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Retina Flashcards

1
Q

what does the retina fo

A

light sensitive tissue - lining the inner surface of the eye

conversion of light into an impulse (phototransuction)

transmits impulses to the brain (conduction)

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2
Q

where does light travel to once it gets to the retina

A
  • light has to travel all the way through to reach the photoreceptors which are in the outer retina
  • and then the neural impulse has to travel all the way back through the layers to the ganglion cell layers to reach the optic nerve
  • light goes through all the layers of the retina and then the impulse goes back out
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3
Q

where is the inner retina located

A
  • towards the virteous - towards the centre of the globe
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4
Q

where is the outer retina located

A

towards the sclera

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5
Q

what is located in your outer retina

A
  • photoreceptors are in your outer retina
  • retinal pigmented epithelium is in the outer retina

light has to pass through to reach the outer retina

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6
Q

what is the function of the pigmented outer layer

A

outer layer = a single layer of pigmented cells which absorbs light and prevents light scatter within the eye ball- (retinal pigmented epithelium)

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7
Q

what is the function of the inner neural layer

A
  • contains photoreceptors
  • rods and cones

and neural cells

posteriolly located - optic retina - anterioly the pigmented layer continues but not the neural layer non - visual retina

light has to pass through the ganglion cells to reach pigmented layer and rods and cones

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8
Q

where does light have to pass through to reach the pigmented layer of rods and cones

A
  • light has to pass through retinal ganglion cells to reach the pigmented layer of rods and cones to be phototransduced into a neural impulse
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9
Q

describe the macroscopic structure of the neural retina

A

neural retina is attached at the

ora serrata

margins of the optic nerve head

bound externally by bruchs membrane and internally by the virteous

continues with the optic nerve posterioly (exit site of ganglion cell axons from the eye)

thickness varies from 0.56mm near the optic disc to 0.1mm in the ora serrata

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10
Q

what is the ora serrata

A
  • the ora serrata is a serrated junction between the retina and the pars plana of the cillary body

transition from simple non receptive tissue to multilayered photosensitive tissue

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11
Q

describe the macroscopic structure of the posterior pole

A

where most of our central vision happens

  • ‘’area centralis’’

between superior and inferior arteries

cone dominated

it is subdivided into the macula, fovea and foveola

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12
Q

describe the macroscopic structure of the macula lutea

A

5.5mm diametre area

3mm lateral to the optic disc

surrounds the fovea (an area within the macula which has high acuity vision)- and a higher cone density

lutea = yellow from yellow xanthophyll cartotenoid pigments in cone axons

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13
Q

describe the macroscopic structure of the fovea centralis

A
  • 1.55 diameter zone in the maccula
  • depression surrounded by slightly thickened margins

area of finest detail vision

  • no blood vessles - avascular - if light has to reach down towards the outer layer (photoreceptors) then you dont want blood vessles blocking the light
  • maximal conc of cones
  • no rods
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14
Q

describe the function of the optic disc

A

this is where all of our axons leave the eye

  • because of that their is no photoreceptors - and it therefore forms a blind spot in our vision

the optic disc = 20 degrees from the fovea - and that corresponds with a blind spot that = 20 degrees from our blind spot of our centre of vision

  • 1.55mm and 3mm medial to the fovea

central retinal artery and vein enter and leave the eye

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15
Q

describe the nerve fibres anterior to the optic disc

A

the nerve fibres anterior to the optic disc (within the eye) are non myelinated

the nerve fibres posterior to the optic disc - are myelinated (the ones that go to the brain)

forms an anatomical boundary between the myelinated and unmyelinated axons

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16
Q

describe the peripheral retina

A

remainder of the retina outside the posterior pole

rich in rods fewer cones - wheras at the fovea you have a high concentration of cones - optic disc has no rods or cones

only one layer of ganglion cell bodies

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17
Q

describe the neural retina

A

neural retina is firmly attached at the ora serrata and margins of the optic disc

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18
Q

where does the area centralis/ posterior pole lie

A

area centralis / posterior pole lies between the superior and inferior temporal arteries and is cone dominated

