Retina lab Flashcards
(42 cards)
1
Q
what is parafovea ?
A
- outside the fovea
2
Q
how is the retina positioned?
A
- the retina is positioned such that at the top of the image you have choroidal vasculature and the vitreous humour at the bottom
3
Q
how does retina tissue look like in reality ?
A
- the tissue looks blue but in reality when we take histological sections of the human retina , it is transparent because it has to allow photons of light to transmit through without being reflected, we need those photons of light to reach the outer segment of photoreceptor cells where we have chromoproteins that will absorb the photons of light and turn that into electrical signal
4
Q
how does light normally impinge on the retina ?
A
through the vitreous to the area where the outer segment of photoreceptors is located
5
Q
what is structure of RPE?
A
- simple epithelium
- single monolayer of cells
- cuboidal
- apical processes
- have brown melanin granules - which absorbs photons of light that don’t get absorbed by outer segment of photoreceptors
- this prevents the photons of light interfering with vision
6
Q
what do we have on the outer surface of RPE?
A
capillaries- provide oxygen and nutrient supply to localised tissue , melanocytes and the RPE
- oxygen and nutrients can also diffuse through the RPE cells and released into the interphotoreceptor matrix - which is the space between the outer segments and then go feed the outer five layers of the retina
7
Q
what do we have between the RPE and the capillaries ?
A
bruch’s membrane
8
Q
what does the inner segment of photoreceptor contain ?
A
- rods and cones
- high density of mitochondria
- endoplasmic reticulum
- golgi apparatus
9
Q
what does the outer segment of photoreceptor contain?
A
- membranous discs which contain chromoproteins - which absorb the photons of light
10
Q
what are the dark blue dots ?
A
- nuclei of photoreceptor cells - stained with blue stains
11
Q
what is the outer nuclear layer ?
A
- contains the nuclei pf photoreceptors
12
Q
what is the outer plexiform layer ?
A
- where the processes of photoreceptors are located going up to a pedicule which is the synaptic region of cone and a spherical which is the synaptic region of rod
13
Q
what are the muller cells ?
A
- one of the main glial cells
- soma in the inner nuclear layer and sends processes which run to furthest extent of the retina
14
Q
what is the outer/external limiting membrane?
A
- where the muller cells interact directly with the photoreceptors at the external layer of the outer nuclear layer
- you get tight junctions forming between the muller cells processes and the the base of the inner segment of photoreceptor cells
- we get this membrane because we need to keep the environment of the interphotoreceptor matrix different from within the retina
- we need to control the amount of water and ions in the retina
15
Q
what is the inner nuclear layer ?
A
- muller cells
- bipolar cell - span the entire depth of the inner nuclear layer and part of the outer plexiform layer is the point at which you have synaptic connections between photoreceptor cells and bipolar cells
- amacrine cells ( 49 types)
- horizontal cells
- interplexiform neurons
16
Q
what are bipolar cells?
A
- bipolar cell - span the entire depth of the inner nuclear layer and part of the outer plexiform layer is the point at which you have synaptic connections between photoreceptor cells and bipolar cells
- send projections into the inner plexiform layer
- ## then they synapse with cells in the ganglion cell layer
17
Q
how can you tell the ganglion cell layer ?
A
- they have a larger nucleus
18
Q
what is the importance of networks being formed between cells in different retinal layer ?
A
- all the cells in different layers are interconnecting with each other - a network is formed
- as you have absorption of photons of lights in the chromoproteins in the outer segments- this induces a electrical signal to be generated and passed from photoreceptor into bipolar cell- and pass into ganglion cells
- retinal ganglion cells pass information back to the brains
19
Q
what is the function of retinal ganglion cells?
A
- retinal ganglion cells have the ability to form action potential
- action potential is sent along the axon
- axons runs up towards the inside of the eye and turn 90 deg and runs across the inner surface of the retina and projects back to the optic disc and exits the eye through optic disc into optic nerve to the chaism
20
Q
what is the nerve fibre layer ?
A
- axons of ganglion cells come together
21
Q
what is the inner limiting membrane ?
A
the junctions that form between muller cell processes on the opposite side of retina and ganglion cell
22
Q
what feeds the outer 5 layer of the retina ?
