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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

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
The RPE ______ membrane faces the _____ retina, and numerous _______ envelop tips of the photoreceptor ______ segments.
Apical membrane faces the neural retina, and numerous | microvilli envelop tips of the photoreceptor outer segments.
26
which 4 things prevents a physically attached connection between the RPE and brunch’s membrane
osmotic pressure fluid transport interphotoreceptor matrix presence of vitreous
27
what are the 6 major functions of the RPE
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
28
what does the ageing of the RPE result in
accumulation called lipofuscin Due to incomplete degradation of phagocytosed outer segment material by the RPE (which is also extruded into Bruch’s membrane)
29
as well as lipofuscin, what else accumulates in the RPE/Bruch's membrane due to an ageing RPE and why
dead cells as cell density declines with age which results in increased demand on remaining cells
30
By age 80, __% of RPE cytoplasmic space is filled with lipofuscin, compared to __% at age 40
By age 80, 90% of RPE cytoplasmic space filled with lipofuscin, compared to 8% at age 40
31
how is lipofuscin seen on Fundus Autoflorescence
bright glow
32
where is the peak density of lipofuscin seen
parafovea | highest ratio photoreceptor:RPE cells
33
where is the highest ratio of photoreceptor:RPE cells found
parafovea
34
in which 3 ways is lipofuscin toxic to the retina
can break down organelle membranes increases photo-oxidative damage mechanically damages cells
35
how are short wavelength sensitive cones different in morphology to long and medium wavelength sensitive cones of the photoreceptors
short wavelength sensitive cones have longer inner segments and smaller pedicles long and medium wavelength sensitive cones have a similar morphology
36
which layer of the retina is the outer segment located and what does it contain
the photoreceptor layer contains tightly packed membrane discs full of visual pigment
37
where on the retina is the max rod photoreceptor density found
18 deg eccentricity from the fovea
38
where on the retina is max cone density found
the fovea
39
what is the estimated number of rod photoreceptors found in the retina
110-125 million
40
what is the estimated number of cone photoreceptors found in the retina
6.3 - 6.8 million
41
which photoreceptor changes with age and how/by how much
rods Rod density decreased by 30% in central 28.5°retina
42
Rod density decreased by __% in central ____ retina
Rod density decreased by 30% in central 28.5°retina
43
where is the initial loss of rods in the retina in the ageing eye and what happens to the remaining rods
in parafovea outer segments of remaining rods expanded to fill gaps
44
what do bipolar cells synapse/convey signals from and to with in the retina
from photoreceptors and horizontal cells in the OPL to amacrine and RGCs in the IPL
45
how many types of bipolar cells are there in humans and what is 1 of them exclusive to
11 | one is rod pathway specific the remainder are cone pathway specific
46
which 2 pathways are bipolar cells involved with
``` 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
name 2 types of bipolar cells and state the difference between the 2
Midget and Diffuse Midget - synapse with few PRs Diffuse - synapse with many PRs
48
what are the 2 types of bipolar cells which process short wavelength information
blue & giant bi-stratified
49
name the 2 interneurons
horizontal and amacrine cells
50
Horizontal cells synapse with _____________ and _______ ____ at the level of the ____, and connect with each other via ___ __________.
Horizontal cells synapse with photoreceptors and bipolar cells at the level of the OPL, and connect with each other via gap junctions.
51
how do horizontal and amacrine cells communicate information
laterally across the retina
52
horizontal and amacrine cells provide a feedback signal to ___________ and feedforward to ________ _____
horizontal and amacrine cells provide a feedback signal to photoreceptors and feedforward to bipolar cells
53
Amacrine cells synapse with ________ _____ and _____ at the level of the ____
Amacrine cells synapse with bipolar cells and RGCs at the level of the IPL
54
how many amacrine cells are there in humans
at least 25
55
name 3 types of retinal ganglion cells
midget cells parasol cells bistratified RGCs
56
how much of the retinal ganglion cells do midget cells make up
80%
57
which pathway do the midget RGCs start and what does this do
parvocellular pathway they have small receptive fields/small dendritic feet (high SF sensitivity), show colour antagonism.
58
which RGC has high spatial frequency sensitivity
midget RGCs
59
how much of the retinal ganglion cells do the parasol cells make up
10%
60
which pathway do the parasol RGCs start and what does this do
magnocellular pathway have larger receptive fields/large dendritic feet/trees (low SF sensitivity), respond strongly to transient/fast moving stimuli.
61
which RGC has low spatial frequency sensitivity
parasol RGCs
62
what type of info do RGC parasol cells process
red green colour opponent info
63
Bistratified RGCs form start of _________ pathway, and carry _____-_______ colour opponent information.
Bistratified RGCs form start of koniocellular pathway, and carry blue-yellow colour opponent information.
64
ON-bipolars synapse with?
ON RGCs (respond to light onset or light on dark background)
65
OFF-bipolars synapse with?