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19
Q

where does the maccular lutea lie and what is it responsible for

A

macula lutea lies within the area centralis/posterior pole and is responsible for high acuity vision

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20
Q

where is the fovea located

A
  • the fovea is a depression within the maccula containing maximal cone concentrations
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21
Q

what happens and the optic disc and decribe the nerve fibres anterior and posterior to the optic disc

A

optic disc is where the retinal ganglion cell axons leave the retina and therefore is a blind spot

anterior to the nerve fibres = non myleinated and posterior to the nerve fibres = myelinated

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22
Q

where does the peripheral retina lie and what does it contain

A

the peripheral retina lies outside the posterior pole and it contains higher rod density

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23
Q

what happens in the outer layer of the retina

A

phototransduction - the conversion of light to neural impulses

  • light comes down to the photoreceptors - you have the retinal pigmented epithelium which prevents light scatter - the rods and cones which are photoreceptors convert light into a neural impulse - they synapse in the outer plexiform layer with the bipolar cells and the ganglion cells where they synapse - and then the ganglion cell axons travel continously with the optic nerve where it is sent back to the brain for processing and analysis
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24
Q

list the names of the layers of the retina

A 
inner limiting membrane 
nerve fibre layer 
ganglion cell layer 
inner plexiform layer 
inner nuclear layer 
outer plexiform layer 
outer nuclear layer 
external limiting membrane 
photoreceptor layer 
retinal pigmented epithelium
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25
Q

what are the three different cell types in the retina

A
  • photoreceptors - rods and cones

(responsible for transduction)

neuronal cells

biopolar

horizontal

amacrine

retinal ganglion cells

responsible for conduction

gial cells - mullers cells, astrocytes - responsible for support

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26
Q

where are the rods and cones situated

A

rods and cones are situated on the outer retina in the retinal pigmented epithelium

  • specalised neurons which convert light into neural impulses (phototransduction) - comversion of light into a nerual impulse
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27
Q

describe the structure of photoreceptors

A
  • inner and outer segment seperated from the cell body by the external limiting membrane

inner segment has lots of mitchondria

  • the outer segment- contains photopigments - opsins - responsible for phototransduction - (where light gets turned into a nerual impulse)

axons pass into the outer plexiform layer where they synapse with bipolar and horizontal cells

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28
Q

where are opsins located

A

in the outersegment of photoreceptors

opsins convert light into a action potential

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29
Q

what does the outer nuclear layer contain

A

the outer nuclear layer contains the cell bodies of the rod and cone cells

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30
Q

what is the external limiting membrane

A

situated at between the photoreceptors and the cell bodies of the rods and cones (outer nuclear layer)

  • provides mechanical support to the retina
  • made up primarily of mullers cells (retinal glial cells)
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31
Q

describe the structure and fucntion of rods

A

115 million in each eye

100- 120um long

black and white vision (sense contrast, brightness and motion)

max spectral sensitivity = 496nm (referring to wavelengths of light

photopigment = rhodopsin

you have a lot more of them because the peripheral retina -which is a lot more of your eye - contains a higher density of rods and cones

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32
Q

what photopigment do the rods contain

A
  • rods contain the photopigment - rhodopsin- rhodopsin contains retinal and scotopsin
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33
Q

describe the structure and function of cones

A
  • 6.5 million ( you have fewer cones than rods but they are more important than rods)
  • 60- 75 micrometres long

fine resolution , spatial resolution and colour vision -

their density is highest in the centre of our vision

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34
Q

what photopigments do your cones have

A

you have 3 types of opsin - so we are able to appreciate colour - short wavelength (blue)

medium wavelength (green)

long wavelength (red)

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35
Q

what is disc shedding

A

discs are in the outer segements of photoreceptors and they contain all the opsins

recycling of photopigment occurs in the rpe and takes picoseconds

discs are constantly made and broken down

shed at once in the early morning

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36
Q

what is phototransduction - what happens in dark conditions

A
  • the conversion of light into a action potential

in dark conditions - their is no light hitting your photoreceptors

relatively depolarised

in their depolarised state they release glutamate which is inhibitory neurotransmitter

in the dark you dont want photoreceptors to be firing of signals so you release an inhibitory neurotransmitter

