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C&M Neuroanatomy > Week 11: Visual Field Defects > Flashcards

Week 11: Visual Field Defects Flashcards

1
Q

What is vitreous humour?

A

viscous jelly like substance that lies between the lens and the retina; it keeps the eyes spherical

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2
Q

What is refraction and when does it occur?

A
  • bending of light ways
  • occurs when light passes from one transparent medium e.g air to another e.g cornea
  • light is slowed down as it moves from one media to another
  • both the cornea and the lens perform refraction
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3
Q

What does accommodation mean?

A

lens changing shape to see closer images

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4
Q

How does the lens change shape?

A

Due to contraction of ciliary muscles which relieves tension on the zonule fibres, allowing the lens to become rounder

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5
Q

What does emmetropic mean?

A
  • emmetropic eye = normal

- focuses parallel light rays on the retina without the need for accomodation

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6
Q

What is hyperopia?

A
  • far sightedness
  • when eyeball is too short
  • light rays are focused behind the retina
  • accommodation is needed for distant objects, and near objects cannot be brought into focus
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7
Q

In hyperopia, which lens do you need to correct vision?

A

convex

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8
Q

What is myopia?

A
  • nearsightedness
  • when eyeball is too long
  • light rays converge before retina
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9
Q

In myopia, which lens do you need to correct vision?

A

concave

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10
Q

How does corrective laser surgery, or photorefractive keratectomy, correct vision?

A

uses a laser to reshape the cornea and increase or decrease the amount of refraction possible

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11
Q

What is the function of the pigmented epithelium in the retina?

A
  • provides nutrients which allows photoreceptors to operate
  • contains melanin which absorbs any light not absorbed by the retina
  • improves resolution by stopping stray rays bouncing around in the eye
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12
Q

Which excitatory neurotransmitter do bipolar neurones release onto ganglion cells?

A

glutamate

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13
Q

Explain phototransduction?

A
  • conversion of light energy into electrical signals
  • in the dark photoreceptors are depolarised and continually release glutamate
  • light causes depolarising channels to close, hyperpolarising the membrane potential and reducing glutamate release
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14
Q

In rods, what are photoreceptors called?

A

rhodopsin

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15
Q

In cones, what are photoreceptors called?

A
  • one of 3 different colour sensitive opsins

- red cones longest wavelength, then green then blue

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16
Q

What is retinal?

A
  • resides inside opsin proteins
  • retinal is a form of VitA that is essential for vision
  • when retinal is hit by light, it changes shape and activates the opsin molecule
  • this allows phototransduction
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17
Q

What are the two types of retinal bipolar cells?

A
  1. ON bipolar cells depolarise in response to light

2. OFF bipolar cells hyperpolarise in response to light

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18
Q

Which receptors are expressed by ON bipolar cells?

A

mGluR6 & TRPM1

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19
Q

Which receptors are expressed by OFF bipolar cells?

A

AMPA & kainate receptors

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20
Q

What happens in the ON/OFF pathway if we have medium intensity light that suddenly gets brighter?

A
  • cone is hyperpolarised
  • on and off bipolar cells are attached to on and off ganglion cells
  • so the off pathway decrease glutamate release onto the ganglion cell to decrease firing
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21
Q

What is the receptive field?

A

the area of the retina that causes any change in response of a neurone

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22
Q

Why do we have a surrounding receptive field?

A

due to lateral inhibition:

  • comes from amacrine cells as they form inhibitory synapses with a ganglion cell
  • this allows the retina to compare different things
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23
Q

What is Young-Helmholtz Trichromatic Theory

A

“any colour can be made of red, green or blue”

  • at each point in the retina, there exists a cluster of 3 receptor types, each type being maximally sensitive to either red, green or blue
  • when all cone types are equally active, we percieve white
  • so within your eye are receptors that receive waves of light and translate them into one of three colours: blue, green, and red. These three colours can then be combined to create the entire visible spectrum of light as we see it.
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24
Q

What is colour opponency?

A
  • colour is coded with an opponent process: two “colours” are compared with one colour reducing ganglion cell activity and the other increasing it
  • this explains the colour wheel
25
Q

What are the two opponent pathways?

A
  1. Red & Green

2. Blue & yellow

26
Q

What is melanopsin and what is its function?

A
  • 5th photopigment
  • melanopsin is sensitive to light across the extent of the retina and directly activates ganglion cells
  • encodes luminance
27
Q

Where is melanopsin expressed?

A

ipRGCs

28
Q

What are ipRCGs required for?

A
  • for normal photoentrainment of the circadian clock

- pupillary light reflex

29
Q

What are the 3 layers of the lateral geniculate nucleus and what do each contain?

