres originate from what part of the retina?

Answer 9

nasal retina

Question 10

Crossed fibres are responsible for what part of the visual field?

Answer 10

temporal visual fibres

Question 11

Uncrossed fibres originate from what part of the retina?

Answer 11

temporal retina

Question 12

Uncrossed fibres are responsible for what part of the visual field?

Answer 12

nasal visual field

Question 13

When there is a lesion at the optic chiasm, what visual deficit occurs?

Answer 13

bitemporal hemianopia

Question 14

A right sided lesion posterior to the optic chiasm leads to what visual defect?

Answer 14

left homonymous hemianopia in both eyes

Question 15

A left sided lesion posterior to the optic chiasm leads to what visual defect?

Answer 15

right homonymous hemianopia in both eyes

Question 16

Bitemporal hemianopia is typically caused by?

Answer 16

enlargement of pituitary gland tumour

Question 17

Homonymous hemianopia is typically caused by?

Answer 17

stroke (cerebrovascular accident)

Question 18

What is macular sparing?

Answer 18

visual field loss that preserves vision in the center of the visual field

Question 19

Damage to the primary visual cortex leads to?

Answer 19

contralateral homonyous hemianopia with macula sparing

Question 20

Homonymous hemianopia with macular sparing is typically due to?

Answer 20

stroke

Question 21

The area representing the macula receives blood supply from?

Answer 21

posterior cerebral arteries from both sides

Question 22

In light, the pupillary reflex causes the pupil to?

Answer 22

constrict

Question 23

In darkness, the pupillary reflex causes the pupil to?

Answer 23

dilate

Question 24

Pupil constriction causes?

Answer 24

decreases spherical aberrations and glare
increases depth of field
reduces bleaching of photo-pigments

Question 25

Pupillary constriction is mediated by what nerve?

Answer 25

parasympathetic nerve within CN III

Question 26

Pupil dilation causes?

Answer 26

increases light sensitivity in the dark by allowing more light into the eye

Question 27

Pupillary dilatation is mediated by what nerve?

Answer 27

sympathetic

Question 28

Describe the afferent pathway of the pupillary reflex.

Answer 28

rod/cone photoreceptors > bipolar cells > retinal ganglion cells > pupil specific ganglion cells exit posterior 1/3 of optic tract > lateral geniculate nucleus

Question 29

Afferent reflex pathways from each eye synapse on what nuclei on both sides of the brainstem?

Answer 29

Edinger-Westphal

Question 30

Describe the efferent pathway of the pupillary reflex.

Answer 30

Edinger-Westphal nucleus > oculmotor nerve > synapses at ciliary ganglion > short posterior ciliary nerve > pupillary sphincter

Question 31

What is the direct light reflex?

Answer 31

constriction of pupil of the light stimulated eye

Question 32

What is the consensual light reflex?

Answer 32

constriction of pupil of the non-light stimulated eye

Question 33

Explain the neurological basis of the consensual light reflex.

Answer 33

afferent pathway on either side alone will stimulate efferent pathway on both sides

Question 34

What happens to pupillary reflex with right afferent defect e.g. damage to optic nerve?

Answer 34

no pupil constriction in both eyes when right eye is stimulated with light, normal pupil constriction in both eyes when left eye is stimulated with light

Question 35

What happens to pupillary reflex with right efferent defect e.g. damage to right 3rd nerve?

Answer 35

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 36

What happens to pupillary reflex with unliateral afferent defect?

Answer 36

Difference response pending on which eye is stimulated

Question 37

What happens to pupillary reflex with unliateral efferent defect?

Answer 37

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

Question 38

What is the relative afferent pupillary defect?

Answer 38

Partial pupillary response still present when the damaged eye is stimulated

Question 39

What test elicits the response from the relative afferent pupillary defect?

Answer 39

swinging torch test

Question 40

What happens in the swinging torch test with the relative afferent pupillary defect?

Answer 40

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

Question 41

What is the swinging torch test?

Answer 41

alternating stimulation of right and left eye with light