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37
Q

in light conditions describe the process of phototransduction

A
  • you have a cascade that is initiated by a photon in the photopigment in the rods this would be (rhodopsin) this hyperpolarises the photoreceptor

stops the release of glutatmate- and therefore that generates an impulse

it is a graded response- greater light intensity (more photons) arriving in your photoreceptor results in a greater reduction in neurotransmitter release and therefore a larger impulse

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38
Q

describe the process of phototransduction

A
  • phototranduxtion = a process that occurs in the retina where light is converted into electrical impulses that can be understood by the nervous system
  • primarily takes place in photoreceptor cells where their are two types - rods and cones

phototransduction in rods - positively charged sodium ions flow into rod cells - causes cells to be in a depolarised state leading to the continous release of the neurotransmitter glutamate - inside the rod cell their is a substance called rodopsin which is made up from opsin and retinal

  • when their is a light stimulus present gultamate release is inhibited
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39
Q

what is the main function of photoreceptors

A

photoreceptors convert light into neural impulses via phototransduction - they are formed of an axon seperated form the inner and outer segment of the external limiting membrane

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40
Q

what does the outer segment and inner segments of photoreceptors contain

A

the outersegments are where we have the discs and is where the phototransduction happens

the inner segment contains mitchondria

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41
Q

what are the functions of rods and what is their photopigment called

A

rods give black and white/ night vision and sense contrast - their opsin is called rhodopsin

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42
Q

what are the functions of cones and what are their opsins called

A

cones give fine resolution and colour vision - they have three opsins absorbing different wavelengths to provide a visible spectrum

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43
Q

where are the cell bodies of photoreceptors located

A

cell bodies of photoreceptors are in the outer nuclear layer

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44
Q

how are discs renewed

A

discs are constantly renewed viewing disc shedding to ensure continued unbroken vision

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45
Q

when does phototransduction take place

A

phototransudction takes place when opsins absorb a photon causing a cascade resulting in hyperpolarisation of the cell and cessation of glutamate release which is a inhibitory neurotransmitter

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46
Q

describe the retinal pigmented epithelium

A

continous monolayer of cuboidal/coloumnar epitheliel cells

basal aspect lies on bruchs membrane

apical surface associated with photoreceptor outer segments

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47
Q

what are the functions of the rpe

A

functions

physical

optical

metabolic/ biochemical

transport

when examined from aove they form a highly organised hexagonal pattern of homogenously sized cells

48
Q

what is bruchs membrane

A

connective tissue layer

2-4 micrometres thick

acellular

has 5 layers

basement membrane of rpe
inner collagenous zone

middle elastic layer
outer collagenous zone

basement membrane of the endotheliel cells of the choriocappilaris

outer collagenous zone

basement membrane of the endotheliel cells of the choriocapillaris

49
Q

what are the age related changes that can happen with bruchs membrane

A
  • age related changes in bruchs membrane lead to an accumulation of extracellular material between bruchs and rpe = drusen
50
Q

describe the choroid

A
  • posterior portion of the middle vascular layer (uvea)

provides nutritonal support for the outer 1/3 of the retina , especially photoreceptors

absorbtion of light by the choroidal pigment

51
Q

what is situated at the apex of the choroid

A
  • layer of capillaries immeaditley under bruchs membrane

more of a preforated vascular net than a network of capillaries

provides rpe and photoreceptor nourishment and remove their metabolic waste

52
Q

what structures lie underneath the photoreceptors

A

the rpe cups the outer segments
bruchs membrane lies beneath

then finally the chorioid outermost

53
Q

describe the structure of the rpe

A

the rpe has a metabolic, optical and structural role

and forms a highly organised hexagonal pattern

54
Q

describe the struture of bruchs membrane

A
  • bruchs membrane is an acellular tissue layer comprised of 5 layers
55
Q

what happens in amd

A

extracellular material accumulates by bruchs membrane and the retinal pigmented epithelium known as drussen

56
Q

what does the chorioid provide support to

A

the choroid provides nutritional support for the outer 1/3 of the retina

57
Q

how does the choroid provide nutritional support to the retina

A

provides nutritional support via the choriocappilaris - a vascular bed of cappillaries adjacent to bruchs membrane

