Visual pathways (special senses)

Question 1

What makes up the eyeball?

Answer 1

• Optical front end
• Retina
• Optic disc at back

Question 2

What 3 things make up vision?

Answer 2

Eyeball, connections and brain

Question 3

What makes up the connections in vision?

Answer 3

• Optic nerve
• Chiasm
• Optic tract
• Lateral Geniculate Nucleus (LGN)
• Radiation

Question 4

What parts of the brain are used in vision?

Answer 4

• occipital
• temporal
• parietal
• frontal

Question 5

What is the optic nerve ?

Answer 5

• Collection of all the ganglion cella
• Exits the back of the eye through a hole in the sclera
• The optic nerve head can be seen at the back of the eye (aka optic disk)

Question 6

What are the different parts that you would see in a healthy eye ?

Answer 6

Optic nerve, macular, fovea

Question 7

What is wrong in this image ?

Answer 7

Swollen optic nerve = Worry increase pressure

Question 8

What is wrong in this image ?

Answer 8

Cupped optic nerve = glaucoma

Question 9

What is wrong in this image ?

Answer 9

Pale optic nerve - Nutritional deficiency

Question 10

If pupils are same size then where would the problem you are looking for be?

Answer 10

If pupils are same size problem is in the sensory afferent pathway

Question 11

If pupils are different in size then where would the problem you are looking for be?

Answer 11

motor efferent - sympathetic innervation of the pupil

Question 12

How would you test pupils ?

Answer 12

Technique for Testing Pupils;

• Measure pupil diameter in light and dark conditions
• The less reactive pupil is the abnormal pupil
• Test the direct response
• Shine the light in one eye and examine the
  response in the same eye
• Test the indirect response
• Shine the light in one eye and examine the
  response in the same eye
• Check for a relative afferent pupillary defect (RAPD)
• Shine the light on one eye for 2-3 seconds, then
  rapidly move to the fellow eye
• Normal response is either no change in size, or a
  brief constriction and returning to the same
  state (“hippus”)
• A pupil with an RAPD will paradoxically dilate
  when the light moves towards it
• Check for accommodation — alternating fixation on a distant then a near target

Question 13

What are the pathologies associated with small, asymmetrical and large pupils ?

Answer 13

Small pupils;
*Horner’s syndrome
* Uveitis
* Drugs (i.e pilocarpine)
* Neurosyphilis (ii.e Argyl Robertson0
* Long-standing Holmes-Adie pupil(s)
* Corgenital miosis or microcoria

Asymmetric pupils;
* Physiological anisocoria (20% of population)

Large pupills;
* 3rd nerve palsy
* Sphincter damage
* Drugs
* Holmes-Adie pupil(s)

Question 14

What does Glaucoma look like and how would you test for it?

Answer 14

Massive cup

RAPD - one on right would paradoxically dilate as it isn’t as good as the one on the other side

Question 15

What are the features of the Lateral Geniculate Nucleus (LGN)?

Answer 15

Lateral Geniculate Nucleus (LGN);
- First synapse after info leaves retina joins brainstem at LGN
- Big afferent centre in brain
- Has lots of layers; some take info from same side and some takes info from other side (temporal)
- Has Magnocellular (moving big info) and Parvocellular (static small info) different types of visual information

Question 16

What would the cause for a mild ptosis with a small pupil?

Answer 16

sympathetic palsy - horners

Question 17

What would the cause for a more obvious ptosis with a big pupil?

Answer 17

parasympathetic problem, if down and out 3rd nerve palsy

Question 18

What are the features of Magnocellular ganglion cells?

Answer 18

Magnocellular ganglion cells;
* Large axons — lots of myelin — respond quickly
* Receive information from large number of photoreceptors
* Movement, brightness, depth perception
* Project to parietal lobes — the ‘where’ stream

Question 19

What are the features of Parvocellular ganglion cells?

Answer 19

Parvocellular Ganglion Cells;
* Thin axons — less myelin — respond slowly
Receive information from small number of photoreceptors
* Detail of objects assisting in recognition
* Project to temporal lobes — the ‘what’ stream

Question 20

After the Lateral Geniculate Nucleus (LGN) what is the next synapse?

Answer 20

After the Lateral Geniculate Nucleus (LGN) the next synapse is the Occipital lobe

Question 21

What is the line of Gennari?

Answer 21

The line of Gennari are myelinated fibres running from LGN to synapse in layer 4 of the ‘striate’ cortex

Question 22

What is the function of Occipital Lobe in vision?

Answer 22

• Relay station
• Retinotopic map - direct physical relationship between spots on the retina and spots in the occipital lobe - so if you damage part of occipital lobe will lose certain part of vision (see image)

Neural tuning is present - specific populations of cells will respond to;
- colour
- spatial frequency
- orientation

Question 23

What is Ocular Dominance and Amblyopia ?

Answer 23

Ocular dominance occurs where one eye is stronger than the other and the poorer eye is deprived of a clear image usually due to a uncorrected refractive error or a squint (Amblyopia/’lazy eye)

We can patch the good eye to force other to develop more (can only really do when young due to plasticity as this is a critical period of visual development - do screening for this in UK)

Question 24

How can we treat Ocular dominance/amblyopia ?

Answer 24

• Patching
• Glasses
• Correct squint
• Improve input into the lazy eye

Question 25

Give a summary of where lesions in the visual tract can occur and the symptoms of them?

Answer 25

See image

Question 26

What are the different causes of a Retinal Lesion and what would this look like?

Answer 26

Retinal Lesion; - Age related Macular Degeneration (AMD) - Diabetic eye disease (missing middle of vision in these 2 - image) - Retinal detachment (everything turns upside down)

Question 27

What would a lesion of the right optic nerve cause?

Answer 27

Total blindness of the right eye

Question 28

What are the 2 types/causes of chiasmal lesion and how may vision in these eyes look?

Answer 28

Chiasmal lesions give Bitemporal Hemianopia so below have this, just different extents; Pituitary tumour; - Grows from underneath the chiasma and presses on the bottom part chiasm - because of this worse vision in upper quadrant so may only see hand movements there but in lower quadrant can see counting fingers Craniophayngioma; - Grows from above the chiasma and presses on the top part chiasm - because of this worse vision in lower quadrant so may only see hand movements there but in upper quadrant can see counting fingers

Question 29

What type of tumour is this and how may your patient present?

Answer 29

Pituitary tumour; - Grows from underneath the chiasma and presses on the bottom part chiasm giving a Bitemporal Hemianopia - Worse vision in upper quadrant so may only see hand movements there but in lower quadrant can see counting fingers

Question 30

What type of tumour is this and how may your patient present?

Answer 30

Craniophayngioma; - Grows from above the chiasma and presses on the top part chiasm causing a Bitemporal Hemianopia - Worse vision in lower quadrant so may only see hand movements there but in upper quadrant can see counting fingers

Question 31

What are the most common causes of Post Chiasmal Lesions?

Answer 31

- Stroke - Space occupying lesions (tumours and bleeds)

Question 32

What symptoms would Post Chiasmal Lesions give ?

Answer 32

Remember PIST - A lesion in the parietal lobe would give a quadrantanopia with the opposite side and inferior quadrant lesion - A lesion in the temporal lobe would give a quadrantanopia with the opposite side and superior quadrant lesion - A lesion in the occipital lobe would give you the opposite side homonymous hemianopia.

Question 33

What part of the visual system "sees"

Answer 33

The brain as it creates conscious vision

Question 34

How and where is vision made?

Answer 34

Vision is made in 2 separate functional streams that complement each other creating the overall sense of vision - The 'what' and the 'where' streams