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PART ONE REVISION. > POSTERIOR SEGMENT - Neurosensory Retina > Flashcards

POSTERIOR SEGMENT - Neurosensory Retina Flashcards

1
Q

What is the structure of rod cones from RPE to vitreous?

A

Outer segment (transductive) –> inner segment (region for maintenance of cellular homeostasis) –> nuclear region (outer nuclear layers) –> transmissive region (outer plexiform/synaptic layer)

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2
Q

Which types of cells are present in the inner nuclear layer? (3)

A

(1) bipolar neurons
(2) horizontal cells
(3) amacrine cells

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3
Q

What is the difference between the outer segments of rods and cones ? (2)

A

RODS: cylindrical and contain rhodopsin pigment, made up of vitamin A (night blindness)

CONES: conical and contain iodopsin pigment (colour blindness)

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4
Q

What is the difference in numbers between rods and cones?

A

rods: 120 million
cones: 5 million

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5
Q

what is the maximum spectral sensitivity of the rod cells?

A

496nm

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6
Q

What are the main differences between rods and cones? (4)

A
  1. Rod discs are enclosed with a cell membrane
  2. Rod concentration higher in periphery
  3. Ratio of rod:cone is 20:1
  4. Peak sensitivity of rods is 496nm, cones is 420 (S), 530 (M) and 560 (L)
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7
Q

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?

A

Fovea.
1:1 ratio with cones to allow high resolution of the fovea region.
project to the parvocelllular layers of the LGN (P cells)

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8
Q

Which cell is responsible for retinal scar tissue formation?

A

Astrocytes.

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9
Q

What is the function of muller cells?

A

the main glial cells of the retina which support in architectural and metabolic functions of the retina.
They contribute to the blood retinal barrier.

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10
Q

What is the structure of astrocytes?
What is the function of astrocytes?

A

Honeycomb/pattern formation cells peripendicular to the muller cells

Responsible for laying down scar tissue in injured or diseased retina

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11
Q

What is the structure and function of microglia cells?

A

highly specialised mononuclear phagocytic cells and are first line of defence against pathogen invasion.

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12
Q

What is the maximal spectral sensitivity of the rod?

A

496nm (blue-green light)

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13
Q

Where is the superficial capillary plexus of the retina located in?

A

the nerve fiber and ganglion cell layers, at the same level as the arterioles and major venules

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14
Q

Where is the deep capillary plexus of the retina located in?

A

between the inner nuclear layer and the outer plexiform layer.

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15
Q

Where is the avascular outer retina located in?

A

the FAZ - comprises the outer nuclear layer and photoreceptors

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16
Q

Where is the choriocapillaris layer located?

A

About 30um below the RPE/Bruch’s membrane

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17
Q

The retinal capillaries are surrounded by which type of cells? (3)

A
  1. Astrocyte foot processes
  2. Pericytes (contractile)
  3. Thick basal lamina
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18
Q

What is the flow rate of the retinal vessels? What layers do they supply?

A

High oxygen exchange, low flow (25mm/s)

  1. Nerve Fibre Layer
  2. Ganglion Cell Layer
  3. Inner Plexiform Layer
  4. Inner third of inner nuclear layer
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19
Q

What is the flow rate of the choroidal vessels? What layers do they supply?

A

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

20
Q

What is present in the photoreceptor layer of the retina?

A

Only OUTER SEGMENTS and INNER SEGMENTS (mitochondria) of rods and cones.

21
Q

What is the outer/external limiting membrane?

A

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

22
Q

What is present in the outer nuclear layer?

A

Nuclei of the rods and cones (photoreceptor cell bodies)

23
Q

What is the outer plexiform layer? What is its main function?

A

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.

24
Q

Whatis contained within the inner nuclear layer?

A

Nuclei of the bipolar cells, horizontal cells, amacrine and muller cells

25
Q

What is contained within the inner plexiform layer?

A

Synapses / axons / dendrites between the bipolar neurons and the ganglion cells

Serves the junction of the intermediate vascular plexus

26
Q

What is contained in the ganglion cell layer?

A

The nuclei of the ganglion cells

27
Q

What is contained in the nerve fibre layer?

A

Processes of the ganglion cells which head towards the optic nerve. Contains the superficial vascular plexus

28
Q

What is the inner limiting membrane?

A

Formed by the foot processes of the Muller cells

29
Q

Describe the structure and location of the macula - how long is it?

A

Yellowish oval shape, 3mm lateral and slightly inferior to optic disc. It is 4.5mm in diameter.

30
Q

Why is the macula yellow?

A
  1. Lutein - retina
  2. Zeaxanthin - fovea (cones > rods)

Both are xanthophyll compounds in retinal layers

31
Q

What is the diameter of the macula?
What is the diameter of the fovea?
What is the diameter of the FAZ?

A

Macula: 4.5mm
Fovea: 1.5mm
FAZ: 300 microns.

32
Q

In which layer are flame haemorrhages found?

A

Nerve Fibre Layer - shape and direction of flame is due to direction and passage of nerve fibres

33
Q

In which layer are hard exudates found in the retina?

A

Outer plexiform layer

34
Q

What do hard exudates contain histologically?

A

Eosinophilic masses with contain foamy macrophages with lipid in the cytoplasm

35
Q

What is the most common location for retinal dialysis?

A

Inferotemporal

36
Q

What are the most common histopathological features of lattice retinal degeneration? (5)

A
  1. Liquefied vitreous overlying degeneration
  2. Vitreo-retinal adherence at margin of lesion
  3. Sclerosis of retinal vessels
  4. Retinal atrophy
  5. Discontinuity of internal limiting membrane
37
Q

What is a hard exudate? Where is it located?

A

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

38
Q

What is a subretinal exudate? Which disease?

A

Exudation in subretinal space

Coat’s disease
VHL (Retinal capillary haemangioma)

39
Q

What are cotton wool spots (soft exudates)?

A

Elevated white cloud-like lesions with fimbriated borders

Typically resolve in 6-12 weeks.

40
Q

What is the mechanism behind cotton wool spots?

A

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.

  1. Ischaemia
  2. Embolic
41
Q

What are the conditions associated with cotton wool spots?

A
  1. Ischaemia (RVO, ocular ischaemic syndrome)
  2. Embolus (valve emboli, dep venous emboli, blood cell emboli (Purtcher’s retinopathy)
  3. Infectious (HIV, cat-scratch fever (Bartonella), toxoplasmosis)
  4. Neoplastic (lymphoma, leukaemia, Hodgkins)
  5. Immune-mediated (SLE, sarcoid, GCA, polyarteririts nodosa, dermatomyositis, cryoglobulinaemia)
  6. Blood diseases (aplastic anaemia, pernicious anaemia, multiple myeloma, waldenstrom macroglobulinaemia, factor V leiden etc)
42
Q

What is the process of lactate shuttling?

A

Lactate produced by Muller cells is metabolised by photoreceptors. Photoreceptors in exchange release glutamate which Muller cells metabolise

43
Q

What is the visual field angle of the fovea?
What is the visual field angle of the macula?

A

Fovea: 1 degrees
Macula: 5 degrees

44
Q

How many ganglion cells are there in humans?

A

1 million.

45
Q
A

PART ONE REVISION. (78 decks)

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