Retina Flashcards
what does the retina fo
light sensitive tissue - lining the inner surface of the eye
conversion of light into an impulse (phototransuction)
transmits impulses to the brain (conduction)
where does light travel to once it gets to the retina
- 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
where is the inner retina located
- towards the virteous - towards the centre of the globe
where is the outer retina located
towards the sclera
what is located in your outer retina
- photoreceptors are in your outer retina
- retinal pigmented epithelium is in the outer retina
light has to pass through to reach the outer retina
what is the function of the pigmented outer layer
outer layer = a single layer of pigmented cells which absorbs light and prevents light scatter within the eye ball- (retinal pigmented epithelium)
what is the function of the inner neural layer
- 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
where does light have to pass through to reach the pigmented layer of rods and cones
- light has to pass through retinal ganglion cells to reach the pigmented layer of rods and cones to be phototransduced into a neural impulse
describe the macroscopic structure of the neural retina
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
what is the ora serrata
- 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
describe the macroscopic structure of the posterior pole
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
describe the macroscopic structure of the macula lutea
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
describe the macroscopic structure of the fovea centralis
- 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
describe the function of the optic disc
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
describe the nerve fibres anterior to the optic disc
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
describe the peripheral retina
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
describe the neural retina
neural retina is firmly attached at the ora serrata and margins of the optic disc
where does the area centralis/ posterior pole lie
area centralis / posterior pole lies between the superior and inferior temporal arteries and is cone dominated
where does the maccular lutea lie and what is it responsible for
macula lutea lies within the area centralis/posterior pole and is responsible for high acuity vision
where is the fovea located
- the fovea is a depression within the maccula containing maximal cone concentrations
what happens and the optic disc and decribe the nerve fibres anterior and posterior to the optic disc
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
where does the peripheral retina lie and what does it contain
the peripheral retina lies outside the posterior pole and it contains higher rod density
what happens in the outer layer of the retina
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
list the names of the layers of the retina
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
what are the three different cell types in the retina
- 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
where are the rods and cones situated
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
describe the structure of photoreceptors
- 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
where are opsins located
in the outersegment of photoreceptors
opsins convert light into a action potential
what does the outer nuclear layer contain
the outer nuclear layer contains the cell bodies of the rod and cone cells
what is the external limiting membrane
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)
describe the structure and fucntion of rods
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
what photopigment do the rods contain
- rods contain the photopigment - rhodopsin- rhodopsin contains retinal and scotopsin
describe the structure and function of cones
- 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
what photopigments do your cones have
you have 3 types of opsin - so we are able to appreciate colour - short wavelength (blue)
medium wavelength (green)
long wavelength (red)
what is disc shedding
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
what is phototransduction - what happens in dark conditions
- 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
in light conditions describe the process of phototransduction
- 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
describe the process of phototransduction
- 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
what is the main function of photoreceptors
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
what does the outer segment and inner segments of photoreceptors contain
the outersegments are where we have the discs and is where the phototransduction happens
the inner segment contains mitchondria
what are the functions of rods and what is their photopigment called
rods give black and white/ night vision and sense contrast - their opsin is called rhodopsin
what are the functions of cones and what are their opsins called
cones give fine resolution and colour vision - they have three opsins absorbing different wavelengths to provide a visible spectrum
where are the cell bodies of photoreceptors located
cell bodies of photoreceptors are in the outer nuclear layer
how are discs renewed
discs are constantly renewed viewing disc shedding to ensure continued unbroken vision
when does phototransduction take place
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
describe the retinal pigmented epithelium
continous monolayer of cuboidal/coloumnar epitheliel cells
basal aspect lies on bruchs membrane
apical surface associated with photoreceptor outer segments
what are the functions of the rpe
functions
physical
optical
metabolic/ biochemical
transport
when examined from aove they form a highly organised hexagonal pattern of homogenously sized cells
what is bruchs membrane
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
what are the age related changes that can happen with bruchs membrane
- age related changes in bruchs membrane lead to an accumulation of extracellular material between bruchs and rpe = drusen
describe the choroid
- 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
what is situated at the apex of the choroid
- 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
what structures lie underneath the photoreceptors
the rpe cups the outer segments
bruchs membrane lies beneath
then finally the chorioid outermost
describe the structure of the rpe
the rpe has a metabolic, optical and structural role
and forms a highly organised hexagonal pattern
describe the struture of bruchs membrane
- bruchs membrane is an acellular tissue layer comprised of 5 layers
what happens in amd
extracellular material accumulates by bruchs membrane and the retinal pigmented epithelium known as drussen
