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Medical Retina > Physiology and anatomy of the healthy retina and macula > Flashcards

Physiology and anatomy of the healthy retina and macula Flashcards

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USMLE® Step 1 flashcards
1
Q

which 2 are the synaptic layers where connections between cells occur

A

outer plexiform layer
&
inner plexiform layer

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2
Q

which layer contains axons of retinal ganglion cells and where do these axons exit through

A

retinal nerve fibre layer

exits through the optic nerve head

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3
Q

which layer is between the RPE and choroidal circulation and what does it form inbetween these layers

A

bruch’s membrane

a permeable barrier

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4
Q

which 2 parts of the retina are supplied by the underlying choroidal circulation

A

outer retina
and
foveal avascular region

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5
Q

which 4 parts of the retina are a primary site of AMD and hence affected by age

A

choroid
bruch’s membrane
RPE
photoreceptors

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6
Q

which is the vascular layer between bruch’s membrane and the sclera and what vessel is it supplied by

A

choroid

supplied by the long and short ciliary artery which is derived from the ophthalmic artery

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7
Q

how many layers does the choroid consist of and what are they called

A

3

Haller layer
Sattler Layer
Choriocapillaris Layer

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8
Q

where is the Haller layer of the choroid found and what does it contain

A

closest to the sclera

contains large sized vessels

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9
Q

where is the Sattler layer of the choroid found and what does it contain

A

in the middle (between Haller and Choriocapillaris layers)

contains medium sized vessels

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10
Q

where is the Choriocapillaris layer of the choroid found and what does it contain

A

closest to bruch’s membrane

contains a dense network of fenestrated capillaries

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11
Q

what is the property of a fenestrated capillary layer

A

it doesn’t form a blood retinal barrier and molecules can freely move in and out of vessels

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12
Q

what is the major function of the choroid and at which part of the retina is it particularly important and why

A

to supply the outer retina with metabolites
and remove the waste products

the foveal avascular zone of the
macula

where the inner retinal circulation is absent

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13
Q

which part of the retina contains the greatest density of vessels of the widest diameter and why is this

A

The area beneath the macula

To supply optimal blood supply to this area of metabolic demand

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14
Q

what 3 things do ageing changes cause to the choroid

A

reduced thickness of the choroid

increased intercapillary spacing

a reduction in the
number and diameters of vessels

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15
Q

which 2 things of the choroid decrease with increasing age and what impact does this have

A

Choroidal blood flow and volume

impact of metabolites and removal of waste products from the retina

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16
Q

how many layers is bruch’s membrane composed of and what are they called

A

5

RPE basal lamina

Inner collagenous layer

Elastic layer

Outer collagenous layer

Choriocapillaris basal lamina

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17
Q

what type of structure does the collagen and elastic fibres form with bruch’s membrane

A

a sieve-like structure

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18
Q

Bruch’s membrane provides _______ and _______ for the RPE

A

support
and
anchorage

for the RPE

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19
Q

what 3 things pass from the choroidal circulation to the
outer retina via bruch’s membrane

and what passes in the opposite direction from the photoreceptors and RPE to reach the choroidal circulation

A

nutrients
oxygen
retinoids

metabolic waste products

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20
Q

which 2 disruptions causes an increased density in the strands of the sieve in the ageing of bruch’s membrane

A

Normal turnover of collagen and elastin fibrils is disrupted

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21
Q

Ageing of Bruch’s Membrane

  • Chemical changes & _______ cross-linkage of ______.
  • Normal turnover of _______ and ______ fibrils is disrupted, resulting in increased ________.
  • Deposition of waste materials from ____ in ______ ______.
  • Becomes more resistant to passage of materials between ____ and ______, hence more waste accumulates.
  • ______ accumulation reduces ______ permeability.
  • General age-related increase in the _______ from approx __ μm at birth, to _____ μm in the tenth decade of life.
A

Ageing of Bruch’s Membrane

  • Chemical changes & increased cross-linkage of fibrils.
  • Normal turnover of collagen and elastin fibrils is disrupted, resulting in increased density.
  • Deposition of waste materials from RPE in inner layers.
  • Becomes more resistant to passage of materials between RPE and choroid, hence more waste accumulates.
  • Lipid accumulation reduces water permeability.
  • General age-related increase in the thickness from approx 2 μm at birth, to 4-6 μm in the tenth decade of life.
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22
Q

Name the 3 ways the choroid changes and 1 way bruch’s membrane with age

A

Choroidal thickness decreases vs age
Capillary diameter decreases vs age
Capillary density decreases vs age
Bruch’s membrane thickness increases vs age

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23
Q

Retinal Pigment Epithelium is a _______ of hexagonal cells

A

Monolayer

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24
Q

what does the basement membrane of the RPE form

A

part of bruch’s membrane

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25
Q

The RPE ______ membrane faces the _____ retina, and numerous _______ envelop tips of the photoreceptor ______ segments.