58
Q

what is the purpouse of the retina

A

to convert light into an electrical impulse - also called phototransduction- action potentials are sent down the ganglion cell axons which travel down the optic nerve and they go to your brain via your visual pathway

transmiting impulses to the brain = conduction

59
Q

what does the optic disc correspond to in terms of vision

A
  • blind spot - their is no photoreceptors or neuronal cells here

in conditions such as idiopthathic intracranial hypertension - you can have a enlargement of the optic disc and therefore an enlargement of the blind spot

60
Q

where do the cell bodies of the photreceptors lie

A

the cell bodies of the photoreceptors lie in the outernuclear layer

the photoreceptors lie in the photoreceptor area

the rpe lies just before the choroid starts - the main function of the rpe is to support the retina - it is able to stop the scattering of light and provide a sharp focused image

61
Q

where in the retina do you have the highest concentration of cones

A

the fovea- in the fovea you have no rods at all it is only cones

3 types of cones , red , blue and green - allow you to percieve colour

62
Q

what forms the nerve fibre layer

A

the axons of the ganglion cell layer form the nerve fibre layer

and it is these fibres that then go back towards the optic nerve

63
Q

where is the inner retina and outer retina located

A

inner retina = towards the virteous and the outer retina is towards the sclera

64
Q

what is the outer segment comprised of

A
  • the outer segment is made up of the rpe and the photoreceptor layer

the inner segment is made up of everything else

65
Q

what is the function of the external limiting membrane

A

situated at the junction between photoreceptors and cell bodies of rods and cones (outer nuclear layer)

provides mechanical support to the retina

made up primarily of mullers cells (retinal glial cells) - glial cells are supporting cells in your cns

66
Q

what does the outer nucleus contain

A

contains the cell bodies of rods and cones

67
Q

what is the outer plexiform layer

A
  • no cells - only made up of connections between photoreceptors and bipolar cells and horiaontal cells

layer of neuronal synapses between photoreceptor axons and dendrite from bipolar and horizontal cells

68
Q

what does the inner nuclear layer contain

A

contains the cells bodies of bipolar, amacrine , hroizontal cells

thicker centrally due to higher density of cone connecting bipolar cells and horizontal cells

69
Q

describe the different layers of the retina

A

the nerve fibre layer lies at the top and contains the ganglion cell axons

it sends off its axons which eventually go off towards the optic nerve

inner plexiform layer - contains connections between bipolar cells and ganglion cells - once the ganglion cells have recieved this imformation they will transmit it towards the nerve fibre layer which is where their axons lie and the nerve fibre layer then goes on towards the optic nerve

inner nuclear layer- cell bodies for bipolar cells

photoreceptors detect light and they communicate with bipolar cells and that happens at the level of the outer plexiform layer

external limiting membrane - provides support to the retina - contains mullers cells which are involved in homeostasis

retinal pigmented epithelium lies at the bottom - behind rpe you have the choroid which has a seperate blood supply

choroid is a part of the uveal tract

and everything above that= neurosensory retina

inbetween that you have subretinal space

70
Q

what is the inner plexiform layer comprised of

A

layer of synapses (connections) between bipolar, amacrine, and retinal ganglion cells

71
Q

what does the ganglion cell layer contain

A

contains the cell bodies of retinal ganglion cells

thickest layer of the retina

72
Q

describe the ganglion cell layer

A

their is about 1.2 million ganglion cell bodies - because their are much less ganglion cell bodies compared to the number of photoreceptors in the eye

a single ganglion cell serves several receptors

ganglion cell receptive field - ganglion cell recieves light imformation from photoreceptor layer

your ganglion cells can recieve photoreceptors from the came receptive field

73
Q

what are the two types of retinal ganglion cells

A

on centre and off centre retinal ganglion cells

some of them work better if the light is hitting the centre of the receptive field and that is when they are activated

whereas some are inactivacted if the light is at the centre

74
Q

what will activate the off centre retinal ganglion cells

A

-light hitting the periphery of the receptive field will activate the off centre ganglion cells

because you have overlap of receptive fields and different types of retinal ganglion cellls this allows you to detect different shades of light - the light is detected differently by different ganglion cells