what does the chorioid provide support to
the choroid provides nutritional support for the outer 1/3 of the retina
how does the choroid provide nutritional support to the retina
provides nutritional support via the choriocappilaris - a vascular bed of cappillaries adjacent to bruchs membrane
what is the purpouse of the retina
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
what does the optic disc correspond to in terms of vision
- 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
where do the cell bodies of the photreceptors lie
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
where in the retina do you have the highest concentration of cones
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
what forms the nerve fibre layer
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
where is the inner retina and outer retina located
inner retina = towards the virteous and the outer retina is towards the sclera
what is the outer segment comprised of
- the outer segment is made up of the rpe and the photoreceptor layer
the inner segment is made up of everything else
what is the function of the external limiting membrane
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
what does the outer nucleus contain
contains the cell bodies of rods and cones
what is the outer plexiform layer
- 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
what does the inner nuclear layer contain
contains the cells bodies of bipolar, amacrine , hroizontal cells
thicker centrally due to higher density of cone connecting bipolar cells and horizontal cells
describe the different layers of the retina
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
what is the inner plexiform layer comprised of
layer of synapses (connections) between bipolar, amacrine, and retinal ganglion cells
what does the ganglion cell layer contain
contains the cell bodies of retinal ganglion cells
thickest layer of the retina
describe the ganglion cell layer
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
what are the two types of retinal ganglion cells
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
what will activate the off centre retinal ganglion cells
-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
what does the retinal nerve fibre layer contain
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
what is the internal limiting membrane comprised of
-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
what cells are involved in conduction of action potentials
neuronal cells
- bipolar cells , horizontal cells , amacrine cells and retinal ganglion cells
what do bipolar cells do
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
what are the two main types of bipolar cells
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
describe on bipolar cells
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
describe off bipolar cells
stimulated by glutamate
inhibited as glutatmate levels falls
hyperpolarised by cell
what is the difference between on and off bipolar cells
on bipolar cells are depolarised - activated by light
off bipolar cells are hyperpolarised - deactivated by light
describe ganglion cells
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
describe the ganglion cell axons
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
what are horizontal and amacrine cells
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
what are off centre and on centre ganglion cells
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
how do photoreceptors communicate with rods and cones
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
what are the supporting cells in the retina
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
what are mullers cells
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
what is the inner boundary if the retina
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 -
which of the following best describes the function of the choroid
- nutritional support of the outer retina
how does the retina recieve nutritional supply
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
which layer of the retina contains the cell bodies of the photoreceptors
- 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
where is the neural retina most firmly adherent
- 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
in phototransduction when is glutamate released
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
approxiamtley how many rod cells are their in each eye
115 million
describe photoreceptor distribution
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
the outer segment of the photoreceptor cells contain contain what
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
describe the fovea
- 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
how can you tell from the fundus weather it is a left eye or a right eye
- 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
what does the outer segment comprise
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
what are the consitiuents of the outer nuclear layer
rods and cone cell bodies
inner nuclear layer contains bipolar cell bodies
what does the ganglion cell layer contain
the ganglion cell bodies
ganglion cell axons go on to form the optic nerve
where do ganglion cells lie
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
what are muller cells
- supporting cells - they lie in the internal limiting membrane of the retina - and they provide strutural support - + support with regards to homeostasis
what does the outerplexiform layer contain
layer of neuronal synapses between photoreceptor axons and dendrites from bipolar and horizontal cells
what does the retinal nerve fibre layer contain
axons of ganglion cells
unmyelinated until you reach the optic disc
thicker adjacent to the optic disc
prone to damage from high iop
where do the axons of the retinal ganglion cells become myelinated
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
what is the papillomacular bundle
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
in glaucoma what do you have sparing of
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
how to ON bipolar cells respond to light
ON bipolar cells are activated by light - inhibited by dark conditions
and therefore respond to light by depolarisation
how to off bipolar cells respond to light
off bipolar cells are deactivated by light and therefore respond to light by hyperpolarisation
- stimulated by glutatmate which is a inhibitory nt
on centre ganglion cells fire when…..
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
how does the retina recieve its blood supply
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
describe the findings of a central retinal artery occlusion
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
what is the blood retinal barrier
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
