POSTERIOR SEGMENT - Neurosensory Retina Flashcards
What is the structure of rod cones from RPE to vitreous?
Outer segment (transductive) –> inner segment (region for maintenance of cellular homeostasis) –> nuclear region (outer nuclear layers) –> transmissive region (outer plexiform/synaptic layer)
Which types of cells are present in the inner nuclear layer? (3)
(1) bipolar neurons
(2) horizontal cells
(3) amacrine cells
What is the difference between the outer segments of rods and cones ? (2)
RODS: cylindrical and contain rhodopsin pigment, made up of vitamin A (night blindness)
CONES: conical and contain iodopsin pigment (colour blindness)
What is the difference in numbers between rods and cones?
rods: 120 million
cones: 5 million
what is the maximum spectral sensitivity of the rod cells?
496nm
What are the main differences between rods and cones? (4)
- Rod discs are enclosed with a cell membrane
- Rod concentration higher in periphery
- Ratio of rod:cone is 20:1
- Peak sensitivity of rods is 496nm, cones is 420 (S), 530 (M) and 560 (L)
What is the most common location for midget ganglion cells and midget bipolar cells?
What is their synapse ratio with cones?
Where do they project to?
Fovea.
1:1 ratio with cones to allow high resolution of the fovea region.
project to the parvocelllular layers of the LGN (P cells)
Which cell is responsible for retinal scar tissue formation?
Astrocytes.
What is the function of muller cells?
the main glial cells of the retina which support in architectural and metabolic functions of the retina.
They contribute to the blood retinal barrier.
What is the structure of astrocytes?
What is the function of astrocytes?
Honeycomb/pattern formation cells peripendicular to the muller cells
Responsible for laying down scar tissue in injured or diseased retina
What is the structure and function of microglia cells?
highly specialised mononuclear phagocytic cells and are first line of defence against pathogen invasion.
What is the maximal spectral sensitivity of the rod?
496nm (blue-green light)
Where is the superficial capillary plexus of the retina located in?
the nerve fiber and ganglion cell layers, at the same level as the arterioles and major venules
Where is the deep capillary plexus of the retina located in?
between the inner nuclear layer and the outer plexiform layer.
Where is the avascular outer retina located in?
the FAZ - comprises the outer nuclear layer and photoreceptors
Where is the choriocapillaris layer located?
About 30um below the RPE/Bruch’s membrane
The retinal capillaries are surrounded by which type of cells? (3)
- Astrocyte foot processes
- Pericytes (contractile)
- Thick basal lamina
What is the flow rate of the retinal vessels? What layers do they supply?
High oxygen exchange, low flow (25mm/s)
- Nerve Fibre Layer
- Ganglion Cell Layer
- Inner Plexiform Layer
- Inner third of inner nuclear layer
What is the flow rate of the choroidal vessels? What layers do they supply?
Low oxygen exchange, high flow rate (150mm/s)
1. Outer 2/3rds of inner nuclear layer
2. Outer plexiform layer
3. Outer nuclear Layer
4. Photoreceptors
5. RPE
What is present in the photoreceptor layer of the retina?
Only OUTER SEGMENTS and INNER SEGMENTS (mitochondria) of rods and cones.
What is the outer/external limiting membrane?
Formed by Muller cells and serpates the inner and outer segments of the photoreceptors from their cell bodies.
This Bisects area of rods/cones at the level of the nucleus
What is present in the outer nuclear layer?
Nuclei of the rods and cones (photoreceptor cell bodies)
What is the outer plexiform layer? What is its main function?
Synapses / axons / dendrites between rods/cones and bipolar cells and horizontal cells
Watershed zone between outer third of neural retina (photoreceptor) supplied by choroid and inner 2/3rds supplied by the central retinal artery
Contains the deep capillary plexus, most common site for fluid accumulation in CMO.
Whatis contained within the inner nuclear layer?
Nuclei of the bipolar cells, horizontal cells, amacrine and muller cells
What is contained within the inner plexiform layer?
Synapses / axons / dendrites between the bipolar neurons and the ganglion cells
Serves the junction of the intermediate vascular plexus
What is contained in the ganglion cell layer?
The nuclei of the ganglion cells
What is contained in the nerve fibre layer?
Processes of the ganglion cells which head towards the optic nerve. Contains the superficial vascular plexus
What is the inner limiting membrane?
Formed by the foot processes of the Muller cells
Describe the structure and location of the macula - how long is it?
Yellowish oval shape, 3mm lateral and slightly inferior to optic disc. It is 4.5mm in diameter.
Why is the macula yellow?