75
Q

what does the retinal nerve fibre layer contain

A

axons of ganglion cells

unmyelinated - if it was myelinated it would not help with the transparency- until reach the optic disc

thicker adjacent to the optic disc

prone to damage from high iop

76
Q

what is the internal limiting membrane comprised of

A

-the internal limiting membrane -

formed primarily of astrocytes and the flootplates of mullers cells

boundary between the retina and the virteous

role in retinal development

function in adults is poorly understood

77
Q

what cells are involved in conduction of action potentials

A

neuronal cells

  • bipolar cells , horizontal cells , amacrine cells and retinal ganglion cells
78
Q

what do bipolar cells do

A

connect photoreceptors to ganglion cells

cell bodies lie in the inner nuclear layer

orientated perpendicular to the retinal surface

one or more dendrites ( synapses in outerplexiform layer) and on axon synapses in the inner plexiform layer

synapses with either the rod or cone

may transmit photoreceptor signal either directly or indirectly (via amacrine cells)

recieves imformation from one or many photoreceptors

79
Q

what are the two main types of bipolar cells

A

cone bipolar cells - diffuse bipolar cells may synapse with up to 20 cones (exist in peripheral retina)

midget bipolar cells synapse with a single cone (in the fovea)

rod bipolar cells do not synapse directly with ganglion cells but via amacrine cells

80
Q

describe on bipolar cells

A

depolarised by light
inhibited in dark conditions (by the presence of glutamate) - glutamate = a inhibitory neurotransmitter - in dark conditions you have the presence of glutatmate - and therefore action potentials are not triggered

when glutatmate levels fall (in the presence of light) lose inhibitions

depolarised by light

depolarisation - going towards the action potential threshold- you need to reach a certain threshold for the action potential to be triggered - in depolarisation it is going towards that- meaning when light hits the on bipolar cells - it is getting more and more activated and eventually you have a trigger of an action potential - which goes to your ganglion cells which tells your brain you are in light conditions

81
Q

describe off bipolar cells

A

stimulated by glutamate

inhibited as glutatmate levels falls

hyperpolarised by cell

82
Q

what is the difference between on and off bipolar cells

A

on bipolar cells are depolarised - activated by light

off bipolar cells are hyperpolarised - deactivated by light

83
Q

describe ganglion cells

A

they are multipolar cells (one axon/ multiple dendrites)

ganglion cell axons form the retinal nerve fibre layer

80% are midget cells ( project to parvocellular layers of the LGN - high acuity - low contrast

increased layers from periphery (1 layer) to macula (10 layers)

absent at fovea - in embryology ganglion cell layer moves away from the fovea during devlopment - when your born you still have some ganglion cells covering your fovea - and this is why babies have poor va - because fovea is not fully developed yet- as they grow older ganglion cells move away from the fovea to leave only a layer of cone photoreceptors- in a fully devloped retina you dont have any ganglion cells at the level of the fovea

84
Q

describe the ganglion cell axons

A

axons are unmyelinated until they pass through the lamina cribosa beyond which point they become myelinated by oligodendrocytes

axons give rise to the optic nerve

lamina cribosa in a mesh like layer that functions as a opening in the sclera

in glaucoma this is the area where you have the most damage to the ganglion cell axons - this is where if you have an high iop where the damage happens

85
Q

what are horizontal and amacrine cells

A

horizontal cells introduce lateral inhibition to the bipolar cell dendrites

amacrine cells lateral inhibiton to the bipolar cell axon terminal

important and complex neuromodulatory functions

facilitate centre -surround inhibition of the retinal receptive fields

facilitate high singal noise ration

86
Q

what are off centre and on centre ganglion cells

A

on centre - fire when the light hits the centre of the receptive field

off centre - fire when light hits surround receptive field

allows you to detect contrast and motion

87
Q

how do photoreceptors communicate with rods and cones

A

light hits the retina and is picked up by photoreceptors

(rods and cones)

which communicate with bipolar cells

bipolar cells can be ON or OF depending on their response to glutamate

bipolar cells communicate with ganglion cells via horizontal amacrine cells which are responsible for neuromodulation and give rise to centre - surround inhibition of receptive fields