OFF-RGCs (respond to light offset or dark on light background)
66
the retinal nerve fibre layer contains ____ axons and blood vessels of ________ _________ circulation
the retinal nerve fibre layer contains RGC axons and blood vessels of inner retinal circulation
67
Retinal nerve fibre layer Peripheral fibres are overlaid by more _______ fibres with __________ distance from the optic nerve head > ________ in thickness of RNFL
Peripheral fibres are overlaid by more central fibres with decreasing distance from the optic nerve head > increase in thickness of RNFL
68
where in the retina is the RNFL thickest at
the closer you get to the optic disc - it is thickest at the optic disc margin
69
Retinal nerve fibre layer Fibres from the ________ region form the spindle-like ____________ bundle, which enters the __________ sector of the optic nerve head
Fibres from the macular region form the spindle-like papillomacular bundle, which enters the temporal sector of the optic nerve head
70
Retinal nerve fibre layer Temporal fibres describe an ________ path to the _____ (around the papillomacular bundle), whilst nasal fibres take a more ______ route
Temporal fibres describe an arcuate path to the ONH (around the papillomacular bundle), whilst nasal fibres take a more direct route
71
How much % of retinal blood flow does the choroid receive and via which 2 arteries
65-85% via the short and long posterior ciliary arteries
72
how much % of blood flows into the inner retinal layers and which vessel does this flow through
20-30% flows into the retina through the central retinal artery from the ONH
73
how much of the population has a cilioretinal artery
15-20%
74
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
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
which retinal layer are the radial peripapillary capillaries found
RNFL
76
which retinal layer are the inner layer of capillaries found
ganglion cell layer
77
which retinal layer are the outer layer of capillaries found
IPL to the OPL
78
what does the blood in the capillaries drain into
into venules and through the corresponding venous system to the central retinal vein
79
what are endothelial cells of the arterioles and capillaries formed by
tight junctions
80
what surrounds the arteriole and hence maintains it's integrity
smooth muscle
81
what surrounds the capillaries and hence maintains it's integrity
pericytes
82
what condition causes the death of smooth muscle on arterioles and pericytes on capillaries and what does this result in
diabetic retinopathy reduces the integrity of the vessels
83
what is the size of the macula in mm and how much degrees of visual angle is it responsible for
6mm 15-20 degrees visual angle
84
what is the ganglion cell layer thickness at the macula area
more than 1 ganglion cell layer thick
85
what 4 components does the macula consist of
perifovea parafovea fovea foveola
86
what is the foveola encircled by and where does this pass from and to
vascular arcades passing from the optic nerve head, superior and inferior to the avascular zone
87
how large is the fovea in diameter and how much of the visual field does it represent
1. 85mm diamater | 5. 5 deg of visual field
88
how much of the visual field does the foveola represent
1°20’ of the visual field
89
which part of the retina has the maximum cone density and of how much
the foveola | 200,000 cells per mm2
90
how are the foveal cones structured and why
rod-like in shape than peripheral cones due to greater PR density
91
Approximately ___% of retinal ganglion cells (RGCs) are within ___°of the foveola
Approximately 50% of retinal ganglion cells (RGCs) are within 13°of the foveola
92
what is the peak density of RGCs at 1mm eccentricity of the foveola and what is the consequence of this
35,100 (the highest density) Ratio of cones to retinal ganglion cells is lowest in the macular region
93
what is the estimated cone:RGC ratio at foveal centre and what does this allow for as a result
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
what does the high sampling density of foveal cones throughout the visual pathway maximise
spatial acuity at fovea
95
at the foveola, how are all the cells placed and where about
all cells proximal to the photoreceptors are | displaced laterally
96
as seen in OCT - which retinal layers are thicker when adjacent to the foveal pit
GC and IPL layers
97
what is the thinnest part of the retina and why
Foveola due to displacement of second and third order neurones, achieved by elongation of cone cell axons (Henle Fibre Layer).
98
what is the consequence of the foveola being the thinnest part of the retina
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
which part of the retina is thickest and why
parafovea As a result of displacement of the cells from foveal pit, it has ganglion cells up to 6 layers deep
100
what is the foveal region free from
blood vessel and capillary
101
what does the ring of macular vessels arise from
branches of the superior temporal and infero temporal arteries
102
what is the advantage of there being no blood vessels are the fovea
Central vision is not disturbed by the scattering of light by the blood vessels
103
what is the foveal avascular zone reliant on any why
the underlying choroidal circulation for nourishment and waste removal
104
what does macular pigment consist of and what 2 things are they called
mixture of dietary xanthophyll carotenoids lutein and zeaxanthin
105
which 2 places of the retina are the macular pigments lutein and zeaxanthin found
in cone axons of Henle Fibre Layer and interneurones of the inner plexiform layer
106
what happens to the macular pigment with eccentricity and what does become
the distribution drops off dramatically with increasing eccentricity it becomes negligible at 5 deg eccentricity
107
what role does the macular pigment lutein and zeaxanthin have and what does this result in
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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