- Lutein - retina
- Zeaxanthin - fovea (cones > rods)
Both are xanthophyll compounds in retinal layers
What is the diameter of the macula?
What is the diameter of the fovea?
What is the diameter of the FAZ?
Macula: 4.5mm
Fovea: 1.5mm
FAZ: 300 microns.
In which layer are flame haemorrhages found?
Nerve Fibre Layer - shape and direction of flame is due to direction and passage of nerve fibres
In which layer are hard exudates found in the retina?
Outer plexiform layer / outer nuclear layer
What do hard exudates contain histologically?
Eosinophilic masses with contain foamy macrophages with lipid in the cytoplasm
What is the most common location for retinal dialysis?
Inferotemporal
What are the most common histopathological features of lattice retinal degeneration? (5)
- Liquefied vitreous overlying degeneration
- Vitreo-retinal adherence at margin of lesion
- Sclerosis of retinal vessels
- Retinal atrophy
- Discontinuity of internal limiting membrane
What is a hard exudate? Where is it located?
Lipoprotein leakage from blood vessels into retinal resulting in thickening of macula–> in the outer plexiform layer
Form a yellow waxy appearance with well-defined margins
What is a subretinal exudate? Which disease?
Exudation in subretinal space
Coat’s disease
VHL (Retinal capillary haemangioma)
What are cotton wool spots (soft exudates)?
Elevated white cloud-like lesions with fimbriated borders
Typically resolve in 6-12 weeks.
What is the mechanism behind cotton wool spots?
obstruction of retinal arteriole with resultant ischaemia.
Focal hypoxia cause blockage of axoplasmic flow within nerve fibre layer with subsequent deposition of intra-axonal organelles –> CYTOID BODIES.
- Ischaemia
- Embolic
What are the conditions associated with cotton wool spots?
- Ischaemia (RVO, ocular ischaemic syndrome)
- Embolus (valve emboli, dep venous emboli, blood cell emboli (Purtcher’s retinopathy)
- Infectious (HIV, cat-scratch fever (Bartonella), toxoplasmosis)
- Neoplastic (lymphoma, leukaemia, Hodgkins)
- Immune-mediated (SLE, sarcoid, GCA, polyarteririts nodosa, dermatomyositis, cryoglobulinaemia)
- Blood diseases (aplastic anaemia, pernicious anaemia, multiple myeloma, waldenstrom macroglobulinaemia, factor V leiden etc)
What is the process of lactate shuttling?
Lactate produced by Muller cells is metabolised by photoreceptors. Photoreceptors in exchange release glutamate which Muller cells metabolise
What is the visual field angle of the fovea?
What is the visual field angle of the macula?
Fovea: 1 degrees
Macula: 5 degrees
How many ganglion cells are there in humans?
1 million.
True or false?
There are no ganglion cell axons at the fovea.
True.
There is no retinal nerve fibre layer as inner retina and ganglion cell fibres are pushed away to the foveal slope
Which layer is acute CMO seen?Which layer is chronic CMO seen? What is the pathology of CMO?
Pathology: Muller cell necrosis and cystic fluid spaces
Acute: Outer nuclear layer/outer plexiform layer
Chronic: Large cystic spaces extending to GCL.
Which layer are cotton wool spots seen?
RNFL
Which retinal layer are microaneurysms seen?
Inner plexiform/inner nuclear layer (IPL/INL)
Following laser treatment, what layer is hyperreflective on OCT?
What layer is implicated long-term following laser treatment?
Acute stage: hyper-reflectivity of ONL
Long term: RPE loss.
What wavelength of light is used for Argon laser?
Green.
What happens to the centre and periphery of a treated retina area of Argon laser?
Centre: hypopigmented/pale due to glial scar tissue
Periphery: hyperpigmented due to RPE proliferation
Are rods or cones faster at completing dark adaptation?
Cones are faster.
Regarding retinal vascularisation, do the blood vessels form from the arterial side of capillary bed or venous side?
Venous side - increased hypoxic state on this side as there is lower flow.
What factors inhibit myelination of human retina?
- Lamina Cribrosia
- Plasma protein from choroidal circulation
- Factors released by type 1 astrocytes
When does myelination start and stop embryologically?
7 months gestation to 1 month after birth
How far is fovea from optic nerve head?
How far BELOW is fovea from optic nerve head?
- Fovea-ONH - 4mm
- Fovea-ONH (below) - 0.8mm
How far is the blind spot from the fovea (degrees) ?
How big is the blind spot (degrees)
From fovea: 17 degrees
Size: 5-7 degrees in size.