88
Q

what are the supporting cells in the retina

A

distributed throghout axons of cells in the retina and optic nerve

mullers cells, astrocytes and microglial cells

maintain homeostasis , produce myelin and protect and support neurons

89
Q

what are mullers cells

A

principle retinal glial cells

cell bodies sit in the inner nuclear layer

project thick and think processes both inward and outward

these processes are tangled up with cell bodies in nuclear layers and bundles of neural processes in plexiform layers

projections continue to form internal and external limiting membranes

90
Q

what is the inner boundary if the retina

A

virteous

  • inner retina - towards the virteous - towards the middle of the globe - what lies on the inner surface and that is the virteous

outer retina - towards the sclera -

91
Q

which of the following best describes the function of the choroid

A
  • nutritional support of the outer retina
92
Q

how does the retina recieve nutritional supply

A

central retinal artery and vein - supplies the inner retina - supplies from the outer plexiform layer inward

choroid- supplies the outer 1/3 - supplies the retinal pigmented epithelium and the outer nuclear layer

93
Q

which layer of the retina contains the cell bodies of the photoreceptors

A
  • outer nuclear layer - the photoreceptors cover from the outerplexiform layer where they synapse with the bipolar and amacrine cells down to the pigment epithelium which cups the outer segments of them
  • nuclear layers - nuclei are connections of the cell bodies -there are 2 nuclear layers in the retina - a inner nuclear layer and a outer nuclear layer -

inner nuclear layer contains the cell bodies of the bipolar cells

94
Q

where is the neural retina most firmly adherent

A
  • the neural retina is most firmly adherent in the ora serrata and the optic disc margin

the ora serrata is the anterior boundary of the neural retina and is most firmly adherent there - it is also thinnest at the ora serrata
and thickest at the optic disc margin

95
Q

in phototransduction when is glutamate released

A

glutamate is released in dark conditions- glutamate = a inhibitory neurotransmitter

  • in dark conditions you have constant release of glutamate
  • glutatmate is a inhibitory neurotransmitter

under dark conditions you have continous release of the inhibitory neurotransmitter glutamate meaning no signal is sent in the photoreceptors

in your rods you have a opsin called rhodopsin - when light hits your rod - it causes a cascade- activates an enzyme which keeps sodium channels closed and it then becomes relatively hyperpolarised

that hyperpolarsiation inhibits glutamate release- and because glutamate is a inhibitory neurotransmitter on photoreceptors you get generation of an impulse

96
Q

approxiamtley how many rod cells are their in each eye

A

115 million

97
Q

describe photoreceptor distribution

A

there are more rods in your eyes than cones

115 million rods and 6.5 million cones

you have a high cone density in your maccula and fovea but everywhere else in your eye you have a much higher rod density

most of the peripheral retina is full of rods wheras only the central retina has cones it it 6.5 million cones

98
Q

the outer segment of the photoreceptor cells contain contain what

A

discs

photoreceptors have a inner and outer segment

  • the inner and outer segments are sepertated from the axons and nuclei by the external limiting membrane

outersegments are closer to the choroid and bruchs membrane- the rpe cups the outer segments

outersegment contains discs and opsins which are responsible for phototransduction

the inner segments have mitchondria

99
Q

describe the fovea

A
  • it is temporal to the optic disc

fovea = thin - you have the foveal depression- to allow as much light to come through as possible- fovea structure - slightly depressed area with slightly raised area

avacular part of retina

has a high conc of cones

rods are more is the peripheral retina - dark low acuity vision

20 degrees from the fovea = optic disc which has neither rods or cones- at your fovea you have a spike in cone photoreceptors because it is the area of vision where you want high acuity colour vision - the rest of the retina has more rods in it

100
Q

how can you tell from the fundus weather it is a left eye or a right eye

A
  • the optic nerve inserts nasally to the fovea
  • if the optic disc is on the right hand side of the image then it is the patients right eye
  • the fovea is temporal to the optic disc
101
Q

what does the outer segment comprise

A

the outer segment comprises the photosegment layer and the rpe - everything else is a part of the inner segment of the retina

the outer segment is always towards the sclera - the inner part is towards the virteous