A

Apical membrane faces the neural retina, and numerous

microvilli envelop tips of the photoreceptor outer segments.

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26
Q

which 4 things prevents a physically attached connection between the RPE and brunch’s membrane

A

osmotic pressure

fluid transport

interphotoreceptor matrix

presence of vitreous

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27
Q

what are the 6 major functions of the RPE

A

secretion of VEGF and PEDF

phagocytosis - processing the material and releasing in into the choroidal circulation

visual cycle - to regenerate pigment after it being bleached

glia - for exchange of potassium (k+)

epithelial transportation - of water, CI-, vit A and glucose

light absorption - which improves image quality

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28
Q

what does the ageing of the RPE result in

A

accumulation called lipofuscin

Due to incomplete degradation of phagocytosed outer segment material by the RPE
(which is also extruded into Bruch’s membrane)

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29
Q

as well as lipofuscin, what else accumulates in the RPE/Bruch’s membrane due to an ageing RPE and why

A

dead cells

as cell density declines with age which results in increased demand on remaining cells

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30
Q

By age 80, __% of RPE cytoplasmic space is filled with lipofuscin, compared to __% at age 40

A

By age 80, 90% of RPE cytoplasmic space filled with lipofuscin, compared to 8% at age 40

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31
Q

how is lipofuscin seen on Fundus Autoflorescence

A

bright glow

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32
Q

where is the peak density of lipofuscin seen

A

parafovea

highest ratio photoreceptor:RPE cells

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33
Q

where is the highest ratio of photoreceptor:RPE cells found

A

parafovea

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34
Q

in which 3 ways is lipofuscin toxic to the retina

A

can break down organelle membranes

increases photo-oxidative damage

mechanically damages cells

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35
Q

how are short wavelength sensitive cones different in morphology to long and medium wavelength sensitive cones of the photoreceptors

A

short wavelength sensitive cones have longer inner segments and smaller pedicles

long and medium wavelength sensitive cones have a similar morphology

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36
Q

which layer of the retina is the outer segment located and what does it contain

A

the photoreceptor layer

contains tightly packed membrane discs full of visual pigment

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37
Q

where on the retina is the max rod photoreceptor density found

A

18 deg eccentricity from the fovea

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38
Q

where on the retina is max cone density found

A

the fovea

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39
Q

what is the estimated number of rod photoreceptors found in the retina

A

110-125 million

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40
Q

what is the estimated number of cone photoreceptors found in the retina

A

6.3 - 6.8 million

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41
Q

which photoreceptor changes with age and how/by how much

A

rods

Rod density decreased by 30% in central 28.5°retina

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42
Q

Rod density decreased by __% in central ____ retina

A

Rod density decreased by 30% in central 28.5°retina

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43
Q

where is the initial loss of rods in the retina in the ageing eye and what happens to the remaining rods

A

in parafovea

outer segments of remaining rods expanded to fill gaps

44
Q

what do bipolar cells synapse/convey signals from and to with in the retina

A

from photoreceptors and horizontal cells in the OPL to amacrine and RGCs in the IPL

45
Q

how many types of bipolar cells are there in humans and what is 1 of them exclusive to

A

11

one is rod pathway specific
the remainder are cone pathway specific

46
Q

which 2 pathways are bipolar cells involved with

A 
OFF pathway (inhibited by light on receptive field
centre; synapse in the outer part of IPL)

ON-pathway (excited by light on receptive field centre; synapse in the inner part of IPL)

47
Q

name 2 types of bipolar cells and state the difference between the 2

A

Midget and Diffuse

Midget - synapse with few PRs

Diffuse - synapse with many PRs

48
Q

what are the 2 types of bipolar cells which process short wavelength information

A

blue
&
giant bi-stratified

49
Q

name the 2 interneurons

A

horizontal and amacrine cells

50
Q

Horizontal cells synapse with _____________ and _______ ____ at the level of the ____, and connect with each other via ___ __________.