A
  1. Parvocellular layer 3-6 –> contains small cell bodies
  2. Magnocellular layers 1+2 –> contains large cell bodies
  3. Koniocellular layers –> in between layers with very small cell bodies
30
Q

What are the 3 types of retinal ganglion cells? (classified based on which layers they project to)

A
  1. Magnocellular (M-type)
    - larger cell type
    - 5% of population
    - large receptive field
    - important for detection of stimulus movement
  2. Parvocellular (P-type)
    - smaller cell type
    - 90% of population
    - sensitive to stimulus form and fine detail
  3. Non-M non-P (K-type)
    - medium cell type
31
Q

How is input to the LGN from two eyes kept seperate?

A

layer 6 is ipsilateral
layer 5 contralateral
layer 4 ipsilateral

32
Q

What is the LGN target?

A
  • primary visual cortex
  • also known as Brodmann’s area 17 or striate cortex
  • located in the occipital lobe either side of calcarine sulcus
33
Q

How is the primary visual cortex organised?

A
  • orientation columns
  • ocular dominance columns
  • colour processing “blobs”
  • arranged in 6 layers
34
Q

What is an orientation column?

A

column of the cortex that is connected together and all selected to the same orientation of the stimulus

35
Q

What is ocular dominance?

A

the inputs from the two eyes are largely seperate in V1

36
Q

What occurs at the ‘blobs’ in V1?

A

higher, more detailed levels of Colour opponency

colour processing

37
Q

What is meant by blurred vision?

A
  • vision is out of focus/not sharp
  • no distortion / nothing missing
  • no shadows
  • not bent
  • result of a refractive or structural problem
38
Q

What is glare?

A
  • difficulty seeing in bright light

- corneal or lens problem, often due to cataract

39
Q

Which conditions affect the retina?

A
  • wet macular degeneration
  • macular hole
  • macular pucker
  • retinal detachment
40
Q

What could things looking pale be due to?

A
  1. optic nerve diseases - optic neuritis, compressive optic nerve disease, tumours along the visual pathway
  2. conditions affecting the retina
41
Q

What is a ‘floater?

A
  • smudge/ cobweb seen in vision
  • typically moves
  • vitreous haemorrhage/ posterior vitreous detachment
42
Q

If a patient has a homonymous field defect, what is this a sign of?

A

defect of visual pathways

43
Q

If a patient has a heteronymous field defect, what is this a sign of?

A

retinal, optic nerve defect

44
Q

If you have a centre visual field defect, where is the lesion likely to be?

A

macular

45
Q

What does a cecocentral field defect mean?

A

central defect joins in with blind spot

46
Q

An arcuate visual field defect (an arc) is typical of what condition/

A

glaucoma

47
Q

What is cataracts?

A
  • opacity (cloudy) area of the lens
  • common ageing change
  • examine against red reflex or using slit lamp
48
Q

What are some symptoms of cataracts?

A
  • blurred vision
  • glare
  • change in refraction
  • faded colours
  • trouble with bright light
  • trouble seeing at night
49
Q

Explain the blood supply to a healthy retina

A
  • choroid supplies outer 2/3rds of retina, vascular supplies inner 1/3rd
  • requires diffusion from choroid
50
Q

What is the function of retinal pigment epithelium (RPE)

A
  • maintains environments of photoreceptors
  • removes waste product from cones and rods
  • reduce function leads to drusen
51
Q

What is ARMD?

A

Dry age-related macular degeneration:

build up of waste productions from rods and cones

52
Q

What is Drusen?

A

small white/yellow deposits

53
Q

What are the signs of Dry ARMD?

A
  • drusen
  • RPE pigmentation
  • RPE atrophy
  • gradual deterioration
  • particularly affects reading vision
54
Q

What does a photoextraction with lens implant entail?

A
  • cataract surgery
  • usually local anaesthetic
  • takes 10 mins
  • eye may feel swollen but not painful
  • topical steroid for 2 weeks
  • risk of vision loss (1-2%)
55
Q

What is CRAO?

A

Central retinal artery occlusion

56
Q

What are 3 potential cases of CRAO?

A
  1. Embolic e.g carotid artery disease
  2. Giant cell arteritis/ temporal arteritis
  3. Carotid artery disease
57
Q

What is metamorphosia?

A
  • liner objects look round or curved
  • symptom of distortion of the retina
  • distorted vision/ ‘change in form’
58
Q

What is Wet ARMD?

A
  • layer between choroid and RPE thins so vessel moves under retina causing exudate and bleeding
  • rapid loss of vision
59
Q

How do we treat wet ARMD?

A
  • treatment of choroidal neovascular membranes with intravitreal injection of antiVEGF
  • vascular endothelial growth factor (VEGF) stimulates growth of CNM
  • vision loss can be revered

C&M Neuroanatomy (44 decks)

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