102
Q

what are the consitiuents of the outer nuclear layer

A

rods and cone cell bodies

inner nuclear layer contains bipolar cell bodies

103
Q

what does the ganglion cell layer contain

A

the ganglion cell bodies

ganglion cell axons go on to form the optic nerve

104
Q

where do ganglion cells lie

A

in the nerve fibre layer - we look at this with patients who have glaucoma - becuase of the high blood pressure in the eye - you end up with reduced blood flow and ischameic action to the ganglion cell axons as the ganglion cell axons die you have a thinning of the nerve fibre layer

105
Q

what are muller cells

A
    • supporting cells - they lie in the internal limiting membrane of the retina - and they provide strutural support - + support with regards to homeostasis
106
Q

what does the outerplexiform layer contain

A

layer of neuronal synapses between photoreceptor axons and dendrites from bipolar and horizontal cells

107
Q

what does the retinal nerve fibre layer contain

A

axons of ganglion cells

unmyelinated until you reach the optic disc

thicker adjacent to the optic disc

prone to damage from high iop

108
Q

where do the axons of the retinal ganglion cells become myelinated

A

the lamina cribriosa - mesh like structure in the sclera where your ganglion cell axons pass through and it is beyond this point that they become myelinated and form the optic nerve - which is myelinated for fast conduction - oligodendrocytes myleinated them

109
Q

what is the papillomacular bundle

A

the ganglion cell axons

from the fovea to the optic disc the axons travel in a straight line

because the fovea is responsible for high acuity vision they have a direct route to the optic nerve

the peripheral fibres loop around the retinal ganglion cell axons - it is important in the consideration of glaucoma patients - and go to the outer regions of the optic disc

the optic cup has no nerve axons

in glaucoma the pressure affects the outer optic disc first- central fibres tend to be more protected - this is why glaucoma patients lose their peirpheral vision first- only after a long time they begin to lose their central vision

in glaucoma as more of the ganglion cell axons die- their is more empty space - and the empty space we see is the optic cup- this is why in glaucoma you have a bigger cup- as more ganglion cell axons die you have a emptier optic nerve and disc and the empty space which is the optic cup grows

110
Q

in glaucoma what do you have sparing of

A

the papillomacular bundle- is relatively protected until late on - the fibres on the outer bit are affected - if you have fibres which are dead - the peirpheral retina is still working but the retinal ganglion axons are dead and therefore the retina is unable to communicate its imformation to the brain - and you have visual field loss in the peripheral part of your retina

111
Q

how to ON bipolar cells respond to light

A

ON bipolar cells are activated by light - inhibited by dark conditions

and therefore respond to light by depolarisation

112
Q

how to off bipolar cells respond to light

A

off bipolar cells are deactivated by light and therefore respond to light by hyperpolarisation

  • stimulated by glutatmate which is a inhibitory nt
113
Q

on centre ganglion cells fire when…..

A

light hits the centre of the receptive fields they become inhibited if their is light hitting the periphery of the receptive field - they dont fire action potentials

off fire when the light hits and surrounds the receptive field

important to allow you to detect contrast, motion - this is one of the ways the eye is adapted to see motion and to better to see contrast to better see when one object starts and another finishes

114
Q

how does the retina recieve its blood supply

A

dual circulation

choroid supplies the rpe , photoreceptors , and outer nuclear layer

central retinal artery supplies from the outer plexiform layer inward

neither system is sufficent alone - damage to either system comprimises the retina

115
Q

describe the findings of a central retinal artery occlusion

A

attenuated blood vessels

cherry red spot

pale retina

when you have a crao you lose the blood supply to the rest of the retina but the choroidal circulation still works

at the fovea you are still able to see the underlying circulation - which is why you ahve a red spot

116
Q

what is the blood retinal barrier

A

prevents large toxic molecules damaging neural tissues (like blood - brain barrier)

tight junctions between non fenestrated retinal capillary endotheliel cells prevert passage of large molecules in the inner retina

tight junctions between rpe cells prevent passage of large molecules from the choroidal circulation

... (14 decks)

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