A

Horizontal cells synapse with photoreceptors and bipolar cells at the level of the OPL, and connect with each other via gap junctions.

51
Q

how do horizontal and amacrine cells communicate information

A

laterally across the retina

52
Q

horizontal and amacrine cells provide a feedback signal to ___________ and feedforward to ________ _____

A

horizontal and amacrine cells provide a feedback signal to photoreceptors and feedforward to bipolar cells

53
Q

Amacrine cells synapse with ________ _____ and _____ at the level of the ____

A

Amacrine cells synapse with bipolar cells and RGCs at the level of the IPL

54
Q

how many amacrine cells are there in humans

A

at least 25

55
Q

name 3 types of retinal ganglion cells

A

midget cells
parasol cells
bistratified RGCs

56
Q

how much of the retinal ganglion cells do midget cells make up

A

80%

57
Q

which pathway do the midget RGCs start and what does this do

A

parvocellular pathway

they have small receptive fields/small dendritic feet (high SF sensitivity), show colour antagonism.

58
Q

which RGC has high spatial frequency sensitivity

A

midget RGCs

59
Q

how much of the retinal ganglion cells do the parasol cells make up

A

10%

60
Q

which pathway do the parasol RGCs start and what does this do

A

magnocellular pathway

have larger receptive fields/large dendritic feet/trees (low SF sensitivity), respond strongly to transient/fast moving stimuli.

61
Q

which RGC has low spatial frequency sensitivity

A

parasol RGCs

62
Q

what type of info do RGC parasol cells process

A

red green colour opponent info

63
Q

Bistratified RGCs form start of _________ pathway, and carry _____-_______ colour opponent information.

A

Bistratified RGCs form start of koniocellular pathway, and carry blue-yellow colour opponent information.

64
Q

ON-bipolars synapse with?

A

ON RGCs (respond to light onset or light on dark background)

65
Q

OFF-bipolars synapse with?

A

OFF-RGCs (respond to light offset or dark on light background)

66
Q

the retinal nerve fibre layer contains ____ axons and blood vessels of ________ _________ circulation

A

the retinal nerve fibre layer contains RGC axons and blood vessels of inner retinal circulation

67
Q

Retinal nerve fibre layer

Peripheral fibres are overlaid by more _______ fibres with __________ distance from the optic nerve head > ________ in thickness of RNFL

A

Peripheral fibres are overlaid by more central fibres with decreasing distance from the optic nerve head > increase in thickness of RNFL

68
Q

where in the retina is the RNFL thickest at

A

the closer you get to the optic disc - it is thickest at the optic disc margin

69
Q

Retinal nerve fibre layer

Fibres from the ________ region form the spindle-like ____________ bundle, which enters the __________ sector of the optic nerve head

A

Fibres from the macular region form the spindle-like papillomacular bundle, which enters the temporal sector of the optic nerve head

70
Q

Retinal nerve fibre layer

Temporal fibres describe an ________ path to the _____ (around the papillomacular bundle), whilst nasal fibres take a more ______ route

A

Temporal fibres describe an arcuate path to the ONH (around the papillomacular bundle), whilst nasal fibres take a more direct route

71
Q

How much % of retinal blood flow does the choroid receive and via which 2 arteries

A

65-85%

via the short and long posterior ciliary arteries

72
Q

how much % of blood flows into the inner retinal layers and which vessel does this flow through

A

20-30%

flows into the retina through the central retinal artery from the ONH

73
Q

how much of the population has a cilioretinal artery

A

15-20%

74
Q

how many branches does the central retinal artery have

how many layers of the retina does it supply

what are the names of the capillaries and which layer of the retina do each of them supply

A

4

3 layers of capillaries

1) the radial peripapillary capillaries (RPCs) (in RNFL)
2) an inner layer of capillaries (in ganglion cell layer)
3) an outer layer of capillaries (runs from IPL to OPL)

75
Q

which retinal layer are the radial peripapillary capillaries found

A

RNFL

76
Q

which retinal layer are the inner layer of capillaries found

A

ganglion cell layer

77
Q

which retinal layer are the outer layer of capillaries found

A

IPL to the OPL

78
Q

what does the blood in the capillaries drain into

A

into venules and through the corresponding venous system to the central retinal vein