A
- the choroidal vasculature
23
Q
why doesn’t the choroidal vasculature feed the inner layers of the retina ?
A
- there is restriction on how far it can supply oxygen and nutrients due to distance
- photoreceptors use a lot of the oxygen and nutrients because photoreceptors are highly metabolically active
- a lot of the stocks are depleting by the time you get to the inner layer
24
Q
what are primary plexus ?
A
- blood vessels branches of central retinal artery and radiate throughout the retina and form capillaries
- they spread out through the retinal surface through the ganglion cell layer
25
what are deeper plexus?
deep capillary plexus was segmented between the outer of the INL and the outer plexiform layer (OPL)
26
what feeds the inner layer of retina?
primary, intermediate and outer plexus
27
what is difference between ganglion cells and blood vessels bordering either side of the inner nuclear layer ?
- ganglion cells there is no distinct plexus / layer
- blood vessels bordering either side of the inner nuclear layer they tend to run along the boundary between the nucleus layer and plexiform layers
28
what is the difference between nuclei of cones and rods ?
- rod nuclei are smaller
- cones have larger nuclei
- cone nuclei are closest to the external limiting membrane and the inner segments
29
where are the outer segments of photoreceptors ?
- outer segments of photoreceptors don't stop where they appear on the image they project all the way to the back and form interdigitations with RPE cells
- outer segment of photoreceptors interdigitating and sit in between apical processes of RPE cells
30
how does OCT work ?
- sends in a signal and detects any reflections any patterns and turns it into an image
- you shine light into the eye and look at the reflection pattern from different densities of tissue and produces an image
31
why does the nerve fibre layer change in thickness?
- much thicker on the left
- thicker on the left as there are more axons of photoreceptors
- much thicker layer of tissue
- optic nerve is on the thicker part of the nerve fibre layer
32
what is nerve fibre layer ?
- layer filled with axons of photoreceptors
33
why are some regions more light ?
- reflect more light so can be seen easier such as the external limiting membrane
34
where is a point where you get a lot of reflection ?
point where outer segment starts to interdigitate with apical processes of RPE
35
what happens to vitreous as you age
- vitreous has the main connective tissue ( jelly like)( lighter in OCT)
- as you age you get more fluid component building up at the retinal surface ( darker )
- vitreous detachment
36
what is the fovea ?
- region of central retina - in the centre of macula where there is a high concentration of cone photoreceptor cells
- cones on the fovea look more like rods - narrower in diameter
- pack more photoreceptors into a smaller space to increase the resolution of vision
- characterised by a displacement of the inner five layers of the retina laterally to create foveal dip
37
how is the foveal dip caused ?
- the foveal dip is caused by cells with soma in the inner 5 layers of the retina migrating, radially outwards during development.
- the retina originally develops as a flat sheet, then there is a signalling queue that induces migration of nuclei from GCL to INL to migrate radially
- the ONL photoreceptor nuclei migrate centrally to become more densely packed
- this forms the foveal pit
- neurons get laterally displaced
- muller cells processes also get laterally displaced
38
what is Henle's fibre layer ?
THE outer fibre layer of Henle is the foveal portion of the outer plexiform layer of the retina. This layer is composed of the elongated inner processes of the foveal cones and rods
39
why is the foveal pit formed ?
- to reduce scatter over the highest concentration of cone photoreceptor cells
- increase visual acuity within foveal
- have as clear colour vision as possible with out any scatter
- remove the need of having blood vessels coming over the fovea area
- this is why we have foveal avascular zone
40
what is another specialisation we have at the fovea ?
- presence of high concentration of macular pigments
- meso-zeaxanthin (MZ), lutein (L), and zeaxanthin (Z) are the types of macular pigment
- macular pigment is affected by diet
- macular pigment is an anti-oxident - pigment molecules can react with reactive oxygen species - to mop up free radicals and prevent damage
41
why would you want yellow pigment at the fovea?
- to prevent scatter
| - to maximise resolution
42
how would you see HFL?
- you an eccentric angle of approach
- image at the edge of the iris- you can manipulate reflection pattern to visualise these laterally oblique fibres in the HFL