79
Q

what are endothelial cells of the arterioles and capillaries formed by

A

tight junctions

80
Q

what surrounds the arteriole and hence maintains it’s integrity

A

smooth muscle

81
Q

what surrounds the capillaries and hence maintains it’s integrity

A

pericytes

82
Q

what condition causes the death of smooth muscle on arterioles and pericytes on capillaries and what does this result in

A

diabetic retinopathy

reduces the integrity of the vessels

83
Q

what is the size of the macula in mm and how much degrees of visual angle is it responsible for

A

6mm

15-20 degrees visual angle

84
Q

what is the ganglion cell layer thickness at the macula area

A

more than 1 ganglion cell layer thick

85
Q

what 4 components does the macula consist of

A

perifovea
parafovea
fovea
foveola

86
Q

what is the foveola encircled by and where does this pass from and to

A

vascular arcades

passing from the optic nerve head, superior and inferior to the avascular zone

87
Q

how large is the fovea in diameter and how much of the visual field does it represent

A
  1. 85mm diamater

5. 5 deg of visual field

88
Q

how much of the visual field does the foveola represent

A

1°20’ of the visual field

89
Q

which part of the retina has the maximum cone density and of how much

A

the foveola

200,000 cells per mm2

90
Q

how are the foveal cones structured and why

A

rod-like in shape than peripheral cones due to greater PR density

91
Q

Approximately ___% of retinal ganglion cells (RGCs) are within ___°of the foveola

A

Approximately 50% of retinal ganglion cells (RGCs) are within 13°of the foveola

92
Q

what is the peak density of RGCs at 1mm eccentricity of the foveola
and what is the consequence of this

A

35,100 (the highest density)

Ratio of cones to retinal ganglion cells is lowest in the macular region

93
Q

what is the estimated cone:RGC ratio at foveal centre and what does this allow for as a result

A

1:2 - cone:RGC

Allows for each foveal cone to contribute to ON- and OFFpathways.
Results in a low level of neural convergence (small
receptive field size) and allows high sampling density of
foveal cones throughout the visual pathway

94
Q

what does the high sampling density of foveal cones throughout the visual pathway maximise

A

spatial acuity at fovea

95
Q

at the foveola, how are all the cells placed and where about

A

all cells proximal to the photoreceptors are

displaced laterally

96
Q

as seen in OCT - which retinal layers are thicker when adjacent to the foveal pit

A

GC and IPL layers

97
Q

what is the thinnest part of the retina and why

A

Foveola
due to displacement of second and third order neurones,
achieved by elongation of cone cell axons (Henle Fibre
Layer).

98
Q

what is the consequence of the foveola being the thinnest part of the retina

A

Central vision is not disturbed by the scattering of light prior to absorption by the photoreceptors

As a result of displacement of the cells from foveal pit,
parafoveal region has ganglion cells up to 6 layers deep
and is the thickest part of the retina.

99
Q

which part of the retina is thickest and why

A

parafovea

As a result of displacement of the cells from foveal pit, it has ganglion cells up to 6 layers deep

100
Q

what is the foveal region free from

A

blood vessel and capillary

101
Q

what does the ring of macular vessels arise from

A

branches of the superior temporal and infero temporal arteries

102
Q

what is the advantage of there being no blood vessels are the fovea

A

Central vision is not disturbed by the scattering of light by the blood vessels

103
Q

what is the foveal avascular zone reliant on any why

A

the underlying choroidal circulation

for nourishment and waste removal

104
Q

what does macular pigment consist of and what 2 things are they called

A

mixture of dietary xanthophyll carotenoids

lutein and zeaxanthin

105
Q

which 2 places of the retina are the macular pigments lutein and zeaxanthin found

A

in cone axons of Henle Fibre Layer
and
interneurones of the inner plexiform layer

106
Q

what happens to the macular pigment with eccentricity and what does become

A

the distribution drops off dramatically with increasing eccentricity

it becomes negligible at 5 deg eccentricity

107
Q

what role does the macular pigment lutein and zeaxanthin have and what does this result in

A

a protective role, acting as an antioxidant, and filtering out short wavelength light - helping to protect against photo oxidative photo damage

Improves image quality - by selectively absorbing short wavelengths of light and reducing chromatic aberrations

Medical Retina (17 decks)

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